...-granular fracture. These phenomena imply the underlying mechanism of wetting deterioration as the following process: (1) The matrix is softened as sandstone is wetted; and (2) The grains tend to roll more freely and distribute the applied load within the matrix without breaking many other grains...

... that the progressive failure of the rock mass around a tunnel at depth. And the analytic formulas arc given to evaluate the effects of the softening and dilation of the rock mass on the stability of underground tunnel. Some suggestions are also given to improve the support of underground tunnel at great depth. I...

... no support. Progress in laboratory devices, as servo Controlled machines, have led to a more comprehensive analysis of rock behaviour, and consequently, many authors have proposed theories including a softening behaviour: [Egger, 1973, Nguyen Q.S. & Bui,1974, Panet, 1976, Nguyen Minh, Berest 1977, Mroz...