Showing papers on "Lateral earth pressure published in 2013"

Shaking table test on the seismic failure characteristics of a subway station structure on liquefiable ground

Abstract: SUMMARY In order to investigate the seismic failure characteristics of a structure on the liquefiable ground, a series of shaking table tests were conducted based on a plaster model of a three-story and three-span subway station. The dynamic responses of the structure and ground soil under main shock and aftershock ground motions were studied. The sand boils and waterspouts phenomena, ground surface cracks, and earthquake-induced ground surface settlements were observed in the testing. For the structure, the upward movement, local damage and member cracking were obtained. Under the main shock, there appeared longer liquefaction duration for the ground soil while the pore pressure dissipated slowly. The acceleration amplification effect of the liquefied soil was weakened, and the soil showed a remarkable shock absorption and concentration effect with low frequency component of ground motion. However, under the aftershock, the dissipation of pore pressure in the ground soil became obvious. The peak acceleration of the structure reduced with the buried depth. Dynamic soil pressure on the side wall was smaller in the middle and larger at both ends. The interior column of the model structure was the weakest member. The peak strain and damage degree for both sides of the interior column exhibited an ‘S’ type distribution along the height. Moreover, the seismic response of both ground soil and subway station structure exhibited a remarkable spatial effect. The seismic damage development process and failure mechanism of the structure illustrated in this study can provide references for the engineers and researcher. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental analysis of earth pressure against rigid retaining walls under translation mode

Abstract: A series of physical model tests was conducted for the active case of a rigid retaining wall subjected to horizontal translation. The behaviour of a granular retained soil was investigated experimentally using a set of precise miniature pressure cells and particle image velocimetry. The good agreement between the experimental results and the arch-action-based theories for lateral active earth pressure could confirm the arching effect behind the retaining walls in the active translation mode. The distribution of shear strain confirms that, for active wall movement, the failure zone is distinguished from the stationary zone by a shear band behind the wall.

Behavior of Coarse Widely Graded Soils under Low Confining Pressures

Abstract: Colluvial soils are usually coarse and widely graded. Shallow-seated failures occur frequently in colluvial soil deposits duringrain- fallinfiltration.Thispaperinvestigatesthebehaviorofcoarse,widelygradedsoilsunderverylowconfiningpressuresof5e25 kPa encountered in shallow-seated failures. Isotropic consolidation tests, drained triaxial tests, and undrained triaxial tests were conducted on several widely graded soils with different coarse contents but with the same void ratio of 0.62. With increasing coarse content, the soil microstructure changes froma fines-controlledstructuretoacoarse-controlledstructureafteracriticalcoarsecontentofapproximately70%.Siltysandwithgravelwith acoarsecontentclosetothecriticalvalueexhibitsthehighestcompressibilitybecauseofthepresenceoflargeinteraggregatepores.Evenunder very low confining pressures, such soil still shows strong contractive behavior during drained loading, and generates large positive pore-water pressures during undrained loading. This explains why shallow-seated failures occur frequently in colluvial soil deposits caused by rainfall infiltration.Soilswithlowerorhighercoarsecontentsthanthecriticalvaluemayshowdilativebehaviorunderthesamelowconfiningpressures. The critical statefriction angle increases with thecoarse content.DOI:10.1061/(ASCE)GT.1943-5606.0000755.©2013American Society of Civil Engineers. CE Database subject headings: Coarse-grained soils; Compression; Landslides; Microstructure; Shear strength; Soil compaction; Soil pressure.

MCS-based probabilistic design of embedded sheet pile walls

Abstract: A probabilistic approach to the design of embedded sheet pile walls is developed in this paper. The approach is based on Monte Carlo simulation (MCS), and it is used to investigate the performance of the partial factors and different design approaches in Eurocode 7 in achieving the target degrees of reliability. The approach is illustrated through an embedded sheet pile wall design example that has been used in literature for the evaluation of Eurocode 7. The approach deals rationally with the correlated load and resistance, and it bypasses a difficult but frequently asked question in Eurocode 7 (i.e. should the passive earth pressure be considered as a load (i.e. action) or a resistance?). The probabilistic design approach (DA) is also used to explore the effects of the soil unit weight variability and uncertainties in over-digging depth and wall friction. The effects of uncertainties in over-digging depth and wall friction are found to be significant. It is also found that, although the soil unit weight...

Measuring soil pressure within a soil mass

Abstract: Reliable measurement of pressure within a particulate media has frustrated researchers in the field of soil mechanics and soil structure interaction for many years. The difficulty stems from the fa...

Slip-line solution to active earth pressure on retaining walls

Abstract: The slip-line method is commonly used to solve the limit earth pressure on retaining walls, but to date there are still a number of problems that have not yet been solved. Based on limit equilibrium theory, the backfill is considered to be an ideal elastic-plastic material, which obeys the Mohr–Coulomb yield criterion, and is assumed to be an ideal continuous medium that is isotropic, homogeneous and incompressible (or non-expansive). Various factors of influence are considered in the calculation model. An elastic overburden is proposed as a replacement for traditional tension cracks. A new concept – stress singularity – and its stress boundary conditions are introduced, and a statically determinate and solvable mathematical model for the limit equilibrium problem is established without considering the stress–strain relationship of the soil. The slip-line stress field in the plastic zone of the backfill is solved by using the slip-line method, following which the active earth pressure on retaining walls a...

Seismic Earth Pressures on Retaining Structures in Cohesionless Soil

Abstract: Author(s): Mikola, RG; Sitar, N | 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 intensity of the earthquake loading. Failures of retaining structures are most commonly confined to waterfront structures retaining saturated backfill with liquefaction being the critical factor in the failures. Failures of other types of retaining structures are relatively rare and usually involve a more complex set of conditions, such as sloping ground either above or below the retaining structure, or both. While some failures have been observed, there is no evidence of a systemic problem with traditional static retaining wall design even under quite severe loading conditions. No significant damage or failures of retaining structures occurred in the recent earthquakes such as Wenchuan earthquake in China (2008) and, or the large subduction zone earthquakes in Chile (2010) and Japan (2011). Therefore, this experimental and analytical study was undertaken to develop a better understanding of the distribution and magnitude of seismic earth pressures on cantilever retaining structures. The experimental component of the study consists of two sets of dynamic centrifuge model experiments. In the first experiment two model structures representing basement type setting were used, while in the second test a U-shaped channel with cantilever sides and a simple cantilever wall were studied. All of these structures were chosen to be representative of typical designs. Dry medium-dense sand with relative density on the order of from 75% to 80% was used as backfill. Results obtained from the centrifuge experiments were subsequently used to develop and calibrate a two-dimensional, nonlinear, finite difference model built on the FLAC platform. The centrifuge data consistently shows that for the height of structures considered herein, i.e. in the range of 20-30 ft, the maximum dynamic earth pressure increases with depth and can be reasonably approximated by a triangular distribution This suggests that the point of application of the resultant force of the dynamic earth pressure increment is approximately 1/3H above the base of the wall as opposed to 0.5-0.6 H recommended by most current design procedures. In general, the magnitude of the observed seismic earth pressures depends on the magnitude and intensity of shaking, the density of the backfill soil, and the type of the retaining structures. The computed values of seismic earth pressure coefficient (∆Kae) back calculated from the centrifuge data at the time of maximum dynamic wall moment suggest that for free standing cantilever retaining structures seismic earth pressures can be neglected at accelerations below 0.4 g. While similar conclusions and recommendations were made by Seed and Whitman (1970), their approach assumed that a wall designed to a reasonable static factor of safety should be able to resist seismic loads up 0.3 g. In the present study, experimental data suggest that seismic loads up to 0.4 g could be resisted by cantilever walls designed to an adequate factor of safety. This observation is consistent with the observations and analyses performed by Clough and Fragaszy (1977) and Fragaszy and Clough (1980) and Al-Atik and Sitar (2010) who concluded that conventionally designed cantilever walls with granular backfill could be reasonably expected to resist seismic loads at accelerations up to 0.4 g. Finally, numerical models using FLAC finite difference code were quite successful and able to produce a reasonably good agreement with the results of the centrifuge experiments. However, while the finite difference models were able to capture the main aspects of the seismic response observed in the centrifuge experiments, the results of the analyses were highly sensitive to the selection of soil and interface parameters. Therefore, numerical models used for future designs should be carefully calibrated against experimental data to provide reliable results.

Effect of particle fabric on the coefficient of lateral earth pressure observed during one-dimensional compression of sand

Abstract: The effect of initial particle fabric on the one-dimensional compression response of Fraser River sand was investigated. One-dimensional compression with lateral stress measurement was carried out ...

Mechanism of transverse deformation and assessment index for shield tunnels in soft clay under surface surcharge

Abstract: The transverse deformation of shield tunnels may ultimately threaten the safety of tunnel structure.The surcharge above the tunnels is one of the leading factor to cause their transverse deformation.The evolution of transverse defromation of the tunnels under surchage is firstly studied using numerical simulation considering the effect of the elastic resistance of surrounding soil and lateral coefficient of earth pressure at rest.It is found that the development of joint opening and the stress states of both tunnel concrete and bolts are dependent on the variation of tunnel diameter.Thus,the variation of tunnel diameter can be taken as the assessment index to predict the performance of shield tunnels in soft soils.The criteria for tunnel assessment are determined in terms of diameter change.Then,a geometry-based simple method is proposed to study the relationship between joint opening and tunnel squating based on the tunnel crown settlement.The method is verified by the abovementioned numerical simulation.This simple method provides a very convenient way to estimate the safety state of shield tunnels.

Experimental investigation into the influence of stratification on the passive earth pressure

Abstract: In this paper, the effect of inhomogeneous soil condition on the passive earth pressure is studied by using model tests. The model tests are carried out with two soil layers. The tests are compared with the corresponding results for homogenous soil. The shear band formation is identified with Particle Image Velocimetry measurements.

Influence of soil nail orientations on stabilizing mechanisms of loose fill slopes

Abstract: Soil nailing has been used to upgrade substandard loose fill slopes in Hong Kong. Due to the possibility of static liquefaction failure, a typical design arrangement comprises a structural slope facing anchored by a grid of soil nails bonded into the in situ ground. Numerical analyses have been conducted to examine the influence of soil nail orientations on the behaviour of the ground nail-facing system. The results suggest that the use of steeply inclined nails throughout the entire slope could avoid global instability, but could lead to significant slope movement especially when sliding failure prevails, for instance, due to interface liquefaction. The numerical analyses also demonstrate that if only subhorizontal nails are used, the earth pressure exerted on the slope facing may cause uplift failure of the slope cover. To overcome the shortcomings of using soil nails at a single orientation, a hybrid nail arrangement comprising nails at two different orientations is proposed. The numerical analyses illustrate that the hybrid nail arrangement would limit slope movement and enhance the robustness of the system.

Experimental and Numerical Study on Pile Behaviour Under Lateral Load in Clayey Slope

Abstract: Structures such as jetties, transmission towers, elevated highways and various industrial units are often supported by pile foundation on natural or man-made soil slope. The piles on slopes are subjected to lateral load from the super structure, earth pressure from the unstable soil, wave and current actions in case of marine structures, etc. The behaviour of a pile on sloping ground under lateral load is different from that on a horizontal ground. The aim of this paper is to experimentally and numerically evaluate the behaviour of a single pile in sloping clay layer subjected to lateral load. 1 g model tests are performed in laboratory test tank on instrumented pile embedded in clayey bed with varying slopes and shear strength. The behaviour of a single pile placed either at crest or at different distances from crest on slope is evaluated. Static lateral load was applied in a direction towards the downward slope. Numerical study comprise of 3-D finite element analysis using PLAXIS code. The input parameters used for the analysis were validated by comparing the PLAXIS results with the experimental result. A detailed parametric study was then carried out by varying the clay shear strength and the slope angle. Based on the analysis, non-dimensional design charts are prepared for lateral capacity in piles on sloping ground. A worked example is included demonstrating the use of the design charts for pile on clay slope subjected to lateral loading.

Stability of Back-to-Back Mechanically Stabilized Earth Walls

Abstract: Back-to back mechanically stabilized earth (BBMSE) walls are encountered in highway applications such as narrow ramps and turning lanes. However, available literature and design guidelines for BBMSE walls are limited. The objective of this paper is to discuss the stability of BBMSE walls with geosynthetic reinforcement using two-dimensional finite element modeling. The numerical model was validated against an instrumented large-scale test wall. The study was performed to investigate the effect of distance between BBMSE walls and reinforcement length on the failure mechanism, tensile forces in the reinforcement, and lateral earth pressure behind the reinforced zone. The results indicate that each of the back-to-back walls behave independently if the wall spacing to height ratio is more than one. When the ratio is less than one the two walls interact with each other and the earth pressure behind the wall decreases because the failure wedge behind the wall is not fully developed. Thus, the tensile forces in the geosynthetic reinforcement decrease with decreasing the spacing between walls. In very narrow walls, it was observed that the tensile forces decrease when using a single reinforcement layer compared to using overlapping layer.

A Multi-Mode Resource-Constrained Project Scheduling Model With Bi-Random Coefficients For Drilling Grouting Construction Project

Abstract: For calculating the natural frequency of structures such as buildings, chimneys, bridges and silos appropriate analytical formulas exist. However, in the case of retaining walls undergoing the soil pressure at one side, calculating the natural frequency is not a straightforward task and requires the effects of soil-structure interactions to be considered. By modeling the soil as series of linear springs, a new formulation is presented in this article, to calculate the natural frequency of retaining walls. This formula considers the vertical cross sectional width change, and hence, enables us to calculating the natural frequency of retaining walls with different types of backfill. The geometrical properties of the retaining walls and its bending rigidity together with the soil’s modulus of elasticity and its Poisson’s ratio are the most important parameters to calculate. A comparison of the results for retaining walls with constant cross section obtained from the suggested method with those of the software analyses was carried out and good agreement was detected. A second comparison of the results with those of other researchers revealed that the natural frequency of flexible retaining wall is an upper bound for natural frequency of rigid walls. The Selected shape function is also very close to the real shape mode.

Pressure Coefficient in Dam-Break Flows of Dry Granular Matter

Abstract: The propagation of dry granular flows, such as rock and snow avalanches, can be described by depth-averaged models Different from classical shallow-water equations, these models take into account the anisotropy of normal stresses inside the flowing pile through using an earth pressure coefficient in the pressure term A new regularization function for calculating the pressure coefficient in the Savage-Hutter-type models at the early stages of dam-break flows and collapses is proposed In such circumstances the flow lines are significantly curved with respect to the basal surface and a special treatment of the earth-pressure coefficient is required for obtaining a satisfactory agreement with experimental data The comparison between numerical simulations and laboratory experimental data shows an apparent improvement in describing the early stages of dam-break waves over rough beds The comparison with experiments over smooth bed surface exhibits minor evidence of improvement Nonetheless, in this

Seismic active earth pressure from the sloping c - ϕ soil backfills

Abstract: This technical note presents the analytical derivation of an explicit expression for the total seismic active earth pressure from the sloping c-ϕ soil backfills on the rigid retaining walls. The derivation considers several practical aspects such as wall friction and adhesion, tension cracks in the backfill, and a uniform surcharge on the backfill along with both horizontal and vertical seismic loadings. The development of an explicit analytical expression for the critical inclination of the failure plane within the soil backfill is also described. It is shown that the analytical expressions give the same results for simpler special cases previously reported in the literature for both non-seismic and seismic problem conditions.

Analytical solution for Rankine's seismic active earth pressure in infinite slope

Abstract: This paper presents an analytical solution to determine seismic active earth pressure on a rigid frictionless retaining wall of c-ϕ soil backfill with an infinite slope, considering horizontal and vertical seismic coefficients. This solution is a generalized explicit expression and was derived based on the Rankine earth pressure theory and the Mohr-Coulomb yield criterion. To verify the derived solution, a special case was analyzed, and its result is identical to that obtained by earlier researchers. By analyzing the distribution of the seismic active earth pressures along the wall depth, a tension crack zone behind the wall was identified, and the seismic active earth pressure coefficient considering the tension crack was obtained. This study also investigated the effects of wall friction, soil friction angle and dimensionless cohesion, backfill slope, and horizontal and vertical seismic coefficients on the seismic active earth pressure coefficients. Design charts for seismic active earth pressur...