Spatial variations of soil properties occur even within nominally homogeneous soil layers. Therefore, to achieve a reliable geotechnical design, it is necessary to consider local variations of soil properties. Varying soil stiffness leads to spatially variable settlements, implying increasing dynamic forces on passing vehicles. Higher dynamic forces result in additional settlements and simultaneously reduce driving comfort. This process continues steadily until repair of the asphalt pavement is required. The aim of this study was to develop a new mechanically reasoned method for deriving the permissible spatial variation of continuous compaction control (CCC) data from driving comfort requirements. A numerical model was developed that allows modelling of the long-term evenness of asphalt pavements due to passing vehicles, taking into account spatial variation of the subsoil stiffness. The numerical model is based on the subgrade reaction method, modelling the surface and subjacent base courses by a series of spring elements. Thereby, a depth-dependent stress distribution and interactions of the base courses are considered. The initial stiffness of the spring elements is derived from oedometer tests. Depending on the traffic load and utilisation period, the long-term evenness of an asphalt pavement and the effects of a spatially varying subsoil stiffness can be investigated.
Current design practice simplifies complex loading scenarios, i.e. highly cyclic loads from varying direction offshore, using classification methods by combining different cycle packages with constant frequency, mean load level and amplitude. This procedure assumes the resulting accumulated deformation in the soil to be independent of the ordering of the cycle packages, i.e. the validity of miner’s rule. This paper presents an experimental study on the validity of Miner’s rule in non-cohesive soils based on high cyclic direct simple shear tests. The test program comprises monotonic and high cyclic direct simple shear tests in fine silica sand, which is routinely used at Centre of Offshore Foundation Systems. The paper investigates the effect of ordering of the cycle packages on the resulting cyclic deformation accumulation for different loading scenarios with varying mean and cyclic load level. The results are evaluated in terms of the accumulated volumetric and the resulting shear strain. Based on the literature, Miner’s rule is assumed to be valid for a deviation of the relevant variables of < 20 %. Conclusions with respect to the influence of cyclic preloading are drawn and related to current design practices.
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