Abstract:
This paper presents an innovative approach for high water inflow cut-off in tunnel construction. Before using pure polymer-based grouts, a cement suspension is mixed with polyurethane resin and injected. The ratio of resin to cement varies between 0 - 40% and can be easily and individually adjusted in real time during the injection process. The positive properties of cement on the one hand and polyurethane resin on the other hand can thus be exploited in a both technically and economically optimal way, accounting for the actual rock conditions. An implementation in the framework of a rehabilitation of a power plant, where high water inflows are encountered is presented. During the advance of the pressure tunnel, a strong water ingress of approximately 134 l/s is encountered, which is to be sealed, before resuming the main renovation works. The dimensions of the rock fissures vary greatly, making the selection of a suitable injection material more difficult. In such a situation, hybrid injections using a cement suspension with the addition of a twocomponent polyurethane resin appears to present an appropriate solution. Depending on the pressure development during injection, the percentage of cement suspension and polyurethane resin, is correspondingly adjusted. In case of a pressure increase when using pure cement grout, no resin is required. If, however, the cement grout is leaking, with no pressure build-up, as it is the case for big fissures and openings in the rockmass, polyurethane resin is added until the wash-out is stopped and the grouting pressure criterium is reached. The addition of polyurethane resin can be done automatically or manually, while the data including the take of polyurethane resin and cement suspension are recorded at any time. The presented approach shows the applicability of a hybrid injection to successfully treat highly permeable rock mass around sensitive structures such as tunnels.