Geomechanical modelling using a boundary loaded base friction machine

This research deals with the design and demonstration of a modified base friction machine. The Base Friction Method, or BFM for short, was first conceived in the late 1960's by Dr. R.E. Goodman and has been in use since 1973. The premise behind the BFM permits the replacement of gravity in the plane of a two dimensional physical model by drag forces acting along its base. The machine built for this thesis utilizes a stationary base and a moving model, which is a variation of the standard continuous belt machines that have previously been used. This new machine uses air pistons to apply vertical and horizontal boundary stresses to the model, where as most of the previous machines applied a surface pressure to the model in order to increase the unit weight of the material. In order to demonstrate the machine, two case studies consisting of a tunnel sequence with varying vertical and horizontal boundary stresses and a slope sequence are performed.

The machine uses scaled material models in order to simulate movement due to gravity over a time period of a few minutes, as opposed to several years for full scale studies. The models consist of a geologic modeling material where the properties of the material can be scaled to match the properties of the prototype rock in question. The material used in this thesis is a mixture of flour, vegetable oil and Ottawa Sand.The machine demonstrates with considerable accuracy how tunnels and slopes deform under gravity. By applying the boundary stresses, the tunnel sequence demonstrates how changing the confining stress on a tunnel effects its stability.