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This paper presents a series of cyclic 2D direct shear tests on sand-rough material interfaces under constant normal load (CNL) and constant normal stiffness (CNS) conditions. The aim of these tests is to describe the behavior of the soil-pile contact subjected to a large number of cycles due to environmental or anthropic loadings. These cycles (typically 10 or less due to an early rupture) are small (10, 20 and 40 kPa in terms of shear stress). A new interpretation of the direct shear tests is proposed. The sample of soil is schematically composed of a sheared interface and of a buffer under oedometric load. The problem of sand leakage between the shear box and the rough plate, classical phenomenon in this type of test, is focused. The effect of initial density, position of 'center of cycles' in stress plane (mean cyclic variables) and cyclic amplitude is investigated. The cycles are defined by the initial mean cyclic normal stress, the level of initial mean cyclic stress ratio and the normalized cyclic amplitude. Under CNL condition, either dilation or contraction is exhibited, in agreement with the characteristic state developed by Luong (International symposium on soils under cyclic and transient loading, Swansea, 7-11 January, pp 315-324, 1980). The influence of a prescribed normal stiffness is especially considered. It can be highlighted that CNS cyclic paths are always contractive. This contraction results in a drop of mean cyclic normal stress often called degradation of friction. [ABSTRACT FROM AUTHOR]

This paper deals with a laboratory and in situ study on the improvement of lateral friction along inclusions embedded in fine grained soils. Several soil-inclusion interfaces are considered and characterised by direct shear at constant normal stress and at constant normal stiffness, between silt and concrete/silica sand/silica sand + geotextile/silica sand + metallic grid. The performances of metric inclusions arc measured by pull-out tests, compared and simply modelled. Taking advantage of the dilatancy of sand, properly managed, is highlighted. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effects of cyclic shear amplitudes and loading sequences on a soil–structure interface using direct shear tests under a large number of loading cycles. A series of cyclic direct shear tests were performed on a granular soil-rough interface under the constant normal load (CNL) condition. Initially, monotonic interface direct shear tests were carried out as benchmarks to specify test boundaries and proper ranges of assigned cyclic amplitudes. Dry standard Fontainebleau sand in dense and loose conditions and a modified rough surface material were utilized to represent a soil-rough structure interface. A series of CNL cyclic interface direct shear tests was then conducted by varying the applied cyclic shear stress amplitudes and the cyclic loading sequence (small-to-large and large-to-small patterns) with a large number of testing cycles (104). Immediately after the cyclic shear tests were completed, monotonic interface direct shear tests were again performed to examine the post-cyclic behaviour of the soil-rough interface. Test results yielded that the applied cyclic shear stress amplitudes did affect the soil-rough interface by inducing a gradual contraction and an expansion in shear displacement accumulation. The maximum stress ratio could notably influence the volumetric behaviour and shear displacements. The accumulation of mean cyclic displacements was independent of the change in cyclic shear stress amplitudes between two consecutive cyclic loading sequences. The post-cyclic behaviour showed that changing the shear stress cycles between two consecutive packages did not influence the peak stress ratio. [ABSTRACT FROM AUTHOR]

The development and construction of offshore wind farms requires the correct estimation of the friction that can be mobilised at the rock/grout interface. In conventional studies, the shear behaviour of a joint is usually investigated with laboratory tests under constant normal load/stress (CNL), however, in engineering practice, direct shear testing under constant normal stiffness (CNS) has been proved to be more realistic in the assessment of the development of the side shear resistance in rock grouted pile design. In this work, an extensive experimental campaign on the shear response of a weak carbonate rock (limestone) interface with grout is presented, in the frame of offshore wind turbines. First, basic mechanical testing is performed on the two interface materials in order to evaluate their mechanical properties. The output of these tests reveals not only the contrasting properties of the two interacting materials, but also the decreased response of the limestone in the presence of water. A series of monotonic shear tests (both under CNL and CNS conditions) on wet rough limestone/grout interfaces reveal the high impact of adhesion between the two materials to the mechanical response. Based on the monotonic results, a number of CNS shear tests under cyclic loading takes place, where different failure modes are observed dilatant and contractant response. The variability of the failure mode is strongly related not only to the adhesion created with the cast grout, but also to the limestone's micro-structural heterogeneity that manifests already after consolidation. The post-shear morphological state of the interface is analysed, while the variability of the failure surface and the presence of water gouge creation do not allow a clear correlation of the morphologfy to the mechanical response. Overall, the response of this type of weak rock interface where the properties of the grout are significantly higher, is governed by the behaviour of the rock. [ABSTRACT FROM AUTHOR]

The experimental device previously used to study the hydromechanical behaviour of individual fractures on a laboratory scale, was adapted to make it possible to measure flow through porous rock mass samples in addition to fracture flows. A first series of tests was performed to characterize the hydromechanical behaviour of the fracture individually as well as the porous matrix (sandstone) comprising the fracture walls. A third test in this series was used to validate the experimental approach. These tests showed non-linear evolution of the contact area on the fracture walls with respect to effective normal stress. Consequently, a non-linear relationship was noted between the hydraulic aperture on the one hand, and the effective normal stress and mechanical opening on the other hand. The results of the three tests were then analysed by numerical modelling. The VIPLEF/HYDREF numerical codes used take into account the dual-porosity of the sample (fracture + rock matrix) and can be used to reproduce hydromechanical loading accurately. The analyses show that the relationship between the hydraulic aperture of the fracture and the mechanical closure has a significant effect on fracture flow rate predictions. By taking simultaneous measurements of flow in both fracture and rock matrix, we were able to carry out a global evaluation of the conceptual approach used. [ABSTRACT FROM AUTHOR]

Cyclic friction tests between laboratory grown columnar ice and micro-concrete plates were performed at –10°C to study ice–concrete friction under conditions similar to those observed in ice–structure interactions. This paper presents the results obtained in terms of friction coefficients. Effects of time and contact conditions are analysed, and conclusions about the effective physical mechanisms of friction are drawn. These conclusions are validated by a simple model of the ice–concrete contact.Key words: ice, structure, concrete, contact, interaction, friction, law, model, viscoplasticity, roughness.Des essais de frottement cycliques ont été réalisés à –10°C entre de la glace columnaire fabriquée en laboratoire et des plaques de micro-béton. Ils ont permis d'étudier le frottement glace–béton dans des conditions proches de celles observées dans le cas des interactions glace–structure. Cet article décrit les résultats obtenus en termes de coefficients de frottement. Les effets du temps et des conditions de contact sont analysés, ce qui permet de dégager les mécanismes physiques mis en jeu lors du frottement. Ces mécanismes ont été testés dans un modèle simple du contact glace–béton.Mots clés : glace, structure, béton, contact, interaction, frottement, loi, modèle, viscoplasticité, rugosité. [ABSTRACT FROM AUTHOR]

A new experimental apparatus is presented for testing the time-dependent behaviour of interfaces, including in particular interfaces of geomaterials, under constant loading. This apparatus allows the application of two orthogonal loads normal and tangential to the mean plane of the interface, as well as the measurement of the axial and tangential relative displacements. The sample is moulded inside two half shear boxes and the system is designed in such a way that the shear force is applied along the mean plane of the interface. Some preliminary testing was carried out on a clay rock/concrete interface, under a controlled temperature environment. Preliminary results are presented, showing the evolution of the delayed displacements. [ABSTRACT FROM AUTHOR]

This study is a part of a wide multi-scale research based on in situ experiments and laboratory tests. The latest, radial water injections in the centre of the lower joint wall are done at constant normal stress ranging from 0 to 110 MPa and at pressures from 0 to 4 MPa. Four hydromechanical tests have been performed in the L3S laboratory on fractured limestone samples (two diaclase and two bedding plane). The measurement analysis shows a relation between the contact surface variations and the flow values inside the fracture. The hydromechanical modelling performed using 3DEC code can be improved compared with the previous analysis due to the modification of the relation between the joint hydraulic opening and the joint mechanical closure. The gap between simulations and measurements can be related to fracture asperity degradation and turbulent flow that have not been taken into account in the modelling. [ABSTRACT FROM AUTHOR]

The experimental characterization of the thermo-poro-mechanical behaviour of Aegion Fault drilling cores is presented. The heart of the fault is met at a depth of 760 m and consists of clay-rich material on a length of about 1 m. This zone is surrounded by a cataclastic one. Here the thermo-poro-mechanical behaviour of the clayey core is investigated by means of oedometer and triaxial compression experiments. It is shown that softening behaviour under thermal loading is possible. Thermal collapse of the material may thus activate fluid pressurisation inside the fault and trigger fault slip. In addition, the behaviour of the interface between the intact rock and the cataclastic zone is studied by direct shear tests. To cite this article: J. Sulem et al., C. R. Geoscience 336 (2004). [Copyright &y& Elsevier]