Improvement stability of retaining walls in the presence of flow.

Abstract

With the existence of high groundwater level, the head difference between the inside and outside of the excavation may lead to the loss stability of the excavation’s surface. In some cases, the failure mechanism cannot be predicted exactly because of its mechanical complexity as well as a major lack of protection systems and not adopting effective countermeasures against this phenomenon. Several methods of calculating the basal stability with respect to hydraulic failure have been proposed in the literature, sometimes leading to crucial differences in the values of the hydraulic head loss causing the failure. In this thesis, the objective of this study is to analyse the stability of excavation in the presence of water flow around the retaining wall. This, through numerical analysis using the Plaxis 2D finite element code, This work took a real case located in the Ruhr area, Germany to establish the model and analyse the instability of the excavation base surface caused by the groundwater flow and to present the effectivity of an adopted drainage system inside the excavation pit. By using the finite element method (FEM) analysis, the failure mechanism was investigated before applying any countermeasures, and the total length of the adopted countermeasure system was minimised. Also, various position tests were performed on the adopted drainage system to confirm the optimised position. The results of this numerical study allowed the deduction of the importance of the used drainage system by achieving 44% more in the excavating process and they can be provided as reference for the optimised position of the sand columns where they must be applied right by the wall and limited by a critical distance, D/2, half of the embedded depth of the wall. By using the technic of cavity expansion for stone columns installation provide an extra excavation deep, also the reinforced soil surrounding the retaining wall keep stable in which insure the safety of the wall against failure Keywords: circular deep excavation; hydraulic failure of soil; failure of support system, diaphragm walls; lateral land pressure; pore pressures; drainage system; stability analysis, factor of safety, permeability