Finite layer analysis of viscoelastic layered materials

A method is presented for obtaining the creep settlement of strip or circular loadings applied to horizontally layered soil profiles. The solution method involves applying a fourier (strip loading) or Hankel (circular loading) transform to the governing equations, which reduces the two of three dimensional problem to one involving a single spatial demension. This leads to great savings in computer storage and data preparation time, and since an exact solution may be found for each layer of material, the method has advantages over conventional finite layer techniques where field quantities must be approximated at a number of positions within each layer. The type of formulation presented hearein makies it possible to work in terms of the creep functions of the soil rather than the relaxation functions. This has distinct advantages, as it is often easier to measure the creep behaviour of a soil in the laboratory. Numerical techniques are used to invert the laplace and Hankel transforms and this means that any type of creep function (which is invertible) may be used to describe the material properties of the soil.     

The behaviour of an impermeable flexible raft on a deep layer of consolidating soil

Analytic solutions to the problem of the time-settlement behaviour of raft foundations have been limited in the past to flexible or rigid loadings, and have treated the foundation as being completely permeable. In this paper, solutions are presented for smooth circular rafts of any flexibility causing consolidation of a deep homogeneous clay layer, where the raft may be considered permeable or impermeable. Results for the time-dependent behaviour of contact stresses, pore pressures, raft displacements and moment in the raft are presented.     

Ground failure around buried tubes

Summary The hoop forces which develop in circular tubes buried in elastic-plastic ground are investigated. A closed form solution is used to determine the hoop forces which develop when the field stresses in the elastic-plastic ground are initially uniform. The finite element method is used to solve the problem for biaxial field stress. A parametric study is undertaken to assess the influence of tube stiffness and ground strength on the hoop forces, and use is made of elastic stress contours to predict the likely extent of material failure around tubes buried in ground with biaxial prestress.Notation a tube radius - c cohesion - D flexural stiffness of the structure - E _i Young's modulus of structure - E _s Young's modulus of ground - F hoop force (compression positive) - G _s shear modulus of ground - H hoop stiffness of the structure - K coefficient of lateral pressure - N tan²(45+/2) - q ( ₁– ₁)/2 - S _f relative flexural stiffness of the structure - S _h relative hoop stiffness of the structure - t structural thickness - v circumferential displacement - w radial displacement - v _l Poisson's ratio of structure - v _s Poisson's ratio of ground - normal traction acting on the structure - _d deviatoric component of field stress - _h horizontal field stress - _m uniform component of field stress - _v vertical field stress - ₁ major principal stress - ₃ minor principal stress - tangential traction acting on the structure - angle of internal friction of the ground - angle of dilation of the ground