Showing papers on "Lateral earth pressure published in 2006"

Numerical Model for Reinforced Soil Segmental Walls under Surcharge Loading

Abstract: The construction and surcharge loading response of four full-scale reinforced-soil segmental retaining walls is simulated using the program FLAC. The numerical model implementation is described and constitutive models for the component materials (i.e., modular block facing units, backfill, and four different reinforcement materials) are presented. The influence of backfill compaction and reinforcement type on end-of-construction and surcharge loading response is investigated. Predicted response features of each test wall are compared against measured boundary loads, wall displacements, and reinforcement strain values. Physical test measurements are unique in the literature because they include a careful estimate of the reliability of measured data. Predictions capture important qualitative features of each of the four walls and in many instances the quantitative predictions are within measurement accuracy. Where predictions are poor, explanations are provided. The comprehensive and high quality physical data reported in this paper and the lessons learned by the writers are of value to researchers engaged in the development of numerical models to extend the limited available database of physical data for reinforced soil wall response.

Pseudo-dynamic approach of seismic active earth pressure behind retaining wall

Abstract: Knowledge of seismic active earth pressure behind rigid retaining wall is very important in the design of retaining wall in earthquake prone region. Commonly used Mononobe-Okabe method considers pseudo-static approach, which gives the linear distribution of seismic earth pressure in an approximate way. In this paper, the pseudo-dynamic method is used to compute the distribution of seismic active earth pressure on a rigid retaining wall supporting cohesionless backfill in more realistic manner by considering time and phase difference within the backfill. Planar rupture surface is considered in the analysis. Effects of a wide range of parameters like wall friction angle, soil friction angle, shear wave velocity, primary wave velocity and horizontal and vertical seismic accelerations on seismic active earth pressure have been studied. Results are provided in tabular and graphical non-dimensional form with a comparison to pseudo-static method to highlight the realistic non-linearity of seismic active earth pressures distribution.

Deep Excavation: Theory and Practice

Abstract: Introduction Soil Properties and Lateral Earth Pressures Excavation Methods and Supporting System Lateral Earth Pressure Stability Analysis Stress and Deformation Analysis - Simplified Method Stress and Deformation Analysis - Beam on Elastic Foundation Method Stress and Deformation Analysis - Finite Element Method Dewatering of Excavations Design of Structural Components Excavation and Protection of Adjacent Buildings Monitoring System

Cyclic Lateral Load Behavior of a Pile Cap and Backfill

Abstract: A series of static cyclic lateral load tests were performed on a full-scale 4×3 pile group driven into a cohesive soil profile. Twelve 324-mm steel pipe piles were attached to a concrete pile cap 5.18×3.05 m in plan and 1.12 m in height. Pile–soil–pile interaction and passive earth pressure provided lateral resistance. Seven lateral load tests were conducted in total; four tests with backfill compacted in front of the pile cap; two tests without backfill; and one test with a narrow trench between the pile cap and backfill soil. The formation of gaps around the piles at larger deflections reduced the pile–soil–pile interaction resulting in a degraded linear load versus deflection response that was very similar for the two tests without backfill and the trenched test. A typical nonlinear backbone curve was observed for the backfill tests. However, for deflections greater than 5 mm, the load-deflection behavior significantly changed from a concave down shape for the first cycle to a concave up shape for the ...

Introductory Geotechnical Engineering: An Environmental Perspective

Abstract: 1. Introduction 2. Nature of Soil and Rock 3. Granular Soil, Cohesive Soil and Clay Minerals 4. Soil-Water Interaction in the Environment 5. Hydraulic Conduction Phenomena 6. Thermal and Electrical Properties of Soils 7. Soil Compaction (Densification) 8. Cracking-Fracture-Tensile Behavior of Soils 9. Consolidation, Stress Distribution and Settlement 10. Stress-Strain-Strength of Soil 11. Dynamic Properties of Soil 12. Bearing Capacity of Shallow Foundation 13. Lateral Earth Pressures 14. Earth Slope Stability and Landslides 15. Fundamentals of Ground Improvement Systems 16. Selected Environmental Geotechnology Problems

Mechanics of tunnelling machine screw conveyors: model tests

Abstract: Control of the excavation process of an earth pressure balance (EPB) tunnelling machine depends on control of the soil flow through the screw conveyor. An instrumented 1:10 scale model screw conveyor was designed and commissioned, and tests were performed with consolidated kaolin and compacted London Clay and Lambeth Group samples pre-conditioned with soil conditioning agents commonly used in EPB tunnelling machines. During steady-state operation, the measured shear stress acting on the conveyor casing was found to be constant along the conveyor, leading to a linear total pressure gradient. The casing shear stress was approximately equal to the un-drained shear strength of the soil, and the screw torque increased linearly with the casing shear stress. Effects of varying sample strengths, screw speeds, screw geometry and the discharge outlet restriction on the total pressure gradient, casing shear stress, and screw torque are illustrated by the test results. The tests provide new insight into the behaviour...

Pile Behavior Due to Excavation-Induced Soil Movement in Clay. I: Stable Wall

Abstract: A series of centrifuge model tests has been conducted to investigate the behavior of a single pile subjected to excavation-induced soil movements behind a stable retaining wall in clay. The results reveal that after the completion of soil excavation, the wall and the soil continue to move and such movement induces further bending moment and deflection on an adjacent pile. For a pile located within 3 m behind the wall where the soil experiences large shear strain (>2%) due to stress relief as a result of the excavation, the induced pile bending moment and deflection reach their maximum values sometime after soil excavation and thereafter decrease slightly with time. For a pile located 3 m beyond the wall, the induced pile bending moment and deflection continue to increase slightly with time after excavation until the end of the test. A numerical model developed at the National University of Singapore is used to back-analyze the centrifuge test data. The method gives a reasonably good prediction of the induced bending moment and deflection on a pile located at 3 m or beyond the wall. For a pile located at 1 m behind the wall where the soil experiences large shear strain (>2%) due to stress relief resulting from the excavation, the calculated pile response is in good agreement with the measured data if the correct soil shear strength obtained from postexcavation is used in the analysis. However, if the original soil shear strength prior to excavation is used in the analysis, this leads to an overestimation of the maximum bending moment of about 25%. The practical implications of the findings are also discussed in this paper.

Passive Earth Pressure Mobilization during Cyclic Loading

Abstract: The passive resistance measured in a series of full-scale tests on a pile cap is compared with existing theories. Four different soils were selected as backfill in front of the pile cap and the load-deflection relationships under cyclic loading were investigated. The log spiral theory provided the best agreement with the measured passive resistance. The Rankine theory significantly underestimated the passive force, while the Coulomb theory generally overestimated the resistance. The displacement necessary to mobilize the maximum passive force was compared with previous model and full-scale tests and ranged from 3.0 to 5.2% of the cap height. A hyperbolic model provided the best agreement with the measured backbone passive resistance curve compared with recommendations given by Caltrans and the U.S. Navy. However, this model overestimated the passive resistance for cyclic loading conditions due to the formation of a gap between the pile cap and backfill soil and backfill stiffness reduction. Based on the test results, the cyclic-hyperbolic model is developed to define load-deflection relationships for both virgin and cyclic loading conditions with the presence of a gap.

Liquefaction around Pipelines under Waves

Abstract: This paper presents the results of an experimental study on liquefaction around a pipeline buried in a soil exposed to a progressive wave. The soil used in the experiments was silt with d50=0.045 mm. The pore-water pressure was measured in the far field and on the pipe simultaneously. The tests indicate that the buildup of pore pressure and the resulting liquefaction in the soil are influenced by the presence of the pipe. The pore pressure builds up much more rapidly at the bottom of the pipe than in the far field at the same level as the pipe bottom. By contrast, the buildup of pore pressure at the top of the pipe is not influenced radically by the presence of the pipe. The tests further indicate that as the liquefaction initially occurs in the very top layer and develops downwards, this picture changes in the vicinity of the pipe; in the latter case, the liquefaction initially occurs at the bottom of the pipe, and develops along the perimeter of the pipe upwards. The influence of the "no-slip" condition at the pipe surface on the end results has been investigated and found very significant. The influence of the wave height, the influence of the pipe diameter, the influence of the no-liquefaction-regime conditions, and the influence of a sinking pipe have also been investigated.

Pile Behavior Due to Excavation-Induced Soil Movement in Clay. II: Collapsed Wall

Abstract: A series of centrifuge model tests has been conducted to investigate the behavior of a single pile behind a retaining wall that eventually fails due to soil excavation in front of the wall. All the piles are located at 3 m behind the wall where the soil experiences large shear strain (>2%). The induced bending moment and deflection on the pile as well as the soil and wall movements are monitored at regular intervals throughout the tests. It is found that the pile performance depends greatly on the degree of wall instability. After a critical excavation depth, active wedge slip plane and tension cracks developed in the vicinity of the pile. The limiting soil pressure profile deduced from the measured maximum induced pile bending moment profile is established to be much lower than that of a conventional laterally loaded pile. Using the measured soil movements at the pile location as the input data, the calculated pile bending moment obtained using an existing numerical model generally show fair agreement with the measured values when the back-analyzed limiting soil pressures acting on the pile are employed in the back-analysis. The practical implications of the findings are discussed in the paper.

New Approach for Estimation of Static and Seismic Active Earth Pressure

Abstract: To estimate static and seismic active earth pressure (Pad) on a rigid retaining wall, numerical analyses using different step sizes have been carried out in this paper, based on the modified Culmann line method by considering Coulomb’s planar rupture surface. Equivalent pseudo-static seismic forces are considered in the analysis. A new concept of modified unit weight by considering ground surcharge is introduced under static and seismic conditions. By numerical analysis, area of soil (A) has been estimated to obtain the ratio of A/A0 where A0 is θh2, θ is the angle between retaining structure and ground surface and h is the vertical height of the wall. This ratio remains constant for a particular type of soil and has been used to estimate the maximum active earth pressure using force diagram. Results are provided in tabular form for easy calculation of the coefficient of static and seismic active earth pressure. Present results by considering the new technique, compares well with the results obtained by earlier researchers.

Estimation of maximum mud pressure in purely cohesive material during directional drilling

Abstract: Directional drilling requires the use of drilling mud to stabilize the borehole and return cuttings to the ground surface. High mud pressure can result in mud loss, ground heave, damage to buried infrastructure, and other serious problems as a result of either hydrofracture or blowout of the soil surrounding the borehole. First, past research on two ground failure mechanisms is reviewed. A new approach is introduced to estimate maximum mud pressure using a cavity expansion solution, where the non-unit lateral earth pressure coefficient at rest (K 0) is explicitly considered. Finite-element analyses demonstrate that the new approach provides effective estimates of the extent of the plastic zone around the borehole under different geostatic stress conditions. Control of mud pressures to prevent the zone of shear failure extending more than halfway to the ground surface produces a reserve capacity of 20–30% against blowout. An examination of hydrofracture versus blowout indicates that blowout is the most lik...

Passive and active earth pressures in the presence of groundwater flow

Abstract: This paper deals with the effect of seepage flow on the lateral earth pressures acting on deep sheeted excavations in cohesionless soil. The computation of the passive and active earth pressures in the presence of hydraulic gradients is performed using the explicit finite difference method implemented in Fast Lagrangian Analysis of Continua (FLAC) code. The available effective passive earth pressure coefficients in the presence of upward seepage forces are given for both associative and non-associative material. The present solutions show that the soil dilation angle influences the effective passive earth pressures for large internal friction angle values of the soil. They also show that the effective passive pressures diminish with the hydraulic head loss. Good agreement is observed between the present results and those using an upper-bound approach in limit analysis for an associative material. For the active case, the effect of downward seepage forces on the active earth pressures is investigated. The ...

Influence of Torque on Lateral Capacity of Drilled Shafts in Sands

Abstract: As a result of recent changes in the requirements involving hurricane extreme events (e.g., wind velocities), the Florida Department of Transportation has moved away from cable-stayed signs, signals, and lights systems to mast arm/pole structures. Unfortunately, the newer systems develop significant lateral and torque loading on their foundations (e.g., drilled shafts). Current design practice for a mast arm/pole foundation is to treat lateral loading and torsion separately (i.e., uncoupled); however, recent field-testing suggests otherwise. This paper reports on the results of 91 centrifuge tests. 54 of the tests were conducted in dry sand and 37, in saturated sands. The tests varied the lateral load to torque ratios, shaft embedment depths, and soil strengths. The experiments revealed that even though the torsional resistances of the shafts were not influenced by lateral load, the shafts' lateral resistance was significantly impacted by torsion. Reductions in lateral resistance of 50% were recorded for shafts under high torque to lateral load ratios. Using the free earth support assumption and the ultimate soil pressure the soil pressure distribution along the shaft was developed. Using force and moment equilibrium, as well as the applied torque, maximum shear, and moments were computed. The predicted values were found to be within 25% (10% on average, except for the tests in saturated dense sand with polymer slurry) of the experimental results.

Back-calculating vibro-installation stresses in stone-column-reinforced soils

Abstract: An investigation was carried out to study the effect of the vibro-installation of stone columns on the soil state of stress. Post-installation soil parameters and load-settlement records were utilised to back-calculate the ratio of horizontal to vertical soil stress, K*. The load-settlement records were taken from a full-scale field load test, carried out on a single column within an extended group of stone columns. A coupled non-linear finite element formulation was utilised to simulate the test steps and the relevant settlement rate criterion. Post-installation soil parameters were adopted in the simulation in order to account for any vibration- and/or displacement-induced changes in the soil properties. The investigation revealed that the vibro-installation of stone columns significantly alters the soil state of stress. A practical range for the post-installation lateral earth pressure ratio, K*, in the analysed case was deduced. Nous avons etudie les effets de la vibro-installation de colonnes de pier...

A Coulomb-type solution for active earth thrust with seepage

Abstract: A Coulomb-type general solution for active earth pressure on the vertical face of a retaining wall with a drainage system along the soil–structure interface is presented. The soil is cohesionless and fully saturated to the ground horizontal surface. This condition may happen during heavy rainfall and is the most critical, when the active pressure reaches its peak value. In order to solve the problem, a theoretical, closed-form solution for the water seepage through the soil is first developed. This is used in a Coulomb-type formulation, which supposes a plane failure surface inside the backfill when the wall movement is enough to put the soil mass in the active state. The formulation provides Coulomb-like coefficients of active pressure, which solve the problem in a generic way. Comparison with published results obtained by hand calculation shows very good agreement. A table with values of the coefficients of active earth pressure with seepage calculated for selected values of the soil internal friction a...

Soil failure models for vertically operating and horizontally operating strength sensors

Abstract: Soil strength, or mechanical resistance of a soil to failure, has been widely used to estimate the degree of soil compaction. Conventional measurements with cone penetrometers are laborious; therefore, an on-the-go soil strength profile sensor that collects data dense enough to show the spatial within-field variability in soil strength would be a desirable alternative. Because soil failure involves complex interactions among many variables, determining design parameters of a soil strength sensor and interpreting test results could be improved with a theoretical understanding of the soil failure process. Mathematical models to estimate the force required to penetrate (cut and displace) soil with a prismatic cutter traveling horizontally and with a cone penetrometer traveling vertically were developed based on the passive earth pressure theory and the concept of a variable failure boundary. Both models were expressed as additive forms of density, cohesion, and adhesion components of the soil, with each effect multiplied by a corresponding dimensionless number. Charts of dimensionless numbers were developed to investigate the behavior of each strength component at various values of soil internal friction angle, soil-metal friction angle, and tool cutting angle. The models were used in simulation to optimize design parameters of the sensor, including component dimensions and the location and spacing of sensing elements. Based on this optimization, a prismatic sensing tip with a 3.61 cm2 base area and a 60° cutting angle was selected, and the corresponding simulated maximum force and strength measurements were 2.2 kN and 6.0 MPa when operating at speeds up to 5 m s-1. Model validation showed that the extension of the failure boundary was significantly correlated with soil properties such as bulk density, water content, and internal friction angle. The variable failure boundary model developed in this study more consistently and accurately represented field data than did three previously developed modeling approaches.

Performance of a Cantilever Retaining Wall

Abstract: Earth pressure cells, tiltmeters, strain gauges, inclinometer casings, and survey reflectors were installed during construction of a reinforced concrete cantilever retaining wall. A data acquisition system with remote access monitored some 60 sensors on a continual basis. Analyses of the data indicated development of the active condition after translation of about 0.1% of the backfill height. The wall rotated into the backfill as a rigid body, but the top of the stem deflected away from the backfill, approximately equal in magnitude and opposite in direction to the displacement from rigid body rotation. Loading on the wall back-calculated from strain gauge readings was consistent with active earth pressure. The maximum lateral force, about the same as the design value, occurred during compaction of the backfill. Observations that differed from standard assumptions included the passive earth pressure in front of the shear key being less than 10% of the design value and vertical stress below the heel being greater than the toe. Compaction-induced lateral stresses on the stem were sometimes twice the vertical stress.

Soil Restraint to Oblique Movement of Buried Pipes in Dense Sand

Abstract: The soil restraints to oblique movement of buried pipes in dense sand were investigated. Model pipes 0.61 m long with diameters of 152.4, 228.6, and 304.8 mm were obliquely moved from an axial-longitudinal to a lateral-transversal direction in a large scale drag box to study the associated longitudinal and transverse soil restraints on the pipes in the shallow buried depth. All the experimental results indicated that the longitudinal soil restraint to the axial movement of the pipes could be estimated as the product of the average of the vertical and horizontal earth pressures at the centerline of the pipe and the tangent value of the soil-pipe friction angle. For the lateral movement pipes, three different theoretical methods were used to analyze the transverse soil restraint. Among these, the modified Meyerhof approach with the assumption of a rupture surface of logarithmic spiral arc was closer to the experimental results compared to the planar sliding surface approach. For the oblique movement pipes, the longitudinal soil restraint decreases, whereas the transverse soil restraint increases with increasing oblique angle. Moreover, the longitudinal and transverse soil restraint of the oblique angle pipes could be obtained by multiplying the corresponding cosine and sine values of the oblique angle with the associated longitudinal soil restraint of the axial pipe and the transverse soil restraint of the lateral pipe, respectively. The findings also indicate that the scale effects are minor for sizes up to 304.8 mm of the pipe diameter tested herein.

Analysis and Design of Retaining Wall having Reinforced Cohesive Frictional Backfill

Abstract: The case of a rigid wall with inclined back face retaining reinforced cohesive-frictional backfill subjected to uniformly distributed surcharge load has been analyzed using limit equilibrium approach. The analysis considers the stability of an element of the failure wedge, which is assumed to develop in the reinforced earth mass adjoining the back face of wall. The non-dimensional charts have been developed for computing the lateral earth pressure on wall and the height of its point of application above the base of wall. The theoretical findings have been verified by model tests on a rigid wall retaining a dry cohesive-frictional soil reinforced by geogrid strips. Experimental results are in good agreement with the theoretical predictions. A design example has been included to illustrate the design procedure.

Three-Dimensional Nonlinear Finite-Element Soil-Abutment Structure Interaction Model for Skewed Bridges

Abstract: Seismic design of bridges is based on a displacement-performance philosophy This type of bridge design requires that the geotechnical engineer provide abutment-embankment soil springs which are inherently nonlinear To date, a number of experiments have been performed to determine the nonlinear lateral force-displacement capacity of ordinary non-skewed bridge abutments, pile caps and walls Typical highway bridges are wide so that the abutment walls are much wider than they are tall Therefore, the nonlinear abutment backfill response behind a wide non-skewed abutment wall is essentially a two-dimensional plane-strain earth pressure problem However, the estimation of the lateral force-displacement capacity behind a skewed abutment wall is a three dimensional problem that involves bridge deck rotation during dynamic loading The capacity is developed from passive wedge failure in the soil mass which occurs when the frictional resistance along the bottom and the two sides of the wedge are mobilized The mobilized passive resistance is dependent on the bridge displacement, bridge geometry (bridge skew angle, deck width and height), the soil stress-strain properties of the abutment backfill, and ground motion characteristics In common abutment design practice, the abutment load-deformation relationship due to passive resistance is based on load test data or presumptive values where the wall is pushed normal to the soil However, the passive resistance and stiffness for the skewed wall is expected to be smaller than for the ordinary non-skewed abutment wall due to the bridge rotation A three-dimensional model is required to capture the geometry and capacity of the full passive soil wedge behind the skewed abutments walls The objective of this paper is to develop three-dimensional nonlinear finite-element models to estimate soil capacities behind a non-skewed and a skewed abutment wall as a function of wall displacement The predicted force-displacement capacities will be compared with the results obtained from a field load-deformation test of a wall pushed into typical structure backfill The nonlinear force-displacement relationship of the abutments can be used to evaluate the seismic performance of skewed highway bridges

Numerical analysis of passive earth pressures with interfaces

Abstract: Elasto-plastic analysis for classical lateral earth pressures is presented in this paper by applying the explicit finite difference method using FLAC. The numerical model presented here consists of a rigid elastic structure for the gravity wall, a zero thickness interface for modelling the sliding and separation, and a Mohr-Coulomb soil model for the backfill. The rigid wall was pushed into the backfill soil to induce passive failure and the ultimate load required for the failure is calculated. Numerical results are compared with other available solutions and a number of modelling issues in creating an accurate model are discussed. It is hoped that, through these experience learnt, some numerical pitfalls can be avoided by practicing engineers in their future analysis.

Lateral Earth Pressure due to Backfill Subject to a Strip of Surcharge

Abstract: The evaluation of the active earth thrust of backfill, on which a surcharge strip acts, is generally made using a hybrid approach where a thrust increment due to the surcharge strip is calculated using elasticity theory and added to the thrust calculated in absence of the surcharge strip and in failure condition of the thrust wedge. This paper gives a coherent solution to the problem, based entirely on Coulomb’s approach. It presents the analytical solution of the active thrust and of the position of the application point of the thrust.

The influence of the construction process on the deformation behaviour of diaphragm walls in soft clayey ground

Abstract: Conventional numerical predictions of deep excavations normally neglect the construction process of the retaining structure and choose the earth pressure at rest as initial condition at the beginning of the simulation. The presented results of simulation and measurements during the construction process of the Taipei National Enterprise Center show, that such an assumption leads to an underestimation of the horizontal wall deflection, the surface ground settlements as well as the loading of the struts in case of normally to slightly over-consolidated clayey soil deposits. The stepwise installation process of the individual diaphragm wall panels results in a substantial modification of the lateral effective stresses in the adjacent ground. Especially the pouring process of the panel and the fresh concrete pressure causes a partial mobilization of the passive earth pressure and a distinct stress level increase in the upper half of the wall. As a consequence of the increased stresses prior to the pit excavation, up to 15% greater ground and wall movements are predicted. Moreover, the increased stress level due to the installation process of the diaphragm wall leads to substantial higher strut loadings during the excavation of the pit. Copyright © 2006 John Wiley & Sons, Ltd.

Dynamic active earth pressure on retaining structures

Abstract: Earth-retaining structures constitute an important topic of research in civil engineering, more so under earthquake conditions. For the analysis and design of retaining walls in earthquake-prone zones, accurate estimation of dynamic earth pressures is very important. Conventional methods either use pseudo-static approaches of analysis even for dynamic cases or a simple single-degree of freedom model for the retaining wall-soil system. In this paper, a simplified two-degree of freedom mass-spring-dashpot (2-DOF) dynamic model has been proposed to estimate the active earth pressure at the back of the retaining walls for translation modes of wall movement under seismic conditions. The horizontal zone of influence on dynamic earth force on the wall is estimated. Results in terms of displacement, velocity and acceleration-time history are presented for some typical cases, which show the final movement of the wall in terms of wall height, which is required for the design. The non-dimensional design chart proposed in the present study can be used to compute the total dynamic earth force on the wall under different input ground motion and backfill conditions. Finally, the results obtained have been compared with those of the available Scott model and the merits of the present results have been discussed.