Embankments made with marl and other soft clayey rocks result in an agglomerated structure of finite size particles. These particles evolve however, resulting in major changes of the overall behaviour of the aggregate. The development of settlements and the loss of strength in time are the main concerns in practice. The mechanisms leading to the breakage and eventually the destructuration of one single rock particle are investigated using the concepts of unsaturated soil mechanics since wetting and drying cycles, controlled by atmospheric changes, result in strong suction changes and are one of the main reasons for rock degradation. Numerical simulations of the behaviour of individual rock fragments when wetted until full saturation were performed. Several contributing factors, namely suction change rate, initial suction and confinement were investigated. The knowledge learned with the simulation of the degradation of single rock fragments was extended to simulate the behaviour of particle arrangements under some representative stress and suction paths. Some results of suction controlled tests used for the calibration of the models are presented. The calculated behaviour of single particles and aggregates under wetting is discussed and qualitatively compared with experimental observations of the individual rock fragments and the compacted material. The results obtained provide a new insight into the nature of degradation induced by wetting and drying. They provide also a mechanical explanation, at the level of rock fragments, for the overall behaviour of aggregates.

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A bonded elasto-plastic soil model is adopted to simulate self-boring pressuremeter tests. Calibration of the model with results from several natural clays identifies a meaningful parameter range for the simulations. Then a systematic sensitivity analysis of the loading SBPM test curve is carried out with an infinite cylindrical cavity analogue, focusing on the variables and parameters that are specific to the bonded material. This analysis reveals that the effects of mechanical overconsolidation and bonding on the pressuremeter loading curves are very similar. Unloading and strain-holding phases of the test show a greater capability to separate mechanical overconsolidation from bonding. The limited effects of finite pressuremeter length and partial drainage on the simulated curves do not change those conclusions.

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Many constitutive models have been developed to describe the behaviour of soils, but only more recently a limited number of them have paid attention to include effects of structure and consequently destructuration due to volumetric and/or deviatoric straining. Most of them consider isotropic behaviour for strength and structure of soil. In this paper a multilaminate type of constitutive model is presented in which anisotropic strength and anisotropic structure are taken into account. According to the mathematical formulation of the multilaminate framework, this kind of model is capable of taking into account induced anisotropy intrinsically. Inherent anisotropy can be introduced to the model by varying the model properties over sampling planes using a so-called microstructure tensor. Only mechanical destructuration, namely degradation of structure with deformation is considered in this paper. The proposed model is capable to consider anisotropy in bonding and preconsolidation pressure as well as inherent anisotropy in strength thus the hardening of the yield surface and strength parameters can be considered direction dependent. In this paper the drained and undrained behaviour of natural clays is simulated and the effect of different assumptions with respect to structure degradation and anisotropy is evaluated.

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The paper discusses the intrinsic properties, the geological history, the natural structure and the mechanical behaviour of intensely fissured clays from Santa Croce di Magliano, a site located within the East-side border of the Apennine chain (southern Italy). The clays were originally deposited elsewhere and subsequently moved and largely deformed during the Apennine orogenesis, so that their structure appears severely disturbed and fissured. The applicability of a continuum-based approach to describe the mechanical behaviour of a Representative Element Volume (REV, hereafter) of the natural, fissured clay is experimentally investigated by analysing the clay specimen deformation under plane strain compression by means of False Relief Stereophotogrammetry. The results of such analysis show that, despite the intense network of pre-existing fissures, the patterns of deformation - including the eventual development of shear bands within the REV of the natural clay - are similar to those observed for unfissured clays. Triaxial tests were carried out on both natural and reconstituted clay samples and the results were compared with those recognised in the literature to be typical of unfissured clays. Based on such comparisons, the study provides a few essential elements that are useful to define a general framework for the mechanical behaviour of intensely fissured clays.

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Natural and agricultural soils usually possess an aggregated structure; in the sense that they are composed of aggregates and large inter-aggregate pores. Under the natural condition, these soils are usually unsaturated and the large pores are easily drained. The present paper looks at the combined effects of soil structure and partial saturation on the mechanical behaviour of aggregated soils. Conventional and suction-controlled oedometer testing are used to evaluate the soil response at different combinations of saturation and the initial soil structure. The soil structure effects are assessed by comparing the behaviour of aggregated to that of the corresponding reconstituted soil. The effects of suction in reconstituted and aggregated soils are evaluated by testing at different levels of suction.

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This paper compares different approaches to constitutive modelling of natural structured clays by means of experimental data on natural Pisa and Bothkennar clays. The models evaluated are a hypoplastic model for structured clays, its simple elasto-plastic equivalent that requires parameters with similar physical meaning, and advanced elasto-plastic models based on kinematic hardening approach. Hypoplasticity predicts non-linear stress-strain response in the pre-failure region and different stiffness in different loading directions, it thus provides a clear qualitative advance with respect to the simple elasto-plastic model. It gives qualitatively similar predictions with the kinematic hardening models. The structure degradation and the large-strain response are predicted similarly by both the hypoplastic and elasto-plastic models, which show that the critical state soil mechanics theories can be treated successfully within the framework of the theory of hypoplasticity.

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The critical state friction angle, φ_c, is a parameter of interest in many geotechnical analyses dealing with cohesionless soils. However, despite the triaxial test being widely used to estimate this parameter, the accuracy achievable from a limited number of triaxial tests is unknown. Accuracy is of particular interest in industry, where typically only a few soil tests are possible due to budget limitations. Statistical analysis of an extensive high quality triaxial testing program from the literature is used here to obtain guidance on the number, density range, and pressure range of triaxial tests required to reach a specified level of confidence in the critical state friction angle. The adequacy of the estimating methodology is then tested against a smaller and independent set of triaxial tests on the same sand, performed in a commercial testing laboratory. The results suggest about six drained triaxial tests are needed for routine engineering where a precision of ±1.0° may suffice. However, for research or high precision work, more than twenty drained triaxial tests may be needed to determine φ_c to an accuracy of ±0.5° at 90% confidence. In all cases, tested samples should be uniformly distributed across the range of the soil's relative density.

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Measurement of the settlement of a cone submitted to incremental loading allows the determination of a modulus correlated to those obtained using laboratory tests or derived from other in situ tests. This test can be carried out with standard static penetrometer equipment. After stopping the penetration of a static penetrometer cone at a selected depth, an incremental loading test is carried out until the failure of the ground under the cone is observed. Stress strain relationships can be drawn from cone resistance and sleeve friction. In this manner, a modulus and a friction angle can be obtained. Thus the classical CPT log is enriched offering new possibilities. In this paper the development of the first prototype and measuring devices and the proposed testing procedure are presented. A comparison of laboratory and field tests and geotechnical centrifuge models shows the validity of the testing procedure and the chosen interpretation method. The results of site investigations carried out on French national experimental sites are also discussed and compared with high quality borehole expansion test and field measurement of shear wave velocity. These investigations have been carried out using this new testing method in combination with a semi-heavy static Piezocone penetrometer in order to check the potential use for geotechnical design. An attempt is made in this paper to validate the interpretation method of the results, which can be used for routine geotechnical engineering.

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This paper describes an investigation into the performance and pullout capacity of an inflatable anchor system. The anchor system comprises a hydraulically inflated rubber membrane or packer that may be bored into place and then inflated to provide pullout resistance. A series of scaled physical model tests were used to study the anchor performance and pullout capacity. The model tests were done in a calibration chamber using cohesionless sand and anchors of various length, diameter, embedment depth and inflation pressure. The anchor behaviour during pullout is interpreted using finite element analysis that accounts for non-linear soil behaviour, inflation and subsequent deformation of the inflatable membrane, and anchor-soil interaction. The scaled model tests and interpretations assist with identifying the dominant mechanisms affecting the pullout capacity of inflatable anchor systems.

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In order to analyze the instability phenomenon observed along the Northern High Speed Line of Réseau Ferré de France (RFF), soil blocks were taken at a site near the railway line, at four different depths (1.2, 2.2, 3.5 and 4.9 m). Cyclic triaxial tests were carried out on saturated and unsaturated soil specimens. The results from tests on initially saturated specimens showed that the soil taken at 2.2 m depth has the lowest resistance to cyclic loading, in relation to its highest porosity and lowest clay fraction. This soil was then studied at unsaturated state with various initial water contents. Unsaturated soil specimens were first subjected to cyclic loadings to decrease their volume. These cyclic loadings were stopped when the volume decrease was approximately equal to the initial pore air volume, or when the pores filled by air were eliminated and the soil was considered to have become saturated. Afterwards, the back-pressure tubing was saturated with de-aired water and cycles were applied under undrained condition. Significant effect of initial water content was evidenced: the lower the initial water content, the higher the cyclic resistance. This can be explained by the densification of the soil during the initial cyclic loadings.

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The proposed activity chart, which aims to classify soils (<425 μm) using the Atterberg limits, differs from the plasticity chart recently proposed by the author because the inorganic soils with platey clay minerals are classified (in addition to clay percentage) on the basis of their activity rather than on the degree of plasticity as a function of the liquid limit value, currently used by the standards. This is because soils that have the same liquid limit value may have very different characteristics because of both the amount and type of clay minerals contained in the soils. On the activity chart, the silt and the clay zones are subdivided (by two straight lines) in three new groups (low activity, medium activity and high activity) making it possible to classify inorganic soils with platey clay minerals (or their fraction) <425 μm on the basis of the amount and type of clay minerals they contain. The activity chart adapted to predict residual shear behaviour of cohesive soils is also shown. Finally, the distinction between coarse-grained soils and fine-grained soils based on their percentage of clay (<2 μm), might be useful in characterizing and predicting soils' engineering behaviour.

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This paper proposes a new approach for the analysis of shear-induced volume change of granular materials. Following a revisit to the micro-mechanical deformation mechanism and the findings from discrete element method simulations, it is concluded that the double slip-rotation rate mechanism is appropriate for the description of granular materials subjected to shear. The implementation of energy principle with the double slip-rotation rate mechanism provides a new method for the derivation of stress-dilatancy relation under general stress conditions without adopting Rowe's hypothesis of minimum energy ratio. This new approach can be easily extended to take into account the non-coaxility of granular material deformation. The dilatancy formulations proposed by Taylor, Rowe and Matsuoka-Nakai can all be recovered as special cases of the proposed approach. Comparisons with experimental data show that the new stress-dilatancy relation correctly captures the dilatancy behaviour of sand observed in both general 3D stress conditions and simple shear tests.

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This paper aims to illustrate a large-scale test on a pile group and a sheet pile quay wall which were subjected to liquefaction-induced large ground deformation. The sheet pile quay wall was displaced laterally and the 2×3 pile group was forced by the flow of liquefied soil. This experiment was conducted in March 2006 at the National Research Institute for Earth Science and Disaster Prevention (NIED), Hyogo Earthquake Engineering Research Center, Japan. Liquefaction-induced lateral spreading was achieved, and soil moved laterally about 1.1 m behind the sheet pile quay wall. Lateral soil displacement was measured by the inclinometers, and results were in close agreement with the directly observed values. Soil lateral displacement and velocity of soil flow decreased as the distance from the quay wall increased toward the landside. Bending strain records were able to explain the damages to the piles, yielding at the top and buckling at the middle height. Lateral force of the liquefied soil exerted on the piles was obtained using earth pressure (EP) sensors and it is shown that rear row piles (close to the quay wall) received larger lateral forces than front row piles (far from the quay wall). This behaviour is explained by the distribution of displacement and velocity of the liquefied soil throughout the shaking. In addition, the lateral soil force was back calculated from strain gauge data and the results are compared with the ones directly measured by the EP sensors. Then, the limitations and advantages of the back-calculation approach are elaborated in this study. Moreover, the time history of lateral soil force showed no correlation with either soil or pile displacements, while it demonstrated a fairly close correlation with the relative velocity until a specific time. This interesting finding would confirm the rate-dependent behaviour of the liquefied soil, though more data from large scale experiments, field testing and centrifuge model tests are needed in this regard.

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In recent years there has been a surge in the development of new small scale offshore facilities, including minimum facility structures for oil and gas developments as well as offshore renewable energy devices such as offshore wind turbines. In these cases the loading applied to the structure and foundation is significantly different to that applied to more typical larger offshore structures. The weight of the structure is much lower, and the horizontal load and moment applied to the foundation is much higher as a proportion of the vertical load. Design guidance for the combined loading response of shallow foundations under low vertical loads is sparse, and in particular much guidance is drawn from work where the vertical load applied to the foundation is close to the vertical bearing capacity. This paper addresses this lack of data by presenting results of combined loading experiments at low vertical loads on novel shallow foundations known as suction caissons. The experiments are carried out on dry sand at a low relative density to explore the drained response of the foundation. The experiments are successfully interpreted within the framework of work hardening plasticity, and information on the shape of the yield surface and the post-yield behaviour of the foundation is deduced. One of the key results is that the foundation can sustain moments and horizontal loads even when a tension is applied to the foundation.

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For determining shear wave velocity by bender elements, several types of travel time methods have been proposed and are being used commonly. Although the methods have been established over a period of time, there are still many aspects that need to be improved. For example, the ambiguity of arrival time due to near-field effect and the distance measurement for soft sample during testing installation. This study seeks to propose an alternative method which could minimise such ambiguities. In this regard, a method called variable-path length method is proposed, which uses a continuous sinusoidal wave instead of a pulse wave, is applied to a series of tests on reconstituted Kasaoka clay in a modified triaxial apparatus. Based on the results, it is verified that the proposed method can measure shear wave velocity without the ambiguity of arrival time and independent of initial distance between transmitter and receiver. In addition, the proposed method has an advantage to determine phase velocity of shear wave at arbitrary frequency which is useful to study the frequency dependence of geomaterials.

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