Abstract
A horizontal jet grout forepiling method reinforced by steel pipe is one of the useful pre-supporting systems in excavating a tunnel in weak ground. However, the dimension of the grouted column forming forepiles has not been measured and controlled during the executing operation, though it is important to estimate its dimension for the quality assurance and cost management in tunnel construction.
In this paper two new methods for estimating the diameter of a grouted forepile are proposed; One is the indirect method by measuring and controlling the replacing rate of soil with the grouting material. Another is the direct method by measuring the electrical resistance of the grouted material along the forepile by means of an electrical potential technique.
