La stabilité des tranchées profondes forées en présence de boue

The stability of deep trenches excavated by drilling with mud

Directeur de la Société ETANCHEMENTS ET FONDATIONS SPÉCIALES.

Résumé

Considerable progress has been made in Europe during the last ten years with the "slurry trenching" technique of excavating trench "panels" of length L by drilling with mud (Fig. 1), the trench then being filled with concrete fed through a tremie-pipe. The author analyses the stability conditions for a single trench element. The stabilising pressure Ph of the mud must be such as to balance the passive thrust of the ground σIII (Equation 1). The first step in calculating this thrust is an examination of equilibrium conditions in a plane parallel to the "panel" faces (Figs 2 and 3). Arch effects in this plane are assumed to be similar to those in a storage silo. A similar calculation to the one by Caquot for silos yields values for σI and σII ; the equilibrium limit occurs in the plane containing σI and σII which latter is found from σI (Equation 2 and Fig. 4). Theoretical considerations show that σIII does not increase indefinitely with depth, but that it tends to a finite value depending on the width of the "panel". (Equation 3). Possible cohesion of the ground is easily allowed for by applying the "corresponding states" principle (Equation 4). The theory is applied to data observed at an Electricité de France construction site at Gerstheim (Figs 6, 7 and 8), and both sets of results are found to agree satisfactorily.