Abstract
The existence of the threshold hydraulic gradient in clays under a low hydraulic gradient has been recognized by many studies. Meanwhile, most nature clays to some extent exist in an overconsolidated state more or less. However, the consolidation theory of overconsolidated clays with the threshold hydraulic gradient has been rarely reported in the literature. In this paper, a one-dimensional large-strain consolidation model of overconsolidated clays with consideration of the threshold hydraulic gradient is developed, and the finite differential method is adopted to obtain solutions for this model. The influence of the threshold hydraulic gradient and the preconsolidation pressure of overconsolidated clay on consolidation behavior is investigated. The consolidation rate under large-strain supposition is faster than that under small-strain supposition, and the difference in the consolidation rate between different geometric suppositions increases with an increase in the threshold hydraulic gradient and a decrease in the preconsolidation pressure. If Darcy’s law is valid, the final settlement of overconsolidated clays under large-strain supposition is the same as that under small-strain supposition. For the existence of the threshold hydraulic gradient, the final settlement of the clay layer with large-strain supposition is greater than that with small-strain supposition.
Highlights
Analysis of Moving BoundaryIf the time-dependent load is applied at the top surface over a very large area, the excess pore water pressure in the clay layer, u, will increase at all depths of the clay layer, and the increase in u will be equal to the increase of the external load
Advances in Civil Engineering as the Darcian ow, while the water ow in clays deviating from Darcy’s law may be named as the non-Darcian ow
H. e bottom of the clay layer is xed and referenced to the Lagrangian coordinate system. e Lagrangian coordinate a is measured downwards in the direction of gravity. e top surface of the layer (a 0) is pervious, and the bottom surface is impervious. e current vertical e ective stress at Lagrangian coordinate a resulting from the self-weight stress of the clay layer is labeled as σv′0(a). e vertical preconsolidation stress, σv′pc(a), is de ned as the maximum vertical e ective stress experienced by the overconsolidated clay layer
Summary
If the time-dependent load is applied at the top surface over a very large area, the excess pore water pressure in the clay layer, u, will increase at all depths of the clay layer, and the increase in u will be equal to the increase of the external load. For the existence of the threshold gradient, the excess pore water pressure cannot dissipate completely at the end of consolidation. If the excess pore water pressure at the impervious surface is constant during the whole progress of consolidation, on the contrary, the moving boundary cannot reach the bottom of the clay layer
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