56 research outputs found
An investigation into the vertical bearing capacity of perforated mudmats
No full textThe optimal design of a mudmat foundation for a seabed structure maximizes the ratio of vertical compression to pullout capacity, which can be achieved by adding perforations. This paper describes an investigation led by Technip in which solid and perforated mudmats were installed into soft clay. The installation load of the solid mudmats matched the theoretical bearing capacity. Perforations reduced the installation load in proportion to the perforated area. In heterogeneous conditions, a further change in installation load arose due to the shallower failure mechanism. Peak pullout resistance was governed by separation beneath the mudmat, and depended on the width of the grillage elements formed by the perforation.</p
Infiltration-induced Slope Instability: a multi-scale approach
No full textPrecipitation, together with erosion and earthquakes, have been recognized as the main triggering factors of shallow landslides. However, there are relatively few well-documented cases where direct relationships could be established between occurrence and features of shallow landslides, the rainfall characteristics (e.g. intensity, duration) and water retention curves. A field experiment has been performed on a steep forested slope located on the east-facing banks of the river Rhine in Ruedlingen, northern Switzerland. The aim of the experiments was to study the triggering mechanisms of the landslides induced by rainfall. The pore pressure and the degree of saturation, which are linked through the water retention curve, represent two of the main variables affecting the mechanical behaviour of unsaturated soils, and their relationships to rainfall are complex. The difference in the determination of water retention curves at different scales are analysed in this paper for Ruedlingen soil together with their effects on mechanical behaviour at multi-scale
Hydro-mechanical analysis of a surficial landslide triggered by artificial rainfall: the Ruedlingen field experiment
No full textThis paper interprets the hydromechanical behaviour of a steep, forested, instrumented slope during an artificial rainfall event, which triggered a shallow slope failure 15 h after rainfall initiation. The soil's mechanical response has been simulated by coupled hydro-mechanical finite-element analyses, using a critical state constitutive model that has been extended to unsaturated conditions. Failure occurs within a colluvium shallow soil cover, characterised as a silty sand of low plasticity. The hydraulic and mechanical parameters are calibrated, based on an extended set of experimental results, ranging from water retention curve measurements to triaxial stress path tests under both saturated and unsaturated conditions. Rainfall is simulated as a water flux at the soil surface and suitable boundary conditions account for the hydromechanical interaction between the soil cover and the underlying bedrock. The results are compared with field data of the mechanistic and the hydraulic responses up to failure and are found to provide a very satisfactory prediction. The study identifies water exfiltration from bedrock fissures as the main triggering agent, resulting in increased pore pressures along the soil-bedrock interface, reduced available shear strength and cause extensive plastic straining, leading to the formation and propagation of a failure surface.</p
Compressibility of undisturbed silt loam soil – measurements and simulations
No full textThe protection of soils against compaction requires knowledge of the mechanical behavior and properties of structured unsaturated soils and their dependence on soil moisture. This study of an agricultural silt loam soil is based on undisturbed specimens from the plow layer (7-17 cm depth) and two subsoil layers (47-57 cm and 67-77 cm depth) conditioned to five initial suctions (s = 1, 3, 6, 16, 32 kPa) per layer and compressed under drained, confined uniaxial stress. From the resultant total axial stress versus void ratio curves, effective axial stress versus void ratio curves were calculated using a modified form of van Genuchten’s equation (van Genuchten, 1980). The effective axial stress versus void ratio curves were fitted using the unsaturated soil mechanics model by Casini (2012). The effective initial precompression stress, compression, and recompression indices and the soil mechanical parameters N and b were then determined for the plow and subsoil layers. Based on Casini (2012), a model was developed to predict the effective initial precompression stress from the initial void ratio and suction or saturation degree. The Casini (2012) model was successfully fitted to the effective axial stress versus void ratio curves recorded in the confined uniaxial compression tests on the specimens, as well as the relationship of the effective initial precompression stress to the initial void ratio plus the initial degree of saturation and suction. The results show that some measure of soil density (void ratio) is equally as important as soil moisture to describe compression behavior for structured, undisturbed soil
Modelling of soil–structure interaction for a piled bridge abutment in plane strain FEM analyses
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Controlled water-level system for breach analysis of levees within an enhanced acceleration field
No full textCorrect scaling of breach analysis of river levees is a challenging task that is not easily accomplished by physical modelling. Several small-scale physical model tests have been conducted at 1-g level, which cannot truly represent the stress-dependency of soils, whereas the scaling issues arising from centrifuge modelling have not been fully explored.Two key features have to be considered when modelling the prototype behaviour. On the one hand, the whole embankment should be included in the model to ensure that flow nets are valid. This is not always easy to achieve due to space limitations within the strongboxes used. On the other hand, full control of water levels, prior and during breaching, is of principal interest.This contribution shows how both of these features can be modelled for levee breaching by taking advantage of the availability of space within a drum centrifuge and its versatile toolplate
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