Soil Shear Strength Parameters Research Articles

On the interpretation of shear parameters uncertainty with a linear regression approach

Interpretation of the triaxial testing results of soil shear strength parameters is a particular case of simple linear regression. In triaxial testing the parameters of the regression have certain physical interpretation (i.e. the intercept is the cohesion and the slope is the tangent of the internal friction angle). Another important issue is that the fitting of the line is carried out on the other plane to the plane of the Mohr-Coulomb criterion. The results of the fitting need to be later transformed into the soil parameters. This makes the uncertainty analysis of the parameters nontrivial. This study focuses on the two abovementioned issues. Firstly, the transformation formulae for different planes are briefly presented. The methodology of confidence interval estimation is then described. The validity of our approach is verified by computer simulation. The results of the simulation are discussed and the conclusions regarding recommendations for laboratory test planning are drawn.

In Situ Shear Test for Revealing the Mechanical Properties of the Gravelly Slip Zone Soil.

Slip zone soil is usually composed of clay or silty clay; in some special geological environments, it contains gravels, which make the properties of the slip zone soil more complex. Unfortunately, in many indoor shear tests, gravels are removed to meet the demands of apparatus size, and the in situ mechanical property of the gravelly slip zone soil is rarely studied. In this study, the shear mechanical property of the gravelly slip zone soil of Huangtupo landslide in the Three Gorges Reservoir area of China was investigated by the in situ shear test. The test results show that the shear deformation process of the gravelly slip zone soil includes an elastic deformation stage, elastic–plastic deformation stage, and plastic deformation stage. Four functions were introduced to express the shear constitutive model of the gravelly slip zone soil, and the asymmetric sigmoid function was demonstrated to be the optimum one to describe the relationship of the shear stress and shear displacement with a correlation coefficient of 0.986. The comparison between the in situ test and indoor direct shear test indicates that gravels increase the strength of the slip zone soil. Therefore, the shear strength parameters of the gravelly slip zone soil obtained by the in situ test are more preferable for evaluating the stability of the landslide and designing the anti-slide structures.

Effect of silica fume on the ultrasonic pulse velocity of cemented sand

One of the geotechnical engineering strategies for dealing with weak soils in a construction site is to modify their mechanical properties with the aid of soil improvement techniques. Chemical stabilization of soil using cement is one of these effective approaches that can considerably enhance workability and shear strength parameters of soil. However, very limited investigations have been carried out to reveal the effect of silica fume on the ultrasonic pulse velocity (UPV) and the ultrasonic stiffness (Eu) of cement-treated sandy soil. For this purpose, in the present research, a series of UPV tests were performed on sand-cement-silica fume specimens. The cement percentages were 3, 5 and 7% and silica fume contents were 0, 0.25, 0.5 and 1% by weight of dry sand. The cylindrical samples were prepared and cured for 3, 7, 14, 28, 42 and 56 days and tested. The results show that inclusion of silica fume to the cemented sand increases UPV and Eu which this enhancement is more pronounced at longer ages.

SOIL SHEAR STRENGTH PARAMETER ANALYSIS BASED ON BEHAVIOR ANALYSIS OF LANDSLIDE CASE

Slope failure is a complex event. It can provide useful information about the condition of soil parameters on the failed slope in the same way it can provide an opportunity to evaluate the stability of other slopes. To evaluate the occurence of slope failure, unit weight data and shear strength properties of soil are needed, as well as methods of analysis including failure mechanisms. One of the methods used to evaluate landslide events is reverse analysis. In this study, reverse analysis was carried out on landslides that occurred on the slopes of D-D 'and F-F' at the Integrated Campus Building of the Institut Teknologi Kalimantan. The finite element method is used to analyze the safety number of the slopes under review. From the results of the reverse analysis, it was obtained that the soil parameters at the time of collapse in the top layer resulted in the value of unit weight (γ) = 20 kN / m2, Cohesion (c) = 2 kPa and Internal friction angle (φ) = 27 ° . Slope failure occured due to an increase in soil volume weight value, as well as a decrease in soil shear strength parameters, namely cohesion and internal friction angle.

Relationship between the Shear Strength and Microscopic Pore Parameters of Saline Soil with Different Freeze-Thaw Cycles and Salinities

Saline soil is a widely distributed special soil with poor engineering properties. In seasonally frozen regions, the poor properties of saline soil will cause many types of engineering damage such as road boiling, melt sinking, and subgrade instability. These engineering failures are closely related to the shear strength of saline soil. However, there are relatively few studies on saline soil in cold regions. The strength of the soil is always determined by its microstructure; therefore, the study aims to investigate the relationship between the shear strength and microscopic pore structure of saline soil with different freeze–thaw cycles and salinities. The shear strength characteristics of saline soil with different salinities subjected to different freeze–thaw cycles were obtained by triaxial tests. In addition, the microstructure of the soil samples was investigated by scanning electron microscopy (SEM) tests, and the microscopic pore parameters of the soil samples, including porosity (N), average pore diameter (D¯), average shape coefficient (K), surface fluctuation fractal dimension (F), and orienting probability entropy (Hm), were obtained by image processing software quantitatively. Based on the experimental results, the influence of freeze–thaw cycles and salinity on the shear strength characteristics and microstructure of the soil samples were analyzed. Besides that, in order to effectively eliminate the collinearity between independent variables and obtain a stable and reasonable regression model, principal component regression (PCR) analysis was adopted to establish the relationship between the microscopic pore parameters and the failure strength of the soil samples. The fitting results demonstrated that the failure strength of saline soil is mainly related to the size and direction of the pores in the soil, and it has little correlation with pore shape. The failure strength of the soil was negatively correlated with the average pore diameter (D¯) and porosity (N), and it was positively correlated with the orienting probability entropy of the pores (Hm). This study may provide a quantitative basis for explaining the variation mechanism of the mechanical properties of saline soil from a microscopic perspective and provide references for the symmetry between the changes of the macroscopic properties and microscopic pore structure of the saline soil in cold regions.

Mapping soil nail loads using Federal Highway Administration (FHWA) simplified models and artificial neural network technique

This study compiles a broad database containing 312 measured maximum soil nail loads under operational conditions. The database is used to re-assess the prediction accuracies of the default Federal Highway Administration (FHWA) nail load model and its modified version previously reported in the literature. Predictions using the default and modified FHWA models are found to be highly dispersive. Moreover, the prediction accuracy is statistically dependent on the magnitudes of the predicted nail load and several model input parameters. The modified FHWA model is then recalibrated by introducing extra empirical terms to account for the influences of wall geometry, nail design configuration, and soil shear strength parameters on the evolvement of nail loads. The recalibrated FHWA model is demonstrated to have much better prediction accuracy compared to the default and modified models. Next, an artificial neural network (ANN) model is developed for mapping soil nail loads, which is shown to be the most advantageous one as it is accurate on average and the dispersion in prediction is low. The abovementioned dependency issue is also not present in the ANN model. The practical value of the ANN model is highlighted by applying it to reliability-based designs of soil nails against internal limit states.

Correlation of Apparent Electrical Resistivity with Elastic Moduli and Soil Shear Strength Parameters in Yenagoa, Southern Nigeria

Correlation of Apparent Electrical Resistivity with Elastic Moduli and Soil Shear Strength Parameters in Yenagoa, Southern Nigeria

Runout modeling and calibration of friction parameters of Kurichermala debris flow, India

Debris flows account for a substantial economy and property loss in Western Ghats of Kerala, India, especially during monsoon seasons. Wayanad district is an active erosion zone in the plateau margins of Western Ghats, and there is a remarkable rise in the number of debris flows since 2018, due to very high-intensity rainfalls in this region. This study comprises geotechnical investigation, runout modeling, and calibration of friction parameters of Kurichermala debris flow, one of the devastating debris flow events that happened in Wayanad, during the 2018 monsoon. The detailed investigation and back analysis of such events are substantial in calibrating the flow parameters for the region. These parameters can be used for predicting the flow paths of possible debris flows and quantitative risk assessment in the future. The geotechnical investigation provided vital information regarding the soil type and shear strength parameters of the debris flow and has helped in understanding the flow behavior. A dynamic numerical model, rapid mass movements (RAMMS), was used for the back analysis of the debris flow, using the shape information of the flow. For precise calibration using statistical comparison, an image processing tool has been developed, to compare the structural similarity of simulated results with the original shape of debris flow. The dry-Coulomb friction coefficient (μ) was calibrated as 0.01 and turbulent friction coefficient (ξ) as 100 m/s2 for the event, using Voellmy-Salm rheology. The shape predicted by the model had a similarity index of 0.626 with the actual shape of debris flow. The results were found to be in accordance with the field and geotechnical observations. Hence, the results can be used to predict the shape of possible debris flows in the study area. The study is the first of its kind for the region and has significant influence in risk assessment for this highly susceptible landslide zone.

ANN and Neuro-Fuzzy Modeling for Shear Strength Characterization of Soils

We examine the outcome of popular artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) for estimating the shear strength parameters of c − φ soil. A matrix of one hundred twelve datasets collected using in situ and laboratory tests to train and test the ANN and ANFIS models. Standard penetration test number of blows value along with the soil properties taken as input vectors, whereas shear strength parameters like cohesion (c) and angle of internal friction (ϕ) used as target vectors. The minimum validation error has been employed as the stopping criterion to avoid over fitting in the analysis. Out of four developed models, predicted values through two ANN models were close to actual value in comparison to ANFIS models. Statistical parameters such as coefficient of correlation, root mean square error and average absolute error were used as performance evaluation measures. Based on statistical measures it was observed that performances of ANN and ANFIS models were in accordance with the experimental results and it could substitute tedious laboratory work provided sufficient and reliable data source are offered. The results through performance evaluation measures also reveal that ANN and ANFIS models are effective, versatile and useful way to measure the shear strength parameters of soils.

Primjena metode konačnih elemenata za 2D i 3D analize slijeganja izazvanih izgradnjom tunela

Results of a series of 3D and 2D analyses of open-face tunnelling in marly-clayey deposits are presented in the paper. A parametric study was performed to investigate the influence of initial stress state, soil deformability, shear strength parameters, and soil anisotropy, on settlement prediction. Comparison of 2D and 3D results shows that the settlement trough predicted by 2D analysis agrees well with 3D results when an appropriate amount of unloading prior to lining installation is adopted. It is demonstrated that the load reduction factor significantly depends on shear strength parameters of soil.

Non-intrusive reliability analysis of unsaturated embankment slopes accounting for spatial variabilities of soil hydraulic and shear strength parameters

Existing reliability analyses of embankment slopes usually considered the spatial variabilities of shear strength parameters and saturated hydraulic conductivity separately. Additionally, the variability in the soil–water characteristic curve (SWCC) was ignored. A non-intrusive approach is proposed for reliability analyses of unsaturated embankment slopes under four different cases on a steady-state seepage analysis. The spatial variabilities of hydraulic parameters (including fitting parameters, a and n, of SWCC and saturated hydraulic conductivity) and shear strength parameters are accounted for simultaneously. To illustrate the proposed approach, a hypothetical embankment under unsaturated seepage is investigated. The soil parameters of the embankment and foundation are modeled as lognormal random fields and lognormal random variables, respectively, to take into account the inherent uncertainties. Parametric sensitivity studies are then performed to account explicitly for the influence of the spatial variation of hydraulic parameters on the reliability of embankment slope stability. The proposed approach can act as a practical and rigorous tool for estimating the reliability of embankment slopes with small levels of probability of failure (i.e., 10−4–10−3). An interesting finding that the probability of failure of the unsaturated embankment slope decreases with the variability of the fitting parameter n of SWCC is observed and explained.

Reliability of Shear-Box Tests Upon Soaking Process on the Sand Soil in Al-Najaf City

Accurate prediction of the soil shear strength parameters is essential in the reliable geotechnical design of civil engineering structures. This recent paper investigates the effect of the dry testing condition on the shear strength parameters of the sandy soil using the direct shear apparatus and compared with the saturated condition tests in previous researches on the same soil. The dry soil, usually above the water table, is the principal condition of the Al-Najaf city soil in Iraq. Samples are selected from the site of the University of Kufa, which represents the sandy soil of the city. For reliability purposes, the soil is exposed to different pre-soaking durations (one, two, and four weeks) then air-dried for shear tests. The main results revealed that the angle of internal friction (Φ) tested as a dry sample decreases about -6% up to two-weeks soaking then recovered upon four-week soaking about +6%. Compared to the saturated testing, there are increases in F between 6%-17% from saturated tests. Finally, it is recommended to aware in the selection of testing conditions for calculations of the angle of internal friction.

Field direct shear tests on a backfill soil slope and finite element analysis of its reinforcement schemes

The field direct shear test was used to analyze the backfill soil strength of a filling slope, and the slope controlled by different reinforcement conditions was simulated by finite element method base on the shear strength by the field test. The results show that the shear strength parameters of the backfill soil are friction angle φ = 15° and cohesion c = 25 kPa. Reinforced by anti-slide pile with different lengths, the maximum horizontal displacement of the slope can be reduced by 79.7% ~ 81.3% compared with that of the unreinforced slope. The maximum shear strain of the soil is also reduced to some extent, and the sliding surface characteristics and the strain amplitude are weakened.

Assessment of Changes in Shear Strength Parameters for Soils below Circular Machine Foundation

This paper focuses on the response of circular machine foundation resting on different soils (sand and clay) through studying the variation of soil shear strength parameters and strain with the number of cycles. The objective of the current study is to explore the results related to the parameters of the dynamic load (number of loading cycles and frequency of load) related to the circular footing of a machine on the dynamic shear strength parameters (for sand soil (ϕ˚dyn) and for clay soil (Cudyn)) in addition to the amplitude strain foundation. A special setup was designed and manufactured to simulate the vertical vibration of a circular machine foundation. A steel circular machine foundation with a diameter of 150 mm was used to represent the footing. A total of 6 cases were examined to take into account the effects of different parameters including different frequencies (0.5, 1, and 2 Hz); state of sand (medium and dense) which corresponded to relative densities of (50 and 80%), while the state of clay (medium and stiff) corresponded to undrained shear strengths (50 and 70 kPa). All tests were carried out under load amplitude of 2.5 kN. It was found that the rate of increase in shear strength parameters for the soil under a circular machine foundation decreases remarkably when increasing the frequency for both types of soil under the footing. While little change in the shear strength parameters, or even no change was observed under the effect of other locations. Moreover, the amplitude strain decreased when increasing the frequency for both types of soil.

Numerical Modeling of Unfavorable CFA Pile Drilling Conditions

Drilling and installation of deep foundations typically alter and affect surrounding soils and subsequently affect the adjacent structures. Possible effects on the adjacent structures due to the installation of driven piles have been thoroughly investigated in the literature. However, little attention has been given to other pile installation techniques such as continuous flight auger (CFA). In this paper, unfavorable CFA drilling conditions are discussed and investigated using three-dimensional (3D) finite element analyses. The induced settlements around the piles are calculated to assess the possible adverse effects on surrounding structures. The numerical models are validated using laboratory physical modeling of unfavorable soil drilling conditions reported in the literature. The analyses showed that unfavorable drilling conditions might have a major effect on adjacent structures up to two times the pile length. Parametric numerical modeling has also been conducted to study the influence of different parameters such as soil shear strength parameters, pile length, pile diameter, and soil permeability on the deformation adjacent to CFA pile during construction. The results revealed that soil relative density and permeability have a significant influence on the calculated surface settlement. Finally, several pile group drilling scenarios were investigated to gain insight into the optimum scenario for pile drilling. The analyses show that alternating between drilling piles near the structure and those far from it, may significantly reduce the surface settlement during pile construction.

Monte carlo simulation for stability of finite slope subjected to earthquake loading

Analysis of finite slopes is a common practical problem which faces the geotechnical engineering. The aim of the slope analysis is to predict the safety factor against shear failure of the slope which is the ratio between the resisting and the disturbing forces developed along an assumed slip surface. Presence of seismic forces due earthquake lead to more critical situation. The deterministic approaches are employed for this purpose. These approaches do not take into account the uncertainty related to soil properties and/or seismic loads in their procedures. In the present work, a probabilistic approach is adopted using the Monte Carlo simulation technique to study the effect of uncertainty due to soil properties (unit weight, angle of internal friction and cohesion) and seismic accelerations (vertical and horizontal). The results of the work demonstrate that the use of probabilistic approach will yield more accurate results for estimating the safety factor and then economic design of the slope. Also, the results reveal that the statistical properties for the soil shear strength parameters have significant impact on the standard deviation of the output (factor of safety), while the soil unit weight and horizontal acceleration have small effect. However, the vertical acceleration has no effect on it. On other hand, the mean of the output distribution does not affect by the statistical parameters of all input variables. All cases simulated in this study give reliability index (RI) less than 3. Hence, RI values indicate that there are unsatisfactory level of safety for the slope subjected to seismic loading. Finally, the soil shear strength parameters have the same positive significant impact on the safety factor. But, the soil properties and the coefficient of the horizontal acceleration should be selected carefully in the stability analysis due to the effect of their uncertainty on the analysis results.

Prediction of the shear strength parameters from easily-available soil properties by means of multivariate regression and artificial neural network methods

ABSTRACT* Shear strength parameters of soils are essential in civil projects. Two important parameters for these projects are the Ø’ and C’ of saturated soils, which are usually obtained by the triaxial shear test. One TST may take weeks and it costs too much. Also, in a vast project, it is practically unreasonable to carry out a large number of the tests. Therefore, predicting models for shear strength parameters can be used as alternative methods. In this study, an approach was taken to evaluate shear strength parameters by using the database in Isfahan, Iran. For this purpose, 108 soil samples were tested. Different types of multiple regressions and neural networks have been used for prediction of C’ and Ø’ from easily-available soil properties including Atterberg limits, density, percentages of gravel, sand, silt, clay and passing the sieves No. 200. The best relationships between shear strength parameters and soil properties are determined. The results indicated that the multilayer perceptron (MLP) of neural networks showed higher accuracy than radial basis function and multiple linear regressions. Based on the results, MLP with one hidden layer is the best model for SS parameters with R2 = 0.885 for C’ and R2 = 0.845 for Ø’.

Reliability Analysis of Anchor Foundations Subject to Vertical Uplift Forces

Foundations of transmission towers are subject to uplift forces, and the designs are based on deterministic procedures. Present design guidelines on design of anchor foundations are discussed, and limitations as well as need for incorporation of reliability-based design are brought out. Reliability analysis of anchor foundations subjected to vertical uplift forces using the first-order reliability method is performed. The results of the reliability analysis for different distributions of shear strength parameters of soil and the uplift loads in terms of Hasofer–Lind reliability index have been presented. Load and resistance factors have also been presented to enable reliability-based design. A design example is presented to compare the results obtained from this study. The results show that reliability-based approach can lead to an economic design than the conventional factor of safety approach. It is suggested that codes need to incorporate reliability-based designs in practice.

A new large step-tapered hollow pile and its bearing capacity

This paper introduces a new large step-tapered hollow (STH) pile used in a karst area and its construction method. To reveal the advantages of this pile type, a 15 m dia. STH pile in Ji'an Shenzhen Bridge was simulated using Flac3D software. The vertical bearing capacity was assessed by considering the influences of the width and number of the variable cross-sections and the soil characteristics around the pile. In addition, new large STH piles of two different forms were assessed to expand the practical application of such piles. The results showed that, for a large-diameter pile, the concrete utilisation rate and the vertical bearing capacity of the pile were improved by the design of hollow and variable cross-sections. The optimal range of the taper angle for the large STH pile was found to be 2·68–5·36° and the optimal number of variable cross-sections was found to be between two and four. The bearing capacity increased with an increase in the soil shear strength parameters and the pile was deemed suitable for stiff strata. The results of this work could facilitate design practice for large STH piles.

Shear strength parameters of peat soil of district of Asahan by direct shear test

Peat is a wetland ecosystem characterized by the accumulation of organic matter happens for a long time. This accumulation occurs because of the slow decomposition rate compared to the rate of accumulation of organic found in the wetland forest. The purposes of this study were to determine the index properties, to classify the peat soil classification, to obtain the optimum water content and maximum dry unit weight, γd by Standard Proctor test, and to examine the shear strength of peat soil by direct shear test. The peat soil had water content, w of 726.34 % and a specific gravity, Gs of 1.302. Based on ASTM D4427-92, the classification of peat soil was high ash peat and highly acidic. Based on the Standard Proctor test, the optimum water content obtained was 34% and the maximum dry unit weight was 0.518 gr/cm3. The Standard Proctor test increased the value of the dry unit weight of the undisturbed soil samples from 0.154 gr/cm3 to 0.556 gr/cm3. The original internal friction angle, ϕ and cohesion, c were 0.595º and 0.019 MPa while the Standard Proctor test resulted in 3.539º of internal friction angle, ϕ and 0.020 MPa of cohesion, c.