ABSTRACT
The slurry trench method has, since the early 1970s, been used in Norwegian soft clays to construct diaphragm walls to support deep excavations. The technique involves excavation of a deep trench stabilized by a fluid/slurry that exerts a pressure on the trench walls. When the method was used for construction of diaphragm walls for a subway and railway tunnel through central Oslo in the 1970s there was little experience with the method in soft clays. Therefore, a field test program with several test trenches was initiated which included monitoring of ground settlements, pore pressures, and horizontal deformations at depth. The present study analyses results from two slurry trenches at Vaterland, one of size 1×5 m and the other of size 1×1.8 m. These trenches were deliberately brought to failure by drawdown of the supporting slurry. Finite element analysis (FEA) is used to back-calculate the observed behaviour with respect to safety and deformations. The NGI-ADP model is used for the clay at the test site. The results are compared with the observed behaviour and the factor of safety calculated using a simplified analytical approach proposed earlier. The analyses show that the NGI-ADP model can predict failure with satisfying accuracy, and that effect of the trench shape on the stability is well captured.
