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The influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils. These are based on assumptions regarding the interaction between different levels of structure, which still require experimental validation. A study has been carried out to investigate the evolution of fabric in a compacted natural clay during wetting and loading, and the results are presented in this paper. Samples of London Clay were statically compacted to the same initial conditions, dry of optimum moisture content in a Proctor plot, and subsequently taken along complex stress paths involving wetting, loading, or a combination of both. Mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) microstructure investigations were carried out to observe and quantify the change in fabric associated with each path. The soil fabric was observed to change from an aggregate to a matrix type structure along all wetting paths. This transition was found to take place only when the suction was reduced to a value close to zero kPa. Results also showed that fabric changes during yielding were stress path-dependent. It was not possible to find a correspondence between the volume of free porosity and the volume of intra-aggregate pores, as suggested by some authors. Finally, the volume of pore water was found to agree closely with the volume of intra-aggregate pores, providing support to the assumption that in an unsaturated aggregate microstructure the clay aggregations are saturated.

This paper proposes a new approach for modelling coupled nonlinear soil–structure interaction problems by domain decomposition. It is assumed that the soil–structure coupled system is physically partitioned into independently modelled soil and structure sub-domains. A coupling procedure based on the sequential iterative Dirichlet–Neumann coupling algorithm is presented, which utilizes the condensed tangent stiffness matrices at the soil–structure interface to ensure and accelerate convergence to compatibility in successive update of the boundary conditions. As a special case of the proposed approach, the condensed tangent stiffness matrix is approximated via reduced order models of the partitioned sub-domains throughout the coupling iterations. A simulation environment has been developed, utilizing discipline-oriented solvers for nonlinear structural and geotechnical analysis, and is discussed. This tool is used to demonstrate the applicability of the presented coupling algorithm in modelling nonlinear soil–structure interaction problems, highlighting its relative merits compared to interface relaxation algorithms. Furthermore, the developed tool is employed for a case study involving nonlinear soil–structure interaction analysis between a plane frame and soil subjected to ground excavation, where the computational and modelling benefits of the proposed approach and the developed tool are clearly established.

This paper presents a case study of the Bolu highway twin tunnels that experienced a wide range of damage during the 1999 Duzce earthquake in Turkey. Attention is focused on a particular section of the left tunnel that was still under construction when the earthquake struck and that experienced extensive damage during the seismic event. Static and dynamic plane-strain finite element (FE) analyses were undertaken to investigate the seismic tunnel response at two sections and to compare the results with the post-earthquake field observations. The predicted maximum total hoop stress during the earthquake exceeds the strength of shotcrete in the examined section. The occurrence of lining failure and the predicted failure mechanism compare very favourably with field observations. The results of the dynamic FE analyses are also compared with those obtained by simplified methodologies (i.e., two analytical elastic solutions and quasi-static elastoplastic FE analyses). For this example, the quasi-static racking analysis gave thrust and bending-moment distributions around the lining that differed significantly from those obtained from full dynamic analyses. However, the resulting hoop stress distributions were in reasonable agreement.

Interaction between atmosphere and soil has only recently attracted significant interest. Soil-atmosphere interaction takes place under dynamic climatic conditions, which vary throughout the year and are expected to suffer considerable alterations due to climate change. However, Geotechnical Analysis has traditionally been limited to simplistic approaches, where winter and summer pore water pressure profiles are prescribed. Geotechnical Structures, such as cut slopes, are known to be prone to large irreversible displacements under the combined effect of water uptake by a complex vegetation root system and precipitation. If such processes take place in an unsaturated material the complexity of the problem renders the use of numerical analysis essential. In this paper soil-atmosphere interaction in cut slopes is studied using advanced, fully coupled partially saturated finite element analyses. The effect of rainfall and evapotranspiration is modelled through sophisticated boundary conditions, applying actual meteorological data on a monthly basis. Stages of low and high water demand vegetation are considered for a period of several years, before simulating the effect of vegetation removal. The analysis results are presented with regard to the serviceability and stability of the cut slope.

In this study, the evolution of fabric in compacted London Clay has been studied in detail. Samples were statically compacted to the same initial conditions and taken along a number of stress paths – involving both wetting and loading – to different final conditions. Wetting and loading was conducted using both conventional and osmotic oedometers (the latter allowed the suction to be varied in a controlled manner). The study of micro-fabric involved a combination of quantitative measurements of the pore space, using Mercury Intrusion Porosimetry, with qualitative observations of the overall arrangement of particles, using Environmental Scanning Electron Microscopy. The study showed important changes to take place in the soil micro-fabric during wetting, whereas the effect of loading was seen to be less severe. The results suggest that changes in the overall micro-fabric of a compacted clayey soil are strongly stress path dependent.

The performance of the generalized-α, Newmark, HHT and WBZ time integration schemes is examined for a boundary value problem of a deep foundation subjected to various earthquake loadings. The effects of the frequency content of the earthquake excitation and the natural frequency of the numerical model on the performance of the above-mentioned algorithms are considered. The various time integration methods are compared in terms of accuracy, the ability to control high-frequency dissipation and run time. It is concluded from the finite element analysis results that the generalized-α scheme has superior qualities compared to the other algorithms investigated.

This paper investigates recent advances in modelling soil anisotropy. It begins by considering some recent laboratory tests performed in a large hollow cylinder apparatus. The results of these tests show that soil strength is very anisotropic. A brief review of what is probably one of the most comprehensive constitutive models (MIT-E3) that can model anisotropic soil behaviour is then given. This model is then used to predict the behaviour of some foundation problems and of an embankment on soft ground. In all cases the results of anisotropic analyses are compared with those of equivalent isotropic analysis. Such comparison quantifies the potential errors in current practice, which generally assume isotropic soil behaviour.

A variety of radial stress measuring systems are available in the literature, all of which allow the determination of horizontal stresses with a suitably modified odometer. However, most of the experience with such systems has been on saturated samples. A new osmotic odometer was developed to test unsaturated soils under atmospheric conditions. The device incorporated an active radial stress measuring system to determine the full state of stress during a test. Suction control was achieved by means of an osmotic system, whereas suction measurements were made with miniature tensiometers. The main odometer ring incorporated four small strain-gauged diaphragms, together with a compensating system, to ensure that radial deformations were kept to a minimum. To evaluate the performance of the system, data obtained from a number of tests on compacted clay have been analyzed. Results show that the system yields plausible measurements in the majority of cases; however, there were instances when unusual results were observed. These cast some doubt on the viability of using an odometer equipped with a radial stress measuring system—such as the one presented in the paper—to measure horizontal stresses in unsaturated soils. It is recommended that similar tests are performed with different equipment, to verify whether some of the anomalous results presented in this paper represent actual soil response, or are simply an artifact consequence of the chosen testing method.

The kinematic forces induced on piles in two-layered soil medium are investigated using finite element method. Typical layered subsurface condition with the soil properties relevant to Sri Lanka are considered in the present study. Hyperbolic nonlinear constitutive model is used for the soil medium and the soil medium is modelled as a fully coupled system. The effect of the earthquake was simulated by lateral ground acceleration applied to the bedrock. The validity of the results of the proposed model was established by comparing with the trends observed in similar studies reported in the literature. The effects of the stiffness of the soil layers, pile diameter, fixity at the pile head, and a defect present at the layer interface on the kinematic forces are investigated in the present study. Finally, the use of the results of the present study in the design and construction of bored and cast insitu concrete in Sri Lanka are highlighted.