Spatial effects on excavations in deep soft lacustrine clay

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Becker, Patrick and Berhane, Gebreselassie and Kempfert, Hans-Georg (2011) Spatial effects on excavations in deep soft lacustrine clay. In: 7th International symposium TC28 geotechnical aspects of underground construction In soft ground, 2011-05-16 - 2011-05-18.

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Abstract

A case history of a deep excavation in Constance near the lake Constance north of the German Alps is presented in this paper. The excavation was 90 m long, 17.5 to 22.5 m wide and 6 m deep. The underground condition in Constance and the surroundings is known of a deep and soft deposit of lacustrine clay. The spatial effects on the excavation, specially the effects of the construction steps on the deformation behaviour as well as the mobilization of each support element, has been studied by means of back analyses using the Finite Element Method (FEM) with 2D-models. The computed results are compared with the measured data from the project with respect to the time dependency of the soil-structure-interaction and deformation behaviour. For this purpose, additional pore pressure sensors were installed to record the development of excess pore pressure corresponding to different construction stages. Finally, recommendations on numerical modelling of excavations in soft soils are presented, and mobilization factors for support elements and the stress path dependant stiffness of soft soils are described.

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