Controlling Water Ingress through Diaphragm Wall Joints

Abstract

Diaphragm walls frequently form structural retaining elements in civil engineering applications typically acting as permanent foundation walls in cut and cover structures or deep basements. The construction method is appropriate in gravel and sand formations with high water table levels where conventional excavation would be impracticable. Consequently, diaphragm walls are commonly primary barriers to groundwater infiltration but the completed walls may not entirely resist water penetration. Vertical panel joints are particularly susceptible to leaking, but unfortunately ingress through joints or wall panels does not become apparent until exposed by excavating. Moreover, if dewatering is used to reduce ground water levels during excavation, the full extent of infiltration through the walls may not become evident until dewatering is turned off and ground water levels recharge. This paper discusses use of resin injection to successfully control ground water ingress through vertical diaphragm walls joints. The walls formed lengthy approaches to a twin tube tunnel under a river on a high-speed rail link. Soils at the construction site were primarily gravels and clean sands with sustained ground water levels subject to tidal influences, at times ground water level almost equated to ground level. The majority of joints in the diaphragm walls were subject to various levels of water ingress, including running leaks. Adjacent to the tunnel portal, the exposed vertical diaphragm wall joints extended some 18 metres above invert slab level. Conditions leading to water ingress are explained with a discourse on resin selection, the client's involvement, proving of successful resin injection protocol and the practical implementation over a two year period. As with many remedial projects in civil engineering, the successful outcome was reliant on experienced engineers using empirical practices.