Effects of grain size distribution on the initial strain shear modulus of calcareous sand

The soil’s small strain shear modulus, Gmax or G0, is applied in dynamic behavior analyses and is correlated to other soil properties (density and void ratio) for predicting soil dynamic behavior under seismic loadings such as earthquakes, machinery or traffic vibrations. However, for calcareous sands, selecting representative samples for the field conditions is difficult; therefore, almost all measured soil parameters (post-seismic properties) do not reflect exactly the soil state before seismic loading. In some cases of dynamic loading, a change in grain size distribution (GSD) of soils, especially for calcareous sands might occur. Moreover, many of these sand types behave differently from silica sands owing to their mineralogy, particle characterization, soil skeleton, and the continuous changing of particle size. For this reason, a series of isotropic consolidation tests in ranges of confining pressure from 25 to 300 kPa as well as bender element measurements on a calcareous sand and on a reference silica sand were performed in this study. The effects of differences in gradation and in the type of material on the soil’s small strain shear modulus, Gmax, are discussed

Compaction control and related stress–strain behaviour of off-shore land reclamations with calcareous sands

AbstractWhen constructing off-shore land reclamations, one aims to ensure that the final soil mass fulfills certain minimal criteria related to shear strength, stiffness and resistance against liquefaction. In general, these characteristics improve with increasing density of the soil mass, which means that the above criteria are usually condensed into a single one: ‘adequate densification’.Quality control of reclamation constructions therefore focuses on the latter. Technical requirements are written based on one single parameter: the relative density Dr. On the site, this parameter is commonly determined indirectly using correlations with the cone penetration resistance qc, making the CPT the main tool for quality control.The paper presents data gathered during the design and construction of an off-shore land reclamation using calcareous sands. For this specific project, density control had to be done through the use of CPT.Calibration chamber tests were performed to establish the CPT qc–Dr correlation for the specific soil material. This correlation was used to analyse CPT results during construction of the site in order to determine the quality of compaction.In a further stage, an elaborate laboratory study was performed to establish additional correlations between soil parameters and the stress–strain parameters. Furthermore, seismic CPT tests were executed on the site to test the relevance of the laboratory correlations and the ‘relative density approach’ in general.It is shown that off-shore land reclamations have a very erratic stress-history, due to the different processes of depositing the soil material and the various densification methods. This stress-history is of great importance in the stress–strain behaviour of the site. Results also suggest that the CPT does not provide enough data to reliably predict soil stiffness when dealing with crushable materials. Specifically, in situ measurements show that there is no direct correlation between the small strain shear modulus G0 and qc

Monitoring the staged construction of a submerged embankment on soft soil

The present paper illustrates the outcome of the monitoring of the consolidation behavior of a soft foundation soil under a large partially submerged sand embankment. Measurements of settlements and excess pore water pressures showed a good agreement with predictions evaluated using the large strain consolidation theory. The more conventional small strain theory was shown to overestimate the dissipation of pore water pressure and underestimate settlements

The construction of an embankment on an under water dredged sediments storage pond

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