Back analysis of rock parameters for Hoek-Brown criterion

Back analysis of rock mass parameters for Hoek-Brown criterion from direct shear tests has particular importance due to the presence of large number of case histories all over the world. But it turns out that the only proposal presented so far is given by Hoek in 1983, employing Dr.Dunbar's device which simply assumes that the local cohesion is constant for the entire tau, sigma data set. This is indeed not satisfactory for most cases, particularly for slopes and foundations in tension. The paper presents Londe's dimensionless form and a grid search technique to solve this non-linear bi-variate problem. Sample computations showed the validity in favor of the Hoek-Brown criterion against the Mohr-Coulomb criterion.