| Summary: | The basal stability of deep excavations in clay is often analysed using the classical approaches of Terzaghi (1943) and Bjerrum & Eide (1956). Terzaghi’s approach seems to be appropriate to excavation with small depth to width ratios, h/B, whereas Bjerrum & Eide give better results for greater h/B ratios. Not many attempts have been made to unify the two situations. In the present paper, the problem is analysed using upper and lower-bound considering two two-dimensional cases: a basic case, where the rigid stratum was considered deep, not affecting the stability of the excavation, and a case considering a rigid stratum at a certain depth. The embedded length of the wall was assumed null. A proposal for the stability numbers at failure is presented, for a wide range of h/B ratios.
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