An analysis for braced excavations in clay

Xia, Huanliang (1999) An analysis for braced excavations in clay. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This thesis studies braced excavations in clay with centrifuge tests and finite element analyses. -- Centrifuge experiments of 72 g are carried out to investigate earth pressures on the back of sheet piles, forces in the struts, the surface settlement and bottom heaving. The simulated depth of excavation is 11.5 m and the width is 17.3 m. The struts are applied before excavation for the convenience of the tests. Heavy liquid of sodium polytungstate (3Na₂WO₄.9WO₃.H₂O) is used to simulate the soil which would be excavated. The excavations are simulated by draining the liquid during the tests. -- The details of designing the model, preparing the soil, assembling the equipment and experimental procedures are described. Compression and triaxial tests are also carried out to obtain the mechanical parameters for the numerical analysis. -- A finite element analysis is carried out for the model and the results are compared with experimental data and established methods. The Cam-clay model is used for the soil. Eight node rectangular elements with pore pressures on the corners are used for the soil and block elements are used for the sheet piles. The results show that the finite element may predict most behaviour of the excavation. -- The finite element model is used to perform parametric studies where each layer of struts is applied after the soil of the corresponding layer is excavated. The effects of variation of the properties of soil, the stiffness of sheet piles and struts and the vertical distances between the struts are investigated.

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