Jack-Pierre Piguet

Thermal convection of fluid in fractured media

Abstract This article shows the importance of thermal convection caused by fluid circulation through the fractures in rock masses. Expressions for the different heat transfer terms at the discontinuities, either between the fluid and the rock or within the fluid itself, are given. Including this phenomenon in a modelling process led us to propose a development of the UDEC code. The computational algorithm is based on the differences between the rates of convective and conductive heat transfers. The results obtained, using a simple model representing two blocks separated by a horizontal fracture, suggest that the convection phenomenon should not be neglected in modelling thermal flow in fractured rock masses. Convection is sensitive to the hydraulic aperture (pore fraction) of the fracture, the circulation velocity and the viscosity of the fluid. Comparison with another finite difference code has given satisfactory results.

Measurement of natural stresses in a Provence mine (Southern France)

Abstract Stress measurements were carried out in the Arc syncline using drifs in a lignite mine. Eleven sites were investigated using the flat jack and hydraulic fracturing (or stimulating) methods. Two stress states were found to coexist, one isotropic, the other highly anisotropic. The orientations of the principal stresses are not homogeneous and an orientation ranging from E-W to NE-SW predominates locally. This does not accord with the regional stress field. The vertical stresses are systematically underestimated.

Stability analysis of lateritic waste deposits

Abstract In open-pit mines covered with lateritic soil, the sterile ground is stored in specially prepared sites. The waste area must then be enhanced in order to extend storage capacity. To better understand the effect of an elevated dump, typical laboratory tests (triaxial and oedometer tests) have been performed on the lateritic material. The waste disposal site has been modeled using both limit equilibrium and finite element methods. Different types of finite element models have been run; they take the variation of Youngs modulus with depth into account and simulate the effect of construction over various phases. Modeling results are then compared with in situ measurements.