Mechanism of grout bulb expansion and its effect on ground uplifting

Abstract

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.

A variational method for calculating the longitudinal deformation of a shield tunnel in soft soil caused by grouting under tunnel

“…Numerical simulation is often used in the analysis of grouting and uplifting behaviors of underground structures. The methods used to simulate the grouting process include the strain method (Scheweiger and Kummerer, 2004; Nicolini and Nova, 2000), pressure method (Contini et al , 2007; Wisser et al , 2005) and expansion rate method (Zhang et al , 2012, 2011). Since the accuracy of the numerical simulation depends heavily on the soil constitutive model and parameter values, these simulation methods can only qualitatively simulate the expansion effect caused by grouting and cannot directly reflect the influence of construction parameters such as grouting amount, grouting rate and grouting pressure.…”