218 research outputs found

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

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    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

    Hydraulic conductivity of a dense prehydrated GCL: impact of free swell and swelling pressure

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    Exposure to liquids with high electrolyte concentrations or high cation valence present in landfill leachates can cause significant increases in hydraulic conductivity of clays due to a reduction in the thickness of the double layer. Methods to prevent compression of the interlayer are: prehydration of the bentonite, compression with increasing the solids content and addition of polymers. The aim of this study is to evaluate the performance of a dense prehydrated GCL (DPH GCL) compressed during manufacturing and pre-hydrated with a polymeric solution. A series of hydraulic conductivity tests with deionised water, sea water and a 0.01 M CaCl 2 solution were performed on single sheet and overlapped DPH GCL samples. Free swell and swelling pressure tests have also been performed with this solutions and with a series of KCI and CaCl 2 solutions with a concentration varying from 0.001 M to 1 M. The overlapped samples were analysed in large scale laboratory permeameters at different effective stresses. In addition, swelling pressure tests on single sheet samples were conducted to analyse the swelling behaviour of the factory prehydrated GCL. The concomitant effect of prehydration, addition of polymeric compounds and densification increased the hydraulic performance of GCLs under aggressive conditions. The use of bentonite paste to seal the overlap in presence of seawater was shown to be crucial. The swelling pressure test may be proposed as an alternative to the swell index test to characterize the swelling behaviour of polymer prehydrated GCLs

    Load-settlement behaviour of three pile groups: a case study

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    The paper presents the case study on the construction of three 48m diameter steel tanks, each founded on a group of 422 displacement cast in-situ piles. The three tanks are close enough to each other to induce interaction. The movements of the tank foundations have been monitored during the hydro-testing of the steel tanks, and during the subsequent working stage of the tanks. The bearing layer for the pile group is a 5 m thick stiff sand layer at a depth of about 20m, overlain by a very heterogeneous soft fill containing sand pockets, and underlain by a very thick slightly overconsolidated clay. The authors present some short and long term settlement prediction for the tanks, based on soil parameters derived from CPT on site, and compare this to the measured settlements. The initially derived soil parameters are re-evaluated in order to predict the long term settlement for the full life span of the construction

    Small-strain shear modulus and strength increase of cement-treated clay

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    A simple nondestructive technique was used as an alternative method to monitor the hardening of cement-treated clay as a function of time. The principle of this monitoring technique is based on the use of bender elements to measure the small-strain shear modulus (G0) at various time intervals. The strength increase was monitored by conventional unconfined compression testing. Experimental work was carried out on Kaolin clay treated with Portland cement and blast furnace slag cement at different dosages. The results showed that G0, as well as strength, of cementtreated samples increases logarithmically with time. However, blast furnace slag cement produces a slower hardening rate early after mixing. It was found that for each binder type, the G0 increase and the strength increase, when normalized, follow a common trend. Such a hardening function may be used as the basis of a strength prediction rule. The functions obtained are in good agreement with data on other cement-treated inorganic clays published in the literature

    Deep Foundations on Bored and Auger Piles

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