Microstructural approach and transfer water modelling in highly compacted unsaturated swelling clays

Abstract

A compacted smectite clay was studied in order to understand the swelling phenomenon. The in#uence of the sample initial state on the swelling mechanisms was demonstrated. A complete physical}chemical and mineralogical characterization of the clay was achieved using X-ray by re#exion and thermal methods. The X-ray di!raction by transmission method allowed to describe the various levels of the hydrated clay organization and the microstructure evolution. The pore distribution and the water partition are shown. Other important parameters: water retention, inter-layer distances, particle size, number of layers per particle were examined. This information gives the ability to follow the swelling which occurred in two steps, and to calculate the swelling potential versus the water content, or the void ratio. In application to this study, a water transfer in unsaturated clay was studied with the laws of continuous medium mechanics. A "nite di!erence program was used to examine two cases: prevented and free swelling in an oedometer. In order to take into account the material deformation, the swelling potential was introduced in the di!usion coe$cients. The simulation results of the water transfer obtained on this basis, were in good agreement with the experiments.

Large-Scale Molecular Dynamics Simulation of the Dehydration of a Suspension of Smectite Clay Nanoparticles

“…At ρ b < 1.25 g/cm 3 , P s ≈ 0; i.e., water is bulk-liquid-like. At ρ b = 1.25 to 1.65 g/cm 3 , it becomes increasingly positive with decreasing water content, in agreement with experimental observations . Finally, at ρ b > 1.65 g/cm 3 , we predict very large total suctions consistent with the nucleation of vapor bubbles in the simulated system.…”

“…The results presented above validate various experimental hypotheses based on calorimetric, X-ray diffraction, and gravimetric water sorption experiments regarding the ordering of hydration and dehydration and the coexistence of different hydration environments in smectite films. ,,,− Specifically, our results show that smectite dehydration proceeds through the following sequence of partially overlapping steps: first, the shrinking of large pores concurrently with an increase in particle stacking; second, the drainage of water films located on the external surfaces of clay stacks; third, the drainage of the remaining mesopores associated with the stacking defects; finally, the dehydration of crystalline hydrates proceeding roughly from 3- to 2- to 1-layer hydrates but with extensive coexistence of these species.…”

“…At ρ b = 1.25 to 1.65 g/cm 3 , it becomes increasingly positive with decreasing water content, in agreement with experimental observations. 106 Finally, at ρ b > 1.65 g/cm 3 , we predict very large total suctions consistent with the nucleation of vapor bubbles in the simulated system. For comparison with the values shown in Figure 8b, the Young−Laplace equation (r, where 2γ = 72.8 mN/m is the surface tension of pure liquid water at 298 K) predicts that the total suction in bulk liquid water containing a spherical bubble of vapor with the radius of a single water molecule (0.15 nm) should be on the order of 1000 MPa.…”

Swelling of Shales: A Multiscale Experimental Investigation

“…Considering that the thickness of an elementary clay layer is 1 nm, we infer that the clay particles contain about 100 elementary layers. The number of elementary layers per clay particle assessed here is consistent with the value obtained in a dry state through X-ray diffraction by the transmission method . By scanning through the whole observation zone, we find that the clay particles preferentially orientate along the vertical axis of the image (see Figure c).…”

Modelling the thermomechanical volume change behaviour of compacted expansive clays

“…The microstructural pores are assumed to be always saturated. This assumption is supported by the experimental observation made by Saiyouri et al (2000), showing that increasing suction (s) reduces the interlayer distance and the interlayer can be considered saturated even at a suction as high as 100 MPa in the case of bentonites. Furthermore, it has been observed that the effects of suction (s) and net mean stress (p) on microstructural volume changes are similar; the microstructural behaviour is reversible (Gens & Alonso, 1992).…”