University of Twente Student Theses


The evolution of shear bands under rapid drawdown conditions in variably permeable porous soils

Pater, W.H. (2016) The evolution of shear bands under rapid drawdown conditions in variably permeable porous soils.

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Abstract:Rapid drawdown (RDD) is a specific slope stability problem in geo-mechanics that can be approached both deterministically and probabilistically and simulated numerically with the Finite Element Method (FEM) or Random Finite Element Method (RFEM) on Multi-scale levels. The field (large-scale) boundary problem is simulated herein with a coupled- (water flow- solid skeleton) deformation formulation, assuming an elastic medium using the Random Finite Elements Method (RFEM). This renders an assessment of the probability of a slope sliding from gravitational-, seepage- and water-boundary forces corresponding to RDD. On the pore-scale, the effect of non-homogeneity in the degree of saturation is closely studied using the RFEM on an element level. The element (small-scale) analysis however implemented an elastic-plastic constitutive relationship. These differences in simulating recoverable deformation (elastic) and irrecoverable deformation (elastic-plastic) are applied for “computational” convenience to enable running the developed algorithms for these two computationally demanding problems on a personal computer. The two analyses are inseparable however and demonstrate the promising results attainable despite the use of an “elastic” description for the large-scale slope problem. The heterogeneity that results from random permeability fields are found to strongly influence the location and magnitude of hydraulic gradients and shear stresses in both the large- and element-scale representation of an idealized partial immersed levee under RDD. Presence of such random field enhances shear bands development at local (elements) scale that might trigger levee’s (mass) collapse during or after RDD. Close-ups are shown for the evolution of shear bands of soil elements under compression and subsequent decompression conditions that are found prevalent during RDD. When considering plasticity the decrease in effective pre-consolidation pressure
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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