Active Lateral Earth Pressure Research Articles

Hyperbolic stress-strain behaviour of sandy soil under plane strain unloading condition and its application on predicting displacement-dependent active earth pressure

This study investigates the displacement-dependent lateral earth pressure of sandy soil in active state. 3D DEM numerical simulations of plane strain unloading test (unloading in the minor principal stress direction) are carried out firstly to acquire the hyperbolic stress–strain relationship of sandy soil. The initial modulus of sandy soil is observed to increase with the increasing of major principal stress, initial lateral earth pressure coefficient and relative density, while the failure ratio is little influenced by these factors. A simplified hyperbolic model calibrated by the DEM results are then developed to calculate the displacement-dependent active lateral earth pressure of sandy soil. It was found that the hyperbolic model can well predict the variation of lateral earth pressure distribution at intermediate active state of T- (Translation) and RB- (Rotate about the base) mode of retaining structure movement. But it can hardly capture the lateral earth pressure distribution on retaining structure under RT- (Rotate about the top) mode due to significant rotation of principal stress direction. According to the theoretical analysis, the required retaining structure displacement leading to the limiting active state is varied along the retaining structure, and it also dependents on the initial stress state as well as the relative density.

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.

Temperature-dependent lateral earth pressures in partially saturated backfills

Stability analysis of retaining structures supporting variably saturated backfills is a topic of great significance in civil engineering. However, the backfill soil may be exposed to elevated temperature; this may result in changes of the saturation state, thus posing temperature-dependent effective stress, variable suction stress and different hydro-mechanical characteristics to partially saturated soils. In the present work, the significant impact of elevated temperature is incorporated into the soil-water retention curve and suction stress-based effective stress formulations. Accordingly, the lower bound theorems of limit analysis in conjunction with finite element and second-order cone programming are adopted so as to thoroughly examine the impact of elevated temperature on the coefficients of lateral earth pressure acting on a model retaining wall backfilled by two hypothetical partially saturated soils; a granular material (sand) and a cohesive material (clay). The effective stress-based formula for the strength of variably saturated soils is implemented to modify the conventional Mohr–Coulomb yield criterion. In general, it was shown that for unsaturated clay backfills, the active lateral earth pressure decreases while the passive lateral earth pressure increases with increasing the induced temperature; however these influences were observed to be small for the sand backfill.

Quantification of the Active Lateral Earth Pressure Changes on Retaining Walls at the Leading Edge of Steep Slopes

Retaining walls may become unstable when the steep slope angle of the top of the wall (β) is greater than the internal friction angle of the earth behind the wall (φ). To examine this behaviour, an active earth pressure model test setup was designed with inclined backfill behind the wall, and corresponding finite element simulations were performed at the same dimensions. The active earth pressure variation patterns of the retaining wall under two displacement modes were studied: translation (T mode) and rotation around the bottom of the wall (RB mode). The experimental results corresponded well to the finite element simulation results. The study found that the experimental results coincided well with the results of the finite element simulation. The active earth pressure and the location of the resultant force points are both connected to the wall displacement pattern and slope angle.

Active lateral earth pressure of geosynthetic-reinforced retaining walls with inherently anisotropic frictional backfills subjected to strip footing loading

In this paper, a detailed numerical study is conducted to evaluate the lateral earth pressure acting on geosynthetic-reinforced retaining walls with an anisotropic granular backfill subjected to strip footing loadings. To this end, the well-established lower bound theory of limit analysis coupled with the robust second order cone programming (SOCP) and the finite element discretization method is exploited and implemented in the stability analysis of reinforced retaining structures. For the finite element limit analysis, a number of constraints associated with the lower-bound axioms are satisfied, including element equilibrium, discontinuity equilibrium, boundary conditions and the yield criterion enforcement. By adopting second-order cone programming (SOCP) optimization, the nonlinear Mohr-coulomb failure criterion is simulated using three nodal auxiliary variables defined as functions of nodal stresses generated at each point. In addition, the primal-dual interior-point algorithm is adopted to gain the optimal solution for the unknown stress variables in the SOCP optimization problem. Accordingly, the contribution of soil inherent anisotropy to the influence ofa number of parameters on the lateral earth pressure is thoroughly examined. It was observed that as the anisotropy ratio increases (the horizontal friction angle decreases) and the number of reinforcement layers decreases, the coefficient of active earth pressure increases in all cases of geosynthetic-reinforced retaining structure. Decreasing the number of reinforcement layers in the retained backfill will be translated into an equivalent softened material; hence, increasing the active earth pressure coefficient. In addition, the increase in the anisotropy ratio leads to the overall decrease in the shear strength of the backfill soil, causing the retaining structure to reach the limit state earlier at smaller displacements, thus giving rise to the increase in the coefficient of active lateral earth pressure. The rate of increase in the coefficient of active earth pressure with anisotropy ratio grows with the increase in the foundation width and load intensity and the decrease in the foundation-wall distance.

Design of soilbag-protected slopes in expansive soils

Slope failures and slope slides of expansive soils are usually characterized by shallow sliding along the surface crack. Soilbag is an effective method to prevent and control slope failures and slope slides of expansive soil. Currently, soilbag protection for expansive soil slopes has been commonly designed using empirical methods, which led to many failures of soilbag-protected slopes, or high-cost. In this paper, a new design method of the soilbag-protected slopes in expansive soils is proposed based on the balance between the soilbag friction and the active lateral earth pressure induced by the swelling pressure of expansive soils. Specifically, the friction between the soilbags is assumed to be in direct proportion to the soilbag heap-up height. The active lateral earth pressure acted on a layer of soilbag is calculated along with the total height of the slope. Moreover, the width of soilbag layers is calculated from the balance of the sum of soilbag friction and the total active lateral earth pressure along with the soilbag height and expressed by the height of slopes. For the convenience of soilbag construction, the heap-up unit of soilbags is proposed for different slope heights of expansive soils.

Evaluation of required connection load in GRS-IBS structures under service loads

This study presents an evaluation of the connection load (To) and stress-strain conditions right behind the facing of a Geosynthetic Reinforced Soil – Integrated Bridge Structure (GRS-IBS) based on field instrumentation data obtained from an abutment constructed in Virginia. The observations from this site are compared against other projects in Delaware and Louisiana. The lateral stress distribution obtained from the field was observed to be lower than the active lateral earth pressure distribution but higher than predicted using the bin pressure method. The results from all sites showed that the reinforcement strains measured in the field were below the maximum geosynthetic strains allowed in the design of GRS-IBS. The distributions of both lateral stresses and reinforcement strains with depth were found to be approximately uniform. The To values for the Virginia structure were obtained based both on reinforcement strain and lateral stress data, which agreed well with each other. All sites indicated the existence of lateral stresses behind the facing, which contributed to the development of To. The normalized To values for all GRS-IBS projects evaluated in this study showed that the theoretical tributary area approach outlined in MSE design can be conservatively adopted to predict To in the design of GRS-IBS.

Optimal Design of Cantilever Retaining Wall Using Relief Shelve: A Review

The sectional dimensions of retaining wallessentially depends on the active lateral earth pressure acting on it. Many researchers have struggledon researches to minimize the effective lateral pressure and to adopt the optimized and economical design for retaining walls. Provision of relief shelves to retaining walls reduces the lateral earth pressure, this type of retaining wall is considered as a special type of retaining wall. For high cantilever wall, there will maximum bending moments and shear force for which providing relief shelves will be beneficial.This paper conducts thorough review of analysis and design of cantilever retaining wall with and without relief shelves, study the effect of provisions of relief shelf as aplatform in cantilever retaining wall. The arrangement of the reinforcement at the critical junction where relief shelve platform connecting to the stem wall is to be analyzed and studied to feasibility to install actual on site. Keywords: Cantilever retaining wall, relive shelve, lateral earth pressure, economical design, finite element method Cite this Article: Ajinkya S. Saraf, Ajay G.Dahake. Optimal Design of Cantilever Retaining Wall Using Relief Shelve: A Review. International Journal of Structural Engineering and Analysis . 2020; 6(1): 29–39p.

Axisymmetric active lateral earth pressure for c- soils using the stress characteristics method

The slip line or Stress Characteristics Method (SCM) is used to analyze the active lateral earth pressure in the axisymmetric case. In this paper, in addition to the retaining walls in the axisymmetric and plane strain conditions that studied in the past, a new model of the retaining wall in the axial symmetry is considered, which widely used in the design of grain silos, buildings and road constructions. The effects of the various parameters, including cohesion and friction angle of the soil, wall and backfill slopes and soil-wall interface adhesion and friction angle on the lateral earth pressure have been evaluated for all cases of the retaining walls. Based on the proposed theory, a computer code has been developed for the plane strain and axisymmetric cases. Also, finite element modelling is used to verify the results of the SCM. Comparison of the results indicated the accuracy of the proposed method. Furthermore, the effect of the plastic critical or tension crack depth has been evaluated and indicated that neglecting the plastic critical depth is not conservative.

Estimating total resisting force in flexible barrier impacted by a granular avalanche using physical and numerical modeling

Flexible barriers are a promising tool for protection against extremely rapid landslides such as debris flow and debris avalanches. With landslide impacts of any size, the total force induced within the barrier and transferred to the anchorage is a fundamental question to design. Current practice limits the investigation to flow parameters, neglecting the behavior of the structure, which can vary significantly. This paper describes steps taken to quantify the total force induced within a flexible barrier. It describes laboratory experiments of dry granular flow against rigid and flexible barriers with observations of resisting force and other filling processes that provide an understanding of the behavior and possible flow–structure interaction for larger scale rapid landslides. Results from the experiments suggest that for granular flows with high discharge the current practice sufficiently quantifies the total force, and for those with lower discharge, the total force is better characterized by active lateral earth pressure calculations. Test results were also used to validate an adaptation to an existing depth-integrated numerical model for landslide mobility to quantify the total force. This model was then used to estimate the resisting forces induced within a full-scale flexible barrier impacted by a controlled debris flow.

Active earth pressure on translating rigid retaining structures considering soil arching effect

Accurate determination of active earth pressure distribution on rigid retaining wall including the magnitude and height of application of its resultant is of immense importance for designing the earth retaining structures. In this paper, an analytical solution based on the soil arching effect is presented. According to Mohr’s stress circle, a new relationship between active earth pressure and normal stress on failure surface at any depth from backfill surface is obtained. By analysing parabolic arch of minor principal stresses, a new coefficient of active lateral earth pressure is proposed. The problems that the vertical static equilibrium equation of differential flat element considering soil arching effect is not reasonable are analysed. Then, based on the limit equilibrium of differential flat element, new formulas relevant to the distribution of active earth pressure, the magnitude and height of application of its resultant are derived. The effects of backfill internal friction angle, wall–soil friction angle, wall height, surcharge load and backfill unit weight on those formulas are investigated in detail. In addition, the comparisons of the predictions by proposed equations with available test data as well as existing solutions are carried out, which implies adequate accuracy of the proposed solutions for all ratios of wall–soil friction angle to internal friction angle.

Static and seismic active lateral earth pressure coefficients for c-ϕ soils

In this paper, the active lateral earth pressure is evaluated using the stress characteristics or slip line method. The lateral earth pressure is expressed as the lateral earth pressure coefficients due to the surcharge, the unit weight and cohesion of the backfill soil. Seismic horizontal and vertical pseudo-static coefficients are used to consider the seismic effects. The equilibrium equations along the characteristics lines are solved by the finite difference method. The slope of the ground surface, the wall angle and the adhesion and friction angle of the soil-wall interface are also considered in the analysis. A computer code is provided for the analysis. The code is capable of solving the characteristics network, determining active lateral earth pressure distribution and calculating active lateral earth pressure coefficients. Closed-form solutions are provided for the lateral earth pressure coefficients due to the surcharge and cohesion. The results of this study have a good agreement with other reported results. The effects of the geometry of the retaining wall, the soil and soil-wall interface parameters are evaluated. Non-dimensional graphs are presented for the active lateral earth pressure coefficients.

The Effects of the Soil-Wall Adhesion and Friction Angle on the Active Lateral Earth Pressure of Circular Retaining Walls

Lateral earth pressure on retaining walls is a widely researched classical problem in geotechnical engineering. This study investigates the active lateral earth pressure on a circular retaining wall using the stress characteristics method in the presence of soil-wall adhesion and friction. A computer code was developed for determining the lateral pressure of soil on the wall as well as the lateral pressure coefficients upon receiving the required input parameters. The principle of superposition was implemented to determine the lateral earth pressure coefficients. The effects of the soil-wall adhesion and friction angle on the lateral earth pressure were studied under active conditions. Moreover, the effects of these parameters on the characteristics network and failure region were demonstrated. The results showed that the coefficient of lateral earth pressure due to cohesion increased with increasing adhesion at the soil-wall boundary.

Evaluation of the static and seismic active lateral earth pressure for c-f soils by the ZEL method

The method of Zero Extension Lines (ZEL) has been used to evaluate the static and seismic active lateral earth pressure on an inclined wall retaining inclined c-f backfill. The equilibrium equations along the Zero Extension Lines have been solved using the finite difference method. A computer code is prepared to analyze the retaining wall, calculate the ZEL network and the distribution of the active lateral earth pressure behind the retaining wall. The total active force on the retaining wall was defined as the lateral earth pressure coefficients due to the soil unit weight, the surcharge and the soil cohesion. The variation of the active lateral earth pressure coefficients with changes in different parameters, such as the inclination of the earth and wall, the friction angle of the soil, the adhesion of the soil-wall interface, the horizontal and vertical pseudo-static earthquake coefficients have been obtained. The results have been obtained for soils with associated and non-associated flow rules. The effect of the dilation angle has also been considered. The results obtained in this study are very close to those of other methods and confirm that the ZEL method can be successfully used to evaluate the lateral earth pressure of retaining walls.

Numerical study on lateral bearing capacity and failure mode of geosynthetic-reinforced soil barriers

In addition to vertical surcharges, geosynthetic-reinforced soil (GRS) structures have recently been used as barriers to resist lateral forces from natural disasters such as floods, tsunamis, rock falls, debris flows, and avalanches. The stability of such structures is often evaluated by conducting conventional external stability analyses with an assumption that the reinforced soil mass is a rigid body. However, this assumption contradicts the flexible nature of reinforced soil. In this study, finite element (FE) models of back-to-back GRS walls were developed to investigate the behavior of GRS barriers subjected to lateral loadings. The FE results indicate that GRS barriers subjected to lateral loadings fail internally. The failure model and the lateral bearing capacity depend on the aspect ratio (L/H: ratio of wall width to wall height) of GRS barriers. When 0.5 3.0, passive soil failure occurs within GRS barriers at the side subjected to the lateral force. As L/H increases, the lateral bearing capacity of GRS barriers increases to approximately three times the active lateral earth pressure at L/H = 0.7 to the passive lateral earth pressure at L/H = 3.0. In addition to the effect of L/H, the internal soil failure predicted by FE analyses suggests that the soil shear strength plays a major role in determining the lateral bearing capacity of GRS barriers. A hypothetical case study of a GRS barrier against a tsunami force is provided and an improved method is discussed.

Composite Properties from Instrumented Load Tests on Mini-Piers Reinforced With Geotextiles

Abstract Four pairs of large-scale instrumented geosynthetic reinforced soil (GRS) square columns were load tested to study the effects of varying reinforcement strength to spacing ratio, to discern the lateral pressures during construction and during load testing, and to derive shear strength parameters of the GRS composite. Each pair was identical in every respect, except one was loaded with a dry-stacked concrete masonry unit (CMU) facing in place and the other without. Lateral pressures during construction were found to be small for the facing type used in this study. Also, based on the derived GRS composite shear strength parameters, it was found that (1) the GRS composite Mohr–Coulomb envelopes are not parallel to those for the unreinforced soil; (2) the reinforcement increased the composite cohesion compared to the unreinforced soil (cohesion increases with decreasing spacing and increasing reinforcement strength); (3) the composite friction angle is less than that of the unreinforced soil (friction angle increases with decreasing reinforcement strength and increasing spacing); (4) as the composite friction angle increases, the active lateral earth pressure coefficient decreases; and (5) the benefits of reinforcing a soil become increasingly significant as the reinforcement spacing decreases.

Lateral earth pressures on flexible cantilever retaining walls with deformable geofoam inclusions

The present study explores the potential application of geofoam in reducing the lateral earth pressures on flexible cantilever walls retaining cohesionless and dry backfills. Results of 1-g physical model tests addressing the behavior of yielding cantilever retaining walls with expanded polystyrene (EPS) and extruded polystyrene (XPS) geofoam compressible inclusions are discussed. The effect of relative flexibility of the wall as well as the characteristics of the cohesionless backfill and geofoam on the active earth pressures were investigated in this context. A finite difference code was validated against the lateral earth pressures and backfill strains observed in the tests. Experimental results indicate that the shape of active pressure distribution diagram behind a cantilever retaining wall is non-linear and varies depending on the wall flexibility and characteristics of deformable layer. Geofoam inclusions provide reduction in lateral earth pressures, however the positive contribution of the compressible buffer decreases as wall relative flexibility increases. Reduction of the lateral earth loads is associated with the formation of a wider, non-linear and more stable failure zone induced from the combined influence of the flexural deformations of the cantilever wall and the arching effect induced at the lower half portion of the cohesionless backfill retained by the flexible wall-deformable panel system. Parametric numerical analyses were performed to extend the predictions of the lateral earth pressure coefficients for various combinations of backfill, deformable inclusion and structural attributes by validated numerical model. Based on the results of the parametric analyses, design charts and regression models were proposed to predict active lateral earth pressure coefficients and point of application of the lateral load on the flexible cantilever earth retaining walls with and without deformable geofoam layers.

Field Behavior of a Geogrid Reinforced Soil Retaining Wall with a Wrap-Around Facing

Abstract The earth pressure and deformation characteristics of a geogrid reinforced soil retaining wall were monitored during and for a period of 1.5 years after construction. Both vertical and lateral soil stresses were recorded with vibrating-wire earth pressure cells, and the reinforcement deformations were measured using flexible displacement sensors. The maximum vertical foundation pressure along the wall’s reinforcements occurred at the center of the reinforcement, gradually decreasing towards the front and back ends. The measured lateral earth pressure within the reinforced soil wall is non-linear along the wall height, and the value is less than the theoretical active lateral earth pressure. The distribution of tensile strain along the reinforcements within the lower portion of the wall has two peak values. The potential failure surface of the wall closely follows the theoretical Coulomb failure surface of an unreinforced backfill.

Behaviour of geogrid reinforced soil retaining wall with concrete-rigid facing

Monitoring was carried out during construction of a cast-in-situ concrete-rigid facing geogrid reinforced soil retaining wall in the Gan (Zhou)-Long (Yan) railway main line of China. The monitoring included the vertical foundation pressure and lateral earth pressure of the reinforced soil wall facing, the tensile strain in the reinforcement and the horizontal deformation of the facing. The vertical foundation pressure of reinforced soil retaining wall is non-linear along the reinforcement length, and the maximum value is at the middle of the reinforcement length, moreover the value reduces gradually at top and bottom. The measured lateral earth pressure within the reinforced soil wall is non-linear along the height and the value is less than the active lateral earth pressure. The distribution of tensile strain in the geogrid reinforcements within the upper portion of the wall is single-peak value, but the distribution of tensile strain in the reinforcements within the lower portion of the wall has double-peak values. The potential failure plane within the upper portion of the wall is similar to “ 0.3H method”, whereas the potential failure plane within portion of the lower wall is closer to the active Rankine earth pressure theory. The position of the maximum lateral displacement of the wall face during construction is within portion of the lower wall, moreover the position of the maximum lateral displacement of the wall face post-construction is within the portion of the top wall. These monitoring results of the behaviour of the wall can be used as a reference for future study and design of geogrid reinforced soil retaining wall systems.

Coulomb wedge analysis of cuts in steep slopes: Discussion

The purpose of this discussion is to point out that adaptation of Coulomb wedge analysis to infinite slopes is not applicable in the strict framework of statics. However, the presented numerical results are valid and indeed instructive in practical terms (i.e., for “nearly” infinite slopes). Following are points leading to the conclusion of this discussion: (1) Some foundation engineering handbooks include the derivation of Coulomb’s equation for the resultant of the active lateral earth pressure (e.g., Bowles 1988). Following this derivation, one realizes the implicit assumption in the basic formulation that the wall retains a finite wedge of soil; otherwise, an expression is rendered in which Pa = f (∞·0), where f () symbolizes a function. A mathematical finite value of this expression is not obvious. The writer, however, used and further simplified eq. [2], which is an intermediate result in the derivation of Coulomb’s equation where a finite value is a priori assumed. The legitimacy of this operation as applied to infinite mass is questionable. (2) It is perhaps more instructive to obtain Pa using the graphical approach; i.e., the force polygon. To simplify the presentation and without any loss of generality, the problem is restricted to cohesionless soil and to a case where the resultant Pa is horizontal (i.e., δ = 0). While β φ, a finite value of Pa is obtained. If α φ. Here W→∞ as α→β. Hence, R and Pa must also approach infinity. In the case where α = β β = φ (for cohesionless soil), where α is only differentially greater than β, the writer’s numerical results derived using Coulomb analysis are practically correct, and the conclusions are indeed instructive. In fact, the discusser has used some of the same numerical results for the last 15 years as benchmarks in assessing the performance of computerized stability analysis of reinforced slopes in which automatic search for the critical results is utilized. In such cases Pa should equal the sum of the mobilized force in all reinforcement layers. The critical slip surface then degenerates to nearly a plane emerging on the inclined crest at a significant distance from the top of the wall; i.e., practically an infinite slope.