Journal of Engineering Geology

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One way of reduction of leakage from beneath of earth dams is using of one contact clay layer with very low permeability and intermediate to high plastisity and connectig it to core of dam. Since, most of fine-grained soil in environtment of dam have low plastisity and preparing it from another place is not economic, use of bentonite in order to improvement of engineering characteristic of borrowed clay is suitable way.
In this search effect of bentonite on geotechnical properties of fine-grained soils with low plastisity are evaluated. Results of this research show that hydraulic conductivity, consolidation coefficient, dry density, colifornia bearing ratio (CBR),.....are decreased with increase in bentonite content but optimum moisture , Aterberg limits , cohession and so on are increased with bentonite addition. Finally, with analysis of obtained result, optimum percent of bentonite is offered in order to improve of engineering properties of used clay in contact region.

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Subsurface dams is accordant with nature structure which is useful for water resources management, especially for preventing unused underground water. Regarding to reservoir alluvium, geological and geotechnical characteristics of this type of dam is important. Therefore, in present study, characteristics of the underground reservoir alluvium in Mastbandy area (South of Ardestan-North East of Isfahan) has been investigated. In this regard physical and mechanical properties of reservoir alluvium has been determined, using in situ and laboratory tests. Test results show that the type of alluvium is mostly non uniform dense granular soils without plasticity. Also its permeability is medium to high. Due to the porosity obtained from tests and the depth of the reservoir sediments (5 to 12 meters), in the case of subsurface dam construction, its volume would be about 200000 cubic meters. In general, due to full and empty of reservoir, loading and unloading cause the settlement. Since almost reservoir sediment are gravel and sand, the settlement is mainly immediate settlement. Due to obtained mechanical parameters, the amout of immediate settlement is equal to 16 milimeter

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Introduction
Texture coefficient (TC) is a method of quantification rock texture by using the image of rock thin sections and image analysis. Many researchers have studied the effect of TC on engineering properties in different rock types (Ozturk et al., 2014). Also, some researchers are expressed that engineering properties of sedimentary rocks are mainly influenced by rock texture (Fahy and Guccione, 1979; Ulusay et al., 1994; Eberli et al., 2003; Khanlari et al., 2016; Ajalloeian et al., 2017). Carbonate rocks which are mainly sedimentary rocks are used in many different projects in Iran. In this research by using of TC, rock texture is quantified and also effects of TC are investigated on engineering properties of some carbonate rocks.
Grain shape and size can be quantified by the length (L), width (W), area (A) and perimeter (P) which are used to formulate the tow coefficients including aspect ratio (AR) and form factor (FF). Also, packing density can be quantified by area weighting of grains (AW) which is the relative proportion of matrix and grains. Angle factor (AF) is used to quantify the angular orientation of grains that is calculated only for elongated grains. The AF is computed by class weighted system applied to acute angular differences between elongated grains (Howarth and Rowlands, 1986, 1987).
High values of these factors can be interpreted as a rock texture which influences the geotechnical properties. The quantitative assessment of rock texture is formulated by these factors in Eq. (1) (Howarth and Rowlands, 1987). 
                     Eq. (1)
where N₀ and N₁ are the numbers of grains whose aspect ratio is below and above tow, respectively; FF₀ and AR₁ are the arithmetic mean of discriminated FF and AR, respectively; and AF₁ is proposed to divide the AF value by 5 (AF₁=AF/5).
TC equation is presented to evaluate mechanical properties like strength and drillability in different rocks, but some researchers found a high correlation between TC with other engineering properties of rocks. Generally, many researchers proposed TC as a good approach of describing and classifying different rocks and predicting some engineering properties in some rocks (Howarth and Rowlands, 1987; Ersoy and Waller, 1995; Ozturk et al., 2004; Alber and Kahraman, 2009; Ozturk and Nasuf, 2013; Ozturk et al., 2014).
Material and methods
28 samples of carbonate rocks were gathered from different Formation of Iran. Rock thin section for each sample was made to calculate TC value. TC was determined by a new method of image analysis. Also, some rock mechanics tests including unit weight, water absorption, porosity, point load index, uniaxial compressive strength (UCS), slake durability index and Los Angeles abrasion loss are conducted. Rock samples are tested according to the international standard ISRM (2007). The dependent variable is engineering properties and the independent variable is TC. The best nonlinear relations with highest correlations (R²) were aimed to predict the engineering properties, to clarify the relationships between them. The efficiency of each prediction equations was investigated by the root mean square error (RMSE) and value account for (VAF). In each samples belonging to the same Formation, regression analysis has been done and compared to the results of all samples and also for UCS and previous equations presented by other researchers.
Results and discussion
There is a significant correlation between TC with some engineering properties. Highest correlation is between TC and UCS (R=0.942) and the lowest with point load index (R=0.635). Overall, when the TC increased, parameters like unit weight, point load index, USC, and durability index increased too, but water absorption, porosity, and Los Angeles abrasion decreased. Increasing TC is correlated with enhancing geomechanical properties of carbonate rocks. Improving engineering properties of rocks (like UCS, Brazilian tensile strength, Young’s modulus, density, shore hardness, porosity and point load index) by increasing TC value are presented by different researchers on different rocks (Howarth and Rowlands, 1987; Ersoy and Waller, 1995; Azzoni et al., 1996; Ozturk et al., 2004; Alber and Kahraman, 2009; Ozturk and Nasuf, 2013; Ozturk et al., 2014). However, in this research, data is limited to carbonate rocks that are abundant sedimentary rocks. Some researcher mentioned that geomechanical properties of sedimentary rocks are mainly influenced by texture (e.g. Fahy and Guccione, 1979; Ulusay et al., 1994; Eberli et al., 2003). In addition, It is mentioned that the strength of carbonate rocks are related to the various textural parameters (Tugrul and Zarif, 2000; Torok and Vasarhelyi, 2010; Jensen et al., 2010; Ajalloeian et al., 2016). Carbonate rocks don't have varied mineralogy's, but the texture in these rocks could be variable.
Results show that the highest correlation index is between TC and UCS and its correlate according to the other investigation (Howarth and Rowlands, 1987; Ozturk et al., 2004). TC equation doesn’t cover all the criteria of rock texture, but it has a good correlation with some engineering properties of carbonate rocks. It can be possible to predict UCS, density and water absorption with VAF accuracy with more than 70 percent and lowest RMSE. TC can be showed some engineering properties of carbonate rocks. Therefore, it can be used in the preliminary design of the project for rock mechanic purposes and obviously, time and cost will be reduced. Moreover, it is very useful for a situation that suitable and enough samples cannot be extracted. It is important that rock samples don’t have any alteration and weathering of minerals and macroscopic heterogeneity.
 
 
Conclusion
In this research, the effect of texture coefficient as a factor that represents the texture of rocks on physical, mechanical and durability properties of carbonate rocks in some parts of Iran was evaluated. Furthermore, it is a time-consuming process to determine the TC of rock, but preparing rock thin sections and microscopic analyses are a part of the preliminary studies in engineering geology. When image analysis methods which are used to determine TC, the time is shortened and accuracy will be increased. TC can be calculated simply by image analysis, but it doesn't cover all the criteria of rock texture. In addition, in TC equation, some factors play an important role, but some factors don’t have a direct effect, and these factors are not fully acknowledged in the original concept of TC. TC equation is presented to evaluate mechanical properties like strength and drillability in different rocks, but some researchers found a high correlation between TC with other engineering properties of rocks. The results indicate that TC value has a direct correlation with UCS, density, durability index and point load index and also, has a reverse correlation with water absorption, Los Angeles abrasion loss and porosity. The strong relationship is between TC and UCS (R²=0.92) and the weak relationship is between TC and porosity (R²=0.58). With regression analysis and TC value, it could be predicted UCS, density and water absorption with accuracy more than 70% VAF which considering previous equations and the proposed equation obtained from this research for UCS., it is showed that although the same trend exists, the noticeable difference is available. However, more studies are needed for investigating by more samples and different rock types and statistical analysis. 
./files/site1/files/123/7Extended_Abstract.pdf

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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.

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The urban development of Tabriz faces numerous geological and engineering challenges due to the presence of Neogene argillaceous-marly rocks. These rocks exhibit low mechanical strength and bearing capacity, as well as high deformability. This study aims to analyze these rocks and establish practical correlations among their petrographic, physical, and mechanical properties, alongside ultrasonic test results. These correlationscan help estimate uniaxial compressive strength (UCS), compression wave velocity (Vp), and elastic modulus (E). The findings indicate that argillaceous-marly samples, classified as very weak to weak rocks or hard soils with significant deformability, exhibit low compression and shear wave velocities. These samples are predominantly found in yellow, olive green, gray to dark gray, and brown colors throughout the city. The study reveals significant linear relationships between physical properties, mineralogical composition, UCS, and E with seismic wave velocity. Notably, there is a strong correlation exists between compression wave velocity and uniaxial compressive strength, shear strength parameters, cement content, and mineralogical composition in these rocks. These relationships suggest that mineralogy, porosity, density, and slake durability index are key factors influencing seismic wave velocity. Additionally, the variations in textural and microstructural diversity of argillaceous-marly-marly samples contribute to unpredictable mechanical behavior, which can pose potential hazards. Furthermore, a qualitative fissure index (I_Q) was developed usingthe P-wave velocity of the samples to classify them into categories of high fissurability.