Soil-structure Interface Research Articles

Behavior of a Pressure-Grouted Soil-Cement Interface in Direct Shear Tests

AbstractAn interface between compacted soil and a structure is commonly encountered in various geotechnical engineering projects, e.g., soil nails, retaining walls, shallow foundations, pile foundations, and so on. The interface strength depends on the way the soil-structure interface is formed. A cast-in-situ interface is very common in many geotechnical projects. This kind of interface is formed by placing concrete/cement grout over the prepared soil surface. The cement part can be formed over a prepared soil surface in two ways: (1) by normal gravity grouting and (2) by pressure grouting. In this study, a series of interface direct-shear tests was performed between compacted, completely decomposed granite (CDG) soil and cement grout under saturated conditions with different grouting pressures and normal stresses. The behaviors of the shear-stress–displacement curves of the soil-cement interface are similar to those of CDG soil. Grouting pressure and normal stress have influence on the behavior of the s...

In-house calibration of pressure transducers and effect of material thickness

Pressure transducers are increasingly used within soil mass or at soil-structure interface for appraisal of stresses acting at point of installation. Calibration of pressure transducers provides a unique relationship between applied pressure and voltage or strain sensed by transducer during various loading conditions and is crucial for proper interpretation of results obtained from pressure transducers. In the present study an in-house calibration device is used to calibrate pressure transducers and the study is divided into two parts: 1) demonstration of developed calibration device for fluid and in-soil calibration of pressure transducers; 2) effect of soil layer thickness on the earth pressure cell (EPC) output. Results obtained from the present study revealed successful performance of the developed calibration device, and significant effect of sand layer thickness on the calibration results. The optimum sand layer thickness is obtained as 1.5 times the diameter of EPC.

New Load Transfer Hyperbolic Model for Pile-Soil Interface and Negative Skin Friction on Single Piles Embedded in Soft Soils

A proper load transfer model describing the pile and surrounding soil interaction is important for accurately predicting the behavior of piles. In this paper, a new load transfer hyperbolic model for the pile-soil interface is developed based on soil-structure interface tests reported in the literature, which consider the characteristics of increasing initial shear stiffness, the development of shear strength at the pile-soil interface, the loading, step by step loading, unloading, and reverse loading shearing behavior of the pile-soil interface with consolidation. The proposed model was validated by the close agreement between the computed results and published case histories. Further studies based on the proposed model considering negative skin friction on single piles under pile head load and/or surcharge were subsequently conducted. It was found that the pile-soil interface undergoes complicated shearing, and the depth of the neutral plane (NP) and the skin friction along the pile shaft vary during consolidation. The magnitude of the pile head load and pile installation time has a significant impact on the depth of the NP and the dragload. Pile capacity was shown to decrease with consolidation.

A New Apparatus for Evaluation of Contact Erosion at the Soil–Structure Interface

Abstract The interface between clay core-wall and concrete cut-off wall is one of the weakest parts of high earth and rockfill dams. An unsuitable design can cause contact erosion at the interface or shear failure surfaces, and eventually this will harm the safety of the dam. A new soil–structure contact erosion apparatus was developed for the evaluation of contact erosion at the interface under high stress, high hydraulic head, and large shear deformation. It consists of a soil–structure model base, a seepage pressure system, a confining pressure system, an axial pressure system, and a data acquisition system. The seepage pressure system simulates the seepage erosion effect at the interface, and the maximum seepage pressure is 2.0 MPa. The confining and axial pressure systems simulate the triaxial stress state of the interface and the large shear deformation of the soil structure; the maximum confining and axial pressures are 2.0 MPa and 4.0 MPa, respectively. The data acquisition system can monitor pore pressure dissipation and settlement. Two repeatable experiments on the interface between a kind of highly plastic clay and a concrete cut-off wall were conducted to verify the scientific utility of the new apparatus. The new apparatus was found to be capable of yielding fairly consistent results in repeatable experiments. The new apparatus will prove an effective tool for studying a reasonable connection form of concrete cut-off wall and core wall in high earth and rockfill dams.

Elastoplastical Analysis of the Interface between Clay and Concrete Incorporating the Effect of the Normal Stress History

The behaviour of the soil-structure interface is crucial to the design of a pile foundation. Radial unloading occurs during the process of hole boring and concrete curing, which will affect the load transfer rule of the pile-soil interface. Through large shear tests on the interface between clay and concrete, it can be concluded that the normal stress history significantly influences the shear behaviour of the interface. The numerical simulation of the bored shaft-soil interaction problem requires proper modelling of the interface. By taking the energy accumulated on the interface as a hardening parameter and viewing the shearing process of the interface as the process of the energy dissipated to do work, considering the influence of the normal stress history on the shearing rigidity, a mechanical model of the interface between clay and concrete is proposed. The methods to define the model parameters are also introduced. The model is based on a legible mathematical theory, and all its parameters have definite physical meaning. The model was validated using data from a direct shear test; the validation results indicated that the model can reproduce and predict the mechanical behaviour of the interface between clay and concrete under an arbitrary stress history.

ANSYS implementation of damping solvent stepwise extraction method for nonlinear seismic analysis of large 3-D structures

A three-dimensional Damping Solvent Stepwise Extraction (DSSE) method is developed and implemented in the ANSYS finite element software for nonlinear seismic analysis of large-scale structures resting on an unbounded visco-elastic soil. Given a larger introduced artificial damping and arbitrary soil–structure interface geometry, the DSSE method provides a more efficient and accurate way to calculate the interaction forces of the unbounded soil within the framework of finite elements. In order to consider the effect of the artificial damping on structures, an Interface-Coupling element established with interface nodes in generalized structure substructure is developed through the element-based partition of the damped soil elements. The Newton–Raphson iteration method is employed along with the Newmark assumptions for the nonlinear analysis of generalized structures. The Newmark algorithm for damped bounded soil is also employed to assure the accuracy and convergence of the interaction system. User Programmable Features (UPFs) available in ANSYS is used to incorporate DSSE method. Also, a complete toolkit for general seismic soil–structure interaction (SSI) analysis is created using scripting-based ANSYS Parametric Design Language (APDL) and Graphical User Interface (GUI). The proposed technique is applicable to arbitrary sophisticated structure models, irregular soil domain, and provides the selection of the artificial damping without depending on the domain size of bounded soil. Two validation examples are presented to demonstrate the accuracy and efficiency of the proposed method. Moreover, an optimal case is suggested in view of engineering practice based on the comparison among the results from several sets of computational parameters including domain size, amount of artificial damping, and extraction steps. Nonlinear seismic analysis of high arch dam in south-west China is also presented to illustrate the analysis procedure, and demonstrate the capabilities of the method.

Excess Pore Pressures Around Underground Structures Following Earthquake Induced Liquefaction

Underground structures located in liquefiable soil deposits are susceptible to floatation following an earthquake event due to their lower unit weight relative to the surrounding saturated soil. This inherent buoyancy may cause lightweight structures to float when the soil liquefies. Centrifuge tests have been carried out to study the excess pore pressure generation and dissipation in liquefiable soils. In these tests, near full liquefaction conditions were attained within a few cycles of the earthquake loading. In the case of high hydraulic conductivity sands, significant dissipation could take place even during the earthquake loading which inhibits full liquefaction from occurring. In the case of excess pore pressure generation and dissipation around a floating structure, the cyclic response of the structure may lead to the reduction in excess pore pressure near the face of the structure as compared to the far field. This reduction in excess pore pressure is due to shear-induced dilation and suction pressures arising from extensile stresses at the soil-structure interface. Given the lower excess pore pressure around the structure; the soil around the structure retains a portion of this shear strength which in turn can discourage significant uplift of the underground structure.

Universal Calibration Device for Fluid and In-Soil Calibration of Pressure Transducers

Evaluation of stresses generated at soil-structure interface or within the soil mass influences the design decisions of substructures. Though many analytical techniques are available, actual measurement of these stresses is of prime importance from analytical and construction view point. The measurement of stresses also provides valuable information for validating constitutive theories of geo-material behaviour and computational techniques for examining soil-structure interaction problems. Calibration of pressure transducer involves application of known pressure to the transducer and obtaining the relationship between applied pressure and pressure cell output. In absence of such relationship, interpretation of data obtained using transducers is highly questionable. Present study describes details of indigenously developed universal pressure transducer calibration device, developed by modifying the conventional triaxial apparatus. It allows demanding task of fluid and in-soil calibration of pressure transducers, which was not possible with existing calibration devices. Performance of the developed device checked using three different types of transducers revealed accurate and repeatable results.

Coefficients of active earth pressure with seepage effect

A calculation method for the active earth pressure on the possibly inclined face of a retaining wall provided with a drainage system along the soil–structure interface is presented. The soil is cohesionless and fully saturated to the ground surface. This situation may arise during heavy rainstorms. To solve the problem, the water seepage through the soil is first analyzed using a numerical procedure based on the boundary element method. Then, the obtained pore-water pressure 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 coefficients of active pressure with seepage effect which can be used to evaluate the active earth thrust on walls of any height. A series of charts with values of the coefficients of active earth pressure with seepage calculated for selected values of the soil internal friction angle, the wall–soil friction angle, and the wall face inclination is presented.

The Research Methods of Mechanical Characteristics on the Soil-Structure Interface

There are general three kinds of means to research the mechanical properties of soil-structure interface, and they are soil-structure contact experimental studies, constitutive model and numerical calculation. Through the tests, the observation and measurement results in different experimental conditions can be obtained about soil-structure interface stress-strain characteristics, and then basing on the existing constitutive model theory researchers can put forward reasonable explanation to the phenomenon of the tests. Finally the constitutive model theory can be applied to the numerical calculation to predict and reproduce the test phenomenon, so as to fully reveal the nature of the soil-structure interface mechanical characteristics.

Effects of embedment including slip and separation on seismic SSI response of a nuclear reactor building

Abstract The seismic response of nuclear reactor containment building considering the effects of embedment, slip and separation at soil–structure interface requires modeling of the soil, structure and interface altogether. Slip and separation at the interface causes stress redistribution in the soil and the structure around the interface. The embedment changes the dynamic characteristics of the soil–structure system. Consideration of these aspects allows capturing the realistic response of the structure, which has been a research gap and presented here individually as well as taken together. Finite element analysis has been carried out in time domain to attempt the highly nonlinear problem. The study draws important conclusions useful for design of nuclear reactor containment building.

A coupling method for soil structure interaction problems

SUMMARYThis paper describes a soil‐structure coupling method to simulate blast loading in soil and structure response. For the last decade, simulation of soil behavior under blast loading and its interaction with semi buried structure in soil becomes the focus of computational engineering in civil and mechanical engineering communities. In current design practice, soil‐structure interaction analysis often assumes linear elastic properties of the soil and uses small displacement theory. However, there are numerous problems, which require a more advanced approach that account for soil‐structure interaction and appropriate constitutive models for soil. In simplified approaches, the effect of soil on structure is considered using spring‐dashpot‐mass system, and the blast loading is modeled using linearly decaying pressure–time history based on equivalent trinitrotoluene and standoff distance, using ConWep, a computer program based on semi‐empirical equations. This strategy is very efficient from a CPU time computing point of view but may not provide accurate results for the dynamic response of the structure, because of its significant limitations, mainly when soil behavior is strongly nonlinear and when the buried charge is close to the structure. In this paper, both soil and explosive are modeled using solid elements with a constitutive material law for soil, and a Jones–Wilkins–Lee equation of state for explosive. One of the problems we have encountered when solving fluid structure interaction problems is the high mesh distortion at the contact interface because of high fluid nodal displacements and velocities. Similar problems have been encountered in soil structure interaction problems. To prevent high mesh distortion for soil, a new coupling algorithm is performed at the soil structure interface for structure loading. The coupling method is commonly used for fluid structure interaction problems in automotive and aerospace industry for fuel sloshing tank, and bird impact problems, but rarely used for soil structure interaction problems, where Lagrangian contact type algorithms are still dominant. Copyright © 2012 John Wiley & Sons, Ltd.

Seismic Passive Earth Pressure with Seepage for Cohesionless Soil

The authors deal with the computing seismic passive earth pressure acting on a vertical rigid wall. The wall is provided with a drainage system along soil-structure interface and retains the cohesionless backfill subjected to water seepage. A general solution for the seismic passive earth pressure is presented. The solution is based on Coulomb's theory wherein seismic forces are assumed to be pseudostatic. The solution considers the pore water pressures induced by water seepage and earthquake shaking. Some important parameters are included in the solution. The parameters are the soil effective internal friction angle, wall friction, soil unit weight, and horizontal and vertical seismic acceleration coefficients. The comparison of the total seismic passive earth pressure in horizontal direction from the present method with published works indicates that the present method may be reasonable. The variations of the passive earth pressure coefficient with the soil effective internal friction angle are investigated for different wall friction angles and seismic forces. The effect of the water seepage on the seismic passive earth pressure is also investigated.

Arbitrary Lagrangian Eulerian formulation for soil structure interaction problems

Simulation of soil structure interaction problems becomes more and more the focus of computational engineering in the last decades in the civil engineering community. In many applications in civil engineering, the Lagrangian formulation is the main approach for soil structure interaction problems. For the last decades, various approaches have been investigated in fluid and structure mechanics, to solve fluid structure interaction problems, including Arbitrary Eulerian Lagrangian (ALE) formulation and meshless methods as Smoothing Particle Hydrodynamics (SPH). These two approaches are more common in fluid mechanics than structure and civil engineering, where the classical Lagrangian formulation is still dominant for numerical simulations. The Lagrangian formulation, where the mesh moves with material is mainly used to solve problems in solid mechanics, and civil engineering for soil structure interaction problems. For small deformation, Lagrangian formulation can solve soil structure interface and material boundary accurately; the main limitation of the formulation is high mesh distortion for large deformation and moving structure. One of the commonly used approaches to solve these problems is the ALE formulation which has been used with success in the simulation of fluid structure interaction with large structure motion such as sloshing fuel tank in automotive industry and bird impact in aeronautic industry. In this paper, devoted to ALE formulation for civil engineering problems, the mathematical and numerical implementation of the ALE formulation and the contact algorithm are described. In order to validate the ALE algorithms, and prove its ability for civil engineering applications, we consider two different applications. First we perform the simulation of a shock wave propagation generated by a detonation of an explosive. In the second application, we consider a soil structure coupling problem, using an ALE formulation for the soil which undergoes large mesh deformation, and a Lagrangian formulation for the structure. A contact algorithm is performed at the soil structure interface.

Experimental Study on Shear Mechanical Characteristics of Soil-Structure Interface under Different Normal Stress

The direct shear mechanical characteristics of soil-structure interface under different experimental condition were studied systematically using the DRS-1 high normal stress direct and residual shear apparatus. The results show that the normal stress is an important factor which determines the mechanical characteristics of soil-structure interface. The curve of shear stress-shear displacement presents strain softening when the normal stress<3MPa, linear hardening when =3~5MPa and strain hardening when12MPa, separately. At the same time, the volume of the soil expands when <3MPa and contracts when >3MPa. But the volume of the soil expands and contracts simultaneously during the process of direct shear when =3MPa.The roughness of the interface influences not only the shape of the shear stress-shear displacement curve but also the shear strength of the interface. Under same normal stress condition，the shear strength of interface increases with the roughness but the influence degree of interface roughness reduces gradually with the increase of normal stress. The grain breakage degree is different under different normal stress. It increases evidently with the increase of normal stress.

Flexural response of surface strip footings resting on reinforced viscoelastic foundation beds

A generalized method of analysis has been proposed to determine the flexural response of a surface strip footing resting on a compacted granular foundation bed overlying a clay layer of soft to medium consistency with geogrid/geomat/ geocell reinforcement at their interface. The footing and the reinforcement are idealized as beams with sufficient flexural rigidity. The compacted granular bed and the clay layer are idealized by Winkler springs and four-element standard viscoelastic Burger element respectively. The rationality of choosing Burger model to represent the time-dependent behavior of compressible viscoelastic medium has been elucidated. A non-uniform variation of the subgrade modulus is assumed along the width of the footing at the soil-structure interface. Governing differential equations, predicting the response of the reinforced foundation bed under the given loading condition, are developed; and solved using the Finite Difference Method (FDM). Based on the convergence study, optimal size of mesh segment is determined; and the correctness of the study has been established by comparing the solution from a degenerated case with the standard solutions available in literatures. Effect of variation in the viscoelastic parameters of the Burger model on the flexural response of the reinforced foundation bed has been discussed. It is shown that the Burger model can be degenerated to any lower order models by proper modifications in the viscoelastic parameters of the Burger model. Significant variation in the bending moment of footing is observed with elapsed time, thus revealing the necessity of considering the effect of time in the design of reinforced viscoelastic foundation beds.

Elastoplastic constitutive modelling of soil–structure interfaces under monotonic and cyclic loading

This paper is dedicated to the non-linear numerical modelling of the soil–structure interface. Thus, in a first part, after the presentation of the constitutive model, the soil–structure interface interaction is treated in terms of direct shear test simulations. A strategy for the interface model parameters’ identification is also presented. This strategy is linked to the similitude of soil–structure interface behavior and the soil behavior, regarding the interface surface roughness. In a second part, the performance of the numerical simulations are verified numerically against published results for soil–structure experimental shear tests. Finally, as an application, interface stress paths are studied in axially loaded pile–soil systems and load transfer mechanisms are identified.

Seismic Analysis on Soil-Structure Interaction of Buildings over Sandy Soil

During earthquakes seismic waves propagate from the bedrock through the soil layers and damage structures on the surface. The understanding of local site effects on strong ground motion is of particular importance for the mitigation of earthquake disasters as well as future earthquake resistant design. This paper presents an idealized two dimensional plane strain finite element seismic soil-structure interaction analysis using Abaqus V.6.8 program. The analysis performed by considering three actual ground motion records representing seismic motions with low, intermediate and high frequency content earthquakes. Through these analyses, influence of different subsoils (dense and loose sand), buildings height, in addition to the frequency content of the earthquake have been investigated on amplification, acceleration response and stress propagation on the soil-foundation interface. Results illustrate that both sandy soils amplify seismic waves on the soil-structure interface because of the soil-structure interaction effect.

Advantages of an analysis of soil-structure interaction in a frequency domain

With the computer power available an analysis of a total soil-structure system has become possible. In this paper the advantages of an analysis performed in an frequency domain is shown: the condensation to the primary degrees of freedom, thereby conserving all the characteristic properties of the system, is straightforward; material damping based on rheological models can be considered easily; and even nonlinear problems may be investigated. The formulation is developed in a total displacement formulation, where the motion is driven by forces acting at the soil-structure interface, or more generally, at so-called interaction nodes. The total displacement formulation is compared with the classical approach, where the unknowns are the relative deformations with respect to the rigid base of the structure. These unknows are produced by inertial forces acting on the masses of the structure. In the conclusion the total displacement formulation in the frequency domain is suggested for structures with embedded elastic foundation built on a sub-grade which requires extended modeling for the mechanical representation of the structure and the sub-grade.

Dilatancy of the interface between a structure and gravelly soil

Dilatancy is one of the key properties of the soil–structure interface. A number of monotonic and cyclic shear tests were analysed to derive the rules and the dilatancy mechanism of the interface between a structure and a gravelly soil; diverse influential factors were considered, such as soil type, roughness of the structure and normal stress. The volumetric change due to the dilatancy consists of a reversible and irreversible dilatancy component, each of which has different mechanisms, different rules and different control factors. The reversible dilatancy component is strongly dependent on the direction of the applied shear after an initial application of shear loading. The irreversible dilatancy component gradually increases owing to the continued application of shear and exhibits a close relationship with the evolution of the physical state. The volumetric change that is due to the dilatancy mainly depends on part of the tangential displacement which corresponds to the deformation of the soil that is constrained by the structure; such a part of the tangential displacement is significantly dependent on the state of the entire tangential displacement, on the normal stress and on the features of both the structure and the soil. The roughness of the structure, the behaviour of the soil and the normal stress have significant effects on the dilatancy behaviour of the interface.