Coefficient Of Lateral Earth Pressure Research Articles

Evaluation of the lateral earth pressure coefficients at-rest in granular soil deposits using the anisotropic components of S-wave velocity

Determination of the lateral earth pressure coefficients at-rest (K0) in natural soil deposits is an important issue in geotechnical and geological engineering. In this study, evaluation of this parameter in a granular soil deposit was examined by using two anisotropic components of the S-wave velocity (SV and SH-wave components). To this end, thirteen pairs of P- and S-wave seismic refraction profiles were acquired at two different granular sites in Iran. The collected shot gathers were processed, from which the SV and SH-wave velocities were derived. The SV-wave velocities were obtained by using the Multichannel Analysis of Surface Waves (MASW) method while the SH-wave velocities were extracted by utilizing the Multichannel Analysis of Love Waves (MALW) technique. The reference K0 values in the soil deposits were calculated by the Mayne and Kulhawy's formula based on the friction angles (φ′) and overconsolidation ratios (OCR) determined from laboratory tests. The curves of the reference K0 values versus the SH/SV velocity ratios at both sites strongly confirmed the feasibility of K0 evaluation from the velocity components. To develop a global equation for K0 evaluation in granular soil deposits, a general regression analysis was conducted on the obtained data from this study combined with those reported in the literature. The results showed that reliable values of K0 can be estimated using the SH/SV velocity ratios. The findings of this study may appropriately serve as references for economic and non-invasive in-situ K0 identification in granular soil deposits using the surface wave methods.

An Experimental Study of Compaction Grouting on Its Densification and Confining Effects

Compaction grouting (CPG) involves the injection of high viscosity mortar-type grout under relatively high pressure that displaces and compacts the soil in-place. Many case studies around the world prove the effectiveness of CPG to treat liquefiable soils. In these studies, mostly CPG has been developed and used on the basis of practical experiences, its densification and confining effects are not well understood until now. The objective of the present study is to bring out densification and confining effects of CPG. This paper presents a laboratory experimental study carried out to model a CPG treated ground. The study includes the experiments performed to decide appropriate consistency of grout material and appropriate relative contribution of factors such as overburden pressure, grout volume, injection speed and injection pressure that ensures efficient grouting. The effects of CPG are quantified in terms of lateral earth pressures and lateral displacements that are further defined in terms of coefficient of lateral earth pressure, K, and densification factor in the soil around grout column. This leads to a better understanding of its densification and confining effects. Although in practice, majority of the works with CPG have been related to its densification effect and lesser attention has been given to its confinement effect, in present experimental study, its confinement effect were prominent. Also at the farthest locations usually where field tests are carried out, its densification effect could not be found experimentally but its confinement effect was clear.

Estimation of Active Earth Pressure on a Translating Rigid Retaining Wall Considering Soil Arching Effect

By analysing the actual catenary arch of minor principal stresses under Rankine rupture surface, a new coefficient of lateral active earth pressure is proposed. And based on the limit equilibrium theory, new formulas of lateral active earth pressure on translating rigid retaining structures is derived, considering effects of soil arch and stress on rupture surface as well as surcharge stress. Further, the effects of the parameters (i.e., backfill internal friction angle, wall-soil friction angle, wall height and surcharge stress) on active earth pressure and its coefficient, active earth thrust and height of its application are investigated. In addition, the comparisons between the proposed methods by this study and others as well as existing test data, show that the predictions by this study are better accordant with results of the model test.

Experimental Study of Shaft Resistance of Model Piles in Fluidized and Nonfluidized Fine Sand

Torpedo piles installed by dynamic penetration have been used as anchors in the Brazilian offshore oil production infrastructure practice for two decades. Dynamic penetration aided by fluidization of the soil during pile penetration is now being contemplated as a method of installation that would allow deeper penetration. The two key design questions in connection with torpedo piles are how far they penetrate and what their pullout capacity is. In a companion paper, the authors addressed the first question, whereas in the present one the second question is attended through laboratory tests using model piles, essentially pipes simulating torpedo piles without wings. The model piles were installed in two different ways: by fluidization, which enabled the piles to sink by their own weight, and by monotonic jacking. Pullout tests were then performed on the model piles in both fluidized and nonfluidized sandy soils prepared at two initial relative densities. Results from the laboratory tests indicate that shaft uplift capacity of fluidized piles is essentially independent of the sand initial relative density. The measured values of the coefficient of lateral earth pressure (Ks) derived from the fluidized model tests are lower than those reported for other methods of pile installation, in some cases being lower than K0. Finally, the shaft resistance of fluidized piles increases after installation as the soil reconsolidates and particles rearrange.

Analytical prediction for ground movements and liner internal forces induced by shallow tunnels considering non-uniform convergence pattern and ground-liner interaction mechanism

Current studies for tunneling-induced ground movements provide little information on the complex interaction between the tunnel liner and the surrounding soils. In particular, little attention is paid to the internal force analyses for segment liners based on the non-uniform convergence deformation pattern. This paper presents a closed-form analytical solution for the prediction of ground deformation and liner internal forces induced by shallow tunnels in clays. The non-uniform convergence deformation pattern is incorporated as the boundary condition of displacements between the ground and the liner. We investigated the difference between uniform radial and non-uniform convergence deformation patterns on the surface settlements and lateral deformation of soils. In general, good alignment was obtained between the predicted ground deformation caused by the non-uniform convergence model and field observations for tunnels in clays. In addition, the influences of sensitive parameters on the ground movements induced by tunneling were evaluated based on the non-uniform convergence pattern, including the soil and liner properties, the geometric properties of tunnel, the tunnel depth, the excavation gap and other main parameters. Furthermore, these solutions offer a more comprehensive framework for understanding the ground-liner interaction mechanism and the circumferential distribution of internal forces for segment liners. Parametric analyses were used to measure the influences of the lateral earth pressure coefficient on the axial forces and bending moments of tunnel liners. Results are provided on a theoretical basis to estimate the interaction behavior between the tunnel liner and the surrounding soils correctly.

Shaft and base resistance of non-displacement piles in sand

This paper presents the results of three-dimensional, finite element analyses performed with an advanced, two-surface-plasticity, constitutive sand model to investigate the response of non-displacement piles to axial loading. The analysis domain is carefully meshed such that the formation and evolution of shear bands next to the pile shaft and near the pile base can be properly captured. Analyses considering various soil profiles and pile geometries show that the mobilized lateral earth pressure coefficient K along the pile shaft increases with increasing relative density and decreasing initial confining stress. The ultimate unit base resistance is independent of pile diameter, increasing with increasing relative density and increasing initial confining stress at the pile base. Based on the analysis results, design equations are proposed to estimate the limit shaft resistance and ultimate base resistance of non-displacement piles in sandy soil. In proposing these relationships, the pile slenderness ratio is considered. The effect of layer proximity to the base of the pile or pile base embedment in a layer is also considered.

Laboratory investigation on the compressibility of Singapore marine clays

ABSTRACTThe compressibility characteristics of Singapore marine clay in reconstituted and undisturbed states were studied using oedometer, constant rate of strain, Rowe cell, and isotropic consolidation tests. The intrinsic compression curve of the reconstituted clay was found to be similar to that proposed earlier with some minor deviations at low vertical stresses of less than 100 kPa. The field and laboratory compression behaviors were found to be similar, hence the laboratory curve could be used as a reference for interpreting the field behavior. Factors affecting the measurements of compression index and yield stress were discussed. As the coefficient of lateral earth pressure at the top upper clay was close to 1, the compression curves of vertically and horizontally trimmed samples were almost similar. The yield stress was mainly controlled by the strain rate; i.e., the higher strain rate resulted in the higher yield stress. Constrained modulus as derived from cone penetration tests and flat dilatometer tests were also examined and compared with laboratory test results. The in situ tests showed the decrease in constrained modulus with depth and generally the dilatometer test was found to register a higher modulus value.

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.

Prediction of vertical pressure in a trench as influenced by soil arching

A series of model tests was performed to investigate the effect of soil arching on the vertical pressure imposed on the bottom of a trench during backfilling. Soil arching can reduce some portion of the vertical pressure generated by the overburdening soil weight in a trench. To determine theoretically the vertical pressure based on the available formula, two unknown factors must be found: (1) the horizontal stress acting on the trench wall, which is related to the lateral earth pressure coefficient, and (2) the wall friction mobilized between the fill soil and the trench wall. However, appropriately determining those two factors is extremely difficult. Therefore, this paper proposes a novel method using the soil arching coefficient to capture the vertical pressure. The soil arching coefficient is here defined as a constant value that depends on neither the internal friction angle of the backfill soil nor the width of the trench. Qualitative and quantitative tests show good agreement between the vertical pressure predicted by the proposed method and experimental data measured in both laboratory and field tests.

Effects of the lateral stress on the inner frictional resistance of pipe piles driven into sand

The inner frictional resistance of pipe piles depends on the degree of soil plugging. Many factors including pile diameter, lateral stress at the pile tip and geometrical conditions of piles could influence the soil plugging. In this paper, the effects of inner sleeves attached at the pile base on the inner frictional resistance are discussed, particularly highlighting the lateral stresses at the sleeve using small-scale steel pipe piles penetrated into a medium dense sandy ground. A closed-ended pile of the same diameter was also tested to compare it with similar open-ended piles. The results of incremental filling ratio (IFR) and plug length ratio (PLR) were also discussed. A simple method was also proposed to evaluate IFR and PLR for the sleeved piles since they have originally been defined for non-sleeved piles. The results of the IFR indicate that all the piles penetrated under partially-plugged or unplugged state producing smaller penetration resistance than a similar closed-ended pile. The results of the corrected IFR give a better indication of the soil plugging of the sleeved piles, particularly at shallow penetration depths. The results also suggest that the inner frictional resistance increase with the sleeve height. The results of the coefficient of lateral earth pressure, K h also indicate that K h increases with the sleeve height. The effects however become less significant at higher sleeve heights. Therefore, we can recommend the use of the inner sleeve as an improvement method to increase the bearing capacity of open-ended piles installed in sandy grounds.

Numerical Evaluation of Earthquake Settlements of Road Embankments and Mitigation by Preloading

AbstractThis article presents an assessment of the effects of pore water pressure generation of the soil foundation on the seismic road embankment response. Numerical simulations were carried out to study the preloading technique as an improvement method for reducing the liquefaction potential and the induced settlements in a sandy soil profile. The analyses showed that the use of preloading reduces the induced settlements mostly because of the increase in lateral confinement in the superficial soil layers that results from an increase of the coefficient of lateral earth pressure at rest (ko). The research also showed that the efficiency of the countermeasure method was limited to cases in which earthquakes produced a liquefaction zone lower than the depth of the overconsolidated soil.

Experimental study on the coefficient of lateral earth pressure in unsaturated soils

Accurate measurement of lateral earth pressure coefficient, k , is a key step in any geotechnical investigation. Since conventional approaches for obtaining this value leads to high risk of uncertainty in the results, this paper introduces a new experimental approach for measuring the value of k , particularly in unsaturated soils. Details of the new instrument designed for this purpose is provided in the manuscript, which is capable of obtaining k value of unsaturated soils in a range of matrix suction or degree of saturation. Finally, some test results are presented that examine the accuracy of the novel apparatus in order to measure the coefficient of lateral earth pressure in unsaturated soils.

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.

Experimental Investigation on Crushing of Granular Material in One-Dimensional Test

A series of one-dimensional compression tests have been carried out on three kinds of granular materials in a dense state to investigate their mechanical and crushing behaviours. A new testing apparatus that can simultaneously measure the axial and lateral stresses acted on the cylindrical specimen was also developed. Experimental results show that the break-point stress on e – log p curve is the largest for glass beads ballotini. A rise in compression index with the increasing axial load is observed for all three granular materials. The lateral earth pressure coefficient at rest Ko for the three granular materials slightly increases with the increasing axial load and attains a steady value between 0.25 and 0.3 at the initial loading stage. The value for Ko markedly increases as the axial load is removed during the unloading process. The axial strain of Masado is the largest at the same axial load level due to its mineral hardness. Experimental results demonstrate that the crushing degree of granular material is greatly influenced by the loading modes and conditions.

Elastoplastic problem for noncircular openings under Coulomb’s criterion

An elastoplastic problem is considered for elliptical, arched, square and polygonal cross-section openings on the assumption of Coulomb’s limit equilibrium and varied lateral earth pressure coefficients in intact rock mass. The problem is solved using the method of small parameters and the finite element method. The elastoplastic solutions are obtained for mutually influencing underground openings. The mechanisms of concentration of vertical stresses in a pillar established between mutually influencing openings are determined.

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.

Photoelastic Sensors for Determination of Horizontal Stress and Koin 2-Dimensional Granular Assemblies

This paper described the use of photoelasticity and digital image analysis to determine horizontal stress (σh) and to estimate the lateral earth pressure coefficient at rest (Ko) in 2-dimensional particulate assemblies. Square 25.4 by 25.4 mm (1.0 by 1.0 in.) glass plates with 12.7 mm (0.50 in.) circular holes at their centers served as the photoelastic force sensors. Digital image processing and analysis quantified the intensities of the light colors at key locations of high stress concentration in the loaded sensors. The light colors were separated into red, green, and blue (RGB) components. It was shown that the R-intensity was the most sensitive to the applied stress and thus was used to determine the induced stresses. Calibration charts between relative red intensities and applied stress were developed. The calibrated sensors were attached to the sidewalls of the test box so that horizontal stress in 2-dimensional particulate assemblies could be measured. The relative red intensities from the sensors at the sidewalls of the test box were converted to horizontal stress values from which Ko could be estimated. The results showed that quantified intensities of light colors can be used for estimating stress in experimental photoelasticity.

Effect of Overconsolidation on K in Centrifuge Models Using CPT and Tactile Pressure Sensor

Abstract Assessing the state of stress in soil in the free field, as defined by the vertical and lateral earth pressures, is important in some geotechnical problems such as the design of underground structures and estimation of soil liquefaction potential. Unlike the vertical earth pressure, several factors can influence the lateral earth pressure, particularly overconsolidation. This is typically accounted for by relating the coefficient of lateral earth pressure at rest, K0, with the estimated overconsolidation ratio (OCR). The corresponding relations available in the literature are related to the K0 occurring for a given OCR during unloading, and do not take into account the unloading–reloading effect that may be present in centrifuge tests. In this paper, the relationship between the coefficient of lateral earth pressure at rest, K0, and overconsolidation ratio, OCR, is investigated for the whole loading–unloading–reloading condition. Four centrifuge model experiments were conducted on Ottawa F#55 sand. Two of the models were tested using a tactile pressure sensor to measure K0 and the other two models were tested using a miniature cone penetration test (CPT) system. The paper concludes with recommendations for centrifuge operation when testing overconsolidated sand in the centrifuge.