Dynamic behavior of soils partially grouted by a foaming process.

Abstract

Chemical grouting is widely used as a method of improving the mechanical behavior of weak soils. The present practice in chemical grouting is to fill the soil voids entirely by injecting grout to refusal. Past experience has shown, however, that only a slight amount of grouting material deposited at inter-particle contacts is required to improve the mechanical behavior of cohesionless soils. One of the main objectives of this research was to develop a method of bonding the particles together at their contacts without filling up the pore space. Chemical grout was converted into foam by adding an appropriate type of surfactant and by using a foam generator. The liquid forming the foam film deposits at the inter-particle contacts, and the air in the foam occupies the residual void space. Three sands with different gradations and particle shapes were grouted to varying degrees of cementation by this process in the laboratory, and tested in a Modified Hall Resonant Column Device to study their dynamic behavior. The test results show that the shear modulus increased with an increase in the degree of comentation up to certain point; thereafter, the modulus remained unchanged or slightly decreased with an increase in the amount of cement. The shear modulus also increased with elapsed time after grouting and eventually approached a constant value. Confining pressure has little influence on the modulus. The damping ratio of the sands lies between 1% and 2% and is little influenced by the degree of cementation. The damping ratio decreases, however, with an increase in confining pressure and elapsed time. Pendular elements were used to model the grout at the contacts and an empirical model was developed to predict shear modulus and shear wave velocity of the foam grouted sands. The unconfined compressive strength of foam grouted sands increases with an increase in the degree of cementation; furthermore grouted sands display brittle type failures. Macroscopic foam-water displacement experiments indicate that the foam displaces pore water by a piston like action with no or little fingering. Possible applications of foam as an in-situ barrier are also proposed.