The diaphragm wall method, by which high reliable earth retaining walls can be constructed, is mostly adopted for excavation works on large-scale deep underground structures in soft clay grounds. It is essential to stabilize slurry trench walls, when the diaphragm wall method is adopted in soft clay grounds. Consequently, it is most significant to elucidate the ground conditions and mechanism to establish the slurry trench wall stability. In this paper, the ground conditions and mechanism for stabilizing slurry trench walls in soft clay grounds are discussed based on the field data. The main conclusions are summarized as follows:
The slurry trench wall stability in soft clay grounds can be judged being based on the consolidation condition and the value of cu/p.
The lateral pressure (sum of water and earth pressures) acting on the slurry trench wall in soft clay grounds decreases from the state at rest to the active state due to the trench wall displacement towards excavation side, followed by balancing with the slurry pressure, and that results in the slurry trench wall stability.
The diaphragm wall method using slurry trench has increasingly been applied to soft clay grounds in Japan. In order to ensure the reliability of this method, it is important to elucidate the stability mechanism of slurry trench excavation in soft clay grounds. Dibiagio et a1.(1972) and Tamano et a1.(1996) have measured mechanical behavior of diaphragm walls during slurry trench excavation in soft clay grounds and discussed stress conditions over the trench walls. Despite these reports, the mechanism of trench wall stability in soft clay grounds has not clearly been elucidated yet, because of the difficulty for directly measuring earth and water pressures acting on trench walls.