Passive Earth Pressure Coefficients Research Articles

Influence of residual stress and soil dilatancy on the load capacity of jacked pile

ABSTRACT Pile jacking is one of the commonly adopted techniques for installation of displacement piles. The present study investigates the evolution of residual stresses during the pile jacking process and its subsequent impact on the pile load capacity with a particular emphasis on the soil dilatancy angle. The simulations have been carried out following an updated Lagrangian-based finite element framework employing ABAQUS. The magnitude of radial to vertical residual stress ratio coincides with the passive earth pressure coefficient within a radial zone of 6D and reduces to the at-rest coefficient beyond 20D. Owing to the enhanced stress-state, the load capacity of jacked pile is markedly higher than the in-place one with a predominant contribution from the shaft resistance. A small increase in soil dilatancy results into significant enhancement of residual radial stress and extent of influence zone, which further leads to increased load capacity in jacked pile through enhanced shaft resistance.

Determination of Passive Earth Pressure on a Cantilever Retaining Wall in a Narrow Foundation Pit Based on Logarithmic Spiral Sliding Surface

The distribution of passive earth pressure on a cantilever flexible retaining wall in a narrow foundation pit is significantly affected by the adjacent retaining wall and the width of the foundation pit. The deformation mode of the cantilever retaining wall rotating around the displacement zero point makes the soil layer below the displacement zero point retain a nonlimit passive state. The functional relationship between soil mechanical parameters and horizontal displacement in the nonlimit state region, considering the influence of displacement, is established. A new combined failure mode of the soil mass in the passive zone of the narrow foundation pit is proposed, which is the logarithmic spiral fracture surface in the nonlimit state region and the broken line fracture surface in the limit-state region. On this basis, a passive earth pressure calculation model of a narrow foundation pit is proposed and solved by differential layer method. The solution of the passive earth pressure coefficient strictly meets the static equilibrium conditions in vertical and horizontal directions as well as the moment equilibrium conditions. A numerical example is used to analyze the influence of the width of the foundation pit. The smaller the narrow foundation pit width, the greater the passive earth pressure in the lower soil layer and it even greatly exceeds the Coulomb earth pressure distribution. The earth pressure distribution acting on the lower part of the wall near the zero point of displacement decreases sharply and bends. The passive earth pressure distribution is calculated by the theoretical method and compared with the laboratory model test results as well as the engineering test results. It is found that the proper selection of the initial soil mechanical parameters affects significantly the magnitude and distribution of lateral pressure in the nonlimit state region. When the internal friction angle of soil φ0 is small, the lateral pressure in the lower nonlimit state area is relatively small. When both φ0 and δ0 are small, the pressure distribution is closer to the test results and the existing theoretical calculation results.

Unconfined compressive behavior of column with geogrid-encased recycled aggregate: Test and simulation

Geogrid-encased recycled aggregate column (ERAC) undergoes particle breakage during loading due to aggregates’ discreteness and brittleness, significantly affecting the engineering properties. To quantify particle breakage and investigate the shape effect on ERAC, this paper conducts five unconfined compression tests and discrete-continuum coupled numerical analyses on ERAC. Tests study the particle breakage, geogrid strain, and load-settlement response. Test results show that all relative particle breakage is less than 10% (maximum up to 9.02%), and only mass loss of less than 0.4% is noticed during loading. The relationship between the ultimate bearing capacity and relative breakage is established. From longest to smallest column, geogrid increases the bearing capacity by 40.59% with a 1.11% strain increment, and large diameter column has plastic strain exceeding 2%. Simulations study geogrid strain, coefficient of radial stress (Kps), particle displacement, contact force distribution, and porosity change. Simulation results show that the maximum overestimation in coefficient of passive earth pressure (Kp) used in the design is 21.7% compared with Kps value. A slight escaped particle in numerical simulation corresponds to a slight mass loss of less than 0.4% in the test. The contact force for Test-A, -B, and -C increases by 1176%, 4979%, and 1559% after loading. The porosity at Sphere A-1 increases by 55.33% due to volumetric expansion, particle movement, and settlement.

Estimation of seismic passive earth pressure coefficients for caissons in c-φ soils with a 3D log-spiral failure wedge

Passive resistance offered by soil to any embedded structure has been of significant interest to researchers since the inception of the concept. The present study deals with the estimation of passive earth pressure coefficients in seismic conditions that will control the passive resistance offered to a caisson embedded in c (cohesion) – φ (friction) soil in presence of surcharge loading. The three-dimensional (3D) geometry of failure wedge (log-spiral in vertical plane and oval in horizontal plane) has been obtained from the results of numerical analysis and past experimental studies. The critical failure surface has been obtained in the presence of all resisting components [unit weight (γ), cohesion (c) and surcharge (q)] by minimizing the passive resistance. Thereafter, seismic passive earth pressure coefficients for cohesion component (Kspc), surcharge component (Kspq) and unit weight component (Kspγ) have been obtained separately corresponding to the critical failure wedge obtained in the previous analysis. Limit equilibrium method of analysis in conjunction with pseudo-static approach has been used to perform the analyses. Charts for a variety of caisson geometry, soil and site condition and seismic condition have been prepared to facilitate prediction of passive resistance in a more economical and reliable manner since unique failure wedge has been considered for all the components instead of separate failure wedge which would be impractical.

Seismic passive earth pressure resistance for caisson in layered soil using modified pseudo‐dynamic approach

AbstractThe determination of seismic passive earth pressure resistance is of utmost importance during the analysis of geotechnical structures. In the present study, seismic passive earth pressure coefficient for caisson embedded in n‐layered soil is computed using modified pseudo‐dynamic method. Limit equilibrium method of analysis considering poly‐planar failure wedge has been adopted in the study and parametric variation of geometry of failure wedge has also been studied. The current study proposes formulation for variation of horizontal and vertical seismic acceleration profile with depth through various layers and studies the effect of number of layers, relative depths of various layers and relative soil friction angle in those layers, soil‐wall friction angle, horizontal and vertical seismic acceleration coefficients and normalized width of caisson. The study has been extended for submerged soil and the effect of excess pore pressure has been investigated. The results of the present study have been compared with previous theoretical studies and found to be in good agreement. It is observed that the extent of failure wedge formed in front of caisson increases with increasing soil friction angle, soil‐wall friction angle, horizontal seismic acceleration coefficient and width of caisson.

Earth Pressure of the Trapdoor Problem Using Three-Dimensional Discrete Element Method

Load transformation from the yielding part of the soil to the adjacent part is known as the soil arching effect, which plays an important role in the design of various geotechnical infrastructures. Terzaghi’s trapdoor test was an important milestone in the development of theories on soil arching. The research on earth pressure of the trapdoor problem is presented in this paper using the three-dimensional (3D) discrete element method (DEM). Five 3D trapdoor models with different heights are established by 3D DEM software PFC 3D. The variation of earth pressure on the trapdoor with the downward movement of the trapdoor, the distribution of vertical earth pressure along the horizontal direction, the distribution of vertical earth pressure along the vertical direction, the distribution of lateral earth pressure coefficient along the depth direction, the magnitude and direction of contact force chain are studied, respectively. Related research results show that the earth pressure on the trapdoor decreases rapidly after the downward movement of the trapdoor, and then reaches the minimum earth pressure. After that, the earth’s pressure will rise slightly, and whether this phenomenon occurs depends on the depth ratio. For the bottom soil, due to the stress transfer caused by the soil arching effect, the ratio of earth pressure in the loose area decreases, while the ratio of earth pressure in the stable area increases. With the trapdoor moving down, the vertical earth pressure along the depth in the stable zone is basically consistent with the initial state, which shows an approximate linear distribution. After the trapdoor moves down, the distribution of earth pressure along with the depth in the loose area changes, which is far less than the theoretical value of vertical earth pressure of its self-weight. Because of the compression of the soil on both sides, the lateral earth pressure coefficient of most areas on the central axis of the loose zone is close to the passive earth pressure coefficient Kp. The existence of a ‘soil arch’ can be observed intuitively from the distribution diagram of the contact force chain in the loose zone.

Seismic Stability Analysis of Caissons under Earthquake Forces Considering 3D Log-Spiral Failure Surface

Bridge failure is mostly caused by geotechnical failure. Because caissons are the automatic choice for foundation systems for marine structures, such as bridges and wind turbines, this study addresses the determination of seismic passive earth pressure coefficients for caissons. In the present study, a realistic three-dimensional (3D) failure wedge was assumed to be formed behind caissons of different widths on the basis of the past results of experimental and numerical studies. The limit equilibrium method of analysis was adopted to determine the seismic passive earth pressure coefficients due to the cohesion component, surcharge component, and unit weight component. The current study takes into account the relative width and depth of the geotechnical structure and returns a series of design charts and tables for different soil-soil friction angles, soil-wall friction angles, and horizontal and vertical seismic acceleration coefficients. The results were compared with previous experimental and theoretical studies and found to be in excellent agreement.

Influence of transient flow during infiltration and isotropic/anisotropic matric suction on the passive/active lateral earth pressures of partially saturated soils

In this study, the influence of transient flow on the active and passive lateral earth pressures of variably saturated backfills is thoroughly evaluated employing the lower bound theorems of the finite element limit analysis with second-order cone programming. In order to account for the tempo-spatial variations of suction stress within the soil stratum during infiltration, a closed-form solution derived for one-dimensional transient flow through variably saturated porous media is adopted. The unsaturated ground condition is simulated by incorporating the well-established unified effective stress approach into the soil yield function. The soil medium is considered to be both isotropic and anisotropic, due primarily to the various distributions of suction stress along different directions within the partially saturated porous medium. In order to model the soil suction stress anisotropy, an iterative procedure is employed by differentiating between the mobilized suction stress within the horizontal and vertical planes. In general, the influence of the transient flow condition is magnified for cohesive soils compared with granular backfills. In either case, such an effect is more noticeable for the active lateral earth pressure as compared to the passive counterpart. In the anisotropic condition, while the suction stress anisotropy within the soil medium has fairly negligible influence on the contribution of transient flow to the lateral earth pressure coefficient in the active state, the influence of elapsed infiltration time on the passive earth pressure coefficient turns out to be more at play at lower anisotropy ratios.

A closed-form logarithmic spiral method for seismic passive earth pressure in anisotropic sand

The shear strength of soils is always anisotropic due to the compaction and deposition history. A closed-form logarithmic spiral method combined with an anisotropic failure criterion is proposed to estimate the seismic passive earth pressure coefficient and failure surface of anisotropic sand. The seismic condition is implemented by the pseudo-static approach. The results obtained by the proposed method are validated by methods in the literature and by the finite element method based on a proposed anisotropic Drucker–Prager model. The comparisons show that the method is effective and efficient. In addition, the seismic passive earth pressure coefficients considering various backfill slopes and various soil-wall frictions are presented for reference in engineering design.

Passive earth pressure of vegetation rooted soils based on limit analysis and quasi-static approach

Although it has been recognized that vegetation roots have a positive effect on the stability of geotechnical structures, few quantitative studies have been performed on the effects of vegetation roots on earth pressures. In this paper, based on the upper bound limit analysis theory and quasi-static method, a new method for calculating the seismic passive earth pressure of vegetation rooted soils is proposed, which considers both the hydrological and mechanical effects of vegetation roots on the passive earth pressure. The proposed method is validated by some existing solutions. The effects of root parameters of shrubs (root transpiration rate, root tensile strength, and root depth), angle of the soil slope surface with the horizontal, and wall interface friction angle on the seismic passive earth pressure coefficient are also investigated. The results show that the passive earth pressure coefficient increases with the increase of root transpiration rate, root tensile strength, root depth, angle of the soil slope surface with the horizontal, and wall interface friction angle. Compared with the mechanical effect, the hydrological effect of vegetation roots on the passive earth pressure coefficient is more obvious. The effects of root parameters on the passive earth pressure ranked in descending order of sensitivity are root transpiration rate, root tensile strength, and root depth. In addition, the effect of vegetation roots on the passive earth pressure becomes more significant with the increase of internal friction angle. The proposed method can provide a reference for the local reinforcement of multi-stage slopes with vegetation.

A generalised Newmark method with displacement hardening for the prediction of seismically induced permanent deformations of diaphragm walls

This paper presents a generalised Newmark method (GNM) incorporating a displacement hardening mechanism for the prediction of permanent displacements accumulated by diaphragm walls during earthquakes. A key feature of the proposed approach is the adoption of an evolution law for the critical acceleration, which links its current value to the accumulated wall permanent displacements. This displacement hardening mechanism is based on a simplified relation between the average plastic shear deformations experienced by the passive zone of soil below dredge level and the mobilised soil friction angle. This relation is determined indirectly by the evolution of the passive earth-pressure coefficient with wall displacement/rotation, as obtained in quasi-static model wall experiments. The proposed approach has been validated by comparing its predictions with the experimental data obtained in centrifuge model tests of cantilevered and propped walls. In spite of the simplifying assumptions on which it is based, the GNM has demonstrated that it is capable of capturing the essential features of the retaining structures’ kinematics and provides realistic predictions of permanent wall displacements.

Passive earth pressures with sloping backfill based on a statically admissible stress field

Passive earth pressure is a fundamental problem in the field of soil-structure interaction. In this study, a fully plastic solution obeying the Mohr-Coulomb criterion was successfully developed to estimate passive earth pressure against rigid retaining walls with various sloping backfills, wall roughness, and wall rear face inclination. The numerical procedures using a shooting technique and the 5th order adaptive Runge-Kutta method were successfully developed for boundary-value and initial-value problems, respectively. The developed procedures successfully coped with the numerical integral in non-smooth domains then statically admissible stress fields in the sloping backfills are explored. The stress distributions together with the trajectories of principal stresses in various sloping backfills are presented to demonstrate the load transfer mechanisms of cohesionless soil in various geometries of the backfill. The effects of the wall roughness, the wall rear face inclination, and backfill inclination on the load transfer mechanism of the cohesionless soil behind the retaining wall are investigated. The obtained results of passive earth pressure coefficients (Kp) are validated by comparing with an exact solution and some well-known experimental works. Thus, highly accurate values of passive earth pressure coefficients on rigid retaining walls with various sloping backfills, wall roughness, and wall rear face inclinations are provided for engineering practice.

A log-spiral limit equilibrium analysis for passive earth pressure under the effect of unsaturated seepage conditions

In the current state of the study regarding passive earth pressure, the majority of literature was limited in scope to dry or saturated cases. However, most soils in practical engineering are unsaturated. Based on the log-spiral failure mechanism, this paper develops a limit equilibrium (LE) analysis to evaluate the passive earth pressure under the effect of steady unsaturated seepage conditions. For assessing the effect of suction stress on passive earth pressure, a suction stress-based effective stress representation is incorporated into a limit equilibrium analysis. The analytical formula of passive earth pressure coefficient is derived using the moment equilibrium equation for the backfill defined by a log-spiral slip surface. An optimization procedure is developed to search for the minimum passive earth pressure coefficient and the critical failure surface via MATLAB. A parametric analysis is performed to investigate the effects of some key parameters on passive thrust. Besides, examples of two different cases are given to verify the effectiveness of theoretical results. Results indicate that suction stress can increase the magnitude of the passive earth pressure coefficient and the suction-induced effect highly depends on the seepage conditions and soil types.

Influence of soil amplification and backfill angle on seismic earth pressure coefficients by pseudo dynamic method

ABSTRACT The knowledge of earth pressure concepts plays a major role to design a retaining wall. The most traditional pseudo-static methodology as proposed by Mononobe–Okabe gives the direct approximation of earth pressure in seismic condition. This paper utilised the pseudo-dynamic methodology to figure out the seismic earth pressure on rigid wall with cohesion less backfill along with considering the effects of time, phase difference, soil amplification factor along with the variation in seismic velocities. The main contribution is the soil amplification and backfill inclination which is not given much attention before. By considering the above factors coefficients the seismic earth pressure against retaining wall is determined. The coefficient of seismic passive earth pressure decreases with the increase of soil amplification keeping other properties as standard values. The value of coefficient of seismic active earth pressure increases with increase of soil amplification. The comparison is also done without taking backfill angle for both coefficients of seismic earth pressures. The influence of all the soil properties like backfill angle, wall friction angle, soil friction angle, non-dimensional parameters are shown in tabular format as well as in the graphical with respect to the soil amplification which is more realistic towards the design.

An attempt to apply the kinematic method of rigid solids in the study of bearing capacity of shallow foundations

Abstract In the geotechnical engineering field, shallow foundations are frequently needed to ensure good fieldwork stability. They are also intended to permanently and uniformly transmit all load pressure on the seating floor. However, numerous mechanical constraints, such as bearing capacity of foundations, durability, stability, design of shallow foundations, lead, unfortunately, to a serious realization challenge. Finding an adequate solution presents the main goal and effort of both scholars and professionals. Indeed, the corresponding drawback is observed through the high number of reported damages that occurred in the structure of foundations and the punching failure. The failure mechanisms of shallow foundations, verified in full size or on scale models, show “sliding surfaces” and rigid (solid) blocks, which can be described with the kinematic method of rigid solids. The main objective of this study is the application of the kinematic method of rigid solids in the study of the stability of shallow foundations with respect to punching, the purpose of which is to determine the bearing capacity factors Nc, N γ, and the passive earth pressure coefficient Kp of foundations. In this context, two mechanical models have been proposed with 5 and 7 rigid solids, and a program developed via the MathCAD environment is applied to check the validity of the two previous models. The kinematic method of rigid solids gives results very close and comparable with that of Caquot/Kerisel for the factors of the bearing capacity and passive earth pressure coefficient - the ratio Kp - according to the five- and seven-solid model.

Analytical solution for displacement-dependent passive earth pressure on rigid walls with various wall movements in cohesionless soil

Current design practice of retaining wall is generally based on Rankine’s and Coulomb’s earth pressure theories that are subjected to some important limitations. In the present study, an analytical solution for displacement-dependent passive earth pressure on rigid walls is proposed by assuming a linear relationship between the passive earth pressure coefficient and displacement. Based on Coulomb’s theory, the passive ultimate earth pressure coefficient is modified in order to adapt the earth pressure model to various wall movements. The proposed solution is verified with reported experimental data and shows good agreements. Based on the observed experimental data, the normalized passive ultimate displacements (sp/H) are obtained and found to be related to the n value which indicates the location of rotation center. By performing curve fitting, an exponential function of sp/H and the parameter n is proposed. Further, the influence of n value on the distribution of the proposed displacement-dependent passive earth pressure under various wall movements are studied. The proposed analytical model provides an effective approach to calculate the distribution of displacement-dependent passive earth pressure on rigid walls with various wall movements in cohesionless soil.

A new modification to Mononobe-Okabe's pseudo-static model for passive earth pressure prediction using homogeneous differential equation

Mononobe-Okabe's model is the most commonly used pseudo-static method of estimating seismic lateral earth pressures behind retaining wall worldwide. This method cannot predict the distribution of the lateral earth pressure and the overturning moment accurately. Hence, this research proposed a new modification to the original M-O model using the homogeneous differential equation within the framework of limit equilibrium. The proposed model gives an exact prediction of the M-O model when considering the coefficient of passive earth pressure and different predictions for the distribution of the lateral earth pressure. The point of application of the resultant earth force is found to vary with the input parameters and not fixed at 1/3 of the height of the wall as in the original M-O model. The obtained results are also compared with the analytical and experimental models and they are found to be comparable with them.

Passive Resistance of Retaining Walls Supporting Layered Cohesionless Backfill: A Plasticity Approach

A theoretical model was developed to determine the seismic passive earth pressure on vertical cantilever retaining walls supporting a two-layered cohesionless backfill with a loose sand layer overlying a dense sand stratum. Seismic inertial forces were considered in the analysis by employing the classical pseudostatic approach. The theoretical formulation was developed based on the method of stress characteristics, which does not require any predefined failure mechanism to initiate the analysis. The charts are presented in terms of passive earth pressure coefficient, which includes the contribution of both the layers. In addition to the generation of the actual failure mechanism, rapid mobilization of stresses at the layer interface and at the wall backface is presented in the form of normalized stress contours. The failure surface and the passive earth pressure distribution behind the wall were found to be nonlinear, with different input parameters. The passive resistance of backfill soil decreased in the presence of the loose sand layer resting on the denser soil stratum.

DEM-FDM numerical investigation on load transfer mechanism of GESC-supported embankment

This paper presents a numerical investigation on the load transfer mechanism of geosynthetic-encased stone column supported embankment. A coupled numerical model is developed by combining the discrete element method (DEM) with the finite difference method (FDM). A parametric study is then conducted on several governing factors such as the encasement length (Lenc), geosynthetic stiffness (J), the strength of foundation soil (cu), embankment height (Hemb), and area replacement ratio (αE). The predicted stress concentration ratio (SCR) under the embankment load is smaller than that under rigid loading (i.e., under the equal strain condition of the composite foundation). The predicted coefficient of the lateral pressure (Kps) lies between the coefficient of earth pressure at rest (K0) and the coefficient of passive earth pressure (Kp). Particularly, the bearing capacity of the GESC would be overestimated when substituting the confinement with Kp in the calculation. The shear stress at the column-soil interface (τcs) is less than the ultimate shear stress, and its development would be retarded with depth.

Significance of flow rule for the passive earth pressure problem

Determination of earth pressures is one of the fundamental tasks in geotechnical engineering. Although many different methods have been utilized to present passive earth pressure coefficients, the influence of non-associated plasticity on the passive earth pressure problem has not been discussed intensively. In this study, finite-element limit analysis and displacement finite-element analysis are applied for frictional materials. Results are compared with selected data from literature in terms of passive earth pressure coefficients, shape of failure mechanism and robustness of the numerical simulation. The results of this study show that passive earth pressure coefficients determined with an associated flow rule are comparable to the Sokolovski solution. However, comparison with a non-associated flow rule reveals that passive earth pressure coefficients are significantly over predicted when following an associated flow rule. Moreover, this study reveals that computational costs for determination of passive earth pressure are considerably larger following a non-associated flow rule. Additionally, the study shows that numerical instabilities arise and failure surfaces become non-unique. It is shown that this problem may be overcome by applying the approach suggested by Davis (Soil Mech 341–354, 1968).