Journal of Engineering Geology

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The Kandovan village is one of the tourist attractions in East Azarbaijan province of Iran, whose rural houses were excavated within the cone-shaped pyroclastic rocks (in terms of local called keran) several hundred years ago. The present paper discusses the role of engineering geological properties of Kandovan pyroclastic rocks. Kandovan pyroclastic rocks have low resistance against weathering and erosion because their components are plagioclase minerals and pumice fragments with low resistance, welding, sorting and high sphericity and rounding. Although weathering and erosion along existing joints and fractures is the most important causative agent of cone-shaped forms but there is the possibility of further damage of rocks due to continuing these processes. High porosity of rocks has caused that their high capacity for water absorption. High water absorption percent increased sensitivity of rocks against expansion and contraction by freezing-thawing and wetting-drying cycles and low hardness and low their internal strength caused the rocks weathered and disintegrated due to environmental factors. Furthermore, the weak texture of the pyroclastic rocks have caused easy erosion of those by surface waters and wind.

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Tanks are structures for storing fluids that are made in different sizes, shapes and genera. Today using of tanks for water, petroleum products storage, and industrial wastes, has been developed significantly. The buried rectangular concrete tanks are used for water supply in most cities in our country. Soil-structure interaction is one of the most important issues in seismic behavior of buried tanks. With respects to code 123 that has suggested Mononobe-Okabe equation for dynamic pressure of earthquake excitation, the purpose of this research is to achieve the dynamic pressure of soil during earthquake. The obtained results have been compared to analytical and other experimental researches. Therefore, a series of small-scale experimental tests were conducted using 1g shaking table testing in the laboratory of physical modeling at University of Tehran. The results illustrate that dynamic force and pressure from Mononobe-Okabe and Wood equation are greater than experimental testing results. However Seed-Whitman equation is closer to experimental results.

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Introduction
One of the most sensitive and important issues in some civil engineering projects is slope design and application. The process of slope design always involve many uncertainties. Hence, it is impossible to accurately comment on its stability or instability. Most of the uncertainties in the slope stability analysis are related to the nature of materials, geometry, environmental conditions, model errors, and measuring errors as well. Therefore, the slope stability analysis with a deterministic approach which uses the concept of safety factor would often not result satisfactory. Consequently, the use of probabilistic methods is more advised. Accordingly, in recent years, the probability analysis has been used to slope stability analysis. In these analyses, the effective quantities of slope stability are considered as statistical distributions, and the reliability coefficient would then be a statistical distribution. Likewise, one of the approaches to simulate uncertainties in the probabilistic analysis is to use the variation coefficient. If the variation coefficient changes, the probability of failure will change accordingly. When the variation coefficient becomes a larger number, costly solutions are required to reduce the probability of failure. If the variation coefficient becomes low, the reliability will be increased and the required costs to reduce the probability of failure will be decreased. Therefore, determining the amount of variation coefficient in these analyses is very important. Furthermore, the correlation coefficient between the quantities is another effective parameter in computing the probability of failure.
Material and methods
In this research, the stability analysis of the slope facing the spillway of the Shiraz Kavar dam has been done in two probabilistic and deterministic methods. Since circular slip probability is more likely than other types of failure, in the analysis of the stability of this slope, the problem of circular failure is very important, and an appropriate equilibrium program should be used for circular failure analysis. Therefore, SLIDE software was used to slope stability analysis. For material behavior, the Hook-Brown failure criterion was applied. In order to determine the strength parameters of the criterion, Geological Strength Index (GSI), uniaxial compressive strength (UCS) and rock constant parameter m_i were used. For crushed rock with a moderate quality of crushing, the GSI quality of the rock mass was about 23 to 38, which the average value of that for the rock mass of the overflow was assumed 35. Also, the uniaxial compressive strength of the rock was evaluated about 50 to 100 MPa with an average value of 75 MPa. In addition, the value of m_i was 10, and due to mechanized drilling, the disturbance factor was considered to be 1. The amount of unit weight was assumed to be 22 kN/m³. The initial model used for deterministic and probabilistic analyses, is the Morgenstern-Price model. To conduct probabilistic analyses, Monte Carlo simulation was performed using random sampling method (RS-MC) and 200,000 sampling were used to converge the simulation results. To determine the coefficient of variation and the probability distribution of UCS, GSI and m_i, the proposed values ​​of Hook (1998) were applied and for unit weight (γ) James Rodriguez and Sitar (2007) studies were used. Also, the minimum and maximum values ​​of UCS and GSI are determined based on the results of experiments, and Third Sigma rule was utilized for m_i and γ quantities. Since the earthquake phenomenon is rarely of great intensity and the number of small earthquakes is higher, therefore the truncated exponential distribution function can be in good agreement with the results of the earthquake. Usually, the maximum magnitude of the earthquake acceleration coefficient is twice that of the average.
Results and discussion
In the presented paper evaluation denotes that the safety factor computed by probabilistic analysis is given as a distribution function. The function provides a clearer view of failure condition. However, a deterministic analysis only illustrates a certain value for the failure. In addition, the results of the probabilistic analysis show that it is possible to optimize the dip of the slope; such that it remains completely stable and the volume of earthwork is also minimized. Therefore, by using probabilistic analysis, the optimal dip of the slope was determined. In these circumstances, the amount of earthwork was decreased by 28,000 cubic meters. Also, the sensitivity analysis of the variation coefficient and correlation coefficient between parameters are analyzed. The results of the sensitivity analysis of the failure probability versus the variation coefficient of the quantities showed that the quantities of sensitivity factor for static conditions is greater than the corresponding pseudo-static, and the GSI amount is the highest, while the specific gravity has the least effect on the probability value. In addition, the analysis indicated that if the GSI coefficient of over 21% is selected, the probability of a static failure is higher than the permissible limit. Also, increasing the variation coefficient of quantities by as much as 50% exhibits that the probability of static failure is still below the permissible limit. Also, the correlation coefficient between UCS and GSI shows that the higher variation coefficient of the quantities is chosen, the more variations of failure probability compared to . In the case of pseudo-static conditions, variations in the failure probability are linear in relation to , while in static conditions, these changes are exponential for an increase of 50% in the variation coefficient. Also, to reduce the coefficient of variation by 50%, the probability of static failure for different values of  is approximately zero.
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Introduction
Expansive soils are a very common cause of extreme damages because they are susceptible to volume change due to a change in water content. Geotechnical problems associated with the expansive soils are well documented in different literature. As a result, a clear understanding of the behavior of such soils is required for the effective design of structures and infrastructures on these soils. The effects of hydrocarbon pollutants as a flooding fluid on the swelling potential of an expansive soil during wetting and drying cycles have not been considered in the previous researches. The aim of this research is to study the properties of an expansive soil with different flooding fluids, i.e. distilled water and solutions of glycerol with 10 and 20% through a number of cycles of wetting and drying tests under constant surcharge pressure.
Material and methods
The soil that was used in this work was a highly expansive clay soil (according to the classification by McKeen (1992)). It was prepared by mixing 20% bentonite and 80% kaolin. This soil was classified as a clay with high plasticity according to the Unified Soil Classification System (USCS). The optimum water content in the standard compaction test was 18.11% and the maximum dry unit weight was 16.27 kN/m³.
Distilled water and solutions of glycerol with concentrations of 10 and 20% were used for flooding the samples. To prepare the glycerol solutions, the required amount of glycerol was mixed with distilled water.
For making compacted samples for testing, the needed air-dried soil was weighed and the required water was added to it to reach the desired water content (4% below the optimum water content according to the compaction curve). The soil and water were mixed by hand and then was kept in a plastic bag for 24 hours to allow the uniform distribution of moisture in the soil. Samples were prepared by static compaction of the moist soil in a special mould.
A conventional oedometer was modified to allow the wetting and drying tests to be conducted under controlled surcharge pressure and temperature. During wetting and drying, the vertical deformation of the sample was measured by using a dial gauge. The variation of water content with void ratio during wetting and drying cycles was determined by using the information from the duplicated samples.
Results and discussion
Fig. 1 shows the variations of vertical deformation during wetting and drying cycles for samples that were flooded with distilled water and solutions of 10 and 20% glycerol. This figure illustrates that by increasing the number of cycles the amount of irreversible deformation is reduced until the equilibrium condition is achieved where the deformation due to wetting and drying is nearly the same. These results indicate that by increasing the concentration of glycerol the equilibrium condition with reversible deformation is reached in a fewer cycle of wetting and drying than the sample that was flooded with distilled water.

Figure 1. Wetting and drying cycles for different quality of flooding fluids
The results of void ratio versus water content at the equilibrium conditions for the samples flooded with distilled water and solutions of 10 and 20% glycerol (that were obtained from duplicated samples) are shown in Fig. 2. This figure displays that the paths of drying-wetting for different flooding fluids are nearly S-shaped curves. It is also seen in this figure that the order of the curves in this space is dependent on the percent of glycerol, the curves for the sample flooded with distilled water and 20% glycerol are located at the top and bottom of the space of void ratio against water content.

Figure 2. Water content-void ratio paths for different quality of flooding fluids
The change in the thickness of the diffuse double layer (DDL) affects on the swelling behavior of soil. The thickness of DDL is dependent on factors such as valency and concentration of cations, temperature, and dielectric constant. The value of dielectric constant for water is 80 and for solutions of 10 and 20% glycerol are 74.9 and 71.8, respectively. The magnitude of the attractive and repulsive forces between clay particles are inversely and directly depended on the value of the dielectric constant. The reduction in the value of the dielectric constant causes an increase in the attractive forces and leads to a reduction in the thickness of DDL. When the flooding fluid is a solution of glycerol, the initial chemical composition of pore fluid in the sample is changed. The chemical composition of pore fluid has different effects on the structure of clay soil such as changes in the thickness of DDL. When the flooding fluid is distilled water the pore fluid of samples has a dielectric constant of about 80. Therefore, the values of attractive and repulsive forces are not changed because of the same dielectric constant of flooding fluid and pore fluid. The results of tests on these samples (flooded with distilled water) show that by repeating the wetting and drying cycles the potential of swelling is reduced and after several cycles a reversible equilibrium condition is attained as depicted in Fig.1. When the pore fluid is the solution of glycerol, the attractive forces are increased due to the reduction of the dielectric constant of pore fluid and causes a reduction in the thickness of DDL. The shrinking of DDL is led to the formation of flocculated structure in the soil and results in pasting of particles together leading to the reduction potential of swelling. When the concentration solution of glycerol is increased the dielectric constant is decreased, the magnitude of attractive forces is increased and the degree of flocculation of the soil structure is increased that is yielded to a reduction of swelling potential.
Conclusion
Effect of different flooding fluids on the properties of an expansive soil during wetting and drying cycles were studied. The following conclusions can be drawn from the present research:
-After a number of wetting and drying cycles, the observed irreversible          deformation was diminished and equilibrium was achieved. The solution of glycerol causes more reduction in the potential of swelling than distilled water.
-The wetting and drying paths in the space of void ratio and water content are S-shaped curves. The variations in the void ratio of samples flooded with the solution of glycerol are smaller than distilled water../files/site1/files/142/babaei.pdf