Showing papers on "Lateral earth pressure published in 2011"

Centrifuge model test on the face stability of shallow tunnel

Abstract: This paper is an investigation of face stability on a small-scale tunnel model in a geotechnical centrifuge. By making use of symmetry, half of the tunnel cross section was considered. The support at excavation face was provided by a piston, which was adjusted during flight. Some aspects on the collapse at tunnel face are investigated for different overburden pressures: failure mechanism, surface settlement, stress acting at tunnel face, and the required face support counteracting the earth pressure. Ground deformation was observed through a transparent wall and measured by digital image correlation. The results from centrifuge model tests were compared with theoretical models.

Experimental Analysis of Shear Zone Patterns in Cohesionless for Earth Pressure Problems Using Particle Image Velocimetry

Abstract: The evolution of shear zones in cohesionless sand for earth pressure problem of a retaining wall is experimentally investigated using a non-invasive method called particle image velocimetry. It is an optical technique for measuring surface displacements from successive digital images. Small scale laboratory tests are performed for active and passive cases of a rigid retaining wall subjected to horizontal translation, rotation about its toe and rotation about its top. Attention is focused on the effect of initial sand density on distribution of volumetric and deviatoric strain. The results for initially dense sand are qualitatively compared with corresponding ones obtained with X-rays at Cambridge University.

Some remarks on the coefficient of earth pressure at rest in compacted sandy gravel

Abstract: In compacted coarse-grained materials, the stress state is largely influenced by the compaction procedure and by the characteristics of the single grains (mineralogy, shape). In this work, two compacted sandy gravels with the same grading but different grain properties have been tested in a large soft oedometer to highlight this influence. In the first part of the paper, the effect of oedometric ring deformability on the stress state is quantified in the framework of elastoplasticity. It is then shown that, for the adopted apparatus and for the tests carried out, the error in the measurement of the coefficient of earth pressure at rest K 0 caused by ring deformability is very small. The two tested materials, compacted by wet tamping, behave differently because of their different grain properties, showing, respectively, small and large grain breakage. In primary loading, the more crushable material has values of K 0 that compare well with Jaky’s (J Soc Hungarian Archit Eng 355–358, 1944) equation at any stress level and for every tested soil density. For the material with stronger grains, only very loose specimens that have undergone little or no compaction have a similar behaviour, while the denser specimens show the typical behaviour of overconsolidated soils, with values of K 0 initially larger than that suggested by Jaky (J Soc Hungarian Archit Eng 355–358, 1944) for normally consolidated soils, tending to it only at the largest applied stress values. By considering the complex combined effect of tamping and grain crushing on the stress state and on the overconsolidation ratio of the soil at the end of compaction, these experimental evidences have been qualitatively explained.

Earth pressure measurements on buried HDPE pipe

Abstract: An understanding of the stress distributions that act on buried pipes plays a key role in the development and use of design methods for these structures. The radial stresses that develop on buried flexible pipes have been investigated by a number of researchers through experimental, analytical and numerical methods. However, direct measurements of soil contact stresses acting on small-diameter pipes have not been possible, since commercial earth pressure cells are large, and the stiffness of the cell relative to the soil material is known to influence the measured stresses. A new technique is described for measuring the radial contact stresses acting on buried pipes, and experimental studies are reported that demonstrate the effectiveness of this new technique for measuring contact pressures for both loose and compacted sand backfills. Comparison of the measurements with computations from elastic soil–pipe interaction theory reveals significant discrepancies in the magnitude and distribution of radial pre...

Seismic Passive Earth Pressure Behind Non Vertical Wall with Composite Failure Mechanism: Pseudo-Dynamic Approach

Abstract: This note shows a study on the seismic passive earth pressure behind a non-vertical cantilever retaining wall using pseudo-dynamic approach. A composite failure surface comprising of an arc of the logarithmic spiral near the wall and a straight line in the planar shear zone near the ground, has been considered behind the retaining wall. The effects of soil friction angle, wall inclination, wall friction angle, amplification of vibration, horizontal and vertical earthquake acceleration on the passive earth pressure have been explored in this study. The results available in the literature for passive pressure, on the basis of pseudo-static analysis are found to predict the passive resistance on the conservative side and the assumption of a planar failure surface is found to overestimate the passive resistance for higher wall friction. An attempt has been made in the present study to overcome both the limitations simultaneously. The present results are compared with the existing values in the literature and found a reasonable match among the values.

Coupling mechanism of roof and supporting wall in gob-side entry retaining in fully-mechanized mining with gangue backfilling

Abstract: We analyzed the deformation characteristics of overlying stratum in backfilling with fully-mechanized and retaining roadways along the gob area coal mining technology, and established a mechanical model for the roof key stratum of retaining roadways along gob under the conditions of backfilling and fully-mechanized coal mining technology. Using Winkler elastic foundation theory, we analyzed a part of the key stratum under the action of elastic foundation coupling problem, and derived deflection analytical expressions. Combined with specific conditions, we obtained the deflection curves for the roof key stratum of retaining roadways along gob under the conditions of backfilling and fully-mechanized coal mining technology. On this basis, we adopted the Coulomb’s earth pressure theory to solve the problem of lateral pressure of the gangue filling area on the supporting wall beside the roadway and to provide the theoretical basis for reasonable selection of the distance between gangue concrete wall and roof and further discussion on the supporting stability of roadway.

Passive earth-pressure coefficients by upper-bound numerical limit analysis

Abstract: A three-dimensional (3D) numerical implementation of the limit analysis upper-bound theorem is used to determine passive horizontal earth-pressure coefficients. An extension technique allowing dete...

Prediction and interpretation of the performance of a deep excavation in Berlin sand

Abstract: This paper describes the application of a generalized effective stress soil model, MIT-S1, within a commercial finite-element program, for simulating the performance of the support system for the 20-m-deep excavation of the M1 pit adjacent to the primary station “Hauptbahnhof” in Berlin. The M1 pit was excavated underwater and supported by a perimeter diaphragm wall with a single row of prestressed anchors. Parameters for the soil model were derived from an extensive program of laboratory tests on the local Berlin sands. This calibration process highlights the practical difficulties both in the measurements of critical state soil properties and in the selection of model parameters. The predictions for excavation performance are strongly affected by the vertical profiles of two key state parameters: the initial earth pressure ratio, K0; and the in situ void ratio, e0. These parameters were estimated from field dynamic penetration test data and geological history. The results showed good agreement between c...

Compressive pressure dependent anisotropic effective thermal conductivity of granular beds

Abstract: In situ planetary thermal conductivity measurements are typically made using a long needle-like probe, which measures effective thermal conductivity in the probe’s radial (horizontal) direction. The desired effective vertical thermal conductivity for heat flow calculations is assumed to be the same as the measured effective horizontal thermal conductivity. However, it is known that effective thermal conductivity increases with increasing compressive pressure on granular beds and the horizontal stress in a granular bed under gravity is related to the vertical stress through Jaky’s at rest earth pressure coefficient. The objectives of this study were to examine the validity of the isotropic property assumption and to develop a fundamental understanding of the effective thermal conductivity of a dry, noncohesive granular bed under uniaxial compression. A model was developed to predict the increase in effective vertical and horizontal thermal conductivity with increasing compressive vertical applied pressure. An experiment was developed to simultaneously measure the effective vertical and horizontal thermal conductivities of particle beds with needle probes. Measurements were made as compressive vertical pressure was increased to show the relationship between increasing pressure and effective vertical and horizontal thermal conductivity. The results of this experiment showed quantitatively the conductivity anisotropy for two different materials and validated the developed model. This model can be used to predict the anisotropic effective thermal conductivity of granular materials under uniaxial compressive pressures, and evaluate the uncertainties in lunar heat flow measurements.

Assessment of the Coefficient of Lateral Earth Pressure at Rest (KO) from In Situ Seismic Tests

Abstract: The coefficient of the earth pressure at rest (Ko) is an important soil parameter that influences shear strength, stress-strain behavior, and compressibility characteristics of both cohesive and cohesionless soils. This paper presents a research study in which the Ko values of natural soil deposits are interpreted on the basis of seismic shear wave velocity measurements made at two research sites in Jiangsu province of China. Seismic piezocone penetration tests and cross-hole seismic logging tests were performed at both sites and these results have been used in two existing Ko-shear wave velocity models for prediction of Ko. The predicted Ko at both sites are compared with values determined utilizing Jaky’s formula via laboratory measured strength parameters. Certain variations between predictions and measurements are noted for soils at shallow depths, which are attributed to stress history and desiccation in these layers. Further analysis developed correction factors that accounted for both soil types and overconsolidation ratio effects. These factors can be used with original models for better interpretation of Ko for overconsolidated clays. This approach showed a reasonable match between interpreted Ko properties from both models and those that utilize laboratory test results.

Geotechnical Aspects of the Bangkok MRT Blue Line Project

Abstract: This dissertation is on the geotechnical aspects of the completed Bangkok MRT Blue Line Project and its extension which is currently under design. There were 18 cut and cover subway stations and nearly 22 km of tunnels constructed by the use of earth pressure balanced shield tunnel boring machines. The soil profile model up to depths of 60 to 65 m consists of seven layers: Weathered Crust and Backfill Material; Very Soft to Soft Bangkok Clay; Medium Stiff Clay; Stiff to Hard Clay; Medium Dense to Very Dense Sand; Very Stiff to Hard Clay; and Very Dense Sand. The strength and deformation characteristics of the Bangkok subsoils are determined from laboratory tests (mainly oedometer and triaxial tests) and in-situ field tests (such as vane tests and pressuremeter tests). Additionally, the small strain behaviour is also investigated using Bender element tests in the laboratory and cross hole seismic tests in the field. The soil parameters needed for the deformation analyses are determined for the Mohr Coulomb Model, Soft Soil Model, Hardening Soil Model, and the Hardening Soil Model with Small Strain Stiffness.

Study on dynamic response of saturated soft clay under the subway vibration loading I: instantaneous dynamic response

Abstract: In this paper, the results of the instantaneous dynamic response of saturated soft clay under the subway vibration loading are presented. Based on the assumption of soil as viscoelastic medium, wave equation under forced vibration of three-dimensional anisotropy is derived, and time–space domain semi-analytical solution is given through Laplace and Fourier transform and their inverse transform using MATALB. Taking Shanghai metro line No. 2 for example, the dynamic monitoring is conducted with embedded earth pressure gauges and pore piezometers around the tunnel, and the horizontal response amplitude of dynamic stress of soil around the tunnel is calculated by the method presented in this paper with the laboratory Global Digital System test apparatus to determine the related calculation parameters. Then, a comparative analysis is made between calculation result and continuous field monitored data, and it is found that the attenuation trend of the two cases agree well with each other both in the horizontal and vertical direction, which indicates that the method presented in this study is reasonable.

Reliability-Based Design for External Stability of Narrow Mechanically Stabilized Earth Walls: Calibration from Centrifuge Tests

Abstract: A narrow mechanically stabilized earth (MSE) wall is defined as a MSE wall placed adjacent to an existing stable wall, with a width less than that established in current guidelines. Because of space constraints and interactions with the existing stable wall, various studies have suggested that the mechanics of narrow walls differ from those of conventional walls. This paper presents the reliability-based design (RBD) for external stability (i.e., sliding and overturning) of narrow MSE walls with wall aspects L/H ranging from 0.2 to 0.7. The reduction in earth pressure pertaining to narrow walls is considered by multiplying a reduction factor by the conventional earth pressure. The probability distribution of the reduction factor is calibrated based on Bayesian analysis by using the results of a series of centrifuge tests on narrow walls. The stability against bearing capacity failure and the effect of water pressure within MSE walls are not calibrated in this study because they are not modeled in the cent...

Soil-structure interaction of an earth pressure cell

Abstract: The output from an earth pressure cell (EPC) is usually related to the normal stress in soil through fluid calibration, where a known pressure is applied to the EPC and the output is recorded. However, distribution of normal stress within a soil is not uniform, and the EPC is not an ideal membrane—bending stiffness affects the response. These factors complicate the performance of the EPC. A calibration procedure for an EPC is reviewed, and it is shown that these controversial sensors can provide an accurate measure of average normal stress if calibrated in soil at a given density. In addition, a soil-structure interaction model is proposed to explain why soil calibration is necessary.

Passive earth pressure on embedded vertical plate anchors in sand

Abstract: Passive earth pressure on embedded anchor plates constitutes a viable resisting force for the design of underground structures. In the current practice, these forces are empirically calculated, ignoring the effects of the depth of embedment and the level of consolidation of the surrounding soil, which takes place during plate installation on the in situ stress levels. Accordingly, wide discrepancies between predicted and measured pullout capacities of these plates were reported in the literature. Numerical model was developed using finite-element technique and the constitutive law of Mohr–Coulomb to simulate the case of a retaining wall partially supported by an embedded anchor plate in sand. The results produced in this investigation showed that the passive earth pressure acting on anchor plates increases due to the increase of angle of shearing resistance and the overconsolidation ratio of sand, and it decreases due to an increase of the embedment depth of anchor. Design theories were developed for the case of embedded anchor plate in overconsolidated sand. The theories developed will satisfy the design needed in terms of allowable pullout load and/or displacement.

Experimental observations of the stress regime in unsaturated compacted clay when laterally confined

Abstract: Construction processes often involve reformation of the landscape, which will inevitably encompass compaction of artificially placed soils. A common application of fill materials is their use as backfill in many engineering applications, for example behind a retaining wall. The post-construction behaviour of clay fills is complex with respect to stresses and deformation when the fills become saturated over time. Heavily compacted fills swells significantly more than the lightly compacted fills. This will produce enhanced lateral stresses if the fill is laterally restrained. The work presented in this paper examines how the stress regime in unsaturated clay fills changes with wetting under laterally restrained conditions. Specimens of compacted kaolin, with different initial conditions, were wetted to various values of suction under zero lateral strain at constant net overburden pressure which allowed the concept of K0 (the ratio between the net horizontal stress and the net vertical stress) to be examined...

Location of Failure Plane and Design Considerations for Narrow Geosynthetic Reinforced Soil Wall Systems

Abstract: The design of a Geosynthetic Reinforced Soil (GRS) wall for internal stability against pullout failure requires computing the reinforcement embedment length. Therefore, the location of failure plane is an important input for this design. The current FHWA MSE wall design guidelines assume the location of failure plane based on Rankine theory. While this assumption holds true for conventional walls it is unconservative for GRS walls under constrained spaces, also known as “narrow GRS walls”. This paper presents a limit equilibrium study to accurately locate failure planes within narrow GRS walls. The critical failure planes within narrow GRS walls are searched using Spencer’s method with a function of noncircular failure plane. The predicted results from limit equilibrium analyses are verified by the experimental data from centrifuge tests conducted on narrow GRS walls. The results indicate that the critical failure plane is bilinear: The failure surface being formed partially through the reinforced soil and partially along the interface between the GRS and the stable wall face. The results show the inclination angles of the failure planes for narrow GRS walls being 10~ 20 less than those calculated by Rankine theory. The effect of wall aspect ratio on the inclination angle of the critical failure plane is investigated for the cases studied in this paper. Design considerations against pullout failure for narrow GRS walls are also discussed at end of this paper.

A Refined Formula for the Allowable Soil Pressure Using Shear Wave Velocities

Abstract: Based on a variety of case histories of site investigations, including extensive bore hole data, laboratory testing and geophysical prospecting at more than 550 construction sites, an empirical formulation is proposed for the rapid de- termination of allowable bearing pressure of shallow foundations in soils and rocks. The proposed expression corroborates consistently with the results of the classical theory and is proven to be rapid, and reliable. Plate load tests have been also carried out at three different sites, in order to further confirm the validity of the proposed method. It consists of only two soil parameters, namely, the in situ measured shear wave velocity and the unit weight. The unit weight may be also determined with sufficient accuracy, by means of other empirical expressions proposed, using P or S - wave velocities. It is indicated that once the shear and P-wave velocities are measured in situ by an appropriate geophysical survey, the allowable bearing pressure as well as the coefficient of subgrade reaction and many other elasticity parameters may be determined rapidly and reliably.

Experimental Study of the Earth Pressure Distribution on Cylindrical Shafts

Abstract: This paper describes the results from an experimental program that has been conducted to investigate the distribution of earth pressure on a cylindrical wall embedded in granular material and subjected to radial displacement. The model shaft has been designed and built using mechanically adjustable segments to control the magnitude and uniformity of the wall movement during the tests. A series of experiments have been performed, and the progressive changes in earth pressure along the shaft have been continuously measured for different wall displacements. Results indicated a rapid decrease in lateral earth pressure when a small wall movement was introduced. When the wall movement reached about 2.5% of the shaft radius, the earth pressure distribution along the shaft became uniform and independent of any additional wall displacement. The experimental results are also compared with some of the available theoretical solutions, and the applicability of these solutions is then examined.

Experimental and Numerical Study of At-Rest Lateral Earth Pressure of Overconsolidated Sand

Abstract: The paper presents a one-meter-height rigid facing panel, supported rigidly at the top and bottom to simulate nonyielding retaining wall system. A set of load cells is used to measure the horizontal force at the top and bottom of the facing panel, which is converted to equivalent horizontal earth pressure acting at the back of the wall. Another set of load cells is used to measure the vertical load at the bottom of the wall facing, both at the toe and the heel. Uniformly graded sand was used as backfill soil. The measured wall responses were used to calibrate a numerical model that used to predict additional wall parameters. Results indicated that the measured horizontal earth force is about three times the value calculated by classical at-rest earth pressure theory. In addition, the location of the resultant earth force is located closer to 0.4 H, which is higher compared to the theoretical value of H/3. The numerical model developed was able to predict the earth pressure distribution over the wall height. Test set up, instrumentation, soil properties, different measured responses, and numerical model procedures and results are presented together with the implication of the current results to the practical work.

Laboratory test for EPB tunnelling assessment:results of test campaign on two different granular soils

Abstract: Earth Pressure Balanced shields are currently the most utilized tunnelling machines throughout around the world. The possibility of using conditioning agents that change the mechanical and hydraulic behaviour of a soil, changing it into a plastic paste and thus permitting soil pressure applications at the tunnel face, is the key point to explain the increasing utilization of this technology. Despite its great importance, not much laboratory researches can be registered on soil conditioning, particularly for cohesionless soils. The conditioning criterion is usually defined on the basis of a trial-and-error procedure developed directly at the job sites. A test that is able to simulate the extraction of soil from the bulk chamber with the screw conveyor inclined upwards, as in real machines, can offer a quantitative indication of the conditioned soil behavior for EPB use. The characteristics of the device and the results obtained on many different types of soil are discussed in order to point out the great importance and quality of results that can be achieved using the proposed test device