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

One-dimensional compression of a crushable sand in dry and wet conditions

This paper presents the results of a series of dry and wet one-dimenional compression tests on a calcareous sand from the Persian Gulf. Calcareous grains crush more easily compared to silica grains, a fact that is mainly attributed to their angular shape and weaker mineralogical and complicates their geotechnical behaviour. With regard to the use of crushable sands in construction projects, the question arises whether the presence of water further influences their crushability, and thus performance. The oedometer tests discussed in this paper, are part of a larger study on the influence of water on the stress-strain behaviour of calcareous sands. Dry samples are prepared in oedometers at a relevant density and either kept dry or flushed with water. Loading occurs in ten increments up until a vertical stress of 8.6 MPa and afterwards the sand is sieved to evaluate crushing. The behaviour of the crushable sand is shown to be significantly affected by the water as soon as crushing is initiated. The total settlements and the crushability are higher for the wet sand. When a distinction is made between primary and secondary compression, it is found that wet sand compresses more than dry sand during consolidation phase, but less during secondary compression phase. As a result, the observed net differences decrease with longer loading time whereas a higher rate of loading furthers the increased compression of wet calcareous sand. The tests are repeated on Molsand, a non-crushable silica sand. For this sand, within the stress range tested, the net deformation is identical for wet and dry conditions. The elevated stresses were not high enough to crush the grains and yield the material. The water dependency of crushable sands already exists at moderate stress levels, so it is of great importance to incorporate the accelerated crushing of wet particles in the geotechnical engineering practice

Triaxial compression tests on a crushable sand in dry and wet conditions

A calcareous sand from the Persian Gulf is subjected to a series of dry and fully drained saturated triaxial shear tests. The samples are prepared at relative densities of 65% and either left dry or saturated. They are consolidated to confining pressures ranging from 50 to 750 kPa, and sheared until shear strains of 20%. It is shown that the stress-strain and strength characteristics of crushable sand are significantly affected by the presence of water. During shearing of wet samples, there is less dilation, the peak is postponed and a lower shear strength is reached compared to dry samples. Crushability is assessed by comparing the granulometry before and after the triaxial tests. While both dry and wet samples show breakage, the wet sand is consistently more crushable. It is stated that the higher crushability of the wet sand suppresses its dilation during shearing

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

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

The F-actin filament capping protein CapG is a bona fide nucleolar protein

Actin works in concert with myosin I to regulate the transcription of ribosomal genes in the nucleolus. Recently, nucleolar actin has been shown to be active in its polymeric form raising the question how actin dynamics is regulated in the nucleolus. Here, we show that the actin capping protein CapG localizes in the nucleolus of cultured cells. CapG transport to the nucleolus is an active and ATP-dependent process. Association of CapG with the nucleolus requires active RNA Polymerase I transcription. In addition, we show that activated Ran GTPase, an interaction partner of CapG, is also transported to the nucleolus. A constitutively active Ran mutant promotes CapG accumulation in the nucleolus indicating that CapG transport to the nucleolus can be supported by Ran. Our results suggest that filamentous actin in the nucleolus might be regulated by actin binding proteins such as CapG. (C

Post-breakage behaviour of laminated glass in structural applications

Firstly is introduced what the post-breakage behaviour of laminated safety glass is, and why it's important to can model it for designing structural glass elements. A general description of post-breakage behaviour and the different possible mechanisms leading to failure are presented. We then focus on the mechanical properties of the interlayer material, more specifically in the perspective to model its behaviour at large strain up to break. Typical results of standard uniaxial tensile tests on SGP samples (SentryGlas (R) Plus, interlayer of DuPont de Nemours) are shortly presented, and we then explain why those are insufficient to calibrate numeric material models to use in finite elements softwares. Finally perspectives for further experimental investigation with aiming to calibrate material models are presented