Three-dimensional finite element analysis of opening interaction in squeezing ground

This paper presents a numerical study of the interaction of twin, horizontally aligned openings, deeply embedded in salt rock. Complex three-dimensional (3D) creep analyses were carried out using the Finite Element (FE) method. Findings show that opening interaction appears to develop with time, whilst increasing the time period between excavations causes a slight reduction in interaction. The FE model was then used to back analyse openings at Boulby Mine, North Yorkshire

Analysis of a laterally loaded rigid cylinder embedded in an elastoplastic

An analytical approach has been developed to predict the response of a rigid disc embedded in elastoplastic media. The governing differential equations are obtained using the principle of minimizing the potential energy. The displacement components in cylindrical coordinates could be represented by Fourier series. The fitted method is used to determine the Fourier series harmonic coefficients. Validation is made against finite element analysis and previously published solutions

Modelling tertiary creep in geomaterials using a continuum damage mechanics approach.

Tertiary creep is often observed in soft rocks and it represents a problem in a mining environment. Tertiary creep behaviour appears due to progressive micro cracking of the material and would result in a loss of strength and stiffness, which may eventually lead to failure and a complete loss of load carrying capability of the material. In this paper, the authors combined the continuum damage mechanics within the framework of hyperplasticity, thus encompassing viscoplasticity and damage within a single theory. The authors present a family of models which obeys the laws of thermodynamics. The entire constitutive behaviour is derived from two scalar potentials; a free energy potential which provides the elasticity law, and a dissipation potential which provides the yield function, the direction of plastic flow and the evolution of a damage variable. No additional assumptions are required. These new models require only few parameters which have physical meanings and are capable of capturing tertiary creep observed in soft rocks

Dynamic response of a laterally-loaded infinite rigid cylinder embedded in a saturated poroelastic medium

In this paper, an analytical solution for the response of a rigid cylinder embedded in a full-space poroelastic medium subjected to a dynamic lateral load is derived. The problem is idealised as a two-dimensional problem. The solution is obtained using Biot’s theory for acoustic waves. In this solution, the displacements of the solid skeleton and the pore pressure are expressed in terms of three scalar potentials. These potential correspond to the wave velocities of the slow and fast compressional wave and to the shear wave. The governing equation for the dynamic motion is expressed in the frequency domain using Fourier transformation and the potentials are shown to be given by Holmholtz equations

On the kinematics of 2D tunnel collapse in undrained clay

A kinematic plastic solution has been developed for ground movements around a shallow, unlined tunnel embedded within an undrained clay layer. In this solution, the pattern of deformation around the tunnel is idealised by a simple plastic deformation mechanism. Within the boundaries of the deformation mechanism, the soil is required to shear compatibly and continuously with no relative sliding at the boundaries. The soil is regarded here as a rigid plastic (Tresca) material. The plausibility of the proposed mechanism is demonstrated by comparison with limit analysis calculations and centrifuge test results

A simple model for tertiary creep in geomaterials

This paper presents a constitutive modelling approach to the viscoplastic-damage behaviour of geomaterials. This approach is based on the hyperelasticity framework where the entire constitutive behaviour is derived from only two scalar potentials: a free energy potential and a dissipation function. The novelty of the new proposed model, in addition to being thermodynamically consistent, it requires only a few parameters which can be derived from conventional laboratory testing. The model has been specically tested for its ability to reproduce a series of triaxial compression tests on core rock samples. The comparison between the viscoplastic-damage model predictions and experimental results show the model is remarkably successful in capturing the stress-strain response at both peak stress and in the region of material softening and the time to reach failure

On the formulation of thermodynamically-consistent viscoplastic-damage constitutive models.

This paper illustrates the formulation of viscoplastic-damage constitutive models using the framework of hyperplasticity. The entire constitutive behaviour is derived from only two scalar potentials; a free energy potential and a dissipation potential. This ensures that the model obeys the laws of thermodynamics

An expansive clay for centrifuge modelling

This paper explores the development of an expansive soil which can be repeatedly reproduced for use in centrifuge models to investigate soil-structure interaction problems involving expansive soils. The study considered two materials, namely a sand-bentonite mixture and a naturally occurring, highly expansive clay. For the natural material, two approaches were explored to create a scaled down fissured structure for use in centrifuge testing. The swell behaviour of the two candidate materials was first investigated by means of oedometer tests and then by centrifuge modelling. The centrifuge tests consisted of layers of compacted clay slabs separated by free draining layers. The study revealed that while the sand-bentonite mixture possessed the potential to swell significantly, the time required to do so was impractical for centrifuge studies. It was however found that the approach used to create a scaled down fissured structure in the naturally occurring clay facilitated rapid ingress of water which allowed for significant heave to take place in a much shorter time frame. The results obtained from the centrifuge test conducted on the reworked clay were compared with an empirical heave prediction method and it was found that the swell obtained from the fissured clay matched the predicted heave profile within three hours

On the formulation of thermodynamically-consistent viscoplastic-damage constitutive models

This paper illustrates the formulation of viscoplastic-damage constitutive models using the framework of hyperplasticity. The entire constitutive behaviour is derived from only two scalar potentials; a free energy potential and a dissipation potential. This ensures that the model obeys the laws of thermodynamics

Physical modelling of lime stabilisation in soft soils around deep excavations

Bored concrete piles have been used widely on commercial developments in London for about the last 50 years. The life of a commercial building is between 25 – 30 years and, as each building is demolished and rebuilt, the piles from the previous buildings remain in the ground causing obstruct ions to the new foundations. This paper describes a preliminary study to explore the viability of sheet piled foundations as a genuine alternative to cast in situ concrete piles and all of the complications inherent in their construction and the obstruction they create to subsequent foundations. If it is possible to u se steel piles as foundations they can be easily removed, recycled and will not cause obstructions for future developments. However, individual sheet piles have relatively low capacity when axially loaded and it is therefore necessary to consider a sheet p ile grou p in conjunction with a pilecap, which can be considered a hybrid foundation; a combination of shallow (pilecap) and deep (sheet pile). A short series of centrifuge tests is reported in which model sheet pile groups in over - consolidated clay were l oaded axially whilst vertical displacements were measured. Equivalent cast in place piles were similarly tested alongside the sheet pile groups by way of comparison