Volumetric Deformation of Natural Clays

Abstract

A theoretical framework to describe the behavior of natural clay is proposed in a new four-dimensional space, consisting of the current stress state, stress history, the current voids ratio, and a measure of the current soil structure. A key assumption of the proposed framework is that both the hardening and the destructuring of natural clay are dependent on plastic volumetric deformation. Two different assumptions about how this destructuring occurs are proposed, based on which two versions of a complete constitutive model have been formulated. The behavior of reconstituted soil can also be simulated by the proposed model as a special case where the structure of soil has no effect on soil deformation. Characteristics of the proposed model are demonstrated through systematic simulations of the influence of soil structure on clay behavior. The simulated behavior of natural clay is compared qualitatively with widely available experimental data. It is seen that the proposed model successfully represents the main features of natural clays with various soil structures.

Theoretical framework for predicting the response of tolerably mobile subsea installations

“…The measured data show higher in situ void ratios at low stress levels (σ'v0 < 10 kPa) than predicted by critical state parameters derived from one-dimensional compression tests at higher stresses (Stewart, 1992). This reflects the high compressibility of clays with high initial water contents (Boukpeti et al, 2012) and justifies our use of a modified shape of NCL and CSL, following Liu & Carter (2003).…”

“…2(a)) which accounts for the additional void ratio at low levels of vertical stress. This feature is required to match the experimental data shown later, and follows the model defined by Liu & Carter (2003). The additional void ratio at low levels of σ'v is represented by the last term on the right-hand side of Equation 2, where ∆ei is the additional void ratio at σ'v = σ'v,i where virgin yielding begins at effective stress, σ'v,i.…”

Behaviour of cemented clay simulated via the theoretical framework of the Structured Cam Clay model

“…2. The reconstituted compression line is taken as a reference for describing the cemented compression curve, which has been successfully done by Liu and Carter [21] and Liu et al [22]. In this figure, e represents the voids ratio for a cemented clay, e * is the voids ratio of the reconstituted clay at the same stress state with the same yield surface, p 0 y;i is the mean effective stress at which virgin yielding of the cemented clay begins, and De is the additional voids ratio, which is the difference in the voids ratio between the cemented clay and the reconstituted clay at the same stress state.…”

A mathematical function to represent S-shaped relationships for geotechnical applications

“…The present authors are not aware of such mathematical formulae that give a reliable description of the whole S-shape relationship. Taking the compression behaviour of soil as an example, the compression equation forms a base for most constitutive modelling of soils and some important geotechnical computations (Burland, 1990;Horpibulsuk et al, 2010;Liu and Carter, 2003;Pestana and Whittle, 1995;Suebsuk et al, 2010Suebsuk et al, , 2011. Because there is no efficient way to describe the whole S-shape compression relationship, a common way to describe it is to divide the curve into several segments and then the segment or the segments of interest are modelled by linear relationships (Butterfield and Baligh, 1996;Khalili et al, 2005;Terzaghi and Peck, 1948).…”