Journal of Engineering Geology

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Shear wave velocity (Vs) is a basic engineering soil property implemented in evaluating the soil shear modulus. Due to a few limitations, sometimes it is preferable to determine Vs indirectly by in situ tests, such as standard penetration test (SPT). However, inaccuracies in measurement or estimation of the influencing parameters have always been a major concern, and thus various statistical approaches have been proposed to subdue the effect of such inaccuracies in predictions of future events. In this article, an innovative approach based on robust optimization has been utilized to enumerate the effect of such uncertainties. In order to assess the merits of the proposed approach a database containing 326 data points of case histories from Adapazari, Turkey were gathered from renowned references. The identification technique used in this article is based on the robust counterpart of the least square problem which is a second order cone problem and is efficiently solved by interior point method. A definition of uncertainty based on frobenius norm of the data is introduced and examined against correlation coefficient of various correlation parameters and optimum values are determined. Finally the results of new correlation are compared with those utilizing a commonly used statistical method and the advantages and possibilities of the proposed correlation over the conventional method are highlighted

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The present study aims to employ intelligent methods to predict shear wave velocity (V_s) in limestone. Shear wave velocity is one of the most important rock dynamic parameters. Direct determination of this parameter takes time, cost and requires accuracy as well. On the other hand, there is no precise equation for indirect determination. This research attempts to provide some simulations to predict V_s using the information obtained several dams located in Iran, using different approaches, including adaptive neuro-fuzzy inference system (ANFIS) and gene expression programming (GEP). 136 datasets were utilized for modeling and 34 datasets were used for evaluating its performance. Parameters such as Compressional wave velocity (V_p), density (g) and porosity (n) were considered as input parameters. The values of R² and RMSE were 0.958 and 113.620 for ANFIS, where they were 0.928 and 110.006 for GEP respectively. With respect to the accuracy of the intelligent methods, they can be recommended for future studies

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 The average of shear wave velocity of the upper 30 m has so far been one of the reliable parameters in seismic site classification in different building codes, despite the numerous weaknesses in the exact explanation of site dynamic characteristics. In this study, an empirical relationship is obtained between the average of the shear wave velocity of the upper 30 m and the average of the shear wave velocity of shallower depths, based on 79 shear wave velocity profiles, in Mashhad. This is followed by the recommendation of proper depths for the dynamic analysis of the site effect based on the information of shear wave velocity profiles and resonance period distribution in the investigated area. The depth of the S-wave velocity profile investigation, required for the analysis of deposit effects has been estimated more than 30 m. whith exception of the southern and western parts of Mashhad (adjacent hillsides). Such depth is estimated as about 80 m for central, eastern, and north-eastern areas, where the resonance period is more than 0.7 s. Therefore, investigation depth of 30 m is only adequate for site classification based on the building codes, and for theoretical analysis deeper studies is needed, in Mashhad

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In many rock engineering projects, accurate identification of rock strength properties is very important. Uniaxial compressive strength is one of the most important features to describe the resistive behavior of rocks which is used as an important parameter in the design of structures especially underground openings. Determination of this parameter using direct methods, including uniaxial compressive strength tests is costly and time-consuming, and also sometimes preparation of standard samples in many rocks is difficult. In such cases, the implementation of some simple and non-destructive tests and using empirical relations can increase the evaluation speed and reduce costs. These relations even regional or local (For example within a geological formation or a single lithology) can help in the estimation of these parameters in order to be used in geotechnical projects. In this study, samples of existing limestones in south west of Tehran (Capital of Iran) were prepared and uniaxial compressive strength, point load, Schmidt hammer and Shear wave velocity tests on which have been performed. Then by the statistical evaluations of the results, the empirical relations between uniaxial compressive strength and the results of other tests are obtained. The comparison between the predicted and observed values of uniaxial compressive strength represents the validity of obtained empirical relations. The application of the proposed relations for limestones in the study area and those with similar geological conditions will provide acceptable results.

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Introduction
When loose sand is subjected to seismic shaking, it tends to volume reduction and settlement. The density of the under layers is revealed in the settlement of the ground surface that causes the destruction of the structures located on ground surface. In dry sand layer, settlement in severe shakings occurs under a constant and effective stress condition and very rapid stress. In this regard, the sand deposit settlement is completed before the end of an earthquake, but if the sandy soil layer is saturated and drainage is limited the condition is prepared of fixed volume situation and the major effect of the seismic shocks is generation of exceed pore water pressure. Therefore, the deposit settlement of saturated sand requires a longer time, varying from a few minutes to a few days, depending on the permeability and compressibility of the soil and the length of the drainage path. The main purpose of the present study is to evaluate liquefaction hazards along Tabriz Metro Line 2 with using Standard Penetration test (SPT) and shear wave velocity (Vs) methods. Also, the probable rate of settlement in the soil layers in study area and correlation with liquefaction potential index (LPI) according to both procedure have been determined and discussed in the following paragraphs.
Material and Methods
In order to evaluate the liquefaction potential of soils using two field methods, geotechnical information of 54 boreholes in Tabriz Metro Line 2 were collected. The types of soil and geotechnical properties can affect the liquefaction potential. In this study, the gravely sand, silty sand, silty and sandy soils were studied. Ground water level is one of the main parameters in in soil liquefaction potential evaluation of soils. Variation of water level in boreholes is 2 to 30 meters. The peak ground acceleration (PGA) is necessary for the analysis of boreholes to evaluate liquefaction potential of soils. PGA values were selected in each boreholes position according to the Iranian Code of Practice for Seismic Resistant Design of Buildings (Code-2800-ver.4) equal to 0.35g (for return period 475 years and design life 50 years). Liquefaction potential of soil layers based on SPT results with appliying Idriss and Boulanger (2010) method has been assessed. Andrus, Stokoe and Jung (2004) procedure was used in shear wave velocity (Vs) method (with assuming cementation and un cementation condition in soils). Liquefaction potential index (LPI) of soil layers was calculated for both field tests results. Then, probable rate of settlement due to liquefaction in saturate soil layers was determined. Tokimatsu and Seed (1978) method applied for SPT results, Yoshimine (1992), Yoshimine et al. (2006) and Yi (2009) procedures have been used in Vs test. Finally, correlation between rate of settlement and LPI results were determined.
Results and discussions
Outcomes of this study can be explained in below:
1. Results obtained from comparison of both methods in liquefaction potential evaluation have been showed, agreement between two methods have been happened rarely. Specially, with assuming cementation condition in soils, LPI obtained from Vs method is more than SPT. Although, different factors can be affected at uncertainties in SPT results such as type of drilling machine, energy efficiency and accuracy of test performing. Also, in shear wave velocity method, maximum velocity for occurring liquefaction in soil layers () related to fines content percentage. It is possible that boundary values in procedure not compatible with geotechnical properties in study area.
2. Evaluation of probable rate of settlements in soil layer in study area have been showed that settlement values obtained from Vs is more than SPT. This condition is compatible with LPI amounts.
Conclusions
In sum up, settlement due to liquefaction in saturate soil layers is one of the important phenomena in geotechnical earthquake engineering. Maximum rate of settlement in soil layers in study area is equal 0.45m based on SPT method and 0.9m according to Vs procedure which should be considered. Accordingly, serious damages can be inflicted to buildings, underground structures and life lines in study area.  Therefore, it is suggested in future researches with using empirical and numerical (or soft computing) methods based on field and experimental tests results a detailed assessment conducted and influence of various parameters on settlement of soil layers be determined and the items listed below should be considered:
- Cementation parameter (C) values of soils in shear wave velocity method maybe not compatible with geotechnical properties in study area. It should be evaluated exactly. 
- In this research, peak ground acceleration (PGA) value was selected based on code 2800-ver.5. As regard to Tabriz Metro Line 2 is beside to Tabriz North Fault, PGA value according to historical earthquake catalogue and seismic risk analysis should be evaluated and seismic hazard have to determine with accuracy. 

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Introduction
Series A of coarse-grained alluvial deposits of Tehran are extended in eastern and north-eastern areas of Tehran. Analyzing and studying of these alluvial deposits from a geological point of view as well as their creation time and general characteristics such as the deposits’ mineral types, their source, and formation conditions, gives a better point of view to geotechnical engineers about exploring their characteristics as well as geotechnical aspects in underground structure design, excavations, and foundation design processes. On the other hand, in order to analyze stability, estimating the factor of safety and the seismic design of these structures, considering their location, which is in Tehran with a high seismic hazard area, the necessity of knowing the exact mechanical and dynamic properties of Tehran's alluvium is felt more than ever.
Material and methods
Due to the grain size of Tehran’s coarse-grained alluviums (series A) as well as high level of cementation of them, it is impossible (or maybe so difficult) to make undisturbed samples in order to do experiments. Such that it is excavated 23 boreholes with 30 to 140 meters depth as well as 17 test wells with 20 meters depth in an area which was extended in 10 kilometers in long which were located in Tehran’s No. 13 and No. 14 districts (as it can be seen in Figure 1). During the excavation of the entrance ramp and tunnel of eastern highway of Tehran, in-situ tests have been done in different sequences. Since it was important to investigate real behavior of these alluviums, different in-situ tests such as plate load test, in-situ shear test, pressuremeter test, and downhole test have been done as well as many laboratory and field tests. Furthermore, (1) X-Ray Diffraction (XRD) and (2) X-ray Fluorescence (XRF) as well as (3) Scanning Electron Microscopy (SEM) methods, have been used to explore the type of minerals and those used in cementation.
 
 
 
 

(ب)
 
 
 
Figure 1. a) Geological plan and the location of boreholes and test wells in the alignment of East Tehran Freeway
Results and discussion
Based on the results of XRD tests, it is quite clear that the largest weight percentages of tested samples are lime and silica.
Calcium and magnesium levels-as the high-power cations in flocculation process-in soil sample No. 1 (soil with high cementation level) are much more than soil sample No. 2 (soil with moderate cementation level).
This is the cause of high cementation level of soil sample No. 1 comparing with soils sample No. 2. A rapid increase in stress level can be seen in in-situ shear test results, in low shear displacements, up to reaching a maximum of τ_p (peak point) and afterwards reduction in shear stress with softening behavior.  
Cohesion and shear strength levels also increase by increasing the depth. According to the plate load tests results, an increase in soil modules changes can be seen in different depths by depth increasing.
Large tendencies to increase in volume and dilation can be seen in under shear load cemented soils, after applying a primary compression on them. A brittle behavior with the occurrence of a certain peak can be seen in cemented samples. The significant increase in strength is directly related to the severe dilation rate, which can be seen in cemented samples results.  The shear strength would be decreased, if this cement is broken during the particles’ displacements.
The results of downhole tests are shown in Figure 2. According to this figure, it has been explored that V_s,30 is about 600 m/s in moderate cemented soils while it is about 850 m/s in highly cemented soils.  Because of the homogeneity and uniformity of sedimentary deposits, shear wave velocity is increasing due to the higher density of the layers and high level of cementation in both of the soil types. However, this increase is not significant at depths above 25 meters.
Conclusion
Based on the results, cementation level of the eastern coarse-grain-alluvium of Tehran is moderate to high and minerals used in cementation of this type of soil are generally carbonated and especially calcite.
Investigating the level of cementation of soil as well as the results of chemical analysis and in-situ tests, it can be found that the strength and deformation parameters of the soil are directly related to the degree of its cementation.
Based on the obtained results, the deformation modulus increases by about 25%, the cohesion by about 55% and the shear wave velocity by about 30% with increasing the degree of cementation (Table 1).
Increases of these parameters are directly related to depth. However, the cementation level does not significantly affect the internal friction angle of the soil.
Table 1. Average results of in-situ shear tests

Deformation Modulus (MPa)	Peak Friction Angle (deg.)	Cohesion (kPa)	USCS	Depth (m)	Sample
50-60	39	30-35	GW-GM	5	Moderately Cemented Soil (M.C. Soil)
75-85	41	50-60	SP-SC	10
85-90	41	50-60	GW-GC	15
95-105	41	50-60	GW-GC	20
60-70	39	35-40	GW-GM	5	Highly Cemented Soil (H.C. Soil)
75-85	39	50-60	GW-GC	10
110-120	42	65-75	GW-GC	15
125-140	41	110-120	GC	20