David Greenwood, PhD, FGS. This paper was first published in GE’s April 1987 edition.
The facility to aggregate single injections of grout into complex shapes in the ground below footings together with the variety of techniques afforded by choosing to vary grout properties, injection pressures and flow rates, makes grouting for underpinning attractive. However it uses natural soil, with its attendant variability, as a working material. Hence precisely relevant data at specific locations of treatment are a pre-requisite for choice of technique, as the processes are sensitive to soil conditions.
The injection of grouts can be by delicate permeation; deliberate squeezing and compaction, which can be extended to controlled jacking of foundations; or by vigorous erosion of jet grouting. This Paper relates these processes and indicates resulting properties of treated ground in the underpinning context making reference to practical examples.