Soil Strength Parameters Research Articles

Risk assessment of a layered slope considering spatial variabilities of interlayer and intralayer

While many studies have analyzed the effects of spatial variabilities of intralayer soil parameters on the probability of failure and risk of layered slopes, there is a paucity of research on the effects of interlayer variability. This paper is intended to investigate the influence of interlayer variability on the mechanical responses of a layered slope, as well as the effects of spatial variabilities of strength parameters of intralayer soils. To characterize the uncertainty of intralayer and interlayer spatial variabilities of layered geologic profiles, an integrated random field is developed using the program of FLAC based on both the two-dimensional random field theory and one-dimensional random process theory. Particularly, the random field for the interlayer transition zone is generated by a linear interpolation technique. Within the framework of Monte-Carlo simulation, a large number of stochastic calculations for a two-layered slope are conducted to evaluate the influences of spatial variabilities of both interlayer and intralayer on the stability and risk of the slope. The results show the failure mode of a two-layered slope changes greatly due to the stochastic layered boundary. It is also noted that the probability and risk of slope failure might be underestimated if ignoring the uncertainty arising from layered boundary and layered transition zone. The proposed equations can provide helpful information when investigating the probability and risk associated with layered slopes.

Influence of Different Industrial Waste Residues on Engineering Properties of High Liquid Limit Soil and Its Microscopic Mechanism

High liquid limit soil has unfavorable engineering geological characteristics, such as strong disintegration, dry shrinkage and easy cracking, and easy uplift when encountering water, which will cause various problems to the engineering. At present, the relationship between the physical and mechanical properties of high liquid limit soil and the characteristics of water-soil interaction is still not clear enough. In this study, the high liquid limit soil of Zhanjiang Avenue was selected to explore the influence of different ratios of three kinds of industrial waste residues (blast furnace slag, carbide slag, and tailing sand) on the high liquid limit soil. Aiming at the common adverse engineering geological phenomena of high liquid limit soil, such as easy disintegration, dry shrinkage crack, and easy uplift in water, the effects of different industrial waste residues on the water-soil interaction characteristics of high liquid limit soil are explored through disintegration and crack tests. In addition, the effects of different kinds and ratios on the free expansion rate, pH, unconfined compressive strength, and shear strength parameters of high liquid limit soil were studied. The improvement mechanism of different industrial waste residues on the engineering properties of high liquid limit soil is discussed in terms of mineral composition and microstructure. Based on the experimental results of this study and considering the cost and engineering practice, it is suggested that the modified carbide slag optimal ratio of high liquid limit soil of Zhanjiang Avenue is 8%. The results can provide certain guidance for the improvement and application of different industrial waste residues on high liquid limit soil to achieve the effect of sustainable development.

Stability evaluation of circular tunnels in cohesive frictional soil under earthquake loading using the modified pseudo-dynamic approach

The peripheral stability of tunnels is maintained by installing support systems in the form of linings. The required resistance of the linings depends on the stresses exerted by the surrounding medium. This study evaluated the support pressure of the lining for circular tunnels in cohesive-frictional soil under earthquake loading by applying the modified pseudo-dynamic approach in the finite element lower bound limit analysis framework. The normal stresses exerted by the surrounding soil vary along the tunnel's periphery, and the tunnel's stability is ensured when the minimum support pressure offered by the tunnel lining is equal to or greater than the maximum normal stress exerted by the soil at the ultimate failure condition. The horizontal and vertical earthquake accelerations, amplitude, and phase of the accelerations were varied with depth by satisfying the stress boundary conditions. The shear strength parameters of soil (cohesion and friction angle), tunnel cover and its diameter, and the parameters owing to an event of an earthquake (acceleration, frequency of primary and shear waves, and the time of shaking) influence the magnitude and location of maximum normal stress along the tunnel's periphery.

Evaluation of the Unsaturated Shear Strength Parameters of Compacted, Heaving Soil Using Geotechnical Properties

Abstract The shear strength is a fundamental property of soil material under structural loads. The determination of shear strength properties of unsaturated soils is challenging and time-consuming. Geotechnical predictive models can be utilized to assess the unsaturated shear strength of heaving soil. This study attempts to propose predictive models to evaluate the unsaturated shear strength parameters of compacted heaving soil. These parameters include the angle of internal friction associated with the net normal stress (ϕ'), angle indicating the rate of increase in shear strength with respect to a change in matric suction (ϕb), and effective cohesion (c'). The geotechnical properties of soils were assessed through laboratory tests such as particle size distribution, consistency limits, specific gravity, modified Proctor compaction test, swelling test, suction test, and advanced triaxial testing. Multivariate analysis was conducted using NCSS 12 software to design the models. The validation of models includes the determination coefficient, probability value, comparing experimental values with predicted values, and comparing the developed models with other model found in recent literature. The models engineered in this study can estimate the unsaturated shear strength parameters of compacted heaving soil with acceptable precision.

Impact on the Geotechnical Properties of Soil mixed with Terrazyme

The financial sustainability and serviceability of any project after standard performance are the most crucial requirements in emerging nations like India. Hence there is a need to find the best possible ways to satisfy the performance as well as economic criteria. The stabilization of soil with bio-enzyme is a revolutionary technique which becoming popular worldwide. Recently there are many bio-enzymes available for soil stabilization such as Fujibeton, renolith, Perma-Zyme, Terrazyme, etc. These enzymes have been proven to be very effective and economical as well as environment friendly in nature. The efficiency of bio-enzyme depends upon the amount of dosage, types of soil and curing period. One such type of bio-enzyme, Terrazyme has been used in the present work. This study shows the effect of Terrazyme on stabilization of soil. Including the improvement in unconfined compressive strength, shear strength and the Atterberg’s limits. The enzyme treated soil shows significant improvement in strength parameters of soil and little improvement in liquid and plastic limit of the soil.

Enhancing the Strength Parameters of Dispersive Soil with Microbes and Jute Fibres as Sustainable Alternative

Enhancing the Strength Parameters of Dispersive Soil with Microbes and Jute Fibres as Sustainable Alternative

Effects of Dry–Wet Cycling and Temperature on Shear Strength and Microscopic Parameters of Coal Measure Soil

Exposed coal measure soil (CMS) found in the mountains of Southern China is significantly affected by the seasonal climate, which makes this region prone to frequent shallow landslides. In this regard, very few studies have focused on the shear strength and microscopic characteristics of CMS subjected to dry–wet cycling and temperature. The aim of this study was to experimentally investigate the effects of dry–wet cycling and temperature on shear strength and microscopic parameters of CMS. We carried out an unconsolidated undrained triaxial test and scanning electron microscopy of CMS obtained from the K209 slope on the Chang-li highway. Our results indicated that the soil shear strength and microstructure parameters significantly decreased before three dry–wet cycles. Above 35 °C, the temperature affected mainly the mean fractal dimension. The soil cohesion was negatively correlated with the fractal dimension and positively correlated with the probability entropy. The surface-crack occurred once the stress value of high temperature was greater than 0.57 MPa. Strain-softening, swelling–shrinkage, low soil strength, and high soil temperature formed the main factors underlying rainfall-induced K209 shallow landslides.

Insight on bulk shear strength parameters of clay using discrete element approach incorporating physics-based interparticle force model

This paper aims to provide insight on factors affecting the bulk shear strength parameters of clay, i.e., the cohesion and internal friction as well as the effects of memory of preconsolidation pressure. A unique Discrete Element Method (DEM) model is built on platy particles with customized particle interaction force model. The particle interaction force model considers non-contact forces (such as the long-range electrostatic repulsion, short-range van der Waals attraction) as well as the direct contact force. The long-range electrostatic forces are calibrated by measurement with Atomic Force Microscope (AFM). Parameters for direct particle contacts of the regular DEM contact model, such as the contact stiffness and the friction coefficient, are calibrated by use of experimental consolidation and direct shear testing data. Computational simulations are conducted on digital clay specimen subjected to virtual direct shear tests. The predicted experimental responses of the digital specimens are consistent with typically observed in experiments including the shear stress-shear strain relationship, volumetric contraction and dilation, shear band formation, etc. From the stress–strain curves, the soil strength parameters are obtained with common experimental criteria. The DEM simulation results show that higher preconsolidation pressure drives more particles to overcome non-contact force into direct contacts and consequently bonding by van der Waals force. Consequently, the bulk cohesion of clay increases with increasing preconsolidation pressure. The results show that bulk cohesion strength is mainly attributed to the attractive interparticle force as well as the interlocking of platy particle, while the bulk internal friction angle is affected by the particle friction coefficient and particle fabric. Overall, the simulation results indicate the experimentally observed macroscopic shear strength parameters c and φ are linked to the microscope characteristics of soil particles and their mutual interactions. The results offer insight on the microscopic properties of particles on the bulk macroscopic strength behaviors. Besides, this work demonstrates a new strategy for simulation-based prediction of bulk soil strength parameters, by incorporating microscale characterization of the interparticle interactions and particle fabric into the particle-based DEM model.

A correlation based on pressuremeter, SPT and CPT tests for characterizing of coastal alluvium: A study for phase 14 South Pars, Iran

Pressuremeter Test (PMT), Cone Penetration Test (CPT), and Standard Penetration Test (SPT) are the key in-situ experiments to directly estimate the in-situ modulus of deformation and strength parameters of soils, which are highly used in coastal alluvium. In addition, CPT and SPT are unique tests for estimating engineering properties that are ideal for onshore regions. These tests are adaptable for coastal alluvium with different saturation levels, which facilitates the determination of the field deformation modulus. Regression analysis, on the other hand, is primarily employed to estimate the empirical relationship between measured parameters and to predict geo-engineering properties. This technique is typically used to estimate the in-situ modulus of deformation and strength parameters from CPT, SPT, and PMT results. The proposed formulas in this paper used regression to correlate and characterize coastal alluvium located in phase 14 South Pars (Assalouyeh) and were compared with previously published equations. As a result of the evaluations, the correlations provided for phase 14 South Pars can be expressed as Em = 0.442 qc + 2.221 (R2 = 0.999) and PL = 0.06 Em0.778 (R2 = 0.515).•This empirical method can be useful for ground assessment and estimating the in-situ modulus of deformation.•This relationship can use as a modification for the original formula used based on CPT-PMT-SPT for alluvium.•This empirical correlation provides fast and reliable data for Southwest Iran nearby the Persian Gulf.

Polynomial chaos surrogate and bayesian learning for coupled hydro-mechanical behavior of soil slope

As rainfall infiltrates into soil slopes, the hydraulic and mechanical behaviors of soils are interacted. In this study, an efficient probabilistic parameter estimation method for coupled hydro-mechanical behavior in soil slope is proposed. This method integrates the Polynomial Chaos Expansion (PCE) method, the coupled hydro-mechanical modeling, and the Bayesian learning method. A coupled hydro-mechanical numerical model is established for the simulation of behaviors of unsaturated soil slope under rainfall infiltration, following by training a cheap-to-run PCE surrogate to replace it. Probabilistic estimation of soil parameters is conducted based on the Bayesian learning technique with the Markov Chain Monte Carlo (MCMC) simulation. A numerical example of an unsaturated slope under rainfall infiltration is presented to illustrate the proposed method. The effects of measurement durations and response types on parameter estimation are addressed. The result shows that with the increase of measurement duration, the uncertainties of soil parameters are significantly reduced. The uncertainties of hydraulic properties are reduced significantly using the pore water pressure data, while the uncertainties of soil strength parameters are reduced greatly using the measured displacement data.

Impact of Strength-Enhancing Admixtures on Stabilization of Expansive Soil by Addition of Alternative Binders

Abstract In this study, the stabilization process is introduced to a clayey expansive soil collected in southern Sweden. The tests examined strength parameters of expansive soil stabilized by different binders using combination of both traditional binders (cement and lime) and alternative materials (slag Merit 5000, fly ash from SCA Lilla Edet and fly ash from coal combustion, ISO certified). The practical goal was to find a binder mixture that is optimized for soil stabilization with respect to technical properties of stabilizing agent as an inert ballast material. The strength of soil stabilized by various binders was examined by velocity of the P-waves propagating through specimens. The results show that introducing slag Merit 5000 as an admixture to cement and lime is an effective approach in enhancing strength properties in weak soil, which increases bearing capacity of soil for planned construction works. The results also shown that a mixture of lime and bio ash yields a better effect in the stabilization of a clay. Soil stabilized with cement, cement/slag and lime/slag becomes resistant to freeze-thaw cycles, which is crucial for construction of roads and building foundations.

Resistance factors for design of slopes in a homogenous soil layer

Traditionally, the factor of safety (FOS) is widely used to account for uncertainties in the design of slopes within the framework of working stress design. As the uncertainties involved in the design of slopes vary, the same FOS may correspond to the different levels of reliability. In this study, the advanced first order reliability method is used to determine the resistance factors for design of slopes in a homogenous soil layer. It is found that the resistance factors depend on the target reliability index, the height of the slope, and the variability of the soil strength parameters. It is difficult to suggest a unique set of resistance factors for design of slopes. Analytic solutions are developed to determine the resistance factors for design of slopes assuming the random variables are normally distributed. An approximate method based on the concept of equivalent target reliability index is also suggested to determine the resistance factors for design of the slope when the soil strength parameters are lognormally distributed. The method suggested in this paper provides a practical way to perform load and resistance factors design of slopes.

Probabilistic stability analysis of qanat tunnels in c-φ soil considering soil spatial variability

Some newly built high-speed railways inevitably pass through the qanat region, which may potentially cause the failure of the qanat tunnels upon embankment and traffic loadings. Thus, it is of great importance to evaluate the stability of the qanat tunnels under surcharge for the design of railways. In the context of the Tehran–Isfahan railway construction in Iran, the soil properties obtained from a series of site investigation and laboratory tests show an important spatial variability. To better consider the spatial variability of soil strength parameters, a series of random adaptive finite element limit analysis (RAFELA) is performed in this study to investigate the stability of the qanat tunnels in the cohesive-frictional soils. The emphasis is placed on the effects of the coefficient of variation and vertical spatial correlation length of the strength parameters (i.e. soil cohesion c and effective fiction angle φ) and the qanat tunnel depth (H/D). Results show that considering the variabilities of both c and φ is more unfavourable to the qanat stability compared to the cases with only one strength parameter (c or φ) variability being considered. Detailed stability evaluation charts are obtained to assess the probability of failure of the qanat tunnels under different conditions.

Mathematical Model for Estimation of Shear Parameters of Alluvial Soils of Kamrup Metro District (Assam, India) from Index Properties

ABSTRACT Projects related to Geotechnical Engineering require thorough ground study to know the soil behaviour thus making it necessary to determine the strength and stability parameters of soil. The soils of Assam are primarily of four types viz., Alluvial (old and new), Piedmont, Hill and Lateritic soils with the alluvium abundantly available in the state. The most important soil parameters are the shear strength parameters, namely, cohesion (c) and angle of internal friction (Φ) which can be obtained using triaxial tests with different drainage conditions. But one triaxial test may take weeks to complete and are very expensive. Moreover, for large projects it is practically preposterous to conduct large number of triaxial tests. Hence, an alternate way is to develop a relation between different parameters which enable us to determine others. The main objective of this study is establishing prediction models that allow the shear parameters to be predicted from soil index properties. For this, three prediction models are developed by combining various soil parameters viz., Liquid Limit (LL), Plastic Limit (PL), Specific Gravity (G) and Optimum Moisture Content (OMC) using Multivariate Regression Analysis (MRA) and Artificial Neural Network (ANN). The results show better performance for ANN than MRA.

Experimental Study on the Effects of Matric Suction on Shear Properties of Polypropylene Fiber Reinforced Unsaturated Clay.

Matric suction has an important effect on the behavior of unsaturated soils, and polypropylene fibers are often used to improve soil. In order to probe into the mechanism of matric suction and fiber reinforcement, triaxial shear tests are carried out with changing matric suction and net confining pressure. Unsaturated clay in the Shaoxing section of East Zhejiang Grand Canal is selected with polypropylene fiber as a reinforcement material in the tests. The results show that the total cohesion intercept and effective internal friction angle of soil increase with the increase in matric suction, while the adsorption internal friction angle decreases gradually. Similarly, the contribution of matric suction to shear strength decreases. The total cohesion intercept is more sensitive to matric suction. As the length of fiber is 12 mm, the shear strength parameters of soil will be improved accordingly, which makes the fiber reinforcement achieve the best. The stress-strain relationship is approximately hyperbolic and strain hardening. The characteristics of strain hardening are more obvious with the increase in matric suction, and the soil specimens present plastic failure. The volumetric strain of specimen is more sensitive to the changing net confining pressure. It increases with the increase in net confining pressure, and increases linearly as the matric suction is zero. The failure modes of triaxial tests are divided into tensile failure and friction failure.

Insights into seismic slope deformation patterns using finite element analysis

Two-dimensional (2D), nonlinear total stress finite-element analyses were performed to investigate the seismic deformation patterns for soil slopes. The numerical parametric analyses consisted of 16 models with soil stiffness and strength parameters selected to isolate the impact of yield acceleration, depth of the sliding mass, natural period of the slope, and the slope angle on the deformation patterns. The results indicate that deeper sliding masses experience notable strain localization at the sliding mass depth, while shallow sliding masses experience more distributed straining throughout the entire soil mass. These factors result in larger displacements for the deep sliding masses relative to shallow sliding masses at small ky, whereas shallow sliding masses experience larger movements at large ky. The numerical simulations also show that an increase in shear wave velocity or decrease in slope height result in smaller displacements, although the effect of shear wave velocity is more significant. Importantly, the slope angle notably affects the resulting displacements and when ky is the same. A steeper slope increases displacements for deep sliding masses but reduces the movements for shallow sliding masses. The deformation patterns in the finite element simulations are inconsistent with the sliding block assumptions commonly employed in seismic slope stability analysis and point to the need to develop empirical slope displacement models from finite element simulations. However, this study shows that to capture fully the factors that affect seismic slope displacement the numerical models analyzed must consider a comprehensive set of slope models that vary the depth of the sliding mass, the shear wave velocity, the slope height, and the slope angle in addition to the yield acceleration.

Effects of Particle Size and Soil Bed on the Shear Strength of Materials in the Direct Shear Test

Generally, direct shear apparatus is used to determine the shear strength parameters of soil and rock for designing a geotechnical engineering structure. However, the size of the shearing box and the soil sample is key for evaluating the shear strength parameters of test materials, and also testing conditions in the laboratory are different from site conditions. This research aimed to focus experimentally on the effect of particle size and the property of subgrade materials that were necessary keys for installing apparatuses for the direct shear test. According to the experimental results based on a 5 x 5 cm shear box, an increase in average particle size and coefficient of curvature could provide higher shear strength in terms of internal friction angle of the sample, but not for the case of higher value of the uniformity coefficient. Using both 5 x 5 cm and 30 x 30 cm shear boxes, a large B/Dmax ratio is not the key for determining appropriate parameters when testing with samples that have a nearly uniform size. Samples varied in thickness of both the ballast and subgrade layers, were investigated and observed by a large shear box. It was found that good properties of subgrade materials affected the shear strength of ballast materials, and they provided underestimates of strength when the bottom of the shearing box was rigid. The modified parameter of ballast materials on the subgrade layer is suggested for obtaining strength parameters reflecting the ballasted track system.

Numerical evaluation of the influence of compaction and soil strength parameters on GRSW

This paper presents a numerical evaluation, using PLAXIS 2D finite element software, of the effects of varying the distance of the heavy compaction from the face in a geosynthetic reinforced soil wall (GRSW). The main effects studied were the tensions in the reinforcements and the horizontal deformations of the face, including the influence of the type of shear strength envelope (total stresses or effective stresses) of the soil. In this study, a young gneiss residual soil (silty sand) was studied to obtain the grain size distribution, index properties and parameters of strength and deformability. This soil was considered for backfill in hypothetical sections of GRSW. The numerical results contributed to a better understanding of the GRSW behaviour, with evaluations closer to real field conditions. In the analyses carried out, when increasing the heavy compaction distance from the face, there are tendencies pointing to the reduction of the tensions in the reinforcements, displacement toward the interior of the soil mass of the points at which the maximum reinforcement tension occurs and reduction of the horizontal deformations of the face.

Probabilistic Analysis of Slope against Uncertain Soil Parameters

The purpose of this article was to investigate the influence of uncertain soil parameters on slope stability problems using the probability method. The most important soil instability is probably the inherent spatial variability of soil properties and its influence on slope safety factors. The probability method is recognized for its validity both in practice and academic research. This method of geotechnical risk management involves uncertain parameters. In this study, randomly selected uncertain parameters were combined with traditional analysis using Bishop’s simple methodology and Monte Carlo simulation. The minimum safety factor and critical slip surface of the slope stability were analyzed by Bishop’s simple method. The influence of uncertain soil parameters was analyzed by the back analysis method with Monte Carlo simulation. The calculation was controlled by a critical slip surface, and the safety factor was equal to 1. The results of the analysis show the minimum safety factor and the significant slippery surface of slope stability with the original soil strength parameters. The new soil strength parameters were recommended by Monte Carlo simulation that was used for improving the soil strength parameters in construction. In addition, probability analysis can identify an insufficient understanding of groundwater level distribution and that the assumption of a uniform distribution increases the probability of failure. Governments can use the results of water level analysis in flood warnings and flood management projects to reduce risks to life and property.

Three-dimensional stability assessments of a non-circular tunnel face reinforced by bolts under seepage flow conditions

This paper aims to develop a three-dimensional (3D) analytical framework to assess the safety factors of realistic non-circular tunnel faces reinforced by longitudinal bolts under seepage conditions from a discretization-based perspective. The axial failure mode of bolts (including the tensile failure of the bolt and the pull-out failure at the bolt-soil interface) paired with the introduction of the interaction zone is employed to describe the reinforcement effect of bolts. A numerical fluid calculation is performed to simulate the 3D seepage towards the non-circular tunnel face, and the resulting pore pressure distribution is extracted and further interpolated to determine the pore pressure of each discrete point on the 3D discretization-based failure mechanism. Within the kinematical approach of limit analysis, the work rate balance equation incorporating the role of the axial force along the interaction zone and the pore pressure due to the 3D seepage is established based on the discretization-based failure mechanism. Afterward, combining the strength reduction method with the dichotomy, the upper-bound estimations of safety factors can be obtained by an optimization process. The developed framework is compared with numerical fluid-mechanical calculations and other analytical methods with respect to an actual horseshoe tunnel, which proves that the developed framework is effective in providing fast and reasonable estimates of reinforced tunnel face under seepage conditions. Parametric analyses are performed to investigate the effect of bolt layouts (including the length and density of bolts) and seepage conditions (including the groundwater level and permeability anisotropy). Finally, a series of design nomograms for various water levels and soil strength parameters are provided for reference.