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Showing 195 results for Type of Study: Original Research
Kazem Saber Chenari, Abolareza Bahremand1, Vahed Berdi Sheikh, Chooghi Bairam Komaki,
Volume 13, Issue 1 (8-2019)
Volume 13, Issue 1 (8-2019)
Abstract
Introduction
One of the main problems in the Golestan province watersheds is the high degree of erosion and soil degradation, so that the equilibrium between the soil process and the soil erosion is unbalanced, and the erosion rate increases from west to east. Among these, the gully erosion and piping have the highest role. Gully is a canal or stream with the headcut with active erosion, sharpened slope and steep walls that results from the destruction of surface flow (usually during or after the occurrence of precipitation), dissolution movements, and small mass movements. The extent of gully in the eastern parts of Golestan province has caused the land degradation of arable land and landscape and has increased the conservation cost and etc. Because of connecting upstream areas of the basin to the downstream areas, gully has particular importance, which provides the possibility of sediment and pollutant transport, road destruction and financial losses to agricultural lands. In order to prevent and control the development of gully processes from a small scale to large one, it is a versatile utility to identify and extract the areas prone to gully erosion.
Due to the high intensity of gully erosion and its increasing growth in the Gharnaveh watershed, the Garnaveh River has an unstable status and severe eroded gully, and in some areas it has a great depth and vertical lateral walls, as well. Therefore, in this research, the watershed of Garnaveh was selected to prepare the risk areas of gully erosion.
The aim of this research is to determine Gully Erosion Hazard zoning using Frequency Ratio and Gupta & Joshi methods (Gully Nominal Risk Factor-GNRF) in the Garnaveh watershed (Golestan province). Ultimately, the accuracy of the model has been evaluated using quality sum method and Kappa coefficient.
Material and methods
The study area is located in the northern part of Iran, Golestan province. The Garnaveh watershed with an area of about 78430 hectares lies between longitudes 370360 E and 414472 E, and latitudes of 4183819 N and 4155267 N (UTM Zone 40).
At first, gully erosion inventory map with the scale of 1:75,000 (dependent variable) for the Gharnaveh watershed has been prepared using multiple field surveys and satellite images. From total gullies, 70% have been selected randomly for building gully erosion hazard zoning model and the remaining ones (30%) have been used to validate the provided model.
In this research, seven data layers including slope percent, slope aspect, plan curvature, lithology formation, land use types, distance from rivers and distance from roads have been selected as gully erosion controlling factors (covariates/ independent variables) and then they have been digitized in ArcGIS software. The amount of Gully density of each factor class has been calculated from a combination of independent and dependent variables, and the rating of classes have done based on Frequency Ratio and Gully Nominal Risk Factor equations. Finally, the Gully erosion hazard zoning map has been drawn from the summation of weighting maps in ArcGIS. In this map, the value of each pixel is calculated by summing the weights of all the factors in that pixel. The pixel values are categorized based on the natural breaks classifier into very low, low, medium, high and very high hazard zones. Then, an accuracy of zoning map has been evaluated by quality sum method and Kappa coefficient.
Results and discussion
The result of affecting factors classification of the gullies shows that loess deposits formation, rangeland, areas with low distance from road and rivers, northwest aspect, low slope amplitude and concave slopes contain the most susceptibility to gullying. The results of frequency percent comparison of gullies in hazard classes show that from all gully zones in the validation step of the GNRF and frequency ratio models %74.52 and %78.11 of zones are located in the high and very high risk classes, respectively. The result of model validation using the quality sum method and a Kappa coefficient show that the frequency ratio model is a more appropriate model for gully erosion hazard zoning (with the quality sum and a Kappa coefficient of 3 and 0.89, respectively) than the GNRF model (having the quality sum and Kappa coefficient of 1.27 and 0.74, respectively).
Conclusion
In this research, the areas susceptible to gully erosion in the Gharnaveh watershed have been mapped with the frequency ratio and GNRF (for the first time) models. For this purpose, 7 affecting factors (independent variable) and 805 gully zones (dependent variable) were provided to measure the hazard maps of gully erosion. The following results are obtained from this study.
- The geology factors were identified as the most effective factors in the occurrence of gully erosion in the Gharnaveh watershed.
- Based on the gully erosion zoning hazard map of the Gharnaveh watershed, more than 70 percent of gullies are situated in the very high and high hazard classes.
- The produced gully erosion hazard map is useful for planners and engineers to reorganize the areas susceptible to gully erosion hazard, and offers appropriate methods for hazard reduction and management, as well../files/site1/files/131/4Extended_Abstract.pdf
Iman Aghamolaie, Gholamreza Lashkaripour, Mohammads Ghfoori, Naser Hafezimoghadas,
Volume 13, Issue 1 (8-2019)
Volume 13, Issue 1 (8-2019)
Abstract
Introduction
The problematic collapsible soils are deposits with wind origin that constitute about 10% of the total area of the earth. Several countries, including China, Russia, the United States, France, Germany, New Zealand, and Argentina have vast areas of collapsible soils. These deposits usually form a semi-stable honeycomb structure and are highly susceptible to sudden changes in the volume reduction due to becoming humid. Collapsibility and other related issues such as different subsidences, land cracks and landfalls seriously damage the infrastructures constructed on these soils.
By the growing rate of urbanization in different parts of the world, the probability of construction on these soils and consequently water availability for these soils will increase; as a result, humidity increases and the collapse of these soils may occur. Therefore, studying the behavior of these types of soils is very important. Over the past six decades, many researchers have studied the collapse mechanism of collapsible soils due to becoming humid. Discussions on this subject are summarized in three categories: traditional methods, soil structure studies, and soil mechanics-based methods. In the present work, collapsibility and its controlling factors in the soils of Kerman city are investigated.
Material and methods
To determine engineering properties of Kerman deposits in this research, the geotechnical information was gathered and 50 core samples were extracted from different parts of the city. The sampling points were selected such that they could have a high overlap. X-ray diffraction (XRD) was applied to determine the mineral type and soil structures while scanning electron microscopy (SEM) was used to study grain arrangement.
Results and discussion
Geotechnical characteristics of the samples collected from Kerman plain deposits include their physical and mechanical properties. Based on the obtained results, this fine-grained sediment generally includes two CL and CL-ML groups. The mineralogy studies of Kerman city soils show that the minerals in these deposits are mainly illite, chlorite, illite-smectite, calcite, quartz, and gypsum. In order to study the collapsibility level of the soils in Kerman through the field studies, samples were taken from different parts of the city and the tests were carried out to determine the physical properties, collapsibility index, and structural studies. Through the SEM analyses, samples related to Haft Bagh area, Motahhari Town, and Pedar Town revealed an open structure and intergranular pores and thus a high level of collapsibility. On the other hand, in the majority of samples taken from the central part of the city, such as Esteghlal Street, Azadi Square, Bahmaniyar Street, and Hafez Street, the soil aggregates generally have corner-to-corner connectivity, with no specific order in their structure, and the arrangement of the particles is random and irregular. The orientation of the particles mostly shows no sharp pattern. In addition to soil particles, they have shown random and disorientated cavities with small sizes, suggesting the density and compactness of the soil indicating a low to moderate collapsibility. In some areas (e.g., Pedar Township and Motahhari Township), crystalline salt and gypsum crystals are clearly seen. It is expected that by increasing the amount of water, these salts dissolve and their effects can be observed as dissolution cavities.
The dissolution of soluble crystals can also reduce the strength of the soil structure and ultimately lead to soil degradation. Calcite crystals are also found in some places in the form of calcite cement among the grains, sometimes as single crystals, and sometimes as lime nodules within the soils of Kerman city. Among the stated criteria in this research, Denisov, Holtz, and Hill criteria, the Russian regulations and ASTM standards were employed to assess the potential of the studied soil collapsing. Based on the criterion of the construction regulations of Russia, it was found that the deposits of the city of Kerman are mainly collapsible (L>-0.1).
Moreover, based on the Denisov criterion (if e/eL>1.5 the soil is non-collapsible, if it is between 0.75 and 1.5, the soil is prone to collapsing, and if it is between 0.5 and 0.75, the soil is severely collapsible), soils of Kerman are within the range of collapse-prone soils. Finally, based on the ASTM criterion, in some areas of the city like Motahhari Town, Pedar Town, and Haft bagh, soils show a high collapsibility. In comparison, in the central parts of the city, the values of this criterion vary between 0.15 and 11, suggesting the presence of soils with a moderate collapsibility. Comparing the results obtained using these criteria it is seen that areas with a collapsible behavior are relatively similar collapsibility results are obtained.
Conclusion
Based on the achieved results, fine-grained sediments of Kerman city are mainly composed of CL and CL-ML groups. Mineralogy results indicate that the minerals in these deposits are mainly illite, chlorite, illite-smectite, calcite, quartz, and gypsum. SEM results for the central part of Kerman city confirm the compressed and densely compact form of soil particles. The results obtained, using the construction regulations of Russia show that the soils in the study area are collapsible. According to the Denisov criterion, they were found to be prone to collapse. Finally, based on the ASTM results for the central parts of the city, soils exhibit a low to moderate collapsibility. However, in some areas of the city, such as Motahhari and Haft bagh, soils show a complete collapsibility behavior../files/site1/files/131/1Extended_Abstract.pdf
Vahid Daneshjoo, Reza Farokhzad,
Volume 13, Issue 1 (8-2019)
Volume 13, Issue 1 (8-2019)
Abstract
Introduction
Nanostructured materials have gained increasing attention of industry and the academia in recent decades, due to their prominent behaviors. In this regard, the building industry is considered to be the major consumer of nanostructured materials in terms of its needs, including strength, resistance, durability and high performance. Studies on nanoscale behavior of cement and concrete to develop new building materials and their applications are of high importance. A typical method for the development of high performance concrete (HPC) often contains various parameters, including the mix of conventional concrete with different types of additives. Nano-Calcium carbonate (Nano-Precipitated Calcium Carbonate) is a nano-sized filler which is used in this research. The results indicate that the higher the optimal content of nano-precipitated calcium carbonate powder, the higher the initial heat of the roller-compacted concrete; also, the resistance of the samples significantly increases over time. However, the level of permeability of roller-compacted concrete decreases by optimal increase of nano-calcium carbonate powder due to its fine grains, filling properties, and high specific level. The results of this study show that the adequate use of this material improves some properties of roller-compacted concrete.
Material and methods
In this study, the content of Nano-calcium carbonate used was selected at 0, 1, 2, 3 and 4 percent replacing a volume of cement consumed in concrete. Type II Portland cement, crushed fluvial sand, and crushed coarse aggregates with a maximum size of 19 mm were used. The aggregates’ grading range in the mix has been selected according to the ACI325-10R. The chemical formula of Nano-calcium carbonate powder is CaCo3 and the average particle size is between 15-40 nm
According to the roller-compacted concrete specifications, 5 mix designs have been used with different proportions of stone materials in preparing of concrete. The samples were made on a vibrating table and in the cylindrical molds of 15 × 30 cm according to ASTM C1176 standard.
By increasing the cement grade, the slope of the Vebe curve increases, which means an increase in speed and reduction in efficiency over time in higher grades. Increasing the cement grade from 275 to 300 kg/m3 leads to increased Vebe time. In other words, it can be said that the efficiency is reduced at a lower rate in lower grades of new roller-compacted concrete mix. The Vebe time of the roller-compacted concrete pavement should be between 30-40 s to achieve optimal efficiency. According to the results of Vebe time, the efficiency of the roller-compacted concrete with the grade of 300 kg/m3 has a better functionality than other mixtures and lasted more than others in the 30 to 40 second range. Accordingly, concrete with a grade of 300 kg/m3, is the compressive strength according to this design.
Determining the compressive strength of cylindrical concrete samples of different ages is done according to the ASTM C39/C39M standard. For permeability test, the BS EN 12390-8: 2009 was used in which the sample should be put under pressure of (0.5±)5 for 72 hours immediately after molding. Determining the tensile strength of concrete cylindrical samples at different ages is done according to the ASTM C496 standard. The peak is obtained using the XRD analysis of the crystallite size by determining the width of the peaks. In interpreting the XRD data, a list of peak resolution and their intensities is observed. To determine the elemental composition of materials, a non-destructive analytical technique is used by X-ray which is so-called XRF (X-ray fluorescence). A scanning electron microscope is a powerful magnification tool and is used to distinguish elements.
Results and discussion
The results indicate that the increased Vebe time occurs by an increase in the percentage of nano-calcium carbonate. In terms of the compressive strength of cylindrical roller-compacted concrete samples, 2% of nano-calcium carbonate at the ages of 7, 28, and 90 days has been effective in increasing compressive strength in higher ages. Such that, at the ages of 28 and 90 days, it is increased by 12% and 15 % compared to the control sample, respectively. The nano content increases over 15% causes decreased compressive strength and thus had negative effects on the rheological properties of the roller-compacted concrete. In terms of tensile strength of the cylindrical roller-compacted concrete samples, 2% of nano-calcium carbonate at the ages of 7, 28 and 90 days has been effective in increasing compressive strength in higher ages, such that at the ages of 7, 28 and 90 days, it has been increased by 25%, 30% and 30 % compared to the control sample, respectively. However, it can also be concluded that the excessive increase has partly reduced the tensile strength.
The variation of the permeability coefficient is a function of concrete porosity and water penetration in the roller-compacted concrete. Also, there are significant changes in the concrete permeability coefficient by adding different percentages of nano-calcium carbonate to concrete.
Adding nano-calcium carbonate up to 2% of cement weight to the roller-compacted concrete reduces the permeability coefficient of the roller-compacted concrete. One of the reasons for this phenomenon is capillary interstice filling in the roller-compacted concrete. Moreover, the nano-calcium carbonate increase of over 2% of cement weight raises the permeability of the roller-compacted concrete.
Adding 4% of nano-calcium carbonate to the roller-compacted concrete pattern increases the intensity of the peaks in the XRD test. Given that the average crystallite size is obtained from full width at half height of the peaks, by increasing the peaks’ intensity and their width at half height of the peaks, we get smaller crystallite size. Also, by adding 4% of nano-calcium carbonate, the widths of the peaks are increased, which means smaller crystals and increased crystallite inner tension.
Conclusion
Nano-calcium carbonate, due to its special features, including a high specific surface area, has a good performance in improving the mechanical properties and durability of the roller-compacted concrete, if it is used at a certain and optimal amount. The roller-compacted concrete with the grade of 300 kg / m3 has better functionality than other mixtures, and lasted more in the 30 to 40 second range.
The mix design containing 2% of nano-calcium carbonate replacing cement, has the highest compressive strength at the age of 7 days and shows 4% increase in resistance compared to a control sample at the age of 7 days. The mix design containing 2% nano-calcium carbonate has the highest compressive strength at the age of 28 days and shows 12% increase in resistance compared to a control sample at this age and improved the compressive strength. The mix design containing 2% nano-calcium carbonate has the highest compressive strength at the age of 90 days and shows 15% increase in resistance compared to a control sample at this age. The mix design including 3% of nano-calcium carbonate replacing cement, has the highest tensile strength at the age of 7 days, and shows 25% increase in resistance compared to a control sample at the same age. The mix design containing 2% of nano-calcium carbonate replacing cement, has the highest tensile strength at the age of 28 days and shows 30% increase in resistance compared to a control sample at the same age. The mix design containing 2% of nano-calcium carbonate replacing cement, has the highest tensile strength at the age of 90 days and shows 30% increase in resistance compared to a control sample at the same age. ./files/site1/files/131/3Extended_Abstract.pdf
Behrooz Samadian, Ali Fakher,
Volume 13, Issue 1 (8-2019)
Volume 13, Issue 1 (8-2019)
Abstract
Introduction
Geotechnical investigations merely through boring and engineering experiments are considered a difficult task as they are highly costly and time-consuming. The identification of large areas initially requires geological studies followed by the inclusion of geotechnical information. Finally, a geological and geotechnical classification is prepared for the entire area. This type of classifications is employed in strategic urban planning and quick selection of geotechnical variables in small-scale projects. The present research performed the steps involved in these investigations and classifications for the city of Sanandaj, Iran. Hence, the geological-geotechnical classification of the city of Sanandaj was presented by integrating the geological information of this city with the geotechnical data obtained from drilled boreholes as well as multiple wells at different locations in this city.
Materials and Methods
This study was conducted on the city of Sanandaj in six steps. The steps involved and their respective objectives are given in summary in Table 1.
Discussion
This study is applicable to those regions with insufficient information on their boreholes. The present study used only 211 boreholes, the distance
Table1. Steps involved in this study
| Objective or result | Title | Step |
| Identifying the general geological characteristics | General geological investigation of the considered region | 1 |
| Determining the rock units and soil layers as well as their outcrops and investigating their appearance | Determining the appearance of the layers through field investigations | 2 |
| Determining the layer types and drawing the longitudinal and lateral profiles | Identifying subsurface layers | 3 |
| Determining the characteristics of geological units and their origin of emergence | Geological classification based on the steps involved in formation of units | 4 |
| a)Collecting the available information, b) controlling the available information, c) completing the information | Determining the geotechnical attributes of geological units | 5 |
| a) Presenting geological-geotechnical classification, b) presenting geological identification criteria to determine the type of a given unit at the site of the project | Presenting a geological-geotechnical classification for the considered region | 6 |
Conclusion
The following summaries can be concluded from this study:
-The step-by-step procedure of integrating geological and geotechnical information was described, through which the geological-geotechnical classification for this city was obtained.
-The geological units identified for Sanandaj were shale, limestone, andesite, and Quaternary, which includes layers of alluvial clay, residual clay, and sand and gravel. The extent and distribution of each of the aforementioned units in Sanandaj were identified and plotted. Moreover, the physical and mechanical characteristics of each of the units as well as their geotechnical hazards were determined and presented.
-In this study, simple geotechnical criteria such as faults, altitude level, and distance from river were identified. These parameters were effective in identification of geological units in Sanandaj../files/site1/files/131/5Extended_Abstract.pdf
Seyed Taha Tabatabaei Aghda, Ali Ghanbari, Gholamhosein Tavakoli Mehrjardi,
Volume 13, Issue 2 (8-2019)
Volume 13, Issue 2 (8-2019)
Abstract
Introduction
In some ports, the dredging and accumulation of a large amount of sedimentary material turned to a serious challenge, because of their sequent environmental and economic effects. These problems clarify the necessity of reusing dredged materials. Often, owing to their poor mechanical properties, they are not applied directly in technically engineering uses, so they require to be improved. Geocell application is one of the methods used for the improvement of soil behavior, which confines the sand mass through itself in the three-dimensional structure. These methods ease the speed of applying emerged it into a perfect option for stabilizing of the granular soil.
In Shahid Rajaee port, by the dredging process for developing new phases, a large amount of calcareous sand is being accumulated near the Persian Gulf coastline. Therefore, in order to provide a solution to reuse these materials, this study attempts to investigate the beneficial influence of reinforcing sand by geocell on its load-beneficial behavior experimented by the plat loading test. For this purpose, a large scale model including circular foundation on reinforced and unreinforced sand has been employed under cyclic loading process.
Material and Methods
Soils
Two types of soils were used in this study. The first type was the sand derived from the dredging process of Shahid Rajaee port which has been used in different layers of the models. The second type of soil was well-graded gravel which has been used only in the cover layer.
Geocell
The geocell in this study were made of heat-bonded non-woven polypropylene geotextiles. Single cells were 110 mm long, 100 mm wide and 100 mm height.
Plate load test
In order to determine the bearing capacity of backfills, repeating plate load test was used with 150 mm diameter. Loading process included four stress levels (250, 500, 750 and 1000 kPa) consisting of 10 cycles each.
Test backfills
Four backfills was made by manually compacting the dredged sand, with tamper up to 350 mm in reinforced cases and 450 mm in unreinforced cases. Then geocells placed and dredged sand filled with accuracy in cells. Finally, a 50 mm thick sand or gravel cover layer, was placed. All lifts were compacted to 70% of relative density with 4% moisture content.
Results and Discussion
PLT results are summarized in Table 1. According to the results, only geocell reinforcement backfills can carry standard truck wheel load (550 kPa). Geocell can increase the ultimate strength of backfills with a sand cover layer by 70% (from 416 kPa to 725 kPa) while in backfill with a gravel cover layer showed 80% increase (from 520 kPa to 960 kPa) in ultimate strength. The gravel cover layer in unreinforced backfills increases the ultimate strength by 25 percent (from 416 kPa to 520 kPa).
Table 1. Results of PLT and performance ratings
| Backfill name | UR-S | GR-S | UR-W | GR-W |
| Maximum stress (kPa) | 416 | 725 | 520 | 960 |
| Settlement at failure (mm) | 4.6 | 9.0 | 15.5 | 14.9 |
| Plastic settlement (mm) | 3.5 | 7.0 | 12.5 | 12.0 |
| Number of load cycles | 10 | 20 | 20 | 30 |
| Bearing capacity ratio (BCR) | 1 | 1.74 | 1.25 | 2.32 |
| Performance rating | 4 | 2 | 3 | 1 |
Kazem Bahrami1, Seyed Mahmoud Fatemi Aghda, Ali Noorzad, Mehdi Talkhablou,
Volume 13, Issue 2 (8-2019)
Volume 13, Issue 2 (8-2019)
Abstract
Aggregates are one of the high demand building materials in construction of structures and their characteristics have important effects on durability and permanence of projects. Abrasion resistance is one of the important features of aggregates that their utilization in concrete and asphalt are affected by texture and lithology of them. As rock consisted of harder minerals have higher abrasion resistance like igneous rocks, due to more siliceous minerals. More varieties in mineralogy compound usually lead to increase in aggregate abrasion. Aggregates that are contained of different minerals usually have less abrasion resistance. Porosity usually decreases the resistance abrasion. In addition to lithological properties, the environment where aggregates are deposited is important in determining resistance-related parameters of aggregates.
Rivers, alluvial fans, and taluses are the main environments where aggregates are deposited. Geological processes, such as weathering and particle movement may cause changes in natural aggregates, hence affecting their abrasion and impact resistance. Rock weathering can results in increasing porosity, producing minerals that are weaker in comparison to their original rock.
In the process of particles transport by stream water, weak parts of aggregates will be omitted. The present study is focused on the relationship between geology medium and the weight loss of aggregate in Los Angeles test.
Methodology
Considering that lithology features in aggregates resistance against abrasion have an important role, in order to examine the effect of various geology environments in abrasion resistance of aggregates, the medium should be chosen having similar lithology. Therefore, the north of Damavand and the south of Daneh Khoshk anticline (north of Dire plain) were firstly chosen by using geology map, satellites images and field study. Damavand zone consists of trachyte and trachy-andesite volcanic rocks. These rocks cover the whole area around the Damavand peak. Also, Daneh Khoshk anticline is covered by thick Asmari formation. The selected environment are in the length of each other. Such that taluses feed alluvial fan and alluvial fans feed rivers. Samples were collected from different area of southern part of anticline. 10 river area, 12 alluvial fan and 6 taluses in the south-west area of Daneh Khoshk anticline (north of Dire plain) were chosen. Los Angeles test has been done according to standard A method ASTM D2216-10, 1990 on samples and the results were analyzed by analogous analyzer.
Results and discussion
Results show that porosity and micro-crack percentage increase, respectively in accumulated aggregate in river, alluvial fans and taluses areas. Also, porosity and micro-crack in various alluvial fans is different and is influenced by the area and length of main channel of alluvial fans’ catchment. The porosity decreases by the increase in the length of channel and area of alluvial fans’ catchment.
The percentages of aggregate weight loss in talus, alluvial fan and river areas decreases, respectively. Based on the obtained results, the lowest rates of weight loss belong to river environments (23.7 % in Daneh Khoshk and 42% in Damavand) whereas the highest rates of weight loss belong to taluses (49.3% in Daneh Khoshk and 48% in Damavand). The alluvial fans have an average state. Another noticeable point is the high weight loss in Los Angeles test in Damavand aggregate. Due to having harder mineral, igneous aggregate have more abrasion resistance, but this research illustrates that the weight loss resulting from Los Angeles test in these aggregates is high. This is because of virtues texture that weakness against the impact as well as their high porosity.
Conclusion
The result of this research indicates that the volume of aggregate weight loss in Los Angeles test is related to aggregate accumulation environment. The extent of aggregate abrasion resistance is lowest in talus medium and increases in alluvial fan and river environment, respectively. The difference in aggregate abrasion resistance in various areas result from geology process differences that applies to aggregates in various environment. The extent of caring particles in talus environment is very low and the type of movement is mass or sliding type in these media, micro-crack and weak parts remains within aggregates. The surface of micro crack is weak such that breaks easily in Los Angeles test due to the pressure results from the impact of aggregate, as well as the impact of steel ball on aggregate leading to aggregate breakages. Aggregates move more distances in alluvial fan and river. Aggregate strike together in riverbed and alluvial fan yielding to aggregates breakages from micro-cracks. As the movement distance increases, aggregates approach more to intact rock. During the particles move, the weathered and weak parts are damaged by aggregate abrasion to riverbeds and alluvial fan, and more resistant and harder aggregates remain. As the water current increases, the aggregates impact each other harder, more resistant micro-crack breakages and this change leads to decrease the weight loss in Los Angeles test.
./files/site1/files/132/1Extended_Abstracts.pdf
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Volume 13, Issue 2 (8-2019)
Volume 13, Issue 2 (8-2019)
Abstract
Introduction
Retaining walls are geotechnical structures built to resist the driving and resistant lateral pressure. In terms of serviceability life, these walls are divided into two groups including short-term structures (temporary), such as urban excavation project, and long-term (permanent) structures, such as Mechanically Stabilized Earth Walls (MSE Walls). Retaining walls are implemented by two main methods including Top-down and Bottom-up. Among the reinforcements applied in the Bottom-up walls, one can name geocells, geogrids, metal strips, and plate anchors. On the other hand, the common reinforcements applied in the Top-down walls are grouted soil nails and anchors and helical (screw) soil nails and anchors.
Plate anchors are burial mechanical reinforcements that have one or multiple bearing plates with a bar or cable to transfer the load to an area with stable soil. Among different types of plate anchor applied in onshore and offshore projects, one can name simple horizontal, inclined, and vertical plate anchors, deadman anchors, multi-plate anchors, cross-plate anchors, expanding pole key anchors, helical anchors, drag embedment anchors, vertically loaded anchors (VLAs), suction-embedded plate anchors (SEPLAs), dynamically-embedded plate anchors (DEPLAs) like Omni-max and torpedo anchors, and duckbill, manta ray and stingray anchors.
The present research reports the results from physical modeling of plate anchor retaining walls under static loading. The evaluation parameters in this work include the geometry, dimension, and reinforcement configuration of plate anchors on wall stability. PIV technique was employed to observe critical slip surface. It is worth mentioning that PIV is an image processing technique firstly used in the field of fluid mechanics to observe the flow path of gas and fluid particles. This method was used in geotechnical modeling by White et al. (2003) and few reports are already available about its application to observe wedge failure of mechanically stabilized retaining walls.
Material and methods
To carry out tests at a laboratory scale, a dimensionality reduction ratio of 1/10 was applied. Thus, all dimensions of the designed retaining wall were divided by 10. As a result, a retaining wall with a height and length of 3000 mm was reduced to a wall with 300×300 mm2 dimensions. To build a retaining wall, a chamber was designed with a length, width, and depth of 1000 mm, 300 mm, and 600 mm, respectively.
The soil used in all tests was the sandy soil supplied from Sufian (in Eastern Azerbaijan, Iran). According to the Unified Soil Classification System (USCS), the soil is classified as poorly graded sand with letter symbol ‘SP’.
To create a perfect planar strain condition and prevent any friction between the footing and the lateral sides of the test box, the footing length was selected 1 mm smaller than the 300 mm width of the test chamber. Therefore, the length, width, and thickness of footing were selected as 299, 70, and 30 mm, respectively.
The length and diameter of applied tie rods were respectively 300 mm and 4 mm, which are the smaller scales of 3000 mm length and 40 mm diameter tie rod. The two sides of the tie rods were threaded to plate anchors and wall facing. Four polished square and circular anchor plates with two different areas were used. The area of small and medium circulars are respectively equivalent to the area of small and medium square plates.
Because no post-tensioning occurs in these plate anchors, the horizontal and vertical distances were both selected as 1500 mm. By applying a dimensionality reduction coefficient of 1/10, a 150 mm center-to-center distance was obtained for reinforcements in the wall. Accordingly, three applied reinforcement configurations including 5-anchor, diamond, and square configurations were used.
To construct permanent retaining wall facing, prefabricated or precast concrete blocks with a thickness of 300 mm were used. Wood (2003) conducted a dimensional analysis and introduced four types of material with different thicknesses for a 300 mm concrete facing in laboratory modeling. Accordingly, a 0.9 mm thick aluminum plate was used in the experiments performed in the present work.
Results and discussion
With an increase in dimensions of anchor plates, an increase in bearing capacity of footing and a decrease in horizontal displacement of the wall are noticed. By comparing the 24 mm footing settlement in three configurations, with changing dimension of the plates from C1 to C2 and S1 to S2 respectively, 63% increases are observed in bearing capacity of the wall.
An increase in anchor plate dimensions results in a significant decrease in wall displacement. Therefore, changing the plates from C1 to C2, S1 to S2 leads to 24% and 28% declination in wall displacement.
By changing reinforcement configuration from square to diamond, diamond to 5-anchore, and square to 5-anchor, respectively, 27%, 31%, and 67.5% increases in bearing capacity for small plates, 9.2%, 27%, and 38% for medium plates are achieved using a comparison of the final loading steps in experiments. An analogy of percentages shows that a decrease in the effect of changing the reinforcement configurations on the bearing capacity of the wall with an increase in plate anchors dimensions is reached.
Conclusion
In the present research, a set of laboratory experiments were carried out to evaluate the stability of mechanical retaining walls reinforced with plate anchors with different geometries (square and circular), sizes (small and medium), and configurations (diamond, square, and 5-anchor). The main results of the present work can be outlined as follows:
• The maximum bearing capacity is for the 5-anchor configuration since it has one more reinforcement. After 5-anchor configuration, the diamond configuration results in a higher bearing capacity compared to the square configuration.
• Circular anchor plates compared to square anchor plates provide a higher wall stability and in the most of the experiments lead to higher bearing and lower displacement in the wall.
• Wall displacement in a diamond configuration with one less reinforcement shows a little difference with 5-anchor configuration. The maximum wall displacement occurs in a square configuration and more wall swelling is observed in the wall middle height due to inefficient anchors configuration in the wall.
./files/site1/files/132/2Extended_Abstracts.pdf
Erfan Naderi, Adel Asakereh, Masoud Dehghani,
Volume 13, Issue 2 (8-2019)
Volume 13, Issue 2 (8-2019)
Abstract
Introduction
Bearing capacity is very important in geotechnical engineering, which depends on factors such as footing shape, stress distribution under footing and failure mechanism of soil. Construction of the footing near a slope affects the behavior of footing and reduces the bearing capacity. Also, construction of structures on soft soil usually involves problems such as excessive settlement, deformation and stability problems. In order to increase the bearing capacity, especially in soft soils, one method is adding stone columns to soils. In this method 15 to 35 percent of unsuitable soil volume is replaced with appropriate material. In this research, the bearing capacity and settlement of a strip footing on a clayey slope reinforced with stone columns is investigated. For this purpose, a series of small-scale model tests was performed on the slope reinforced with both types of ordinary and vertical encased stone columns. The effects of length of stone column and location of stone column on the behavior of footing was studied and the optimum length of column and best location for column were determined. Also, some tests were performed on the effect of group stone columns on the footing and the efficiency of columns was investigated.
Material and methods
In order to determine properties of clay soil, stone column and encasement material, some preliminary standard tests were performed. The stone column material was selected with aggregate size ranging from 2-10 mm considering the scale effect. The performance of stone column depends on the lateral confinement provided from the surrounding soil and this lateral confinement represents undrained shear strength of the soil. In very soft soils (cu<15 kPa), the lateral confinement is not adequate and the stone column cannot perform well in carrying the required bearing capacity. For this reason, a series of undrained shear strength standard tests were carried out on clay samples with different water contents. According to these tests, the amount of water content of clay related to cu-15kPa was equal to 25%; while the natural water content of the clay was 4%. Therefore, the additional amount of water was weighted and added to clay. The apparatus of this research was consisted of two main parts including a test box and a hydraulic loading system. The test box dimensions should be such that for all states of the tests, the stress in the soil applied from the loading would be almost zero at all boundaries of the box. Thus, a box was built to accommodate the clay slope with 150 cm×120 cm×30 cm dimensions. The test box was built using steel material and steel belts were welded around it to prevent the deformation at high loads. The front side of the box was made from two pieces of tempered glass and a 10 cm×10 cm grid was drawn on them, for making the slope during construction and observation of deformations during the loading easier. The model strip footing dimensions were 29 cm length, 10cm width and 4cm height and it was made from steel to have no deformation during the loading. The displacement of the footing was measured using two dial gauges with accuracy of 0.01 mm.
The clay was filled in the test box in 5 cm thick layers and compacted with a special 6.8 kg weight tamper. All model stone columns were constructed using the replacement method. In this method, a 10 cm diameter open ended steel pipe was inserted into the soil and the clay within the pipe was excavated. Then the stone column material charged into the hole in 5 cm layers and each layer was compacted using a 2.7 kg special circular steel tamper with 10 blows. The 5cm compactions were repeated until the construction of ordinary stone column was completed. For construction of vertical encased stone columns, the cylindrical encasement mesh should be constructed first. Then, after excavating the hole, the prepared encasement mesh was placed inside the hole and the aggregates were charged into the hole in 5 cm layers and compacted.
Results and discussion
The loading method used in all tests was a stress control method. Bearing capacity values were determined from pressure-displacement diagrams using tangent method. All test results show that when any type of stone columns was added to slope, the bearing capacity of adjacent footing was increased. Vertical encasing of stone columns leads to a further improvement in the behavior of the footing. Influence of length of ordinary stone columns on the behavior of strip footing near clayey slope, was studied for four different lengths. Results show that, the optimum length of stone columns giving the maximum performance is about 4 times their diameter. Also, the location of column for both ordinary and vertical encased stone columns was studied using a series of laboratory tests and results show that the best location for the stone column is right beneath the footing. Also, group stone column tests resulted that for both ordinary and vertical encased types of stone columns, the group of two columns had a better efficiency than the group of three columns.
Conclusion
In this investigation, some model tests with 1/10 model scale on a strip footing near a clayey slope reinforced with stone columns were performed and the effects of different parameters such as stone column length and location were studied. Based on results from experiments on different states of stone columns, the following concluding remarks may be mentioned:
- The maximum encasement influence was observed when the encased stone column is placed under the footing.
- The optimum length of ordinary stone columns which are placed beneath the strip footing gives the maximum performance more than 4 times to their diameter.
-Bulging failure mode governs when the stone column is placed under the footing. When stone column is not beneath the footing, the failure mode was lateral deformation.
- Comparing the different locations of stone columns in the slope shows that for both ordinary and vertical encased stone columns, the best location having the most influence on the strip footing is under the footing and with increasing the spacing between column and footing, the bearing capacity is reduced.
./files/site1/files/132/7Extended_Abstracts.pdf
Seyed Davoud Mohammadi, Elahe Hosseinabadi2,
Volume 13, Issue 2 (8-2019)
Volume 13, Issue 2 (8-2019)
Abstract
Introduction
In regard to consumptions of oil materials by human, soil contamination causes worriness in environment and geotechnics areas in previous years, such that studying of soils lead to soil refine, soil bearing capacity and soil changing by infiltration of contamination. The rates of problems on environment are different and it depends on soil types and its structure, organic materials values, soil permeability, climate and type of contamination. In viewpoint of geotechnics, many investigations have been done on various contaminated soils that their result leads to optimum application of those as road construction and decrease of costs. In this research, with adding of different percentages of gasoil into the soil, engineering properties of contaminated soils were investigated and its effect on the erodibility of soils was studied. Regarding to the Hamedan oil storages complex extension and lateral installations, the study of contaminated soils are essential. Also, because the location of that complex is at urban area, the environmental risk of leaking of oil materials is available. Thus, the goal of this research is to investigate the erodibility of contaminated soils at the studied area.
Material and methods
Hamedan oil storages complex is located about 17.7 km far from Hamedan city. In order to study engineering geological properties and erodibility of three layers of soils in studied area, the soil samplings were done from three soil layers. Based on the field and laboratory results, all of three soil layers were classified into SM class and had too much lime (Table 1). Testing program is divided into engineering geological tests and erodibility tests. All of the engineering geological tests on the uncontaminated and contaminated soils were undertaken according to ASTM (2000) (Table 2). In order to prepare the contaminated soils and to determine the maximum absorbable gasoil, the soil samples were contaminated by gasoil and some standard compaction tests were undertaken on the soils. According to the test results, upper and lower layers were saturated by 19% of gasoil and middle layer was saturated by 15% of gasoil. After determination of gasoil saturations percentages for studied soil layers, the 7, 13 and 19 percentages of gasoil were added into the upper and lower layers and the 5, 10 and 15 percentages of gasoil were added into the middle layer. Thus, for engineering geological tests, 9 samples of contaminated soils were prepared.
Table 1. Soil properties of studied area
| Lime percentage | Soil type | PI% | PL% | LL% | Sample | Layer |
| 85.15 | SM | 8.99 | 40.65 | 49.64 | L1 | Upper |
| 62.16 | SM | 15.49 | 32.12 | 47.61 | L2 | Middle |
| 88.72 | SM | 15.46 | 27.14 | 42.60 | L3 | Lower |
| Standard No. | Test type |
| ASTM-D422 (2000) | Soil classification |
| ASTM-D4318-87 (2000) | Atterberg limits |
| ASTM-D698 (2000) | Standard Compaction |
| ASTM-D3080 (2000) | ِDirect shear |
| ASTM-D2166-87 (2000) | Uniaxial Compressive Strength |
All of the soil samples for uniaxial compressive strength tests were prepared in maximum dry unit weight and optimum water content. To prepare the soil samples, a split tube mould with 5*10 cm of dimensions was used. Based on that test, the soil samples are set under axial load and failure occurred at the end of the test.
To investigate the effect of gasoil on soil erodibility, first the erodibility tests by using rainfall simulator were done on uncontaminated soils and then, on contaminated soil with different percentages of gasoil. All of soil samples for erodibility test were prepared into the pans with 30*30*15 cm of dimensions and in maximum dry unit weight and optimum water content. The thickness of soil samples were 5 cm and the gravelly drainage layers were 10 cm. The rainfall intensity was equal to rainfall intensity of sampling area (29 mm/hours) and the steepness of soil samples were equals to sampling area steepness (10 to 40 degrees). After catching of runoff and drained water, the eroded soils were weighted and the weight loss of soil samples was calculated.
Results and discussion
All of the engineering geological tests results are shown in Table 3. With increasing of the gasoil percentages, dry maximum unit weights of all three layers have decrease trends while the optimum water contents have increase trends. Surrounding of the soil grains by gasoil and water causes the easy sliding of grains and more compaction. The Atterberg test results shows that liquid and plasticity limits of soil had increase trend with increasing the gasoil. In the middle layer its trend is more than the others. Because the viscosity of gasoil is more than the water viscosity, the adhesion of contaminated soil would be more than the uncontaminated soil and then, the liquid and plasticity limits of contaminated soils are more than the others. The uniaxial compressive strength results show that the undrained strength of contaminated soils would be decrease with increasing the gasoil content. This behavior is the result of sliding of the contaminated soil grains on each other.
The results of erodibility tests results are shown in Table 4. The erodibility would be increase with increasing the gasoil percentages. Also, it would be increase with steepness dips degrees. In compare to the uncontaminated soils, the maximum weight loss of the contaminated soil is 608.3 kg/m2.hr in 15% of gasoil and 40 degrees of steepness in L2 layer. The minimum weight loss of the contaminated soil is 13.33 kg/m2.hr in 0% of gasoil and 10 degrees of steepness in L3 layer. Thus, the assessment of gasoil effect on erodibility of soils is very important.
Table 3. Results of the engineering geological tests on the uncontaminated and contaminated soil samples
| Layers | Gasoil percentage | Liquid limit (%) | Plasticity limit (%) | Plasticity Index (%) | Maximum dry unit weight (g/cm3) | Optimum water content (%) | Internal friction angle (ɸ) | Cohesion (kPa) | Uniaxial compressive strength (kPa) |
| L1 | 0% | 49.64 | 40.65 | 8.99 | 1.65 | 22 | 4.6 | 7.4 | 18.4 |
| 7% | 54 | 40.13 | 13.87 | 1.87 | 10.5 | 4.04 | 6.6 | 8.7 | |
| 13% | 55.67 | 43.71 | 11.95 | 1.88 | 8.5 | 3.26 | 3.7 | 7.8 | |
| 19% | 55 | 40.65 | 14.34 | 1.96 | 3 | 2.3 | 2.75 | 3.5 | |
| L2 | 0% | 47.61 | 32.12 | 15.49 | 1.87 | 14 | 6.97 | 6 | 9.6 |
| 5% | 64 | 40.39 | 23.61 | 2.08 | 9 | 5.73 | 5.5 | 7 | |
| 10% | 66 | 46.63 | 19.37 | 2.11 | 6 | 5.15 | 4 | 6.1 | |
| 15% | 68 | 49.09 | 18.91 | 2.14 | 3.5 | 4 | 2 | 1.25 | |
| L3 | 0% | 42.6 | 27.14 | 15.46 | 1.62 | 22.3 | 2.6 | 10.7 | 22.6 |
| 7% | 56 | 39.27 | 16.72 | 1.92 | 9.5 | 2.41 | 8.5 | 10.5 | |
| 13% | 57.18 | 41.66 | 15.51 | 2.01 | 6 | 2.17 | 7/3 | 7.8 | |
| 19% | 63 | 42 | 20.99 | 2.03 | 3 | 1.45 | 6.9 | 4.4 |
Table 4. Results of the uncontaminated and contaminated soils in different steepness*
| Layer | Gasoil percentage | Dip of 10◦ | Dip of 20◦ | Dip of 30◦ | Dip of 40◦ |
| L1 | 0% | 56.4 | 70.4 | 73.2 | 111.06 |
| 7% | 149.6 | 178.8 | 248.4 | 202.53 | |
| 13% | 166.53 | 227.2 | 241.6 | 278.93 | |
| 19% | 227.86 | 256.66 | 419.86 | 334.66 | |
| L2 | 0% | 30.8 | 102.53 | 156.53 | 317.73 |
| 5% | 58.66 | 142.66 | 151.2 | 324.8 | |
| 10% | 74.93 | 168.66 | 244.53 | 365.73 | |
| 15% | 105.73 | 283.73 | 359.86 | 608.13 | |
| L3 | 0% | 13.33 | 75.06 | 79.46 | 86.26 |
| 7% | 55.2 | 98.53 | 78.13 | 81.06 | |
| 13% | 124.13 | 176.8 | 145.73 | 140.06 | |
| 19% | 196.4 | 279.46 | 200.93 | 210 |
1. According to the grain size analysis test results, all of three layers of soils around the Hamedan oil storage are SM with too much lime.
2. With increasing the gasoil, liquid and plasticity limits of three soil layers had increase trend. its trend in the middle layer is more than the others.
3. According to the erodibility results of contaminated soils, the weight loss of middle layer was more than the other layers because of the middle soil layer had lower percentages of lime.
4. The gasoil causes decrease of soil strength and increase of weight losing. Thus, the uniaxial compressive strength and weight losing have reverse correlation.
5. With increasing of the contamination, the cohesion and internal friction angle of soils would be decrease and then, the erodibility would be increase.
6. Maximum of erosion of contaminated soils was in 15 and 19 percentages of gasoil and it was three times more than that of uncontaminated soils.
7. The critical steepness of uncontaminated soil layers was 40 degrees for all three layers, but it was different for contaminated soils,
8. Regarding to the location of Hamedan oil storages, the environmental risk of oil leakages and erodibility of contaminated soils are certain.
./files/site1/files/132/5Extended_Abstracts.pdf
Hadiseh Mansouri1, Rassoul Ajalloeian, Alireza Nadimi,
Volume 13, Issue 3 (11-2019)
Volume 13, Issue 3 (11-2019)
Abstract
Introduction
Generally, in engineering geology physical and mechanical properties of rocks are investigated in macroscopic scale, and less attention is paid to investigate the texture and microstructure developing in rock during deformation. Salt rock, as a best example of ductile rocks, has attracted the attention of many researchers. Compared to silicate rocks, salt rock exhibits extensively ductile behavior at even low temperature and pressure. In micro-tectonics, salt is important, because of it is useful as an analogue material for understanding the microstructural processes and textural development in silicate rocks. Deformed salt rock can display microstructures developed in silicate rocks at high pressures and temperatures. Regarding the similarity between microstructures of salt rock and silicate rocks, investigation of microstructure and deformation mechanism in salt rock can be helpful in understanding the main cause of the squeezing phenomenon in tunnels.
One of the effective factors on squeezing phenomenon is the structures and microstructures of rock. Rock mass classifications that contain rock mass structures are used in the predicting methods. But, so far, no attention has been paid to the role of rock microstructure in predicting the squeezing phenomenon.
This study is aimed to identify deformation mechanisms occurring in microscopic scale in rocks and lead to tunnel convergent in large scale. To achieve this goal, the microstructures in a naturally deformed Late Pre-Cambrian to Early Cambrian Hormuz salt rock from the active Deh Kuyeh salt fountain in Fars province were investigated using Electron Backscatter Diffraction (EBSD).
Materials and Methods
Deh Kuyeh salt diapir was located at about 27 km NE of Lar city. Salt samples were taken from top of the east and west glaciers (S1 and S2) and from the middle part of diapiric stem (sample S3). Raw samples were first cut dry into slabs (approximately 3´2 ´1 cm). Thin sections were prepared following the procedure of Schleder and Urai (2005) and Urai et al. (1987).
Halite crystallographic orientation data were collected using a Zeiss SIGMAVP FEGSEM. EBSD patterns were collected using an accelerating voltage of 30 kV, beam current of ~ 100 nA and a working distance of about 30 mm. Oxford instruments AZTEC software was used for data acquisition. EBSD large step size (50 mm) mapping was used to examine the overall microstructure in each sample. EBSD data were processed using HKL Channel 5 software.
Results and Discussion
All samples showed relatively similar microstructures. Samples comprise a small number of large grains in a matrix of smaller grains. Most grains were irregular in shape with lobate boundaries and internal distortion. Microstructural study revealed that the ductile flow of the salt was accommodated by dislocation creep and dynamic recrystallization. Salt grains show lattice distortion and a prevalence of low-angle boundaries that are evidence for dislocation creep and recovery processes. Misorientation analysis suggests that (110) <110> and (111) <110> slip systems are responsible for crystal plastic deformation of salt grains. Schmid factor analysis showed that stresses acting on inclined directions lead to the maximum activity of these slip systems.
The observed microstructures in the salt are comparable with the microstructures presented for schist samples from Himalaya region. The rock along Himalaya main trusts also showed evidence of dislocation creep and development of crystallographic preferred orientation. Hence, this article suggests that the rock type and its microstructures are the most important factors in occurrence of tunnel convergent.
Conclusions
This article proposes that deformation mechanisms occurring in micro-scale control the rock behavior in large scale. All rocks can behave as a ductile material depending on the temperature and pressure. In intrinsically ductile rocks like salt rock, presence of many active slip systems facilitates rock deformation under lower pressures and temperatures than silicate rocks. High tectonic stresses in shear zones lead to development of a strong shape preferred orientation and crystal preferred orientation in rocks. These microstructures facilitate rock deformation under stresses exiting in tunnels. It can be said that rock type and tectonic history of the area play the most important role in occurrence of squeezing phenomenon. Other factors such as current stress system in the area control deformation speed in tunnel. It seems investigating microstructures of rocks from tunnel route before and after excavation can be effective in identifying places with high possibility of squeezing.
Fahimeh Salehi Moteahd, Naser Hafezi Moghaddas, Golamreza Lashkaripour3, Maryam Dehghani4,
Volume 13, Issue 3 (11-2019)
Volume 13, Issue 3 (11-2019)
Abstract
Introduction
Mashhad city, the second largest metropolis of Iran, is located in an arid and semi-arid region. Overexploitation of groundwater in Mashhad plain has caused up to 22.5-meter drop in the groundwater level from 1984 to 2013. The groundwater depletion in the unconsolidated aquifer has resulted in subsidence and cracks on the land surface. To determine the land subsidence rate map and the reasons for hot spot subsidence, the latest Envisat images of the ESA Space Agency's Archive for Mashhad plain were used. leveling and GPS data were combined with the radar interferometry results and the annual subsidence rate maps with high precision were obtained. Finally, the geology and soil texture maps of study area are compared to the land subsidence map.
Methods and results
To assess the land subsidence in Mashhad plain three methods of leveling, GPS and Insar are used. Leveling data are available in three profile of
Discussion
The rate and distribution of land subsidence in Mashhad plain are affected by geological factors such as soil texture, deposit thickness, geological structures and groundwater drawdown. The geological and geophysical studies and exploratory drilling results in the Mashhad Plain indicate that the bedrock morphology is very rough. The bedrock outcrops in some places while in some other places covered by more than 300 meters alluvial deposits. Generally, by distance from the mountain, alluvium thickness and as a result the likelihood of subsidence would be increased. Mashhad plain is surrounded by the active and quaternary faults in the north and south edges. In the north of Mashhad plain Marly bedrock is uplifted by Tous fault and outcropped in the north of fault. In the south of Mashhad two normal faults have resulted to the increase of alluvium thickness in south and central of Mashhad plain. The change of river pathway also let to deposition of a sequence of the fine-grained and coarse-grained soils in central of plain between Toos and southern branch of South Mashhad fault (F2).
used to draw the cross section
In order to evaluate the subsurface conditions and its effect on the land subsidence, the soil texture are studied using the deep water wells and piezometers log (Figure 2). Fig. 3 shows the longitudinal section (northwest to southeast) of the area. As it can be observed, the soil texture includes of alternation of fine and coarse grains layers (Figs. 4). In this condition, sandy soils help to shortening the drain path of clayey layers and leads to acceleration of the consolidation. The average rate of annual subsidence in the area is 14 cm for one meter of drop in the groundwater level.
Nowadays, in the urban area, due to the urban sewage waters, there is a rising of groundwater level. Therefore, no land subsidence has occurred in the central parts of the city. It is expected by completion of urban sewage network about 62 million cubic meters of sewage water will be eliminated from the aquifer recharge, which will cause a notable drop in the groundwater level and prominent land subsidence in specific area of the city. Considering the geological conditions and the operation of the existing faults, it is expected that in the case of groundwater drop, no significant subsidence will occur in south of the F2 fault, due to the decrease in the alluvium thickness and to the coarse texture of the soil. But in the northern and northeastern parts of the city, which are located between F2 and the Tous faults, high rate of land subsidence is expected.
Figure 4: The cross section of soil texture and the annual average rate of land subsidence and groundwater level drop
Conclusions
Using the radar interferometry processing, the highest annual rate of subsidence in Mashhad plain is about 32 cm/year. Land subsidence in Mashhad plain has an increasing trend and the geological conditions have a critical role in the subsidence rate and its pattern. Generally, soil texture near the mountain area in South is coarse and grain size decreases toward the center of the plain. But because the outcrop of Marly formation in the north slopes, soil texture is mainly fine grains. In the center of Mashhad plain soil texture constituted of fine and coarse grains which are converted together as inter fingering facieses, which have a critical role in decreasing of the consolidation time and increasing the land subsidence rate. It is predicted by complimenting of the urban wastewater network, the groundwater level will be dropped in the city area and the northwest and southeast subsidence ellipsoids which already can be seen will be connected together. Therefore, the area between F2 and Toos faults, will be shown the highest rate of subsidence, due to high thickness and fine-grained soil texture../files/site1/files/133/5Extended_Abstracts.pdf
Fatemeh Abtahi, Mehdi Hosseini, Akbar Shah Hosseini,
Volume 13, Issue 3 (11-2019)
Volume 13, Issue 3 (11-2019)
Abstract
Introduction
Unsystematic execution of blasting process may result in serious damages. Blasting is a very complex process and almost all of blast designs are made based on empirical relations resulting from trial and error. In recent decades, considerable development of numerical methods has been made possible to achieve high accuracy study of blast effects on surface and subsurface structures. Among these methods are boundary element method, finite difference method and finite element method. It should be mentioned that there is currently no software which might be able to completely simulate blast process. But the UDEC software is able to simulate different aspects of this phenomenon through simplification and focusing on each aspect. Therefore, the UDEC software was selected. In the present study, the modeling has been performed for Ghareh Changool ramp of Zehabad Zinc and Lead Mine against blast loads.
Material and methods
Zehabad Ore deposit is located around 2 km south of Zehabad Village of Tarom Sofla County, 56 km to northwest of Qazvin at 49˚ 25' east longitude and 36˚ 28' north latitude.
The formation surrounding the ore deposit is generally made up of pyroclastics, lavas and sedimentary rocks of Eocene age (Karaj Formation) which have been divided into 22 stratigraphic units. Lithological composition of the tuff units are often rhyolithic to dacitic and the lava units are consisted of rhyolite, dacite and andesite.
To accomplish this study, we took rock blocks from Ghareh Changool ramp. Then, the blocks were cored in the laboratory to provide cylindrical samples for doing uniaxial compressive, triaxial, Brazilian and direct shear tests. Physical and mechanical properties of the tuff samples were determined according to ISRM standards.
In the present study, field studies were done to calculate strength parameters and properties of the joints. Based on these studies, three major joint sets were determined. In order to obtain the shear strength parameters of the joints, the cylindrical samples of andesitic tuff were molded by concrete and direct shear test was done on all of the joints according to ASTM D 4554.
Results and discussion
To simulate the complex conditions of blast process, we used the discrete element software of UDEC for numerical modeling considering the discontinuity of the medium. To do a dynamic analysis, first the model should come to equilibrium in the static state. The space considered to be modeled in the study was a horse-shoe-shaped ramp with 4 m base, 4 m height and 1.5 m arc radius which was located in rocky medium consisting of tuff. The height of overburden above the roof of the ramp was about 190 m. The dimensions of the model in UDEC was 20*20 m2. The behavioral model considered for the rock blocks and discontinuities were the elastic isotropic and surface contact of the joint (elasto-plastic) associated with Coulomb sliding failure, respectively. After defining the absorbing boundary conditions, the dynamic loads were applied to the model based on the defined time period. In mines stability and blasting process, the dynamic load resulting from the blast is often applied to a model as a pulse. By application of dynamic load and considering the other mentioned variations with respect of static analysis, the dynamic response of underground space could be estimated under vibration load of blast or earthquake. To do this, the blast impact wave was applied to the left side of the model as exponential pulse with maximum pressure of 4.41 MPa and time width of 0.7 to 7 msec. The results of the numerical modeling in static analysis indicated that no block would fall (Fig. 1). After application of the blast load, the results showed that there was no falling around the ramp (Fig. 2).
Conclusion
1. In static condition, after initial equilibrium no block was fallen into the ramp, regarding the blocks’ magnification plots, as a result the ramp was stable in the static loading.
2. In dynamic loading case, considering the displacement plots around the ramp and the low values of these displacements, as well as, magnification plot of the blocks 40 msec after the blast it can be said that no block was fallen into the ramp. Therefore the ramp was stable in the dynamic loading case and there was no need to install support system. ./files/site1/files/133/1Extended_Abstracts.pdf
Majid Aslani, Javad Nazariafsha, Navid Ganjian,
Volume 13, Issue 3 (11-2019)
Volume 13, Issue 3 (11-2019)
Abstract
Introduction
Stone column installation method is one of the popular methods of ground improvement. One of the common uses of stone columns is to increase slope stability. Several studies have been performed to examine the behavior of stone columns under vertical loads. However, limited research, mostly focused on numerical investigations, has been performed to evaluate the shear strength of soil reinforced with stone column. The study presented herein is an experimental program, aimed to explore the shear strength of loose sand bed reinforced with stone column. Direct shear tests were carried out on specimens of sand bed material, stone column material and sand bed reinforced with stone column, using a direct shear device with in-plane dimensions of 305*305 mm2 and height of 152.4 mm. Experiments were performed under normal stresses of 35, 55 and 75 kPa . In this study, 4 different area replacement ratios (8.4, 12, 16.4 and 25%), and 3 different stone column arrangements (single, square and triangular) were considered for investigation. The obtained results from this study showed that stone column arrangement had an impact on improving the shear strength of stone columns. The most increase in shear strength and stiffness values was observed for square arrangement of stone columns and the least increase was for single stone columns. This study also compares the equivalent shear strength values and equivalent shear strength parameters (internal friction angle and cohesion) measured during experiments with those predicted by analytical relationships. Results show that shear strength values and shear strength parameters measured from experiments are higher than those obtained from analytical relationships. Accordingly, a corrective coefficient was calculated for each column arrangement to represent the correlation between experimental and analytical results.
Material Properties of Loose Bed and Stone Column
Fine-grained sand with particle size ranging from 0.425 to 1.18 mm was used to prepare loose sand bed, and crushed gravel with particle size ranging from 2 to 8 mm was used as stone column material. The sand material used as bed material had a unit weight of 16 kN/m3 and a relative density of 32.5%, and the stone material used in stone columns had a unit weight of 16.5 kN/m3 and a relative density of 80%. The required standard tests were performed to obtain the mechanical parameters of bed material and stone column material. As the diameters of model scale stone columns were smaller than the diameters of stone columns installed in the field, the particle dimensions of stone column material were reduced by an appropriate scale factor to allow an accurate simulation of stone columns behavior.
Testing Procedure
In this study, large direct shear device with in-plane dimensions of 305*305 mm2 and height of 152.4 mm was used to evaluate the shear strength and equivalent shear strength parameters of loose sand bed reinforced with stone column. Experiments were performed under normal stresses of 35, 55 and 75 kPa.
Two class C load cells with capacity of 2 ton were used to measure and record vertical forces and the developed shear forces during the experiments, and a Linear Variable Differential Transformer (LVDT) was used to measure horizontal displacement. All achieved data from the experiments including data on vertical forces, shear forces and horizontal displacements were collected and recorded using a data logger, and an especial software was used to transfer data between the computer and the direct shear device. All specimens were sheared under a horizontal displacement rate of 1 mm/min.
Testing Program
Experiments were performed on single stone columns and group stone columns arranged in square and triangular patterns. The selected area replacement ratios were 8.4, 12, 16.4, and 25% for single stone columns, and 8.4, 12 and 16.4% for square and triangular stone column arrangements. To eliminate boundary effects, the distance between stone columns and the inner walls of the shear box was kept as high as 42.5 mm. In total, 12 direct shear tests were carried out, including 2 tests on loose sand bed material and stone column material, and 10 tests on stone columns with different arrangements. From the tests performed on group stone columns, 4 tests were performed on single stone columns, 3 tests on stone columns with square arrangement and 3 tests on stone columns with triangular arrangement. Hollow pipes with wall thickness of 2 mm and inner diameters equal to stone column diameters were used to construct stone columns. To prepare the specimens, first, the hollow pipes were installed in the shear box according to the desired arrangement. Then, bed material with unit weight of 16.5 kN/m3 was placed and compacted in the box in 5 layers, each 3 cm thick. Stone material was uniformly compacted to construct stone columns with uniform unit weight. The compaction energy was 67 kJ/m3 in all tests.
Results and discussion
In this paper, the behavior of stone columns under shear loading was experimentally investigated in large direct shear device by performing tests with different area replacement ratios (8.4, 12, 16.4, and 25%), different stone column installation arrangements (single, square and triangular), and different normal stresses (55, 75 and 100 kPa). The key findings of this study are as follows:
1. Shear strength increases with increase of area replacement ratio due to the higher strength of combined soil-stone column system, and due to the increase of stone column area effective in shear plane. The amount of shear strength increase with area replacement ratio is low for ratios lower than 15%. However, this amount is higher for area replacement ratios higher than 15%.
2. For stone columns with equal area replacement ratios, higher shear strength was mobilized in stone columns with square and triangular installation arrangements compared to single stone columns. Among the installation patterns investigated in this study, stone columns with square arrangement experienced the highest increase in shear strength value, while single stone columns experienced the lowest. One of the reasons of shear strength increase in square and triangular patterns is the increase of confining pressure applied by stone columns to the soil between them. Another reason is the increase the total lateral surface by changing the column arrangement from single column to square and triangular patterns. This increased lateral surface increases the lateral force imposed on the stone columns, resulting in higher shear strength mobilization of stone material.
3. The slope increase of shear strength-horizontal displacement curves shows that soil-stone column system has higher stiffness than loose sand bed, and this stiffness varies with area replacement ratio and installation pattern. The maximum stiffness values refer to stone columns installed in square pattern and the minimum values refer to single stone columns. In general, stone column installation pattern has an effective role in increasing stiffness.
4. Results show that shear strength parameters increase in soil reinforced with stone column. The maximum increase in internal friction angle refers to stone columns with square pattern and the minimum increase refers to single stone columns.
5. The equivalent shear strength values measured from experiments are higher than those obtained from analytical relationships. Accordingly, it is conservative to use analytical relationships to calculate shear strength parameters. It is worthy to mention that these relationships assume that the value of stress concentration ratio is equal to 1. Results from this study indicate that the value of stress concentration ratio should be accurately calculated and used in the relationships.
6. As discrepancy was observed between values measured from experiments and those obtained from analytical relationships, corrective coefficients were calculated to modify analytical relationships. These coefficients were computed and presented based on stone column installation pattern, area replacement ratio and the applied normal stress values../files/site1/files/133/2Extended_Abstracts.pdf
Ali M Rajabi, Alireza Sajdeh,
Volume 13, Issue 4 (12-2019)
Volume 13, Issue 4 (12-2019)
Abstract
Introduction
Concrete faced rockfill dams have been considered in recent years more than other types of dams due to their low dependency on the bed and the shape of the valley, as well as the simpler construction technology. In this regard, rockfill dams are a suitable substitute for embankment dams because of higher stability of the body and the availability of rock aggregates. On the other hand, because the permeability of rock aggregates is much higher than other materials, different methods are used to seal these types of dams. One of these methods is the use of non-impermeable concrete facing in the upstream of these dams. This particular type of gravel dams is called Concrete-Faced Rockfill Dams (CRFD). In this study, a contact element with a definition of elastic-plastic failure in the modeling process is proposed to simulate the surface separation and re-contact of the concrete face with the rockfill surface of the dam.
Method
In this paper, behavior of a concrete faced rockfill dam under earthquake loads is investigated. For this purpose, near-field earthquake records with focal depth lower than 15 km (for example Tabas earthquake 1978, M=7.4, and San Fernando earthquake 1970, M=6.6) are used. Moreover, to study the dam behavior under dynamic loads, interaction between concrete face and rockfill part of the dam is investigated and finally, some parameters including displacement, absorbed energy and base shear are evaluated. So, finite element method and Abaqus software is used for the study. Verification of the models is carried out using the results of previous researches by conducting modal analysis and determining natural vibration period. Then, the interaction between the concrete face and rockfill part as well as the effect of water level changes in stability of dam under dynamic load is investigated. Concrete behavior is simulated using concrete damaged plasticity. Therefore, concrete density, compressive strength and tensile strength and elasticity modulus are 2350 kg/m3, 25 MPa, 3 MPa and 29 GPa, respectively. Poisson’s ratio is assumed to be 0.2. Furthermore, 4-node shell elements are used to simulate concrete face and Drucker-Prager constitutive model is used to define rockfill material behavior.
The density and Poisson’s ratio for 2B, 3C and 3B layers are 2150 kg/m3 and 0.35, respectively. The shear modulus values for these layers are respectively 8.93, 2.89, and 3.85 GPa. In order to perform the simulation, the part of the dam structure beside the bed rock and the surrounding rock is considered as fixed bearing, and only the rockfill part and concrete face of the dam is simulated. Based on this assumption that the bed is rigid, there is no need to consider the dam foundation. This method is frequently used in literature review.
All the surfaces of the dam and bed rock are considered as fixed bearing to simulate the real condition where the dam is attached to bed rock and the surrounding rock. The interaction between dam layers is defined as tie. For defining the interaction between rockfill body and concrete face, tangential and normal contacts are defined using penalty method with friction coefficient equal to 0.5. In the next step, the model is meshed using 4-node shell elements for concrete face, 8-node brick and 4-node pyramid solid elements for rockfill body. Rayleigh damping is used to simulate the structure damping. The effective length of the dam reservoir has been determined by conducting several analyzes, so that the minimum required length for reservoir is reached in order to decrease the number of elements of the model.
Results and discussion
1. Interaction between concrete face and rockfill body
The results show that the increase of friction coefficient between concrete face and rockfill part from 0.5 to 0.7 has not affect the displacement of dam crown along the earthquake direction. However, when the concrete face is fixed to the rockfill part, significant changes are induced in dam crown displacement time history. In all cases, the deflection due to the dam weight is increased when the concrete face is attached to the rockfill body. The reason can be attributed to the tied interaction between these layers which results in similar deflection of concrete face with rockfill body and higher deflection of concrete dam crown. However, after the application of earthquake load, the displacement of the dam crown decreased in both analyses when tie interaction is defined between concrete face and rockfill body. In this study, due to the very high volume of analysis and its timeliness, it was not possible to examine the dam behavior in the free vibration regime, and therefore, it is not possible to assume the last displacement values at the end of analyses as the permanent displacement of dam. Figure 1 shows the relative displacement of the dam for the two selected earthquakes with a friction coefficient equal to 0.5 between the concrete face and the gravel body. According to Figure 1, the maximum displacement induced by the earthquake is related to Tabas and then, San Francisco earthquake. Furthermore, the high energy content of the Tabas record has been more effective in inducing greater displacement than the other record.
Figure 1. Lateral displacement of dam crown relative to the dam base for the selected earthquakes; Tabas and San Fernando.
The results also indicate that when the friction coefficient between concrete face and rockfill body is 0.5, the lowest damage occurs in the dam compared to that happens when friction coefficient is 0.7 or when the surfaces are tied. When the tied surfaces are used, the most damages takes place in concrete face, since all rockfill body displacement transmits to concrete face which results in much more concrete damages compared to the other interaction cases.
2. Effect of water level in reservoir on dam behavior
In this section, the effect of water level on seismic behavior of dam is investigated. For this purpose, the dam reservoir is analyzed in three cases including empty, half full and full (90% of dam height). Each study cases are examined under San Fernando and Tabas earthquakes. Figure 2 shows the relative displacement of dam crown in the three water level case for San Fernando and Tabas earthquakes.
Figure 2. Relative displacement of dam crown in three water level cases of empty, half and full for (a) Tabas and (b) San Fernando earthquakes
According to Figure 2, for both earthquakes, the dam crown displacement along the earthquake direction is significantly increased by increasing the water level, so that the maximum displacement in full case is 50% higher than empty case.
Conclusion
In this study, using the finite element method and simulation by Abaqus, the seismic behavior of concrete face rockfill dams has been investigated. For this purpose, the verification is firstly carried out using previous research results in literature. In the next step, nonlinear dynamical analysis is carried out, taking into account large displacements for the models under the earthquake record acceleration. The results illustrate that increasing the friction coefficient between the concrete face and the rockfill body from 0.5 to 0.7 has no significant effect on the displacement of the dam crown under earthquake load. Moreover, by using tie interaction between the concrete layer and the rockfill body, there is a substantial difference in the history of the relative displacement of the dam, and the displacement of the dam due to its weight has been increased. Furthermore, the results of this study exhibit that, with increasing the water level in dam reservoir, the deformation of the crown of the dam along the earthquake application direction has had a relatively significant increase, such that in the full state, the maximum displacement is increased by about 50% compared to that of the empty case. This is while the most damage of concrete is observed in the case when half height of dam in filled by water. Due to the more destructive power of near-field earthquakes and their impact nature, only near-fault earthquakes have been used in this research. Therefore, the results of this study are valid only for the behavior of dam under near-field earthquakes.
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Adel Asakereh, Mahdieh Shabani,
Volume 13, Issue 4 (12-2019)
Volume 13, Issue 4 (12-2019)
Abstract
Introduction
Estimation of Liquefaction is one of the main objectives in geotechnical engineering. For this purpose, several numerical and experimental methods have been proposed. An important stage to predict the liquefaction is the prediction of excess pore water pressure at a given point. In general, there are two important methods for soil dynamics analyses, fully coupled effective stress and uncoupled total stress analysis. The main purpose of this study is to evaluate the model capacity of the finite difference software, FLAC, based on effective stress analysis methods to predict the excess pore water pressure during seismic loading. A level ground centrifuge test conducted during the VELACS project on the Nevada sand with a density of 40%, was utilized to calibrate the numerical model. After the validation of the numerical model, a model was conducted to predict excess pore pressure and consequently the liquefaction for the site of Bandar Abbas Mosque.
Theoretical bases
A fully coupled u–P formulation, where pore pressures and displacements are computed simultaneously and interactively at each time step, is used in FLAC software. This feature is used to simulate the excess pore water pressure time histories during cyclic loading.
The finite difference based software, FLAC, used the Finn model that incorporates two equations correlating the volumetric strain induced by the cyclic shear strain and excess pore water pressure produced during cyclic loading. As mentioned above, the pore water pressure generation can be computed from two sets of equations: Martin et al. (1975) and the Byrne (1991) formulations in which the volumetric strain that was produced in any cycle of loading is depended on the shear strain that was formed during that cycle as well as the previously accumulated volumetric strain.
Modeling and Results
The VELACS model # 1 centrifuge test representing a level ground site constituted of the Nevada sand at 40% relative density has been numerically simulated in the current study to validate the numerical model. The centrifuge model contains a laminar box with slipping “rings” that allows differential horizontal displacements. This was simulated in the FLAC model by free-field boundary conditions which prevent reflection of the waves in the side walls. Figure 1 shows comparison of EPWP time histories ratio of numerical modeling and centrifuge test. Static analysis was carried out before dynamic analysis in order to find initial stress and strain state. At the next stage, the dynamic loads were applied at the base of the model and dynamic analysis was performed.
For numerical modeling the results of the general soil mechanics test on soil samples and standard penetration test performed on the site were used to calibrate the parameters and select the model constants.
Conclusion
The results of numerical modeling have been matched to experimental results of the centrifuge test using both Martin and Byrne formulations, except for the case of 5 m the numerical model has predicted lower excess pore water pressure values than the experimental values. This may be originated from the fundamental assumption of the Martin et al. (1975) EPWP theory, in which excess pore water pressure is directly related to the relevant volume changes. On the other hand, the Martin et al. (1975) model was adopted for one-dimensional measures of shear strain, while, in a 2D analysis under both horizontal and vertical shakings, there are three strain rate measures. FLAC uses some assumptions to solve this problem and it can affect the results.
The results of the numerical model showed liquefaction to a depth of about 5 meters that is almost compatible with the results from the lab, which has declared that the depth 2 to 5 m is liquefiable.
With careful selection of numerical model parameters one can generally use the simulation results to have a general sense on the pore water pressure generation and liquefaction prediction.
./files/site1/files/134/5.pdf
Ehsan Taherabadi Eliyas, ,
Volume 13, Issue 5 (12-2019)
Volume 13, Issue 5 (12-2019)
Abstract
This paper investigates the effect of micropile installation into saturated sandy soil by means of finite element method. The obtained results from numerical modeling are compared with the received data from the site. The validation of software has been done by simulating standard penetration test. The effect of some changes in spacing (3m, 1.6m and 0.8m) and injection pressure (1cm, 2.5cm, 5cm and 10cm boundary displacement) micropiles on liquefaction behavior was discussed. The results show that numerical modeling presented a conservative conclusion about the potential of liquefaction. The modification of soil increased by increasing injection pressure of grout. Also, it was observed that the effect of micropile spacing has less impact than the injection pressures up to 1m free distance of micropiles. Then for closer micropiles, the effect of spacing and the effect of pressure became bold and intensive, respectively. Because of direct relationship between number of SPT and liquefaction potential, it would be necessary to simulate SPT and to validate with the real data, before and next of micropile installation. This approach can be a proper way of forecasting the efficiency degree of modification by micropiles and could save costs and time.
Ehsan Amjadi Sardehaei, Gholamhosein Tavakoli Mehrjardi,
Volume 13, Issue 5 (12-2019)
Volume 13, Issue 5 (12-2019)
Abstract
This paper presents a feed-forward back-propagation neural network model to predict the retained tensile strength and design chart to estimate the strength reduction factors of nonwoven geotextiles due to the installation process. A database of 34 full-scale field tests was utilized to train, validate and test the developed neural network and regression model. The results show that the predicted retained tensile strength using the trained neural network is in good agreement with the results of the test. The predictions obtained from the neural network are much better than the regression model as the maximum percentage of error for training data is less than 0.87% and 18.92%, for neural network and regression model, respectively. Based on the developed neural network, a design chart has been established. As a whole, installation damage reduction factors of the geotextile increases in the aftermath of the compaction process under lower as-received grab tensile strength, higher imposed stress over the geotextiles, larger particle size of the backfill, higher relative density of the backfill and weaker subgrades.
Mahnaz Firuzi, Mohammad Hossein Ghobadi, Ali Noorzad, Ehsan Dadashi3,
Volume 13, Issue 5 (12-2019)
Volume 13, Issue 5 (12-2019)
Abstract
Slope stability could be a major concern during the construction of infrastructures. This study is focused to analyze the slope stability of Manjil landslide that was located 41+400 to 42+200 km along Qazvin-Rasht freeway, Iran. The Manjil landslide, which had 168 m long and approximately 214 m wide, was occurred due to inappropriate cutting in June 2013 and led to destructive and closure of freeway. Slope stability analysis was carried out using a finite element shear strength reduction method (FE-SRM). The PHASE2D program was utilized in order to model the slope cutting and stability of landslide. Slope angle was flatted with 3H:2V geometry and stabilized with piling. The results indicated safety factors of 1.95 and 1.17 in the static and pseudo-static states, respectively, while the maximum bending moment with single pile (SP) in the pseudo-static state was 5.69 MN. Maximum bending moment of the pile around the slip surface was significantly large and more than the bending moment capacity of the pile. Due to the large bending moment on the pile, pile-to-pile cap connections (two pile group: 2PG) should be designed at the toe of the slope. The obtained results showed reduction of this parameter to 2.48 MN. Thus, it can be concluded that 2PG is a suitable stabilization method for the Manjil landslide.
Ahmad Jabari, Mehdi Hosseini,
Volume 13, Issue 5 (12-2019)
Volume 13, Issue 5 (12-2019)
Abstract
In cases such as explosion, fire, deep drilling and geothermal energy extraction, rocks are exposed to high temperatures influencing the rock toughness. Thus, the aim of this study is to investigate the effect of temperature on the fracture toughness of the rocks. In this study, the effect of temperature on the mode I fracture toughness is investigated. To this end, three-point bending tests were performed on semicircular specimens of four types of natural rocks including sandstone, limestone, tuff, andesite, and a series of concrete specimens to determine the fracture toughness. The specimens were first heated to 100, 200, 300, 500 and 700 °C. After reaching the desired temperatures, the specimens were cooled. A series of tests was performed on the specimens at ambient temperature (25 °C). The heating rate in the electric furnace was 15 °C/min in accordance with the temperature rise in fires. Petrographic studies and X-ray diffraction analysis (XRD) were performed to identify the composition of the rocks. Furthermore, the effective porosity and the weight loss of heated specimens were determined to study the behavior of rocks. Comparison of the test results indicated the higher impact of temperature on the fracture toughness of fine-grained rocks. In addition, the fracture toughness decreased by increasing the effective porosity and decreasing the weight loss. According to the results, the mode I fracture toughness of sandstone, tuff, limestone, andesite and concrete specimens underwent a heating-cooling cycle up to 700 °C respectively decreased 45, 17, 44 and 9.5 and 37 percent compared with that of unheated specimens.
Mr Vahid Yousefpour, Mr Amir Hamidi, Mr Ali Ghanbari,
Volume 13, Issue 5 (12-2019)
Volume 13, Issue 5 (12-2019)
Abstract
Sandy soils usually contain different amounts of fines like silt and clay, causing some changes to their shear strength and dilation characteristics. Bolton [1] conducted some experiments on
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