Influence Of Saturation Degree Research Articles

Vertical dynamic response of a floating pile in unsaturated poroelastic media based on the fictitious unsaturated soil pile model

Decades of high-speed railways operation around the world have revealed an increasing number of maintenance issues of pile-supported embankments subjected to long-term dynamic train loads in typical unsaturated soft soil areas. As the physical explanation of vibration characteristics of unsaturated soil piles is a theoretical basis for pile foundation design and pile integrity detection, a developed analytical solution of the vertical dynamic response of a floating pile in homogeneous unsaturated soils is proposed in this work. Based on the fictitious unsaturated soil pile (FUSP) model, the influence of saturation degree on soil shear modulus is considered in governing equations, uncoupled by using potential function and operator decomposition methods. The vertical dynamic response of a floating pile in a frequency domain is derived by employing the pile–soil compatibility conditions and the impedance function transfer method. Time-domain results are obtained by utilizing inverse Fourier transform and the convolution theorem. The correctness of the proposed model is verified by degradation to compare with the two existing solutions. Finally, a parameter study is undertaken to find the most sensitive parameters to the dynamic response of the floating pile in unsaturated soils.

Torsional dynamic response of a pipe pile in homogeneous unsaturated soils

This paper proposed an analytical solution for investigating the dynamic response of a pipe pile subjected to a torsional harmonic excitation torque in unsaturated soils. Based on the wave equations of three-phase porous media, the capillary pressure and inertial coupling effect between water and gas phase are taken into account, as well as the influence of saturation degree on soil’s dynamic shear modulus. The pile is modeled using one-dimensional elastic theory. The dynamic governing equations of outer and inner unsaturated soils are derived by virtue of the separation of variables method. Accounting for the boundary and continuity conditions of pile-soil interface, a closed-form solution for the torsional dynamic response of a pipe pile is derived in frequency domain. The proposed analytical solution is verified by comparing with the two existing solutions available in literature. Finally, a parameter study is undertaken to portray the influence on the dynamic response of a pipe pile.

Experimental study on the influence of saturation degree on unstable behavior within granular material

According to regulations and standards, risks of liquefaction are considered only if a soil is fully saturated. However, some authors have demonstrated that a soil can liquefy even with an initial degree of saturation under 100%. However, those studies remain descriptive and do not provide specific frameworks for evaluating the risk of liquefaction, taking the degree of saturation into account. This article presents an experimental study on the unstable behavior of sand as a function of its initial degree of saturation. Saturation states are defined and three saturation zones are investigated as a function of their pore fluid distribution patterns. Cyclic triaxial tests are performed on Fontainebleau sand to study the unstable behavior of each saturation zone. The results show that a soil can liquefy even if it is not initially fully saturated. They also provide new data on the role of suction and pore fluid compressibility in the unstable behavior of granular materials. The final aim of this article is to study the general unstable behavior of Fontainebleau sand under cyclic loading, and more specifically the influence of the degree of saturation on the triggering of these instabilities.

Suction and rate-dependent behaviour of a shear-zone soil from a landslide in a gently-inclined mudstone-sandstone sequence in the Sichuan basin, China

Bedding-controlled landslides in alternated mudstone and sandstone beds in cataclinal slopes are common in the Sichuan basin and in the Three Gorges area in China. They are characterised by very gentle dip angles of the beds (<10°), and usually exhibit slow creep movements throughout the year. However, during the rainy season, they can have sudden accelerations and undergo large displacements. In this work, the influence of saturation degree, displacement rate and stress state on the shear strength of the shear-zone soil was investigated. The results of the displacement-controlled ring-shear tests show a rate-weakening behaviour even at low rates of displacement. Dually, the shear-controlled tests show that the displacement rate can increase dramatically in response to a slight increase of the shear stress. The threshold stress that triggers large displacement is equal to the rate-dependent residual shear strength of the soil.

Influence of saturation degree and role of suction in unsaturated soils behaviour: application to liquefaction

The effect of the pore fluid compressibility on liquefaction has been studied by various authors. But few papers have been published about the role of suction in cyclic behavior of unsaturated soils. Most of these works use Skempton coefficient B as a reference in terms of saturation degree to analyze their results. The use of B in experimental conditions is convenient, but is not accurate when studying liquefaction behavior, since effects of suction are neglected. In this paper, the influence of saturation degree on mechanical behavior of a soil under dynamic loads is studied. Cyclic undrained triaxial tests were performed on sand samples, under various levels of saturation. Soil-water characteristic curve was used, in order to study influence of suction. The first results confirm that when the degree of saturation decreases, the resistance increases. Initial positive suction tends to stiffen the soil. It also appears that the presence of air delays the occurrence of liquefaction, but doesn’t prevent it. Indeed, liquefaction is observed, whether the soil is saturated or not.

Influence of Saturation Degree on Deamplification of P1 Wave through Multilayered Porous Media

The deamplification model developed by Zendagui et al. has been adapted in this study for the case of P1 wave propagation in porous media in order to investigate the effect of saturation degree on motion coherency at depth. The input wave amplitude distribution function is generated compatibly with the suitable free field coherency model and the top wave amplitudes are evaluated using the transfer matrix method following the Biot’s theory. The results show that even if the saturation degree decreases slightly below the complete saturation, it influences the coherencies of horizontal and vertical motion due to P1 wave incidences. Elsewhere, the generation process shows that in this case, the wave front content, necessary to produce a coherency identical to the Luco and Wong model at the free field, is more focus with less intensity than required in the case of a complete saturation.

Modelling of plastic deformation and damage in cement‐based material subjected to desiccation

AbstractThe present work is devoted to modelling of plastic deformation and damage in cement‐based materials subjected to desiccation and mechanical loading. Basic mechanical behaviours of cement‐based materials and influences of saturation degree on such behaviours are first recalled. Physical mechanisms of damage induced by desiccation process are analysed. An elastoplastic damage model is then proposed for the description of mechanical responses, taking into account the transition from brittle to ductile behaviours with the increase of confining pressure. The model is further extended to unsaturated conditions: a specific damage driving force and generalized effective stress concept for plastic flow are proposed. The procedure of determination of model's parameters is presented. The proposed model is applied to a standard mortar subjected to desiccation process. The main features of mechanical behaviours as well as the influence of saturation degree are correctly described by the proposed model. In particular, the kinetics of desiccation and related damage evolution are well reproduced. As an example of application, the responses of a concrete beam in three‐point bending test with different desiccation conditions is investigated. Again, the numerical simulations are in good agreement with the experimental data. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Precipitation of calcium and magnesium carbonates from homogeneous supersaturated solutions

Homogeneous (unseeded) precipitation of calcium and magnesium carbonates in the CaO–MgO–CO 2–H 2O system in supersaturated solutions was investigated. The induction period ( τ) of spontaneous nucleation and the composition of precipitated solid phases were determined. The influence of saturation degree (chemical affinity) and Mg 2+/Ca 2+ activity ratio in solution on the kinetics of CaCO 3 nucleation was studied. The order of CaCO 3 homogeneous nucleation equals to 4. The surface energy of CaCO 3 nucleus was measured to be 63 mJ/m 2. The main factor which controls the Mg content in the solid phase being formed during unseeded precipitation of carbonates is the saturation index of MgCO 3 in solution.