Soil-structure Interface Research Articles

Bio-inspired geotechnical engineering: principles, current work, opportunities and challenges

A broad diversity of biological organisms and systems interact with soil in ways that facilitate their growth and survival. These interactions are made possible by strategies that enable organisms to accomplish functions that can be analogous to those required in geotechnical engineering systems. Examples include anchorage in soft and weak ground, penetration into hard and stiff subsurface materials and movement in loose sand. Since the biological strategies have been ‘vetted’ by the process of natural selection, and the functions they accomplish are governed by the same physical laws in both the natural and engineered environments, they represent a unique source of principles and design ideas for addressing geotechnical challenges. Prior to implementation as engineering solutions, however, the differences in spatial and temporal scales and material properties between the biological environment and engineered system must be addressed. Current bio-inspired geotechnics research is addressing topics such as soil excavation and penetration, soil–structure interface shearing, load transfer between foundation and anchorage elements and soils, and mass and thermal transport, having gained inspiration from organisms such as worms, clams, ants, termites, fish, snakes and plant roots. This work highlights the potential benefits to both geotechnical engineering through new or improved solutions and biology through understanding of mechanisms as a result of cross-disciplinary interactions and collaborations.

Directionally dependent strength and dilatancy behavior of soil–structure interfaces

Soil–structure interfaces typically exhibit a shear behavior that is independent of the direction of relative displacement due to symmetry in the solid material's surface profile. This experimental study investigates the interface shear behavior of surfaces with asymmetric profiles inspired by the scales of snake skin. The results of shear box interface tests on two sandy soils indicate that the peak and residual interface shear strengths and dilatancy are greater when the soil is displaced against the sharp edges of the asperities (cranial direction) than when the soil is displaced along the asperities (caudal direction). The experimental results indicate that the effect of asperity geometry on the interface shear response can be captured with the ratio of asperity length to asperity height (L/H). Analysis of the stress–dilatancy behavior indicates that interfaces with a relatively short asperity length follow a classical flow rule developed for soils. However, the relationship between the mobilized stress ratio and the dilatancy rate is shown to be a function of the shearing direction and asperity geometry. Implementation of snake skin-inspired profiles on the surface of geotechnical structures may provide benefits in performance and efficiency during installation and service life. In general, the results of this study indicate the behavior of the soil-structure interfaces sheared in the cranial direction is similar to that of interfaces between soil and fully rough surfaces. In contrast, the behavior of the soil-structure interface sheared in the caudal direction shares characteristics with that of interfaces with smooth surfaces, including the mobilization of smaller a interface strength and dilation.

BiLSTM-Based Soil–Structure Interface Modeling

Deep learning (DL) algorithm bidirectional long short-term memory (BiLSTM) neural network is employed to model behaviors of the soil–structure interface in this study, as a pioneer research work to investigate the feasibility of using DL to model interface behaviors. Datasets are collected from 12 constant normal stress and 20 constant normal stiffness sand–structure interface tests. A modeling framework with the integration of BiLSTM is thereafter proposed. The results indicate that the BiLSTM-based model can accurately capture the responses of interface behaviors including volumetric dilatancy and strain hardening on the dense samples and volumetric contraction and strain softening on the loose samples, respectively. The effects of surface roughness, soil relative density, and normal stiffness on the interface behaviors are also investigated using the BiLSTM-based model. The predicted normal stress, shear stress, and normal displacement show good agreement with measured results.

Phenomenological fractional stress–dilatancy model for granular soil and soil-structure interface under monotonic and cyclic loads

The stress–dilatancy relation is of critical importance for constitutive modelling of geomaterial. A novel fractional-order stress–dilatancy equation had been developed for granular soil, where a nonlinear stress–dilatancy response was always predicted. However, it was experimentally observed that after a certain extent of shearing, an almost linear response between the stress ratio and the dilatancy ratio, rather than the nonlinear response, usually existed. To capture such stress–dilatancy behaviour, a new fractional stress–dilatancy model is developed in this study, where an apparent linear response of the stress–dilatancy behaviour of soil after sufficient shearing is obtained via analytical solution. As the fractional order varies, the derived stress–dilatancy curve and the associated phase transformation state stress ratio keep changing. But, unlike existing researches, no other specific parameters, except the parameter related to fractional order, concerning such shift are required. Then, the developed stress–dilatancy model is applied to constitutive modelling of granular soil and soil–structure interface, for further validation. A series of test results of different granular soils and soil–structure interfaces under different loading conditions are simulated and compared, where a good model performance is observed.

Effects of water content on shear properties of bentonite–polymer composite structure

Understanding mechanical behavior at the soil–structure interface is fundamental for safety in engineering and is therefore an important consideration in structural design. Buildings can be deformed or severely damaged by shear forces from the action of earthquakes, waves, or winds. It is therefore necessary to understand the conditions which lead to structural failure at the soil–structure interface under shear action. We investigated the strain and displacement of bentonite–polymer specimens at various moisture contents. Shear failure was investigated using novel shear test equipment consisting of a two-dimensional soil fracture test device and computerized digital image correlation (DIC) technology. Analysis of the shear test results revealed the mechanical properties of bentonite–polymer composite structure under shear stress. Experiments showed that there were four stages in the failure of the bentonite–polymer samples: an increasing stress stage, a pre-damage stage, an abrupt damage stage, and a stable stage. At the instant the shear stress reaches peak value, the strain in the bentonite was greater than that in the polymer at the same position. In the failure stage, the bentonite at the middle and upper levels of the bentonite–polymer interface cracked first. Increased moisture content in the bentonite weakens the shear performance at the bentonite–polymer interface, and brittle failure was most significant when the moisture content was optimal. • A novel type of shear observation equipment was used in this work. • The four stages of shear failure of bentonite-polymer specimens were observed. • The influence of water content on the shear failure mode of bentonite-polymer composite specimens has been deeply studied. • It is found for the first time that the bentonite-polymer specimens exhibit brittle failure under the optimal water content.

Analytical solution of passive resultant force acting on retaining structure in case of an inner pit

ABSTRACT In the past few years, pit-in-pit excavations have become common to maximize urban underground space. Estimating passive earth pressure is a critical prerequisite to using them. However, Rankine and Coulomb’s theory, based on the semi-infinite space assumption, is not suitable for a foundation pit with inner pits. In this study, four cases are identified according to the relative positions of inner pits, and corresponding formulas, based on limit equilibrium analysis, are proposed to calculate the passive resultant force. The analytical expressions of the passive resultant force and the shear failure angle in each case are correspondingly derived. This method is verified with the finite element method (FEM) by comparing the horizontal passive earth pressure and failure surfaces. A few parameters, including the size of the inner pit, the distance between retaining structure and inner pit, the cohesion of soil, and soil-structure interface friction angle, have an effect on the passive resultant force, which is shown by a parametric study. There is one most unfavorable position for an inner pit where the passive resultant force reaches its minimum. This research is intended to provide a theoretical basis for the bracing design of a foundation pit with an inner pit.

End Bearing Capacity Factor for Annular Foundations Embedded in Clay Considering the Effect of the Adhesion Factor

New limit analysis solutions for the end bearing capacity of annular foundations in clay with linearly increasing shear strength are presented in the paper. The strength profile of clay corresponds to a typical case of a normally consolidated clay in deep water, where the strength at the ground surface is defined as zero and increases linearly with the depth. The annular foundation has internal and external radii and is embedded in clay, where the adhesion factor representing the strength at the soil-structure interface is also taken into account. Using the lower and upper bound finite element limit analysis, the end bearing capacity factor of this problem can be obtained based on three considered dimensionless parameters, which are the ratio between the internal radius and the external radius, the embedded depth ratio, and the adhesion factor. The collapse mechanisms of annular foundations in clay are also examined and discussed in the paper to portray the effects of the radius ratio, the depth ratio, and the adhesion factor.

Granular hypoplastic interface model considering surface roughness

The problem of soil-structure interface is an important part in studying of soil structure interaction. The interface between soil and structure is widely present in water conservancy, civil engineering, municipal and transportation projects. Roughness is the main factor affecting the mechanical properties of the contact surface. From this requirement, a new contact model has been developed that takes into account the relative surface roughness. It is based on the granular hypoplasticity. The experimental results are compared with simulations using the Mohr-Coulomb model and the new model, respectively. It is shown that the new models can represent the non-linearity of the mechanical properties of the contact surface and agree well with the experimental data.

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.

Assessment of groundwater depletion–induced land subsidence and characterisation of damaging cracks on houses: a case study in Mohali-Chandigarh area, India

The present study identified groundwater depletion–induced land subsidence by spaceborne differential interferometric SAR (DInSAR) technique and assessed the damaging impacts of land subsidence by characterising the cracks on houses in Mohali-Chandigarh area of India. First, we identified groundwater depletion hot spots using pre-monsoon and post-monsoon groundwater-level (GWL) data of Central Ground Water Board (CGWB), India, for the period of 2005–2018. Both conventional and advanced DInSAR techniques were used to identify temporally consistent subsiding areas and measure precise rates of subsidence in and around groundwater depletion hot spots. We studied the damaging impacts of land surface deformation by characterising the damaging cracks on houses in affected areas. Groundwater depletion and resulting aquifer-system compaction increase effective stress on confining clay layer which leads to stress build-up at the soil-structure interface and causes damaging cracks on houses. A variety of damaging cracks on houses were observed at the affected areas such as Sohana, Landran, Kharar and Kurali localities. We attempted to characterise the damaging cracks on the basis of shape, size, orientation, surface morphology and texture of the cracks; sense of ground movement; and nature of stress build-up at the interface. We identified tensional cracks, compressional cracks and shear cracks with diverse orientations and separation widths. Finally, a comparative assessment of groundwater depletion, land subsidence and damaging impacts on houses has been made. Using DInSAR technique, we identified land subsidence in and around the groundwater depletion areas in Sohana and Landran (both in Mohali City area), Kharar and Kurali (in Mohali district outside Mohali City area) and Sectors 27–28 in Chandigarh with radar line-of-sight subsidence rates of ~6–7.5 cm/year, ~5.5–6.5 cm/year, and ~ 4 cm/year respectively. We observed that the houses in and around Landran appears to be worst affected followed by Kharar, Sohana and Kurali. From this study, it appears that the type of construction of the houses, e.g. prevalence of masonry and reinforced masonry structures, is primarily responsible for the worst damaging impacts of the houses in Landran and Kurali areas besides the magnitude of land subsidence.

Non-isothermal soil-structure interface model based on critical state theory

In energy geostructures, the soil-structure interface is subjected to thermo-mechanical loads. In this study, a non-isothermal soil-structure interface model based on critical state theory is developed from a granular soil-structure interface constitutive model under isothermal conditions. The model is capable of capturing the effect of temperature on sand/clay-structure interfaces under constant normal load and constant normal stiffness conditions. First, the developed model was verified for sand-structure interface in isothermal conditions. Then, it was calibrated for clay-structure interface under non-isothermal conditions. On one hand, a well-defined peak shear stress for the clay-structure interface and, on the other hand, the effect of temperature on the void ratio of the clay-structure interface were captured and reproduced by the model. The importance of interface thickness determination and some differences between the interface thicknesses of clay-structure and sand-structure interfaces are discussed in detail. The additional parameters have physical meanings and can be determined from laboratory tests. The modeling predictions are in good agreement with experimental results, and the main trends are properly reproduced.

Experimental and numerical analysis of axially loaded slender piles implementing a hypoplastic model

Multiple studies have been carried out to estimate uplift pile capacity, within three main categories: i) the experimental method, which is very costly; ii) a simpler method using load transfer mechanisms; and iii) the numerical finite element method (FEM). The predictive capacity of numerical simulation depends mainly on the constitutive model used to model the soil-structure interface at which the load transfers from the pile to the surrounding soil. A reliable constitutive model capable of capturing the main features of soil behaviour based on easily obtained parameters is thus required. The hypoplasticity model is a promising constitutive model in this respect, offering a particular class of rate non-linear constitutive model in which the stress increment is expressed in a tensorial equation as a function of strain increment, actual stress, and void ratio. The hypoplastic model thus requires only eight material parameters (critical friction angle φc , e c0, e i0, e d0 (critical, maximum, and minimum void ratios, respectively), granular stiffness hs, and the model constants n, α, and β), with two additional parameters used to simulate the pile-soil interface (kr and ), which represent the surface roughness and the thickness of the shear zone, respectively. The performance of the model was verified in this work by comparing the numerical results with the experimental results for a single pile model under pull-out force with different surface roughnesses and confining pressures. The resulting good agreement between the numerical and the experimental results confirmed the ability of the hypoplastic model to simulate soil behaviour under complex conditions.

Three-dimensional non-linear seismic analysis of asymmetric structures on elastic soil

An approximate method for non-linear seismic analysis of three-dimensional two-way asymmetric buildings resting on flexible foundations under bi-directional ground motions is presented. To take into account the soil–structure interface effect, the sub-structuring method with frequency-independent soil springs and dashpots was employed. To consider the non-linear behaviour of the structure, a modal stick with five degrees of freedom was used to simulate the multi-degree-of-freedom modal equations for the soil–structure system. Using the bifurcation characteristic of modal pushover curves, the modal stick was modified, by which the coupled modal non-linear translation and rotation deformations were simulated. The seismic responses of two flexibly supported asymmetric buildings (three and eight storeys) were evaluated by the uncoupled modal response history analysis (UMRHA) method employing the proposed modal stick. The seismic responses of the structures were also obtained by employing the rigorous non-linear response history analysis and the results were compared with the corresponding outcomes from UMRHA method. The comparison showed good agreement between the outcomes of the two analysis methods, thus demonstrating that the proposed three-dimensional non-linear analysis technique developed in this study is an effective and applicable tool for dealing with the non-linear analysis of flexibly supported two-way asymmetric-plan structures.

Influence of constitutive model on soil structure interface interaction under axisymmetric condition

This paper mainly studies the performance of axisymmetric radial interaction between soil and structure under radial stress. One of the key points is the research on the mechanical properties of the interface. The latter is now the frontier field, and also the focus of this paper's theoretical analysis. Based on FEM, a large-scale international finite element software, this paper attempts to establish a general comprehensive model with comparative function through the advantages of numerical simulation. After obtaining the results, the analysis focuses on the influence of different materials on the interaction, and summarizes the stress field, strain field, displacement field and stress-strain relationship of the model under different materials.

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.

Discussion of “Effect of Grain Size Distribution of Sandy Soil on Shearing Behaviors at Soil–Structure Interface” by Han-Lin Wang, Wan-Huan Zhou, Zhen-Yu Yin, and Xi-Xi Jie

Discussion of “Effect of Grain Size Distribution of Sandy Soil on Shearing Behaviors at Soil–Structure Interface” by Han-Lin Wang, Wan-Huan Zhou, Zhen-Yu Yin, and Xi-Xi Jie

Closure to “Effect of Grain Size Distribution of Sandy Soil on Shearing Behaviors at Soil–Structure Interface” by Han-Lin Wang, Wan-Huan Zhou, Zhen-Yu Yin, and Xi-Xi Jie

Closure to “Effect of Grain Size Distribution of Sandy Soil on Shearing Behaviors at Soil–Structure Interface” by Han-Lin Wang, Wan-Huan Zhou, Zhen-Yu Yin, and Xi-Xi Jie

Examination of Interface Asperity and Particle Shape on the Mechanical Behavior of Soil-Structure Interfaces Using 3D Printed Models

The influence of surface topography on the mechanical behavior of soil-structure interfaces over a range of particle sizes and shapes is systematically investigated in this research. 3D printed interfaces with different topographies and uniformly graded 3D printed soil particles and two types of natural sands (Ottawa sand 20/30 and Dolomite sand #1, #2 and #3) were employed and tested. Laboratory investigations showed that the shear strength and volume change responses of the 3D printed interfaces are positively influenced with the increase of the inclination of asperities. The proposed wedge friction model successfully explained the distinct mechanical behaviors of soil-structure interfaces under shearing. A “turning point” was found for the interface shear resistance with the increase of the inclination of asperities. When the surface topography produces passive resistance to the soil, the change of the surface topography has little effect on the interface mechanical behavior. The findings from this research will provide insights for soil-structure interface design and discrete element method (DEM) simulations in considering the mechanical behavior of soil-structure interfaces.

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.

On the resistance to heat flow across soil-structure interfaces

A number of recent publications have suggested that in order to reproduce thermal testing of energy piles, a finite value for the geo-contact thermal resistance (geo-CTR) at the soil-structure interface needs to be introduced. There is currently no guidance as to what value the geo-CTR should have. The geo-CTR will have two potential impacts in terms of the use of energy geo-structures, (i) reducing heat exchange efficiency, and (ii) increasing temperature changes and associated mechanical impacts within the geo-structure. This article sets out a new experimental method for quantifying the geo-CTR. The proposed method is based on the imposition of a heat flux through the two solid materials that form the contact. Its novelty rests with the acknowledgement that heat loss is inevitable and that the geo-CTR can be more reliably defined based on heat flow measurements at the actual contact. This concept is demonstrated via numerical modelling of a generic test set-up, where the errors induced by not accounting for heat loss, the interpolation of temperatures to the contact and the presence of the heat flow sensor were assessed. Initial test results are then presented that demonstrate how the method works. These results suggest that for a dry medium sand, while the geo-CTR is sensitive to the soil density, it is small and the effect on heat transfer is also likely to be small. Further testing will explore the relative importance of a number of factors and in particular, the soil type, on the geo-CTR.