Mechanism of grout bulb expansion and its effect on ground uplifting

In order to study the uplifting effect of compensation grouting on ground surface and the upper structures, the ground heave induced by stratum expansion was considered as a stochastic process and the stochastic medium theory was applied to determine the heave and deformation of ground surface under uniform and non-uniform expansion models of spherical grout bulb. The corresponding calculating formulas and simplified methods were derived based on the hypotheses of radial expansion. Then, a numerical model, in which radial velocity was imposed on the outer nodes of grout bulb to simulate the expansion process reaching a required volume strain, was established simultaneously. This new method avoids repeated trial calculation needed in the traditional method which applies a “fictitious” expanding pressure in the grouting elements. The results show that the numerical solutions have good consistency with the theoretical ones. Meanwhile, though the heave resulting from non-uniform expansion is larger than that from uniform expansion for shallow grouting, both of them tend to be convergent with the increasing of grouting depth.