Showing papers on "Lateral earth pressure published in 2014"

A New Pseudo-dynamic Approach for Seismic Active Soil Thrust

Abstract: A critical review of the existing pseudo-dynamic approach is provided and a new pseudo-dynamic approach is proposed based on a visco-elastic behavior of backfill overlying rigid bedrock subjected to harmonic horizontal acceleration. Considering a planar failure surface, closed form expressions for seismic active soil thrust, soil pressure distribution and overturning moment are obtained. The results of this study indicate that the existing pseudo-dynamic method can strongly underestimate the soil active thrust especially close to the fundamental frequency of the backfill, where the soil response is more sensitive to the damping ratio. The acting point of the total seismic active thrust is always found to be higher than that predicted by the traditional pseudo-dynamic approach. The effect of the shear resistance angle and wall friction angle on the acting point increases as the amplitude of the base acceleration increases, whereas their effect is generally small far from the natural frequencies of the backfill.

Impact of Cohesion on Seismic Design of Geosynthetic-Reinforced Earth Structures

Abstract: This paper calculates the thrust of lateral earth pressures exerted by unstable slopes comprised of c-ϕ soil and subjected to seismic (pseudostatic) loading conditions. Although the proposed method can be used for seismic stability analysis of geosynthetic-reinforced earth structures (GRESs), the formulation and results are also applicable to many other relevant earth retention systems. To study the impact of cohesion, the authors develop formulations to determine the seismic active earth pressure coefficient for c-ϕ soils resulting in a closed-form solution. The pseudostatic formulation considers the effect of tensile cracks, backslope inclination, and batter while assuming a log spiral failure surface. Two formulas are presented. One is for the conventional inclination of thrust. The second formulation considers a more feasible inclination of the thrust when it is likely to act against facing units with large setbacks constructed for large batter walls. The authors perform parametric studies and...

Lower-Bound Limit Analysis of Seismic Passive Earth Pressure on Rigid Walls

Abstract: Static and seismic passive earth pressure coefficients for the general case of an inclined wall and a sloping cohesionless backfill were computed by using finite-element lower-bound limit analysis based on second-order cone programming (SOCP). The comparison with the best existing upper-bound solution and the widely accepted solution obtained by the method of stress characteristics has shown that the present lower-bound solutions can provide a safe estimate of the passive earth pressures. Therefore, combining present results and upper-bound solutions can bracket the true value of passive earth pressures. In addition, design tables are presented that allow geotechnical engineers to easily use the present results in practice.

Discrete Element and Experimental Investigations of the Earth Pressure Distribution on Cylindrical Shafts

Abstract: Experimental and numerical studies have been conducted to investigate the earth pressure distribution on cylindrical shafts in soft ground. A small-scale laboratory setup that involves a mechanically adjustable lining installed in granular material under an axisymmetric condition is first described. The earth pressure acting on the shaft and the surface displacements are measured for different induced wall movements. Numerical modeling is then performed using the discrete element method to allow for the simulation of a large soil displacement and particle rearrangement near the shaft wall. The experimental and numerical results are summarized and compared against previously published theoretical solutions. The shaft-soil interaction is discussed, and conclusions regarding soil failure and the earth pressure distributions in both the radial and circumferential directions are presented.

Lateral Earth Pressure behind Walls Rotating about Base considering Arching Effects

Abstract: In field, the earth pressure on a retaining wall is the common effect of kinds of factors To figure out how key factors act, it has taken into account the arching effects together with the contribution from the mode of displacement of a wall to calculate earth pressure in the proposed method Based on Mohr circle, a conversion factor is introduced to determine the shear stresses between artificial slices in soil mass In the light of this basis, a modified differential slices solution is presented for calculation of active earth pressure on a retaining wall Comparisons show that the result of proposed method is identical to observations from model tests in prediction of lateral pressures for walls rotating about the base

Lateral Earth Pressures Acting on Circular Retaining Walls

Abstract: The slip line method has been extended to consider the tangential stress and arbitrary magnitude of wall movement An analytical solution has also been proposed for the arbitrary mode of wall movement, and the soil mass behind the wall can be homogeneous or layered The mobilized internal friction angle of the soil and the soil-wall interface friction angle change with the movement of the wall; this has been widely accepted However, the development of them is not simultaneous The mobilized friction angles are used in the slip line method and the simplified slip line method to yield the nonlimit lateral earth pressure Results indicate that earth pressure decreases exponentially with increasing wall movement Comparisons of the calculated results with measured data and FEM results show that the present analytical method can provide good prediction of the lateral earth pressures and the limit wall movement equal to 03%H is appropriate in the calculation (where H is the excavation depth)

Simplified Method for Calculating Active Earth Pressure on Rigid Retaining Walls Considering the Arching Effect under Translational Mode

Abstract: Based on the limit-equilibrium concept, a new method for calculating the active earth pressure acting on a rigid retaining wall that moves horizontally away from soil mass is proposed. Using this method, the trajectory of the minor principal stress resulting from the soil arching effect in retained soil mass is considered, and the arc-shaped axis of the minor principal stress is approximated to a linear axis using the improved horizontal flat-element method. The effects of soil’s internal frictional angle, its unit weight, the wall–soil friction angle relative to the active earth pressure, and the point of application of the resultant active earth pressure are investigated. Finally, the proposed method is applied to two existing tests for rigid retaining walls with different heights. A comparison of the predicted and measured values shows that the proposed method yields satisfactory results.

Some remarks on the seismic behaviour of embedded cantilevered retaining walls

Abstract: This paper is a numerical investigation of the physical phenomena that control the dynamic behaviour of embedded cantilevered retaining walls. Recent experimental observations obtained from centrifuge tests have shown that embedded cantilevered retaining walls experience permanent displacements even before the acceleration reaches its critical value, corresponding to full mobilisation of the soil strength. The motivation for this work stems from the need to incorporate these observations in simplified design procedures. A parametric study was carried out on a pair of embedded cantilevered walls in dry sand, subjected to real earthquakes scaled at different values of the maximum acceleration. The results of these analyses indicate that, for the geotechnical design of the wall, the equivalent acceleration to be used in pseudo-static calculations can be related to the maximum displacement that the structure can sustain, and can be larger than the maximum acceleration expected at the site. For the structural ...

Distinct simulation of earth pressure against a rigid retaining wall considering inter-particle rolling resistance in sandy backfill

Abstract: The focus of this paper is to analyze earth pres- sure against a rigid retaining wall under various wall move- ment modes with a contact model considering inter-particle rolling resistance implemented into the distinct element method (DEM). Firstly, a contact model considering rolling resistance in particles was generally explained and imple- mented into the DEM. The parameters of the contact model are determined from DEM simulation of biaxial tests on a sandy specimen. Then, the influence of inter-particle rolling resistance in the backfill is discussed by comparing the active and passive earth pressure against a rigid wall subjected to a translational displacement with and without inter-particle rolling resistance in the material. Third, the DEM model con- sidering the rolling resistance is used to investigate active and passive earth pressures while the rigid wall moves in a more general manner such as rotation or translation. The influence of rolling resistance on the earth pressures is examined from the microscopic particle scale (e.g., shear strain field) as well as the macroscopic scale (e.g., the magnitude and action point of resultant earth pressures). Finally, the effect of the initial density and the particle size of the backfill are discussed. The results show that when rolling resistance in the particles is taken into account in the DEM simulation, the simulation results are more appropriate and are in line with practical

Seismic behavior of an inverted T-shape flexible retaining wall via dynamic centrifuge tests

Abstract: In the design procedure for a retaining wall, the pseudo-static method has been widely used and dynamic earth pressure is calculated by the Mononobe–Okabe method, which is an extension of Coulomb’s earth pressure theory computed by force equilibrium However, there is no clear empirical basis for treating the seismic force as a static force, and recent experimental research has shown that the Mononobe–Okabe method is quite conservative, and there exists a discrepancy between the assumed conditions and real seismic behavior during an earthquake Two dynamic centrifuge tests were designed and conducted to reexamine the Mononobe–Okabe method and to evaluate the seismic lateral earth pressure on an inverted T-shape flexible retaining wall with a dry medium sand backfill Results from two sets of dynamic centrifuge experiments show that inertial force has a significant impact on the seismic behavior on the flexible retaining wall The dynamic earth pressure at the time of maximum moment during the earthquake was not synchronized and almost zero The relationship between the back-calculated dynamic earth pressure coefficient at the time of maximum dynamic wall moment and the peak ground acceleration obtained from the wall base peak ground acceleration indicates that the seismic earth pressure on flexible cantilever retaining walls can be neglected at accelerations below 04 g These results suggest that a wall designed with a static factor of safety should be able to resist seismic loads up to 03–04 g

Response of a pile group behind quay wall to liquefaction-induced lateral spreading: a shake-table investigation

Abstract: The response of pile foundations near a quay wall under liquefaction-induced lateral spreading remains a complex problem. This study presents the results of a shake-table test on a 2×2 pile group behind a sheet-pile quay wall that was subjected to lateral spreading. The quay wall was employed to trigger liquefaction-induced large lateral ground deformation. The discussions focus on the behavior of the pile and the soil and on the bending moment distributions within the group pile and the restoring force characteristics at the superstructure. Overall, the piles exhibited apparent pinning effects that reduced soil deformation. In addition, the rear-row piles near the quay wall experienced larger bending moments than did the front-row piles, indicating significant pile group effects. The tests showed that lateral spreading could be a primary cause of larger monotonic deformations and bending moments. It can also be concluded that the monotonic bending moments were significantly decreased due to the presence of slow soil flow. The stiffness at the superstructure was reduced because of accumulated excess pore pressure before liquefaction, and it was recovered during lateral spreading. The present study further enhances current understanding of the behavior of low-cap pile foundations under lateral spreading.

Tactile pressure sensors in centrifuge testing

Abstract: Assessing vertical and lateral earth pressure is important in geotechnical and foundation engineering. Vertical stresses are easy to calculate assuming a geostatic stress condition. However, characterizing the lateral earth pressure is primarily based on judgment and empirical correlations that assume a lateral earth pressure coefficient based on the shear strength parameters of the soil. Effects of factors such as overconsolidation, geologic age, and pre-shaking on the lateral earth pressure magnitude and distribution are difficult to assess using only the empirical correlations found in literature. Direct measurements of the lateral earth pressure in the field, full-scale, and centrifuge models are required to fully characterize these factors. This paper discusses the use of grid-based tactile pressure sensors in centrifuge models to study the effects of overconsolidation and pre-shaking on the lateral earth pressure. A new preparation and calibration procedure for the tactile sensors is discussed in detail. A series of five centrifuge tests were performed using dry and saturated sand in normally consolidated, overconsolidated, and pre-shaken deposits. The measured lateral earth pressure distributions are plotted and evaluated. Precautions and recommendations for the use of tactile sensors in centrifuge experiments are given.

Uplifting behavior of shallow buried pipe in liquefiable soil by dynamic centrifuge test.

Abstract: Underground pipelines are widely applied in the so-called lifeline engineerings. It shows according to seismic surveys that the damage from soil liquefaction to underground pipelines was the most serious, whose failures were mainly in the form of pipeline uplifting. In the present study, dynamic centrifuge model tests were conducted to study the uplifting behaviors of shallow-buried pipeline subjected to seismic vibration in liquefied sites. The uplifting mechanism was discussed through the responses of the pore water pressure and earth pressure around the pipeline. Additionally, the analysis of force, which the pipeline was subjected to before and during vibration, was introduced and proved to be reasonable by the comparison of the measured and the calculated results. The uplifting behavior of pipe is the combination effects of multiple forces, and is highly dependent on the excess pore pressure.

Measurement of contact soil pressure in physical modelling of soil–structure interaction

Abstract: Meaningful measurement of contact soil pressure at the interface of a structural boundary has been a cause of frustration to experimentalists in the field of soil mechanics and soil–structure interaction. The difficulty stems from the fact that most sensing systems involve compliance, which induces a local redistribution of pressure in the soil mass. In effect, the attempt to monitor soil pressure ruins the measurement. The paper uses a concept called the ‘null soil pressure system’, which is an active sensing system requiring that the sensing element be continuously and stringently maintained in an un-deflected state. Results illustrate that the nulling pressure required to maintain the membrane in the un-deflected state is in a 1:1 ratio with the applied soil pressure, and is independent of soil type, particle size and particle arrangement. No hysteresis is noted between loading and unloading, and additional loading cycles align with that of the first loading cycle. Relevance of the system within the re...

Analysis of Liquefaction Effects on Ultimate Pile Reaction to Lateral Spreading

Abstract: Current design methods for piles in liquefied ground assume that the ultimate soil pressures acting on the pile are drastically reduced relative to the reference values in the absence of liquefaction. However, there is controversy about the adopted design parameters and their effects. Furthermore, it has been experimentally shown that soil pressures are not always reduced, but they may increase well above the recommended design values because of flow-induced dilation of the liquefied soil around the upper part of the pile. In view of this, the pile response is simulated in this paper using a three-dimensional, fully coupled dynamic elastoplastic numerical analysis. The methodology is first verified against results from centrifuge experiments and consequently applied parametrically for various pile, soil, and seismic excitation characteristics. It is thus shown that dilation-induced negative excess pore pressures are indeed possible for common pile and soil conditions at the upper segments of the pile, having an overall detrimental effect on pile response. It is further found that, apart from the commonly considered effect of relative sand density, ultimate soil pressures are affected by a number of other dilation-related parameters, such as the effective confining stress, the permeability of the sand, and the predominant excitation period as well as the pile diameter and bending stiffness. To quantify the relevant effects, new multivariable relationships are established and subsequently evaluated against the empirical methodologies that are currently used in practice.

Stability of sheet-pile walls subjected to seepage flow by slip lines and finite elements

Abstract: Stability of sheet-pile walls is often very sensitive to seepage flow. In the presence of seepage flow, the reduction in passive pressure on one side and increase in active pressure on the other side of the wall increase the risk of the instability that may precede instabilities due to piping or ground heaving. In this research the earth pressure behind sheet-pile walls in granular soils is studied. The flow field is computed by the finite-element method and the slip lines (stress characteristics) method is utilised to compute the associated stress field required to compute the effective passive pressure. The same finite-element mesh and interpolation functions are used to solve the flow field and to interpolate the seepage forces in the stress field solved by the stress characteristics method. Comparisons are made to verify the numerical results with those values available in the literature; these show reasonable agreement. The stability of sheet-pile walls is then analysed for a number of different prob...

Seismic earth pressures on retaining structures and basement walls

Abstract: Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading. For instance, no significant damage or failures of retaining structures occurred in the recent Wenchuan earthquake in China (2008) and the subduction earthquakes in Chile (2010) and Japan (2011). To develop a better understanding of the distribution and magnitude of the seismic earth pressures on cantilever retaining structures, a series of centrifuge experiments were performed on model retaining and basement structures with cohesionless and cohesive backfills. This paper provides a general overview of the research program and its results. Overall, for the structures examined, i.e. wall heights in the range 20-30 ft, the centrifuge data consistently shows that the maximum dynamic earth pressure increases with depth, and can be reasonably approximated by a triangular distribution. This suggests that the resultant of the dynamic earth pressure increment acts near 0.33H above the footing as opposed to 0.5-0.6 H recommended by most current design procedures. The current data suggests that cantilever walls could resist ground accelerations up to 0.4 g if designed with an adequate factor of safety.

Active earth pressure of retaining wall considering wall movement

Abstract: The coulomb’s limit equilibrium theory is employed for the active earth pressure calculation of retaining wall considering translational wall movement. It is considered that the earth pressure against the back of the wall is due to the thrust exerted by a wedge of soil between the wall and a plane passing through the heel of the wall. The soil–wall friction angle and internal soil friction angle are obtained via the simulation of the unloading triaxial test. The basic equations are established by considering the force equilibrium of a partial soil wedge. The lateral earth pressure coefficient is achieved through the moment equilibrium of the whole soil wedge. Comparisons illustrating the accuracy of the proposed approach are made with solutions available in the literature.