Journal of Engineering Geology

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Saline soils are of challengeable soils that may cause many problems in civil engineering projects. In this study, volume change behaviour of saline soils and also the effect of improvement and reinforcement on them have been investigated using laboratory tests as well as consolidation test, swelling pressure test and free swelling test. The case study is Amirkabir Highway which connects the cities Qom and Kashan.  Fifty four kilometer of this highway was deformed like waves due to existence of saline soils. The laboratory investigations showed that the studied soil has a considerable swelling potential which appears to be the main cause of damage to the highway pavement, therefore it is decided on improving the subsoil condition. The research program comprises of studying volume change behavior of saline soil, stabilized with lime and epoxy – resin polymer and reinforced with polypropylene fiber. Afterwards, results for two cases of stabilized and non-stabilized samples have been compared. According to the results, the main cause of swelling is soil disturbance and structure destruction of initial soil composition. Considering all of test conditions, it is appeared that, although lime is a traditional stabilization material but is economic for the most geotechnical projects and usage of polymer is suggested only in special applications due to its rapid setting

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./files/site1/files/1Extended_Abstract.pdfExtended Abstract
(Paper pages1-28)
Introduction
The earthquake is one of the most devastating natural disasters that always threats human societies in terms of health and financial issues. Iran is one of the most seismic prone countries of the world due to locating on Alpine- Himalayan Orogenic belt. On the other hand, growing population and increased construction of tall buildings, increases the damages caused by large earthquakes, especially in large cities. Karaj is one of the most populous cities in Iran which there has been considerable industrial and economic development in recent years. When an earthquake occurs, seismic waves radiate away from source and travel rapidly through the earth crust. When these waves reach the ground surface, they produce shaking that may last from several seconds to a few minutes. During earthquakes, different alluviums with different structures show various reactions. It is well-accepted that, besides the earthquake magnitude and fault distance, local geologic conditions, known as site effects, can also exert significant influences on characteristics of the seismic waves such as amplitude, frequency content and duration of strong ground motion at a given location. The seismic ground motion at any site is influenced by the type of soil in that region. Younger and softer soils usually amplify ground motion more than older soils or bedrocks .
There are theoretical and experimental methods to evaluate the site response. In the present study, the Nakamura's H/V spectral ratio method has been used to evaluate the resonance frequency in 37 locations at Karaj site. In addition, a preliminary 1-D site response modelling has been conducted using Deepsoil program according to downhole, array and geology data. Site frequencies obtained from modelling are presented and compared with site frequencies obtained through microtremor measurements.
Materials and Methods
Single station microtremor measurements at the Karaj site were carried out by the International Institute of Earthquake Engineering and Seismology (IIEES) in 2012 with a three-component broadband seismometer (Guralp CMG-6TD). In the present study, we have used 37 microtremor data along the north-southwest profile because at this profile, geological section was available and these stations contained geotechnical boreholes data. Dynamic range of sensor changes between 0.033 -50 Hz and has a natural period of 1 second. 24-bit analog-to-digital (A/D) converter digitized the recorded data. The recording system was operated continuously for about 30 minutes with sampling frequency of 100 Hz. The use of ambient vibrations for analysis of the local site effects has been studied in detail in the framework of the European research project SESAME (Site Effects Assessment Using Ambient Excitations). The recommended guidelines on the H/V spectral ratio technique are the result of the comprehensive and detailed analysis performed by the SESAME participants during three years of investigations (2001-2004).
H/V spectral ratio was carried out by the Geopsy software. The process starts by converting data from binary format to ASCII format. After DC offset removal, eighth order Butterworth band pass filter used within the range of 0.1 Hz to 50 Hz. The Anti-triggering algorithm STA/LTA has been selected to reject energetic transients from ambient vibration recordings, so STA and LTA were considered respectively 1 and 30 second. Minimum and maximum STA/LTA thresholds were selected between 0.2 and 2.5. For each station, the time-series of the record is divided into windows of 40 to 100 seconds in three components with an overlap of 50%. Also, a cosine taper with the length of 5% of the total window length was used at each end.
The amplitude spectra of each selected window is computed with a fast Fourier transform (FFT) and smoothed using the Konno-Ohmachi function (Bandwidth=40). Then, two horizontal components are merged by squared average. Finally, the H/V spectral ratio of Nakamura is applied for each individual window, and the final predominant frequency is obtained by averaging the H/V spectral ratio of all window. The presence of clear peak on H/V spectral ratio curve is indicative of the impedance contrast between the uppermost surface soil and the underlying hard rock, where large peak values are generally associated with sharp velocity contrasts, and is likely to amplify the ground motion. The H/V spectral ratio in some stations shows a clear peak and at the others might show two or multiple peaks which represents the geologically complex areas. Calculated dominant frequency changes between 0.4 and 2 Hz. These low values indicate the existence of basement at greater depths and large thickness of sediments on basement (Parolai et al., 2002).
Site modelling
The results of H/V spectral ratio are affected by the local geologic structure. Based on this assumption, we can produce theoretical H/V curve with knowledge of the geologic structure in the area. One-dimensional modelling is a suitable method to evaluation of the site response due to the local geology which requires geotechnical and geophysical data. In the one-dimensional modelling, it is assumed that all boundaries are horizontal in the infinite media and the response of a soil deposit is predominantly caused by SH-wave propagating vertically from the underlying bedrock. In this present study, one-dimensional modelling was carried out using Deepsoil software. Due to the very small deformations in soils by microtremor and producing a low levels of strain, we applied the linear method to evaluate the ground seismic response during mild earthquake shakes. In this software, homogeneous and isotropic soil profile is considered as N horizontal layers. The site response (transfer function) is evaluated by parameters such as layer thickness (m), density (ρ), shear modulus (G), and damping factor of layers (β), which are obtained from available geotechnical boreholes.
Usually, engineering bedrock is considered for the purpose of numerical modelling. According to TC4 (1994), the seismic bedrock was defined as a layer with a shear wave velocity of more than 600 m/s. Shima (1978) recommended that the upper crust with a shear wave velocity of about 3000 m/s, is adopted as bedrock when large scale structures with longer vibration period are being considered. International building code (ICC2000) has defined the seismic bedrock by a shear wave velocity of more than 760 m/s. According to Unified Building Code (UBC97), bedrock is defined into two groups: A (very hard rock with a speed of more than 1500 m/s) and B (rock with a speed of 760 to 1500 m/s). Therefore, the proposed values of the shear wave velocity are different for considering seismic bedrock. In order to consider the uncertainty of the shear wave velocity in the present one-dimensional modelling, three scenarios for the bedrock, were performed with three speeds of 760 m/s (based on engineering bedrock), 1300 m/s (bedrock geology), and 2500 m/s (corresponding to tuff-andesite of the Karaj basement) at different depths, according to the regional geological map. Then, three scenarios of the numerical modelling were compared with microtremor transfer function.
1. One-dimensional modelling at the Karaj site using downhole data for engineering bedrock (> 760 m/s)
In order to access the shear wave velocity profile for 1-D modelling, downhole data from 21 boreholes were used in nine sites which were available up to the maximum depth of 50 meters at 20 boreholes and 96 meters at A09 borehole. Low thickness of alluvium (about 17-85 meters) was considered with engineering bedrock (>760 m/s) for numerical modelling. The results represent higher frequency range compared with the microtremor data. In some previous studies where engineering bedrock had been defined by shear wave velocity values between 700 to 800 m/s in 1-D modelling, the results of the theoretical model is incompatible with experimental results. Thus, it seems that it is not suitable to consider the engineering bedrock in 1-D modelling.
2. One-dimensional modelling at Karaj site using microtremor array data for geology bedrock (> 1300 m/s)
By considering the seismic bedrock (>760 m/s) at depths of 17 to 85 meters and calculating the one-dimensional transfer function, the peaks in higher frequency compared with the experimental method is observed. According to reliability of experimental H/V results which has been proved by researchers around the world (Haghshenas et al., 2008), the difference between the transfer function results in experimental and theoretical methods indicates that two variables of shear wave velocity or depth of bedrock and alluvium thickness have not been properly modeled. It seems that in order to get better results, it’s necessary to analysis by considering the geology bedrock at greater depth. Tchalenko, et al., (1974) considered lower part of Plio-Quaternary sediments of Hezardareh Formation and Miocene marl-limestone of Upper Red Formation as the bedrock in the Karaj plain. Shafiee and Azadi (2006) computed shear wave velocity characteristics of these geological units throughout Tehran city. Therefore, a mean velocity of 1300 m/s was considered for the geology bedrock during the modelling.
In order to access the shear wave velocity profiles at greater depths, microtremor array stations were designed by seven seismometer with 100 m radius at A09 (site 8) borehole. As it can bee seen, a clear contrast at a depth of about 230 m is observed. Therefore, the modelling was carried out by taking 230 m alluvial thickness on geology bedrock according to lithology of the region. The result of this modelling has shown a peak at frequency range of 0.87 Hz that is compatible with the microtremor peaks at this site. In other site this modelling was performed using array and downhole data. The results indicated that the first effective contrast occurs at depth of 200 to 300 meters.
3. One-dimensional modelling at the Karaj site for basement (> 2500 m/s)
Transfer functions obtained from the previous model, did not cover low frequency peaks in the experimental methods. Therefore, the presence of other low-frequency peaks is either due to the geometry of the sedimentary basin or deep contrast. It seems that due to the geology of the region, tuff- andesite of the Karaj Formation as basement plays an important role in the creation of low-frequency peaks. Therefore, to obtain a better model, deep contrast was considered about 2 kilometers due to differences in the type of bedrock with a shear wave velocity of 2500 m/s. For this purpose, according to the properties of the Upper Red Formation, an average constant speed of 1400 (m/s) was considered in modelling and by changing the thickness of this layer, the modelling was continued in a trial and error manner until the numerical model is consistent with microtremor peaks. The modelling results in nine site indicate that there is basement at the depth of 2000 to 2250 meters.
Two-dimensional model of the Karaj site
Using the one-dimensional analysis and evaluation of the geological map of the area, two dimensional geological structure was rebuilt in studied profiles. Green and gray tuffs and igneous rocks of Karaj Formation outcrops in north of Karaj and constitute the Alborz Mountains. This Mountains eroded by the action of rivers and were deposited in the form of large alluvial fans. Coarse sandy sediments were deposited near mountains wherein energies of rivers and streams were extremely high (site 1 to 4). Furthermore, fine-grained sediments were deposited at far distances by decreasing in the energy of streams (site 5 to 9). Berberian et al (1985) divided B Formation in two parts: heterogeneous deposits of sand, gravel, rock and clay in north of Tehran (Q_bn) and silts and clays of Kahrizak (Q_bs) in south of Tehran. According to 1-D modelling, thickness of this layer is about 200 to 300 m which has been deposited on geology bedrock. As mentioned before, lower parts of Hezardareh Formation at the north of Karaj and Upper red Formation in the south west of Karaj are considered as geology bedrock. Upper Red Formation was deposited with unconformity on tuff-andesite of the Karaj basement at depths of 2000 to 2250 meters.
Conclusions
The use of empirical methods based on microtremor is an efficient way to estimate the site effects in Karaj city, although the use of earthquake records could provide better evidence of the depth and geometry of basement. One-dimensional modelling of shear wave velocity profiles obtained from downhole data and considering the engineering bedrock (> 760 m/s) at depths of 17 to 85 meters, is not a good way to estimate the dominant frequency of alluvium. By considering the greater depth of alluvium and using shear wave velocity profiles obtained from microtremor array, 1-D modelling was carried out for geology bedrock (1300 m/s). Therefore, peak frequency in transfer function at the range of 0.87 Hz has been associated with effective contrast at depths of 200 to 300 meters. It seems that Karaj basement (> 2500 m/s) with about 2 kilometers depth plays an important role in the production of low-frequency peaks in transfer function.
 

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./files/site1/files/1.pdfExtended Abstract
(Paper pages157-174)
Introduction
Considering the fact that the estimation of mode  fracture toughness by testing is time-consuming and expensive. It might be associated with certain practical difficulties. Therefore, many researchers have attempted to propose experimental relationships in order to capture these problems. Gunsallus et al. (1984) and Bhagat (1985) experimentally found that mode  fracture toughness is related to tensile strength. Whittaker et al. (1992) have also proposed a number of relationships between mode I fracture toughness, tensile strength, point load index, uniaxial compressive strength and the velocity of sound waves. Bearman (1999) obtained an experimental relationship between mode I fracture toughness and point load index, while Brown et al. (1997) presented an experimental relationship between this parameter and density. Up to now no significant research effort has been made in this field in Iran, only Ayatollahi and Fatehi addressed rock fracture toughness. Although, Ayatollahi has not presented any experimental relationships. In the present research the three-point bending test was used on a cylindrical specimen containing a straight crack in order to determine the mode  fracture toughness, and the Brazilian test was employed to determine tensile strength.
Materials and Methods
The tests were carried out on six types of rocks, namely gray sandstone,
tuff, lithic tuff, travertine, andesite, and limestone. Sandstone, travertine, and limestone are sedimentary rocks, while andesite is an extrusive igneous rock, and tuff and lithic tuff are pyroclastic rocks (pyroclastic rocks resulting from volcanic eruptions that harden by sedimentation). Therefore, the studied rocks have different origins. In order to carry out the Brazilian and the three-point bending test, cores were prepared from these blocks. In order to perform the three-point bending test, specimens with diameter of 73 mm with a thickness of 30 mm were used. The samples were cut in two semicircular by a cutting machine, and a notch with length of 15 mm is created by a diamond saw.  Notch is vertical in the center of the semicircular samples.
The Brazilian test was performed on disc shaped specimens. In order to perform the Brazilian test, specimens with diameter of 51 mm and thick of 25 mm were used. The specimens are carefully placed under the curved jaws of the machine and then loaded until fracture.
Results and Discussion
A summary of the Brazilian and the three-point bending test results are presented in Table 1. The average value of test result pertaining to each rock is reported in Table 1.
Table 1. Summary of the Brazilian and the three-point bending test results

Specimen	Tensile Strength (MPa)	Fracture Toughness (MPa√m)
Limestone	3.74	1.23
Sandstone	7.14	1.63
Tuff	16.36	2.17
Lithic Tuff	4.34	1.01
Andesite	13.25	1.86
Travertine	8.27	1.14

In this study, it was attempted to propose an experimental relationship between mode I fracture toughness and the tensile strength of the rock.
In order to determine the relationship between the tensile strength and the fracture toughness, the tensile strength vs. fracture toughness diagram was plotted in Excel to obtain Eq. 1 and the coefficient of determination (R²) (Figure 1).

The coefficient of determination (R²) in Eq. 1 shows that almost 80 percent of the mode I fracture toughness variations can be estimated using the linear relationship (Eq. 1). The relationship is applicable for determining the mode I fracture toughness resulting from the three-point bending test on semicircular specimens containing a straight crack.

In the following, the results of this study are compared to those reported by Whittacker (1992) and Zhang (2002).
In order to examine the accuracy of the presented relationships, the Root Mean Square Error (RMSE) measure was used which is computed from Eq. 2. In the best case, RMSE is zero. 

In the relationships,   represents the fracture toughness obtained from testing while  is the fracture toughness estimated using the relationships.
Comparison of the obtained results indicate that the proposed relationship has the capability of precise estimation of the mode I fracture toughness of rocks.
Conclusion
Given the many difficulties associated with the direct estimation of fracture toughness, indirect estimation methods have been proposed. One of such methods is the estimation of mode I fracture toughness using tensile strength. A linear relationship with a coefficient of determination of 0.7977 was proposed. The accuracy of this relationship has been verified by comparing its results to those from previous studies.

 

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./files/site1/files/7.pdfExtended Abstract
(Paper pages 299-318)
Introduction
Bentonite has been used industrially in various construction projects. This material is used, due to its limited hydraulic conductivity, in some cases such as landfill, sealing walls and nuclear waste disposal tanks. Recently, many researchers have investigated the use of bentonite slurry systems for injection into granular soils under static and dynamic loading conditions in order to improve soil engineering performance. In this condition, bentonite slurry is deposited in a loose soil with low pressure and without disturbance in the structure of the soil under injection. Due to the nature of the thixotropy of the bentonite slurry, the injected material is deposited in the form of gel structures in the soil and leads to increasing soil resistance to static and dynamic loads. For suitable soil engineering properties in granular soil, the use of concentrated bentonite slurry is appropriate; high concentrations will limit the penetration of bentonite due to low soil permeability. In order to overcome this limitation, slurry rheological properties such as viscosity must be corrected in order to increase the depth of sand penetration. Other researchers observed that with the reduction of viscosity in the cement slurry with micro-size particles, the amount of its penetration in the sand column significantly increased.
In present paper, due to the lack of studies on the penetration rate of bentonite in sand and also the effective role of bentonite in the mechanical properties of sandy soils, the permeability of sandy soils by bentonite under the influence of change factors such as concentration of bentonite in injection suspension were investigated.
Material and Methods
In the present study, Firoozkooh sand samples with the traditional names of 131, D11 and D1 were used for testing. Different concentrations of bentonite slurry which is used in this study are 3, 5 and 7% of the bentonite to water ratio.
Figure 1 shows the location of the reading of the penetration length and Figure 2 shows variations in the length of infiltration against time for different heights of the pressure head.


Figure 1. The reading point of the penetration length in the sample


Figure 3 shows the variations of penetration length versus pressure heads for samples with a relative density of 70% at concentrations of bentonite slurry of 3, 5 and 7% in different aggregates. It can be stated that while the concentration of bentonite to water increases, the longitudinal penetration of the injected substance into the sample is reduced. For example, in sand 131 with Dr=70% the penetration value at a pressure head of 130 cm for suspension containing 3% bentonite slurry is 100 cm. The same values for samples containing 5% and 7% bentonite are 45 and 20 cm respectively. This is due to the increase in the presence of bentonite slurry (solid substance) in the suspension. The greater amount of solids inside the suspension causes the greater contact between sand grains with solid particles of suspensions. As a result, it causes increasing friction for longitudinal motion. Therefore, with increasing the concentration of suspension the length of its movement in the soil is reduced. Also, due to the increased viscosity of the injectable substance with increasing the amount of bentonite, the forward movement of the suspension under constant pressure is reduced. This is another important parameter that leads to a reduction in the length of the injection by increasing the concentration of the bentonite slurry.
 It is also observed that the variation of penetration in higher concentrations is less than the low concentration. For example, in sand D1 (coarse sand) at a pressure height of 100 cm, the penetration rate at a concentration of 5% increases by 35% compared to a concentration of 3% and at a concentration of 7% increases by 300% compared to the sample containing 3% bentonite. This indicates that at less than 5% concentration the presence of bentonite in the sample is less effective, and the suspension can be more easily move between the pores. This result indicates that by reducing the pores inside the sand, the effect of changing to the suspension concentration is reduced. 


Figure 3. Penetration length versus pressure level for specimens with a Dr=70% in concentrations of bentonite of 3, 5 and 7% in different aggregates; a) fine sand (sand 131); b) moderate sand (sand D11); c) coarse sand (sand D1)

 

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The results of an ongoing FEM parametric study are presented regarding the dependence of the resulting piled raft behavior under lateral load and combination of loads on pile diameter, pile length, arrangement of piles and raft thickness. Taguchi method with Analysis of Variance (ANOVA) was employed to calculate the contribution ratio of these factors on the lateral displacement of piled raft. The obtained results of this study show that the pile diameter is an effective factor in horizontal deformation of the piled raft under pure horizontal load. However, in the case of load combinations, the pile length has the highest participation ratio in reducing the horizontal deformations.
 

 

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In the mechanized boring method, the factors affecting ground surface settlement can be mainly divided into five categories: geometric, geomechanic, boring machines working, operating and management parameters. In urban tunnels bored mainly in shallow soil bed, face pressure can be one of the factors preventing ground settlement. The Line A tunnel in Qom metro project is bored with an EPB (Earth Balance Pressure) mechanized boring machine. The effect of face pressure on ground surface settlement was analyzed in the present study according to five sections of the tunnel. These five sections were selected in different kilometers of the tunnel where settlement gauges were installed and the results could be validated. To investigate the effect of face pressure on maximum ground surface settlement, four pressure levels of 100 kPa, 150 kPa, 200 kPa, and 400 kPa were taken into consideration. These were 1, 1.5, 2, and 4 times of the initial face pressure level, respectively. The ground surface settlement was assessed at four pressure levels using the finite element software, PLAXIS 3D TUNNEL. The results were validated using ground-level instrumentation (settlement gauges) on all sections. The validation showed that the modeling results are in good agreement with the results obtained from settlement gauges.  Comparison of the results indicated that a 4-fold increase in the face pressure led to a maximum decrease of 4.45 mm in the maximum settlement. Therefore, an increase in the face pressure can reduce settlement, although quite minimally. It was also found that an over-increased face pressure (face pressure over 200kPa) not only did not reduce the maximum ground surface settlement but also may lead to passive failure or uplift of ground surface ahead of the shield. 
 

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Materials such as waste tire chips were widely used to improve the strength of soil. The objective of this study is to discuss the residual strength or steady-state behavior of sand-waste tire chip mixtures. A series of undrained monotonic triaxial compression tests were conducted on reconstituted saturated specimens of sand and sand-tire chip mixtures with variation in the tire-chip contents from 0 to 4 percentages by dry weight of soil. The specimens are prepared using dry deposition method of preparation. The influence on residual resistance of varying confining pressure (100, 200, and 300 kPa) and sand mixture relative density (40, 65, and 80%) were evaluated. Tests results showed that by increasing the tire chip contents, the residual strength increased and steady-state lines move to the right of log S_us-e diagram. Also, the residual resistance improvement induced by tire chip inclusions was found to be sensitive to the relative density of samples and applied confining pressure.

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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

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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.
 

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Introduction
Shallow tunnels have a vital role in urban planning, railway and highway transportation lines. The presence of underground cavities can leads to stress concentration and consequently, instability of the spaces against static and especially dynamic loads. Therefore, the aim of this study was to evaluate the effect of elliptical cavity and its inclination on sandstone rock behavior under compressive static and tensile dynamic loads. In order to evaluate the effect of the cavity under static stress conditions, two groups of intact and hole-bearing sandstone cores with 0, 30, 60, and 90 degrees of hole inclination were prepared and tested under uniaxial compressive loading test. During the test, in addition to the stress recording, damage and deformability of the samples were recorded by using the strain gauge, acoustic emission sensor and camera. Split Hopkinson pressure bar (SHPB) test apparatus was used for doing dynamic loading test. Furthermore, the damage process was recorded using a high-speed camera with 10 micro-seconds interval of frame capability. The obtained results showed that presence of the cavity reduced the rock strength in maximum state (θ=0) up to 55% and in minimum state (θ=90) up to 77% of its initial uniaxial compressive strength. Dynamic tensile loading tests illustrate that the elliptical hole near the free end of sample (reflection boundary of compressive wave to tensile wave) is stable due to locating in superposition area, while the other cavity out of the area with each inclination was undergone to spalling failure. Assessment of failure surface using scanning electron microscope and thin section study indicates that the dominant fracture is grain-boundary type and iron oxide cement has a vital role in developing of this type of fracture.