Behavior Of Soil-structure Interface Research Articles

Temperature dependence of soil-structure interface behaviour in the context of thermally-activated piles: A review

Thermally-activated (TA) piles are cost-effective technologies with the dual role of transferring structural loads to the ground while exchanging heat with the surrounding soil as part of shallow geothermal energy systems. As TA piles are subjected to both thermal and mechanical loads, the behaviour on the soil-structure interface is particularly complex and is key for the analysis and design of these structures. The present paper aims to review the current state of knowledge regarding the thermal dependency of soil-structure interface behaviour and provide an overview of experimental results obtained from non-isothermal tests investigating soil and soil-structure interface behaviour. This overview includes comparison of the different experimental equipment and procedures, soil types, initial soil state overconsolidation ratio (degree of consolidation or relative density) and thermal loadings. It was found that it is not straightforward to reach a unique interpretation regarding possible variation of the soil-structure interface behaviour at different temperatures: the framework of the experimental evidence is very complex due to the wide variation in testing conditions. Therefore, it was not possible to compare the studies like-for-like, leading to an apparently ambiguous interpretation of the results. Overall, the consensus across this and other studies is that the potential variation of interface resistance with temperature typically appears to be limited and not very significant.

Role of Initial State, Material Properties, and Confinement Condition on Local and Global Soil–Structure Interface Behavior during Cyclic Shear

Role of Initial State, Material Properties, and Confinement Condition on Local and Global Soil–Structure Interface Behavior during Cyclic Shear

Shear behavior of the sand-concrete interface under cyclic thermal cy-cles

Energy piles - foundation elements also used as heat exchangers - are subjected to daily and seasonal heating and cooling cycles, which might result in the modification of thermo-mechanical behavior of the soil-pile interface. In order to evaluate the effect of the pile’s geothermal activation on a sand-concrete interface, at laboratory scale, a series of direct shear tests were performed using a device adapted for thermomechanical loading. The constant normal load (CNL) direct shear tests were carried out for three different thermal loading scenarios, i.e., at a constant temperature of 13°C, and for two different cooling-heating (8-18°C) cycles. The volumetric deformation after 10 thermal cycles is evaluated, and the shear results are compared.
 A lot of studies [1, 2, 3, 4, 5, 6, 7, 8] have been performed to investigate the thermal effects on the shear behavior of soil-structure interface through direct shear tests. However, in previous studies all the thermal cycles were performed before the shearing phase. Hence, the effect of temperature cycles on the sand-concrete interface after the shear strength has already been mobilized (i.e., interface shear test) has not been well investigated so far. In fact, in real exploitation conditions, the thermal loading is usually added after a part of the mechanical loading or deformation occurred at the soil-pile interface, given the fact that the geothermal exploitation starts only once the building is in operation. To better understand the effects of thermal cycles on the shear properties of sand-concrete energy piles interface after a prior shear phase, a series of interface direct shear tests were performed in laboratory: (1) Reference Test (RT), shearing under constant temperature of 13°C (undisturbed soil temperature below 5 m in the Parisian region, France); (2) Cyclic Test 1 (CT-1), displacement controlled shearing under constant temperature (13°C), 10 thermal cycles (8 to 18°C), finally displacement-controlled shearing until the constant volume state was generated; (3) Cyclic Test 2 (CT-2), shearing to 1/2 of the residual shear strength, 10 thermal cycles (8 to 18°C), finally displacement-controlled shearing until the constant volume state was generated (CT-2 test). The monotonic displacement-controlled direct shear tests were conducted under constant normal stresses equal to 50 kPa, 100kPa and 150kPa that correspond to the typical normal effective stresses acting on the soil-pile interface at different depths.
 Figure 1 presents the volumetric strain (εv) during the thermal cycles of CT-1 and CT-2. The sand samples are characterized by a contractive behavior during each heating phase and followed by an expansive behavior at the high temperature of 18°C. The samples continue to expand in the next cooling phase, then they start to contract when the low temperature of 8°C is constant. The volumetric strain changes are attributed to the thermal-induced particle rearrangement during the heating-cooling cycles. After the 10 thermal cycles, the sand samples show an overall contractive response. The thermal cycles induce more vertical strain on the samples of CT-2 than CT-1 (see Figure 1). The possible reason is that shearing to 1/2 residual shear strength develops more unstable particle rearrangement in CT-2 samples than shearing to the residual shear strength in CT-1 samples.
 The peak and residual interface friction angles of CT-1 and CT-2 after the 10 cyclic thermal cycles are compared with RT in Table 1. The peak interface friction angle of CT-1 is 28.9°, 0.6° lower than the one of RT (29.5°). Whereas a higher peak interface friction angle is mobilized in CT-2 (31.7°). CT-1 is characterized with a residual interface friction angle of 27.9°, which is 0.5° lower than the 28.4° of RT. However, the difference of residual interface friction angles between CT-2 (28.5°) and RT (28.4°) is only 0.1°. To conclude, the effect of the 10 cyclic thermal cycles on the sand-concrete interface is quite limited, it slightly decreases the peak as well as residual interface friction angles of CT-1 and increases these of CT-2.

Experimental investigation of soil–structure interface behaviour under monotonic and cyclic thermal loading

The effect of temperature on the monotonic and cyclic shearing response of a soil–structure interface is of critical importance for the application of thermal-active geo-structures. To investigate this, soils and soil–concrete interfaces were comprehensively tested with a temperature-controlled direct shear device under both fixed temperatures and thermal/mechanical cycles within the range of 2–38 °C. Monotonic and cyclic shearing with various boundary conditions, including constant normal load (CNL), constant normal stiffness (CNS) and constant volume (CV), were conducted to resemble the conditions that thermal-active-geo-structures may experience. The strength properties of the sand, clay, and sand–concrete and clay–concrete interfaces were partially influenced by heating and cooling under all boundary conditions. However, several effects were observed which could affect the performance of thermo-active structures. Heating cycles caused the clay–concrete interface to be overconsolidated, implying a lower excess pore pressure would be generated during shearing. The cyclic CNS tests suggested that the interface strength could degrade due to (thermally induced) cyclic shear displacements, with this effect strongly related to the state of the soil rather than the temperature directly. In these tests, the medium-dense sand–concrete interface degraded to almost zero shear strength after 5 cycles, whereas the clay–concrete interface asymptotically degraded to around 60% of its strength after 10 cycles.

Effect of particle breakage on the behavior of soil-structure interface under constant normal stiffness condition with DEM

Previous studies show that extensive particle breakage occurs at the soil-structure interface, which may influence the shear strength, but a corresponding comprehensive micro-mechanical analysis, particularly with constant normal stiffness (CNS), is missing. In this study, a series of interface shear tests under CNSs are simulated with the discrete element method (DEM) to understand the role of particle breakage at the interface. Through a rigorous calibration process, the interface model in DEM is first validated with identifying micro-mechanical parameters. Then, by modifying the reference tensile strength of particles, the effect of particle breakage on the behavior of soil-structure interface is quantitatively investigated. All results demonstrate that, particle breakage decreases the dilation, normal stress, shear stress, and shear zone thickness in the interface shear test; particle breakage decreases the peak friction angle while increases the residual friction angle at the interface; and particle breakage decreases soil anisotropy at the interface. In addition, the degree of particle breakage is increased by normal stiffness. The findings of this study may provide deeper insights on the role of particle breakage at the interface with CNS and allow engineers to have a better estimation of the interface strength.

Influence of Surface Roughness and Particle Characteristics on Soil–Structure Interactions: A State-of-the-Art Review

The study of soil–structure interface behavior contributes to the fundamental understanding of engineering performance and foundation design optimization. Previous research studies the effect of soil characteristics and surface roughness property on the soil–material interface mechanism via interface shear test. The reviews utilizing past established laboratory studies and more recent tests based on state-of-the-art technologies reveal that surface roughness significantly affects interface shear performances in the studies of soil–structure interactions, especially in peak shear strength development. A preliminary but original investigative study by the authors was also carried out using a sophisticated portable surface roughness gauge to define the material surface roughness properties in order to study the interface behavior parametrically. Additionally, using the authors’ own original research findings as a proof-of-concept innovation, particle image velocimetry (PIV) technology is applied using a digital single-lens reflex (DSLR) camera to capture sequential images of particle interactions in a custom-built transparent shear box, which validate the well-established four-stage soil shearing model. The authors also envisaged that machine learning, e.g., artificial neural network (ANN) and Bayesian inference method, amongst others, as well as numerical modeling, e.g., discrete element method (DEM), have the potential to also promote research advances on interface shear mechanisms, which will assist in developing a greater understanding in the complex study of soil–structure interactions.

Micro-mechanical analysis of soil–structure interface behavior under constant normal stiffness condition with DEM

Micro-mechanical analysis of soil–structure interface behavior under constant normal stiffness condition with DEM

Experimental study on microbubble drag reduction on soil-steel interface

The soil-structure interface behavior is an important concern in ocean engineering design. In some cases, it is necessary to reduce the drag of structure, especially the shear stress on the soil-structure interface. In this study, a series of microbubble drag reduction experiments were first carried out on soil-steel interface. The effects of microbubble volume, moisture content, rotation speed and water types (freshwater and seawater) were investigated. It is shown that the average drag reduction ratio ranged from 15% to 92% under various conditions. With the increase of microbubble volume, the drag reduction effect is improved. Meanwhile, the characteristics of drag reduction were also explored under different moisture content. The drag reduction effect of microbubbles is relatively stable at different speeds.Its is proved that the microbubble drag reduction method can obviously reduce the soil-steel interface drag.

Shaft Resistance of Long (Flexible) Piles Considering Strength Degradation

Soil-structure frictional resistance is an important parameter in the design of many foundation systems. The soil-structure interface area is responsible for load transferring from the structure to the surrounding soil. The mobilized shaft resistance of axially loaded, long slender pile embedded in dense, dry sand is experimentally and numerically analyzed when subjected to pullout force. Experimental setup including an instrumented model pile while the finite element method is used as a numerical analysis tool. The hypoplasticity model is used to model the soil adjacent to and surrounding the pile by using ABAQUS FEA (6.17.1). The soil-structure interface behavior depends on many factors, but mainly on the interface soil's tendency to contract or dilate under shearing conditions. To investigate this tendency, three piles with different surface roughness and under different confining pressures are used. A dilation behavior is observed in the relation of the average shaft resistance with the axial displacement for piles with rough and medium roughness surfaces, while contraction behavior is noticed when shearing piles with smooth surfaces. A large shear strength degradation of about (10%) reduction in the shaft resistance is observed under low confining pressure compared to a lesser reduction value of about (2%) under high confining pressure. Good agreement is obtained between the experimental and the numerical results.

The influence of roughness on cyclic and post-cyclic shear behavior of red clay-concrete interface subjected to up to 1000 cycles

Dynamic shear behavior of soil-structure interface is one of the most commonly problems in engineering practice, especially for the design and stability analysis of soil-structure interaction system subjected to cyclic loading. This paper presents the results of an experimental study on the interface between red clay and concrete that is subjected to a large number of cycles (up to 1000 cycles). Three concrete blocks with different surface roughnesses were fabricated and displacement-controlled cyclic tests were conducted by using a large-scale direct shear device under three different normal stresses (100 kPa, 200 kPa and 300 kPa). The effects of normal stress, roughness and number of cycles on cyclic and post-cyclic shear behavior of interface were then discussed in detail. The test results show that the red clay-concrete interface exhibits softening behavior under different normal stress levels. The mobilized shear stress decreases moderately with the number of cycles and subsequently remains constant after 500 cycles of loading. The response of interface subjected to cyclic loading shows apparent aeolotropy due to shear directions in every cycle. Interface shear stiffness and damping ratio decreases with increasing cycle numbers. The red clay-concrete interface represents an overall contraction behavior in cyclic and post-cyclic direct shear tests. The cyclic loading does not lead to degradation for post-cyclic shear strength.

Three-dimensional elasto-plastic damage model for gravelly soil-structure interface considering the shear coupling effect

The gravelly soil-structure interface was observed to exhibit a significant coupling effect among the orthogonal shear directions due to the three-dimensional shear application in different experimental investigations, which governs major three-dimensional features of the interface. In this paper, initially, a three-dimensional modeling framework is established based on the analyses of interface behavior under different shear coupling conditions. A series of concepts and assumptions are derived in this framework, banking on which a three-dimensional model scheme is proposed by reasonably modeling the shear coupling effect. Afterward, a three-dimensional elasto-plastic damage interface model is developed based on the proposed model scheme and modified formulations of a previous two-dimensional EPDI model. Only a single new parameter is introduced in the three-dimensional shear stress-strain relationship modeling scheme to quantify the three-dimensional shear response of the interface besides already known parameters of the EPDI model. The model can simulate the monotonic and cyclic response of interface along two and three-dimensional shear paths in a unified manner. The performance of the model is validated based on test data from the literature. The model can capture different essential features of the gravelly soil-structure interface behavior under three-dimensional conditions, e.g., coupling effect, volumetric change behavior and aeolotropy.

Analysis of consistent soil–structure interface response in multi–directional shear tests by discrete element modeling

Abstract Structure surface normally owns highly directional properties caused by the properties of the material and the manufacturing process. Proper understanding of soil–structure interface behavior must recognize the structure surface’s highly directional properties and take into consideration its interactions with particulate material. To investigate the mechanical behavior of granular soil–structure interface under multi–directional shear tests, a shear orientation is defined to be an angle θ between the shear direction and the principal rough direction of the directional surface. Using the discrete element method, a series of 3D numerical interface shear tests was conducted, under seven shear orientations ( θ = 0°, 10°, 30°, 45°, 60°, 75°, and 90°). The consistent response of macroscale shear behavior at the interface, loaded by various shear orientations, are presented from the perspectives of the resultant average shear stresses in x – and y – directions and soil volumetric strain. A determination of the thickness of the localized shear band in each specimen is followed by the discussion of particle displacement vector distribution. Furthermore, the evolutions of microscale properties inside and outside the localized shear band, such as the coordination number and material fabric provide a physical meaning or an explanation for the consistent macroscale shear behavior of granular soil–structure interface at a microscale level. The findings emphasize the importance of measuring the horizontal load in x – and y – directions when conducting experimental interface shear tests on rough surface with highly directional properties, because the resultant resistance corresponds to the true resistance of the granular assembly.

Rate effects on the interface shear behaviour of normally and overconsolidated clay

This paper presents a study on the effects of shearing velocity, surface roughness and overconsolidation ratio on the strength and deformation behaviour of fine-grained soil–structure interfaces. The results of shear box direct interface shear tests, augmented with soil deformation measurements from particle image velocimetry analyses, indicate that shearing velocity (i.e. velocity at which the continuum surface is displaced) has a controlling effect on the drainage conditions mobilised during shearing. As shearing velocity was increased, undrained conditions were progressively mobilised, characterised by smaller interface strength and volumetric changes for tests on normally consolidated specimens. Increases in shearing velocity resulted in increases in interface strength for overconsolidated specimens. The results presented herein indicate that, as the magnitude of surface roughness was increased, drained shearing conditions were favoured for a given shearing velocity. Soil deformation measurements indicate that the shear zone where localisation occurs becomes thicker as the surface roughness increases, and the magnitude of soil deformations decreases as shearing velocity is increased. The findings presented herein are relevant for prediction and interpretation of soil–structure interface behaviour, as well as for development of constitutive models that capture the combined effect of shear rate, surface roughness and stress history.

Thermal effects on mechanical behaviour of soil–structure interface

Mechanical behaviour of the soil–structure interface plays a major role in the shear characteristics and bearing capacity of foundations. In thermoactive structures, due to nonisothermal conditions, the interface behaviour becomes more complex. The objective of this study is to investigate the effects of temperature variations on the mechanical behaviour of soils and the soil–structure interface. Constant normal load (CNL) and constant normal stiffness (CNS) tests were performed on the soil and soil–structure interface in a direct shear device at temperatures of 5, 22, and 60 °C. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The sandy soil was prepared in a dense state and the clayey soil was prepared in a normally consolidated state. Results show that the applied thermal variations have a negligible effect on the shear strength of the sand and sand–structure interface under CNL and CNS conditions, and the soil and soil–structure interface behaviour could be considered thermally independent. In clay samples, an increase in the temperature increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The temperature rise had less impact on the shear strength in the case of the clay–structure interface than in the clay samples. The adhesion of the clay–structure interface is less than the cohesion of the clay samples.

Modelling and calibration for cyclic soil-structure interface behaviour

The structural performance of many geotechnical systems (e.g. axially-loaded pile foundations), depends on the shearing resistance at the soil interface, which may govern the load bearing capacity of the foundation. Experimental investigations have shown that this interaction is mainly localised within a narrow shear band next to the structure. Under cyclic loading, a contraction of the soil at the interface may arise (net volume loss), possibly leading to a stress relaxation and thus to a reduction of the load bearing capacity (the so-called friction fatigue). Based on the constitutive similarities between soil continua and interfaces, we propose here the adaption of a Generalized Plasticity model for sandy soils for the numerical analysis of interface problems. In this contribution, the results of an experimental campaign for the parameter calibration of the constitutive model are presented. The tests have been conducted with a ring shear device involving different normal stresses, roughness of the steel plates as well as cyclic loading. The new modelling approach shows promising results and has the additional practical advantage that the interface zone and the soil continuum can both be described with the same constitutive model in general boundary value problems.

Interface response-based soil classification framework

Current soil classification systems based on cone penetration testing (CPT) utilize a combination of the tip resistance (qt), pore pressure (u2), and friction sleeve (fs) measurements as inputs. While the qt measurements are typically normalized by the overburden stress, the fs measurements are often normalized by the net tip resistance, leading to the use of parameters that are dependent on each other. This paper presents the development of a soil classification framework that utilizes a normalized multi-friction parameter (MFP) and the CPT normalized tip resistance. The MFP parameter is obtained from measurements with textured friction sleeves from soundings with multi-sleeve attachments. The use of textured friction sleeves allows for fundamental differences in soil–structure interface behavior and particle sizes to be captured due to the significant degree of shearing induced within the soil. This classification framework was developed with results from over 30 soundings at six different sites. The analysis of samples taken from the field indicates that the proposed framework provides a classification that better agrees with the grain-size distribution for residuum, calcareous and intermediate soils, as compared to existing CPT-based systems. The potential development of a simplified probe with just one additional friction sleeve sensor can provide appropriate classification results and would facilitate adoption for use in practice.

Discrete element modeling of soil-structure interface behavior under cyclic loading

The cyclic shear behavior of the interface between soil and structure at both the macro and the micro level is investigated by interface direct shear tests under constant normal stiffness condition using discrete element modeling. The simulation results are validated qualitatively by the corresponding experiment. The influence of the initial state of the specimen (i.e. soil density and normal stress) on the cyclic behavior is systematically discussed. Moreover, the cyclic accumulative deformation of the interface is carefully studied in the view of the void ratio and the correlation between the final deformations under cyclic and monotonic loading is explored.

SOIL-STRUCTURE INTERFACE BEHAVIOR OF CEMENTED-PASTE BACKFILL MATERIAL MIXED WITH MINING WASTE

The use of mining wastes as a component of cemented paste backfill provides anenvironmentally acceptable method of waste disposal at a lesser cost as the method does not require tailingdams for storing the large volume of wastes. This study determines the applicability of cemented-pastebackfill materials mixed with aggregate quarry wastes as ground support to concrete structures. Aggregatequarry waste with varying fine contents was used as a substitute for sand in cemented-paste backfill and themixture was referred to as cemented-paste tailing backfill (CPTB). Its micro fabric structure was determinedthrough SEM-EDX tests. Test results showed that CPTB with 20% and 40% fine contents has acceptablevalues of strength properties in terms of its unconfined compressive strength and interface friction angle.The unconfined compressive strength in relation to its curing period is in the range of 120 kPa to 150 kPawhich can be described as having stiff consistency. The stress-strain interface behavior between CPTB andconcrete structure was evaluated through a direct shear test using strain rates that simulate the rapid and slowrates of loading. In both conditions, the stress-strain behavior exhibits strain softening. The average interfacefriction angle is 38o which can be associated with its dense condition. The modified hyperbolic model wasapplied to evaluate the soil-structure interface behavior of CPTB. Hyperbolic parameters were formulated topredict the interface shear stress - shear strain behavior of the CPTB when in contact with concretes structureat any value of shear strain and normal effective stress.

Issues involved with thermoactive geotechnical systems: characterization of thermomechanical soil behavior and soil-structure interface behavior

This paper focuses on the main issues discussed during a session on the impact of thermohydromechanical behavior of soils on thermoactive geotechnical systems, and how they could affect the performance of thermoactive geotechnical systems. Both soil behavior as well as soil–structure interaction behavior was discussed. The main observation from the session was that the thermohydromechanical behavior of saturated soils has reached a mature understanding, with several established constitutive models that can be used by engineers. However, there are still opportunities to enhance these constitutive models by considering issues such as unsaturated conditions, anisotropic stress states, cyclic heating and cooling effects, and changes in the preconsolidation stress during heating and cooling. Further there are still opportunities to improve our understanding of soil/concrete interface behavior, including the development of novel testing approaches.

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.