Showing papers on "Lateral earth pressure published in 2012"

Seismically Induced Lateral Earth Pressures on Retaining Structures and Basement Walls

Abstract: The evolution of the methodology for the evaluation of seismic earth pressures on retaining structures and basement walls is reviewed together with observations of field performance. The case history data and data from recent experimental work are used to show that the currently used methods are quite conservative and lead to excessively conservative designs in regions where design PGA exceeds 0.4g. Specifically, the experimental data from seismic centrifuge tests shows that the seismic earth pressure distribution for moderate size retaining structures, on the order of 6-7 m high, is triangular, increasing with depth. Moreover, there is no significant increase in seismic earth pressure between unbraced and braced structures with fixed base, while the loads on free standing cantilever structures are substantially lower owing to their ability to translate and rotate. The significance of the observed seismic earth pressure distributions is that the dynamic force can be applied at 1/3H, as is done for static loading, which substantially decreases the design level seismic moments on the structures.

Effect of Soil Conditioners on the Pressure and Rate-Dependent Shear Strength of Different Clays

Abstract: Tunneling using the earth pressure balance machines method in clayey soils requires the addition of conditioning chemicals to reduce the torque moment of the machine and to guarantee a safe and economical excavation process. Injection of foams and polymers at the cutter head of the tunnel boring machine with subsequent remolding in the pressure chamber transforms the excavated material into a deformable soil paste with preferably low strength and adhesion. The soil becomes more compressible and can develop viscous properties, such that the pressure and rate dependency of the shear strength of the mixtures are of major importance for the proper design and analysis of the tunneling processes. In this paper, the results of vane shear strength measurements on various conditioned clays and clay-sand mixtures at various shearing velocities and applied pressures are presented and analyzed. The results clearly show the effects of the chemicals used and also point out the differences in their efficiency depending on the clay mineralogy. This allows for an improved understanding of the working mechanisms of the chemicals.

Lateral Earth Pressure Coefficients for Anchored Sheet Pile Walls

Abstract: Conventional methods used for the design of anchored sheet pile walls are based on the lateral force and moment equilibrium of active and passive earth pressures and anchor force. Although it has been known for decades that the stress concentration occurs around the anchor level because of the restricted wall movements, this stress concentration is not considered in determining the lateral earth pressures. A parametric study using conventional and numerical methods was performed to investigate the behavior of single-level anchored sheet pile walls, and the lateral earth pressures, wall bending moments, and anchor forces were analyzed. The study results indicate that the conventional methods for the conditions considered and cases studied overestimate the wall bending moments, whereas the anchor forces are underestimated. New lateral earth pressure coefficients that consider the stress concentration around the anchor level were developed and proposed to be used in the design of single-level anchore...

Optimum Design of Gravity Retaining Walls Using Charged System Search Algorithm

Abstract: This study focuses on the optimum design retaining walls, as one of the familiar types of the retaining walls which may be constructed of stone masonry, unreinforced concrete, or reinforced concrete. The material cost is one of the major factors in the construction of gravity retaining walls therefore, minimizing the weight or volume of these systems can reduce the cost. To obtain an optimal seismic design of such structures, this paper proposes a method based on a novel meta-heuristic algorithm. The algorithm is inspired by the Coulomb's and Gauss’s laws of electrostatics in physics, and it is called charged system search (CSS). In order to evaluate the efficiency of this algorithm, an example is utilized. Comparing the results of the retaining wall designs obtained by the other methods illustrates a good performance of the CSS. In this paper, we used the Mononobe-Okabe method which is one of the pseudostatic approaches to determine the dynamic earth pressure.

Earth pressures exerted on an induced trench cast-in-place double-cell rectangular box culvert

Abstract: Earth pressure data from the field instrumentation of a cast-in-place reinforced rectangular box culvert are presented in this paper. The instrumented culvert is a 2.60 m by 3.60 m double-cell reinforced cast-in-place rectangular box buried under 25.10 m of fill constructed using the induced trench installation (ITI) method. The average earth pressure measured across the roof was 0.42 times the overburden pressure, and an average of 0.52 times the overburden pressure was measured at mid-height of the culvert on the sidewalls. Base contact pressure under the rectangular box culvert was also measured, providing field-based data demonstrating increased base pressure resulting from downward drag forces developed along the sidewalls of the box culvert. An average increase of 25% from the measured vertical earth pressures on the roof plus the culvert dead load (DL) pressure was calculated at the culvert base. A model culvert was also tested in a geotechnical centrifuge to obtain data on earth pressures at the t...

Simple wave solution for seismic earth pressures on nonyielding walls

Abstract: Design of retaining walls for earthquake action is traditionally performed by limit analysis procedures—notably the classical solution of Mononobe-Okabe and its variants. Fundamental assumptions of these methods are (1) the static nature of seismic excitation, (2) the compliance in sliding and/or rocking of the base of the wall, (3) the shear failure of the backfill and the soil-wall interface, and (4) the prespecified point of application of soil thrust. Given the restrictive nature of these assumptions, alternative solutions based on wave-propagation theory have been developed that do not require failure of the backfill and thereby are applicable to nonyielding walls. Because of the complex mathematics involved, the use of these solutions in practice appears to be limited. A special integration technique inspired from the seminal work of Vlasov and Leontiev is presented, which simplifies the analysis by providing closed-form solutions suitable for practical use.

Evolution of stabilised creeping landslides

Abstract: A simple analytical model is proposed to quantify evolution of a creeping landslide stabilised by a retaining wall, or by a natural barrier at the bottom of the sliding mass. Development in time of both the landslide displacements and the earth pressure acting on the retaining structure is obtained in the closed form, with the latter given by the classical Terzaghi expression for the average degree of consolidation. Depending on the value of the long-term safety factor, the landslide either eventually slows down, asymptotically approaching final displacements, or the soil behind the retaining wall comes to a passive failure, followed by a post-failure evolution of the landslide. The model is capable of quantifying both scenarios, with some of its features successfully validated against the monitoring and geotechnical data from the two case studies: the Combe Chopin and Ganter landslides in Switzerland. For the Combe Chopin landslide, which came to a standstill, the model has demonstrated its ability to pr...

Finite element analyses of negative skin friction on a single pile

Abstract: This paper presents finite element analyses of negative skin friction on a single pile under various conditions. Negative skin friction is a common problem if a pile is designed in a highly compressible soil. There are two most important parameters in estimating the load caused by negative skin friction: (1) the distribution and magnitude of skin friction and (2) the location of the neutral plane. The neutral plane is the location where the pile and soil settle the same amount or have no relative displacement. Negative skin friction is a very complex phenomenon influenced by many factors. In this paper, a two-dimensional axisymmetric model is built in the finite element program, ABAQUS. The model is first verified with a known case history. A systematic parametric analysis is performed to investigate the influence on both the neutral plane and the magnitude and distribution of negative skin friction along the pile length of various influencing factors, including the consolidation time, the properties of pile/soil interface, the lateral earth pressure coefficient, pile-soil limiting displacement, the intensity of surcharge, and soil stiffness. Based on the analyses, it is found that the location of the neutral plane is significantly influenced by the consolidation time and the stiffness of bearing layer. The distribution and magnitude of negative skin friction is influenced mainly by the pile/soil interface, soil compressibility, and the surcharge intensity. Based on the field measurements from literature and this investigation, a simple design procedure is proposed for estimating the pile load caused by negative skin friction.

Large-Scale Modeling and Theoretical Investigation of Lateral Collisions on Elevated Piles

Abstract: Large deflection is mobilized in elevated piles of nonnavigable piers and some flexible protective systems subjected to lateral ship collisions. Because the current bridge design specifications are only suitable for the design of rigid foundations, new analysis and design methods are required for these flexible elevated piles. A large-scale lateral static load test and an additional three impact tests on piles in low liquid limit silt (ML) soil were carried out in a large soil tank. Both static and dynamic soil pressures on the pile shaft were measured, and then the soil-pile interaction was studied in detail. Based on the results, static hyperbolic p-y curves of the piles were derived for dynamic p-y curve models. Through investigations of three linear and nonlinear soil-pile dynamic interaction models, the dynamic p-y curve models with nonlinear static stiffness coefficients and constant damping coefficients are recommended for the analysis of piles subjected to lateral impact loading. Verified ...

Simplified Analytical Method for Calculating the Maximum Shear Stress of Nail-Soil Interface

Abstract: This paper describes a simplified analytical method that considers postinstallation normal stress, normal stress due to soil dilation, and grouting pressure when calculating the maximum shear stress of the nail-soil interface. Systematic test results from two previous publications were used to verify the accuracy of the proposed method. The Hong Kong design method was also used to determine the maximum shear stress of the nail-soil interface. These analyses confirmed that the experimental data were more accurately predicted by the proposed analytical method. An extensive parametric study was conducted to examine the effects of several key parameters on the maximum shear stress. It was observed that when there was no grouting pressure, maximum shear stress increased with increasing overburden pressure, failure surface distance, dilation angle, or decreased drill hole radius. Analysis using the proposed model also demonstrates that grouting and overburden pressures share an interactional effect. The...

Rainfall induced instabilities: a field experiment on a silty sand slope in northern Switzerland

Abstract: Two full scale field tests were planned and performed successfully on a steep forested slope located on the east facing banks of river Rhine in Ruedlingen, in canton Schaffhausen, northern Switzerland. The aim of the experiments was to study the triggering mechanisms of the landslides due to rainfall. Intensive field investigations were carried out, including in-situ geotechnical tests, characterisation of hydrological properties of the soil and reinforcing effects of vegetation, geological and hydrogeological mapping, and subsurface investigations by means of geophysical methods. Additionally, several series of saturated and unsaturated laboratory tests were conducted on undisturbed and disturbed samples taken from different depths from the vicinity of the selected slope. The test site was intensively instrumented and monitored over a period of 6 months in the course of artificial rainfall and natural precipitation. The instrumentation includes conventional and novel methods to measure pore water pressure, volumetric water content, piezometric height, soil pressure, acoustic emissions, surface and subsurface movements, soil temperature, and meteorological data. This paper introduces briefly the measurements and findings from this multi-disciplinary project, and focuses on numerical and analytical methods used to explain the behaviour of a marginally stable slope before and during the failure induced by rainfall. Simple stability calculations are described that still offer realistic predictions of the status of a slope prone to failure due to increase of the pore water pressure. The basal and lateral reinforcing effects of vegetation and unsaturated shear strength of soil are introduced in these two and three dimensional simulations as well.

Shield machine belt pressure chamber opening operation construction method

Abstract: The invention relates to a shield machine belt pressure chamber opening operation construction method. The method comprises the following steps: adjusting the posture of a shield, setting up tunneling parameters, and injecting bentonite slurry into a shield cutter head and the circumference thereof so as to make the soil mass around a tunnel face and the shield form a clay film capable of blocking off a leakage passage; establishing the air pressure in the soil chamber; carrying out the pressurization and chamber entry, making staff enter a personal gateway to check and change a cutter or even check the cutter head, and the like; carrying out decompression and chamber exiting; and after the operation is completed, injecting bentonite into the soil chamber through a pipeline, and staring the cutter head and a jack to restore the shield tunneling after the soil pressure balance is rebuilt in the soil chamber. The method reduces the gas permeability of a stratum by 30 percent compared with that of the original stratum, thereby meeting the belt pressure requirements, not only ensuring the safety of the workers operating in the soil chamber, but also ensuring the soil mass stability ofthe tunnel face. The method brings about a good strengthening effect and little ground surface deformation; as the reinforcement is carried out inside the tunnel, the method does not occupy ground area and brings about little influence on the ambient environment and urban traffic; and the method has the characteristics of high construction efficiency, short cycle, and low cost.

Seismic Active Earth Pressure on the Back of Battered Retaining Wall Supporting Inclined Backfill

Abstract: Knowledge of seismic active earth pressure behind a rigid retaining wall and its point of application are very important to the design of retaining walls in earthquake-prone regions. This paper presents a detailed study on the seismic active earth pressure and its point of application behind a nonvertical, rigid retaining wall supporting inclined, cohesionless backfill, using pseudo-dynamic analysis that is more realistic to representing the time and phase difference within the backfill. A planar failure surface is considered in the analysis. The effects of soil and wall friction angle, wall and backfill surface inclination, and horizontal and vertical earthquake acceleration on the active earth pressure have been explored. Results are presented in both tabular and graphical nondimensional form, including comparison with other available methods to highlight the realistic nonlinearity of seismic active earth pressure distribution.

Predicting the Earth Pressure on Integral Bridge Abutments

Abstract: The soil adjacent to integral bridge abutments experiences daily and annual temperature-induced cyclic loading due to expansion and contraction of the bridge deck. This causes a particular soil response and complicated soil-structure interaction problem, with considerable uncertainties in design. This paper describes a method of calculating the effects of thermal cycling by using the results of laboratory cyclic stress path testing within a numerical model. Samples of stiff clay and sand were tested in the triaxial apparatus under stress paths typical for behind an integral abutment. Distinct behavior was observed for the two soils, with stiff clay showing relatively little buildup of lateral stress with cycles, whereas for sand stresses continued to increase, exceeding at-rest and approaching full passive pressures. To explore the implications of these findings on the soil-abutment interaction and to estimate the lateral stresses acting on the abutment as a whole, a numerical (finite difference) model was developed with a soil model reproducing the sand behavior at element level. The numerical model gave good agreement with published centrifuge and field data, and indicated that the stress profile specified in some current standards is conservative. Influence of abutment stiffness and wall friction is also quantified.

Modeling the Dynamic Response of Wrap-Faced Reinforced Soil Retaining Walls

Abstract: This paper describes the development of a numerical model for simulating the shaking table tests on wrap-faced reinforced soil retaining walls. Some of the physical model tests carried out on reinforced soil retaining walls subjected to dynamic excitation through uniaxial shaking tests are briefly discussed. Models of retaining walls are constructed in a perspex box with geotextile reinforcement using the wraparound technique with dry sand backfill and instrumented with displacement sensors, accelerometers, and soil pressure sensors. Results showed that the displacements decrease with the increase in number of reinforcement layers, whereas acceleration amplifications were not affected significantly. Numerical modeling of these shaking table tests is carried out using the Fast Lagrangian Analysis of Continua program. The numerical model is validated by comparing the results with experiments on physical models. Responses of wrap-faced walls with varying numbers of reinforcement layers are compared. Sensitivity analysis performed on the numerical models showed that the friction and dilation angle of backfill material and stiffness properties of the geotextile-soil interface are the most affecting parameters for the model response.

Soil arching and load transfer mechanism for slope stabilized with piles

Abstract: In this study, the effects of pile spacing and pile head fixity on the moment and lateral soil pressure distribution along slope stabilizing piles are investigated. A slice from an infinitely long row of piles with fixed pile tip in an inclined sand bed was simulated with an experimental test setup. Surficial soil displacements were monitored and relative displacements between soil particles were determined by recording time-lapse images during the test in order to observe the soil arching mechanism on the soil surface. The load transfer process from moving soil to piles and behavior of soil around piles were observed and evaluated by the different test setups. It was observed that decrease in pile spacing causes an increase of load carried per pile. This behavior, which was significantly influenced by the pile head boundary conditions, can only be explained by soil arching that existed between the piles along their lengths.

Unified Solution of Coulomb’s Active Earth Pressure for Unsaturated Soils without Crack

Abstract: Based on the unified solution of shear strength in terms of double stress state variables for unsaturated soils, whilst considering the effect of the intermediate principal stress rationally, the unified solution of Coulomb’s active earth pressure for unsaturated soils without cracks is developed. Comparability of the solution is analyzed and influencing characteristic of each factor is obtained. The research result indicates that: the intermediate principal stress and matric suction have obvious impacts on Coulomb’s active earth pressure for unsaturated soils; Coulomb’s active earth pressure has been decreasing until zero with the increase of unified strength theory parameter and matric suction; Coulomb’s active earth pressure increases with the increase of grading angle of retaining wall and slop angle of backfill, but decreases with the increase of matric suction, effective internal friction angle and matric suction angle, while external friction angle has no obvious influence. The proposed unified solution of Coulomb’s active earth pressure enjoys a wider application, and unified solution of Rankine’s active earth pressure is just the special case. The results are of great significance to soil pressure determination such as slope and foundation pit, and to retaining structures design.

Laboratory Simulation of the Stresses Within Inclined Stopes

Abstract: In the process of mining for earth resources, large underground voids called stopes are created that are later backfilled. For stability analysis of the backfilled stopes, it is necessary to understand the stress developments within the stope while the filling is in progress. Due to an arching effect, a substantial fraction of the fill weight is carried by the stope walls, depending on the physical characteristics of the walls. This paper describes the development of a laboratory model that simulates mine backfilling in an inclined stope and enables determination of the average vertical stress at any depth within the fill. The experimental results are validated against numerical models and stresses determined from an analytical expression. The effect of arching is the least when the stope is inclined at about 80 degrees to the horizontal, giving highest vertical stresses at any depth. This fact is not captured in both the mathematical and numerical models developed in the past and the ones discussed herein. The model tests show that the lateral earth pressure coefficient is closer to K-0 for vertical stopes and k(a) for inclined stopes. In the case of walls with dissimilar frictional characteristics, the analytical expression can still be used with an average value of the wall-fill friction angle.