Soil Friction Angle Research Articles

Large Displacement Finite Element Modelling of the Screw Driving Sounding Test in Sandy Soil Using the Coupled Eulerian-Lagrangian Method

The Screw Driving Sounding (SDS) is a recently developed in-situ testing method for soil/site characterisation. To better understand the mechanism of testing, it is essential to create a simulation model for the SDS test to assist in better understanding the response and in improving the testing process, not to mention the development of empirical correlations to estimate geotechnical parameters for use in design. Complex problems involving large deformations are usually difficult to solve with the classical finite element (FE) method because large deformations can lead to large mesh distortions and contact problems. In this paper, a computational model using the finite element method is developed to simulate the drilling process involved in SDS tests; the Coupled Eulerian-Lagrangian (CEL) approach is used to deal with large deformation problems. The SDS drilling process in a sandy deposit with defined stress states (i.e., relative density and effective confining pressure) is simulated, and the SDS-derived parameters are monitored. Based on the simulation results, a chart was established to correlate the measured SDS parameter with the internal friction angle for different vertical effective overburden stresses. The derived chart is validated with the results of laboratory tests performed on samples taken from several sites in Christchurch, NZ, adjacent to the locations of the SDS tests. The results show that the CEL FE framework can model complex physical processes encountered during the SDS drilling. Moreover, the developed chart can be used to estimate the friction angle of the sandy soil based on the SDS-measured torque at a given depth.

Practical seismic fragility estimation of Japanese railway embankments using three seismic intensity measures

This study proposes a practical fragility estimation equation for Japanese standard models of railway embankments using the peak ground acceleration, peak ground velocity, and Arias intensity. The analytical models were implemented as unreinforced and geosynthetic-reinforced embankment models. A sensitivity analysis of the seismic fragility estimation of the embankment models was conducted on various embankment heights, average values of friction angles in the backfill soil, and tensile strengths of the primary reinforcement. Consequently, a unique formula for the fragility function in the presence of different seismic intensities was successfully presented. The parameters of the fragility function were successfully estimated using commonly used design parameters, such as the embankment height, average value of the friction angle of the backfill soil, and average value of the tensile strength. Additionally, another sensitivity analysis using different seismic databases was conducted to explore the effect of the seismic database on the fragility curve estimation of railway embankments. As a result, using different seismic databases, different fragility curves were obtained. These results highlight the importance of checking the sensitivity of the seismic database when developing the fragility curve.

Stability Evaluations of Unlined Horseshoe Tunnels Based on Extreme Learning Neural Network

This paper presents an Artificial Neural Network (ANN)-based approach for predicting tunnel stability that is both dependable and accurate. Numerical solutions to the instability of unlined horseshoe tunnels in cohesive-frictional soils are established, primarily by employing numerical upper bound (UB) and lower bound (LB) finite element limit analysis (FELA). The training dataset for an ANN model is made up of these numerical solutions. Four dimensionless parameters are required in the parametric analyses, namely the dimensionless overburden factor γD/c′, the cover-depth ratio C/D, the width-depth ratio B/D, and the soil friction angle ϕ. The influence of these dimensionless parameters on the stability factor is explored and illustrated in terms of a design chart. Moreover, the failure mechanisms of a shallow horseshoe tunnel in cohesive-frictional soil that is influenced by the four dimensionless parameters are also provided. Therefore, the current stability solution, based on FELA and ANN models, is presented in this paper, allowing for the efficient and accurate establishment and evaluation of an optimum surcharge loading of shallow horseshoe tunnels in practice.

Efficient surrogate model based probabilistic analysis of helical soil nailed wall under seismic conditions

This study demonstrates an efficient and precise surrogate model to probabilistically analyze the helical soil nailed walls (HSNWs) under seismic conditions. The modified pseudo-dynamic (MPD) approach is employed which produces realistic results in comparison to its former counterparts. The unit weight (γ), internal friction angle of soil (ϕ), and shear wave velocity (Vs ) are chosen as random variables. The influence of the normalized frequency, damping ratio, and size of the helix on the reliability of HSNW is presented in detail. The plots reveal that the proposed surrogate model is an accurate method with the value of coefficient of determination (R2 ) as 0.99 for the present study. In addition to it, it is 99 times more efficient when compared to the direct Monte-Carlo Simulation (MCS) (50000 iterations). For the same input parameters, the minimum number of helical nails required for a safe reinforced wall are less than the grouted and the driven ones, given their larger pull-out capacity. Moreover, the required number of helical soil nails (HSNs) computed from probabilistic analysis are 42.85% more than the deterministic one for a given set of input parameters which lay a strong base for performing the probabilistic analysis for a precise measure of stability.

Study on the Calculation Method of Active Earth Pressure and Critical Width for Finite Soil Behind the Retaining Wall

The method to determine the active earth pressure and critical width for finite soil behind the retaining wall in mountainous areas is one of the concerns of geotechnical engineering. In order to study the active earth pressure distribution of the finite soil against the retaining wall and determine the critical width of the boundary between the finite soil and the semi-infinite soil, this study focuses on investigating a retaining wall with finite cohesionless backfill. The shape of the failure surface is assumed to be a cycloid passing through the heel of the wall in the limit equilibrium state. Considering the deflection of soil principal stress induced by wall–soil friction effect, a calculation method of active earth pressure for finite soil is proposed by using an arc-shaped small principal stress trajectory, and the rationality of this method is verified. On this basis, a calculation formula of the critical width for finite soil is proposed. The influence of the internal friction angle and the wall–soil friction angle on the critical width of finite soil is examined. The results indicate that the active earth pressure of finite soil presents a nonlinear drum distribution along the height of the retaining wall under the failure mode of the cycloidal surface. The maximum value of active earth pressure is close to the bottom of the wall. The critical width of finite soil decreases with the increase of the internal friction angle, and its variation rate decreases gradually. The critical width of finite soil increases with the increase of the wall–soil friction angle, and its variation rate also increases gradually. Under different internal friction angles and wall–soil friction angles, the critical width values of finite soil calculated by the assumption of the cycloidal failure surface are smaller than those calculated by the Coulomb earth pressure calculation method.

Experimental Analysis of the Fire-Induced Effects on the Physical, Mechanical, and Hydraulic Properties of Sloping Pyroclastic Soils

The paper investigates the changes in the physical, mechanical, and hydraulic properties of coarse-grained pyroclastic soils, considered under both wildfire-burned and laboratory heating conditions. The soil samples were collected on Mount “Le Porche” in the municipality of Siano (Campania Region, Southern Italy), hit by wildfires on 20 September 2019. The area is prone to fast-moving landslides, as testified by the disastrous events of 5–6 May 1998. The experimental results show that the analyzed surficial samples exhibited (i) grain size distribution variations due to the disaggregation of gravelly and sandy particles (mostly of pumice nature), (ii) chromatic changes ranging from black to reddish, (iii) changes in specific gravity in low-severity fire-burned soil samples different from those exposed to laboratory heating treatments; (iv) progressive reductions of shear strength, associated with a decrease in the cohesive contribution offered by the soil-root systems and, for more severe burns, even in the soil friction angle, and (v) changes in soil-water retention capacity. Although the analyses deserve further deepening, the appropriate knowledge on these issues could provide key inputs for geotechnical analyses dealing with landslide susceptibility on fire-affected slopes in unsaturated conditions.

Effect of Oil Contamination on the Behavior of Collapsible Soil

Loessial soil is moisture-sensitive soil susceptible to settle when fully saturated. In this study, efforts were made to investigate the effect of oil pollutants on mechanical behavior of soil. The loess soil was contaminated by 2,4,6,8 and 10% dry weight of lamp oil and gasoline. Atterberg limits, direct shear, unconfined compressive strength (UCS) and scanning electron microscope (SEM) tests were performed to evaluate the behavior of oil-contaminated collapsible soils. The results of Atterberg tests showed that the plasticity of the soil decreased, due to the reduction in the thickness of the absorbed surface layer and double water layer. According to the direct shear test, with increasing contamination up to 10% of lamp oil and gasoline, the cohesion of the soil was decreased from 14.5 kPa to 7.3 kPa and 7 kPa, respectively, which was due to the reduction in soil plasticity and diffuse double-layer. Because of the lubrication of soil particles, the internal friction angle of soil was reduced from 18.5° to 13.6° and 13.9° for 10% lamp oil and gasoline. UCS of contaminated soil increased in low strains due to the apparent cohesion of hydrocarbons and it decreased 31% for gasoline and 53% for lamp oil at high strains due to the softening behavior of the contaminated soil. SEM test revealed that hydrocarbons covered the soil particles and changed the soil fabrication to dispersed skeleton. Generally, collapsible soil contaminated with different lamp oil and gasoline contents showed a decrease in shear strength and UCS with increasing oil content.

The Effects of Salt-Lake Salt Solution on the Strength of Expansive Soil

Expansive soils are widely distributed and often cause serious damage to structures. Hanzhong expansive soil and Yulin salt-lake solution were adopted to investigate the effect of salt-lake salt solution on the strength of expansive soil. Expansive soils modified with salt-lake salt solutions with different concentrations (0.1, 0.5, and 1.0 mol/L) were evaluated by X-ray diffraction (XRD), Atterberg limit, free swelling, no load swelling ratio, and triaxial compression tests. The improved expansive soil research using salt-lake salt solution was carried out based on the macroscopic mechanical characteristics. Test results showed that the addition of salt-lake solution effectively inhibited the expansibility of soil. With the increase of the concentration of salt-lake solution, liquid limit, plastic limit, plastic index, free expansion rate, no load swelling, cohesion, and internal friction angle of expansive soil were decreased in varying degrees, and stress-strain relationship curve gradually showed strain softening trend. The reason for the above results was believed to be that salt-lake salt solution reduced the force between particles on shear surface and reduced mutual hindrance.

Neural Network-Based Prediction Model for the Stability of Unlined Elliptical Tunnels in Cohesive-Frictional Soils

The scheme for accurate and reliable predictions of tunnel stability based on an artificial aeural network (ANN) is presented in this study. Plastic solutions of the stability of unlined elliptical tunnels in sands are first derived by using numerical upper-bound (UB) and lower-bound (LB) finite element limit analysis (FELA). These numerical solutions are later used as the training dataset for an ANN model. Note that there are four input dimensionless parameters, including the dimensionless overburden factor γD/c′, the cover–depth ratio C/D, the width–depth ratio B/D, and the soil friction angle ϕ. The impacts of these input dimensionless parameters on the stability factor σs/c′ of the stability of shallow elliptical tunnels in sands are comprehensively examined. Some failure mechanisms are carried out to demonstrate the effects of all input parameters. The solutions will reliably and accurately provide a safety assessment of shallow elliptical tunnels.

An Overview: Relationship of Geological Condition and Rainfall with Landslide Events at East Malaysia

Tropical country like Malaysia is rich with residual soil and nurtured with high rainfall amount on average 2,550 mm per year. From 2009 until 2018, there are many landslide events reported in the news at Ranau, Sabah and Canada Hill Miri, Sarawak that occurred during rainy season and the landslide recurs within same location over the years. The objective of this study is to determine the relationship of landslide events with geological condition and rainfall at Ranau, Sabah and Canada Hill Miri, Sarawak. Historical landslide data were obtained from local news, previous researchers, and local authorities. Integrated review was conducted to meet the objective. In summary, both areas are prone to landslide due to the high average amount rainfall recorded and the geological properties that are susceptible to landslide occurrence namely shale interbedded with sandstone. Sandstone and shale contact are easily accessible by water weaken the contact surface lead to landslides incidents. Besides, Shale classified as highly plastic soil due to high amount of clay. Clay soil depends on its matric suction to sustain its strength towards sliding. Thus, increasing of pore pressure from rain infiltration reduce the matric suction and eventually reduce the shear strength. Ranau is located at seismically active area compare to Miri and other locations in Sabah crossing Lobou-Lobou fault, Mensaban fault and Mesilou fault. Theoretically, slope instability due to earthquake happened because the cementation of soil may be broken and lead to lesser roughness between soil surfaces resulting in reduction of internal friction angle and cohesion of soil.
 HIGHLIGHTS
 
 Rainfall-induced landslides are the common landslides phenomenon worldwide including East Malaysia.
 However, due to the high number of seismic activity, Earthquake-induced landslides should not be neglected as one of slope failure phenomena in East Malaysia
 Combinations of both Rainfall and Earthquake are required to be investigated due to the presence of both landslide triggering factors from historical data at East Malaysia
 
 GRAPHICAL ABSTRACT

Estimation of the unsaturated shear strength of expansive soils in relation to capillary water-retention curve

The hydromechanical behavior of expansive soils is one of the challenging topics in geotechnical engineering. Direct measurements of unsaturated shear strength in the laboratory are complicated and time-consuming. This work introduces a novel model to estimate the contribution of suction to the shear strength of expansive soils. Non-linear relationships in the space of suction and shear strength can be clearly observed, which indicates that the friction angle (ϕb) changes with the evolution of suction. Capillary saturation has been used to upscale suction from pore-scale stress to macroscopic stress using the capillary part of soil-water retention curve. Experimental results indicate that the relationships between capillary suction stress and shear strength show linear properties. However, the friction angle (ϕs) contributed by capillary suction stress to shear strength is not equal to the internal friction angle (ϕ) of saturated soils. The proposed model uses the shear strength value measured at any specific unsaturated state to obtain the evolution of friction angle (ϕs). Results show that the effect of different reference points on computed strength can be ignored. The proposed model is successfully validated with historical data of various kinds of expansive soils from literature.

Design of reinforced cohesive soil walls accounting for wall facing contribution to stability

Where granular materials are not easily available, local cohesive soils are increasingly employed in geosynthetic reinforced soil walls as a cheap and sustainable option. Conventional design methods do not yet account for the beneficial effect of cohesion in reducing the amount of required reinforcement. Similarly, the contribution of the face to stability is rarely accounted for, despite plenty of experimental evidence in its favour. In this paper, a semi-analytical method based on limit analysis is developed for the design of reinforced soil walls in frictional–cohesive backfills accounting for the wall contribution. A parametric analysis was conducted to evaluate the effect of soil cohesion and friction angle, facing batter, block width, location of the reaction force acting on the face, facing–backfill interface friction, facing–foundation interface friction and reinforcement length. Dimensionless design charts providing the required amount of reinforcement for lengths recommended in design standards are provided for both uniform and linearly increasing reinforcement distributions. It emerges that accounting for the presence of cohesion and the facing element can lead to significant savings in the overall level of reinforcement, and that tension cracks can be particularly detrimental to wall stability for highly cohesive soils so they cannot be overlooked in the design.

Centrifugal Test and Instability Model Analysis of Excavation Surface Stability of a Shield Tunnel in a Clay Layer

In order to study the variation law of support pressure and instability mode of excavation face under different soil parameters, a complete set of centrifugal model seepage test device is independently developed. The results of centrifugal tests with different C/D (where C is the overburden thickness of the tunnel and D is the tunnel diameter), internal friction angles, and heights of water head show that with the increase of the retreating displacement S of the excavation surface, the support pressure P of the excavation surface can be divided into three stages: rapid decline (S < 1.5D%), slow rebound after reaching the limit support pressure Plim (1.5D% ≤ S ≤ 3D%), and gradually reaching the stable value (3D% < S). With the increase of C/D, the limit support pressure on the excavation face gradually increases and tends to be stable. For different soil properties, when C/D > 1.5, the limit support pressure on the excavation face tends to be stable. With the increase of internal friction angle, the limit support pressure decreases gradually, and its influence on support pressure can be ignored when φ > 40°. With the increase of height of water head Hw, the limit support pressure increases linearly. By establishing a numerical analysis model and analyzing the instability modes of soil under different C/D, internal friction angles, and cohesion, the instability mode of soil in front of the excavation face can have a great correlation with C/D of the soil and internal friction angle, while the influence of cohesion is minimal. With the increase of C/D, the soil changes from overall failure to local failure, the change of C/D mainly affects the height of soil arching effect and the width of the wedge below, while the internal friction angle mainly affects the width of the wedge and the instability angle of soil.

Study of the Mechanical and Microscopic Properties of Modified Silty Clay under Freeze-Thaw Cycles

Silty clay can be found in the alpine region of the Qinghai province, China, where it is subject to annual freeze-thaw cycles. To investigate the static mechanical properties of silty clay modified by basalt fiber and basalt powder under the action of freeze-thaw cycles, triaxial compression tests and scanning electron microscope tests were conducted on the soil. The test results revealed that varying the number of freeze-thaw cycles resulted to different effects on the soil mechanical strength, which tended to increase after 2 cycles, but then tended to decline when subjected to 5–10 cycles. After 20 freeze-thaw cycles, soil strength reached a dynamic equilibrium state. The shear strength of basalt fiber soil and basalt powder soil increased by 7.55% and 5.12%, respectively, compared with that of normal soil under 30 freeze-thaw cycles. Subsequently increasing of the number of freeze-thaw cycles differentially affected the cohesion and internal friction angle of normal soil and admixture soils, and these soils gradually tended to stabilize at a mechanical strength higher than the initial value. Basalt fibers reinforced the soil to a higher degree than basalt powder at a dosage of 0.4% based on dry soil mass. The stress-strain curves of the three soil types can be simulated using the hyperbolic model. The results of the study can provide some theoretical reference for practical engineering in seasonal frozen soil areas.

Seismic Stability of Dual Tunnels in Cohesive–Frictional Soil Subjected to Surcharge Loading

In this study, a self-developed adaptive finite element limit analysis (AFELA) code was adopted to explore the stability of dual tunnels in cohesive–frictional soil subjected to surcharge loading and seismic action. Parametric studies of different influential factors, including the depth of tunnels, horizontal distance between tunnels, seismic acceleration coefficient, unit weight, cohesion and internal friction angle of soils, were conducted using the AFELA code. An adaptive meshing technique was adopted for optimal accuracy and efficiency, and a pseudostatic method was used to simulate the seismic action. Strict upper bound (UB) and lower bound (LB) results with relative errors of less than 7% were acquired. Detailed design tables were presented to facilitate the engineering design, and three typical failure patterns, including single side-wall failure, half-cross-shaped failure and cross-shaped failure, corresponding to different stable levels, were summarized for a deeper insight into how the failure mechanism evolved under different conditions. The results indicated that the variations in soil unit weight and void depth affected the seismic bearing capacity almost linearly. Furthermore, the dual tunnel system is vulnerable to seismic actions, and the stability of tunnels was further undermined by the adverse effects of additional seismic-caused interactions between two adjacent tunnels.

Probabilistic assessment of geosynthetic reinforced soil walls using ANN-based response surface method

ABSTRACT An artificial neural network-based response surface method is proposed to demonstrate the probabilistic performance of the geosynthetic reinforced soil (GRS) walls backfilled with cohesionless soil. Response surfaces are formed either in terms of performance functions or design outputs of the GRS walls using the uniform design method to achieve better accuracy of the response surface in predicting the reliability of walls. The probabilistic assessment of two GRS walls is performed using the proposed approach. In the first problem, the feasibility and efficacy of the present method on the probabilistic performance evaluation are examined. Also, the effect of variability of different input variables on the reliability index of the wall is analysed. Results show that the soil friction angle is the most sensitive parameter affecting the overall stability of the wall. A well constructed GRS test wall is further assessed using the present approach under the finite difference numerical scheme. The proposed method is proved to be an efficient technique in evaluating the reliability of more complex reinforced soil walls despite having any explicit closed-form solution of the limit state functions. Further, Sobol sensitivity indices of the input variables on the outputs are evaluated for both problems.

Study on the influence of composite soil on the slope stability of farmland during in land consolidation

To improve the stability of sloping farmland, the optimum ratio for parameter of composite soils was determined. Plain and mixed composite soils were prepared with three improved materials of glutinous rice glue, wood fibres and coarse sand for laboratory to tests and experiments. For different moisture and soil contents, the shear strength, cohesion and internal friction angle of the composite soils were analysed and the proportions were adjusted based on the suitability of plant growth. Slope stability analysis was performed in combination with the case of slope farmland improvement. The results show that the soil improvement materials were affected by the different moisture content, the degree of influence of moisture content on soil shear strength and parameters: wood fibre composite soil > glutinous rice glue composite soil > coarse sand composite soil > plain soil. The soil amendments affected the soil mechanical properties and effectively improved soil stability, the degree of influence of soil amendments on the soil shear strength and parameters: wood fibre composite soil > glutinous rice glue composite soil > coarse sand composite soil. According to the shear strength and total biomass, the optimum contents of glutinous rice glue, wood fibre and coarse sand in the mixed composite soil were 1.5%, 2.5% and 15%. The case application shows that the minimum safety factor of the mixed composite soil was higher than the plain composite soil at slopes of 10°, 15° and 20°. The overall slope stability of the mixed composite soil was improved with different moisture contents, which is suitable for plant growth.

Stability and Deformation Responses of Earth Slopes Subjected to Multiple Natural and Manmade Hazards

Multiple hazards such as rainfall, earthquake, and excavation may occur simultaneously, and the stability (factor of safety) and deformation (movement) behaviors must be investigated to prevent loss of life and properties. In this study, the stability and deformation behaviors of earth slopes subjected to the individual and simultaneous occurrence of these events are investigated using a coupled Geotechnical–Hydrological finite-element method (FEM). First, the finite-element model was validated against a case history and a widely used limit-equilibrium method (LEM) considering site-specific soil properties and rainfall records. The shape and the size of the critical failure surface obtained from the field investigation coincided well with those calculated using FEM and LEM. Also, the predicted onset of slope failure (after eight days of rainfall) coincided well with the real-time occurrence of the slope failure. The validated finite-element model was then used to predict the stability and deformation responses of earth slopes subjected to several possible scenarios, including individual and simultaneous occurrences of these events. The rainfall–excavation scenario indicated that the slope would have failed two days before the recorded time if the slope had a vertical cut width of 4.25 m. The rainfall–earthquake hazard scenario caused the slope to move horizontally by 799 mm. The parametric study conducted by varying the friction angle of the slope soil by ± one standard deviation (STD) with 10% covariance showed that the slope would have failed one day later and two days prior to the mean friction angle, respectively, when subjected to rainfall. Also, varying the friction angle by +1 STD and −1 STD failed the slope for 0.5 m above and 0.4 m below the cut width for the slope with mean friction angle when subjected to excavation, respectively. Further, the percent increase in the horizontal movement of the slope soil with friction angle by +1 STD and −1 STD compared to mean friction angle was 56% and 18%, respectively, when subjected to earthquake.

New Empirical Approach for the Estimation of Soil Cohesion and Friction Angle in 2D Form for Site Investigations

This paper presents the multiple linear regression (MLR) models developed from electrical resistivity and seismic refraction surveys for quick prediction of subsurface soil’s shear strength parameters. A total of four parameters have been considered with electrical resistivity and seismic refraction velocity as the independent variables: and soil cohesion and internal friction angle as the dependent variables. In order to mitigate the effects of nonlinearity of resistivity and velocity, both datasets were initially log-transformed to conform with the fundamental assumptions of regression analysis. Two models were therefore built based on the strong multiple linear relationships between explanatory and response variables, with coefficient of determination (R2), 0.777, p-values, < 0.050, Durbin-Watson value, 1.787 and multicollinearity, 1.185. The obtained models’ coefficients were transferred and used for the estimation of 2D models soil cohesion and internal angle of friction for validation. Thereafter, the developed models demonstrated good performance, having subjected to accuracy assessment with results at < 5%, and < 10% for the root mean square error (RMSE) and weighted mean absolute percentage error (MAPE) respectively. Therefore, the new developed soil’s shear strength MLR models have provided continual description of soil properties in two-dimensional form, enhancing the subsurface information for site investigations as compared, to one-dimensional information from the invasive method.

Stochastic analysis of railway embankment with uncertain soil parameters using polynomial chaos expansion

This paper focuses on the stochastic response of railway embankments considering the uncertainties in soil cohesion and friction angle. The non-sampling stochastic method concerning generalised polynomial chaos (gPC) expansion was employed for the dynamic numerical simulation. The uncertain parameters, including soil cohesion and friction angle, were defined by the truncated gPC expansions. Furthermore, the system’s response, namely, the displacement and acceleration of different embankment sections, was presented by the gPC expansion with unknown deterministic coefficients. The stochastic Galerkin projection was used to calculate a set of deterministic equations. The unknown gPC coefficients of the system’s response were determined by a non-intrusive solution as a set of collocation points. In addition, the results of these analyses were compared with classical Monte Carlo simulations. It is essential to note that although only a few collocation points have been used, the results are in good agreement with the MC sampling method. One of the main objectives of this study is to demonstrate the accuracy of the results and the time efficiency of the proposed non-sampling method in quantifying the uncertainty of stochastic systems compared to the sampling procedure (e.g. Monte Carlo simulation).