Safety of deep slopes excavated during construction of underground structures

Abstract

During construction of the Prague subway in the suburbs, a technology of deep slope excavation has been applied. Where excavation is cheaper in comparison to driving is expected, this technology is usable when appropriate conditions are expected on site. From the point of view of the environment, the steeper the slope is, the loss of possible smaller building lots is less. This means that during the construction of the underground structure, the construction of residential buildings and civic amenities can always be in progress in larger areas. Moreover, the excavation of slopes is cheaper the steeper the slope is. The optimization of the slope to be as steep as possible starts with a well known trick given by Prochazka and Koudelka (2001). For given internal parameters an optimal slope can be obtained. On the other hand, if some internal parameter is unknown, it can be a design parameter of the optimization. Similarly, for vertical slopes, the technique of nailed soil can be applied. The optimization in this case is attained from the professional program PLAXIS. This program can be connected with scale modeling on physically equivalent materials. Application to completed construction of one part of the Prague subway will be carried out. The material parameters are given, the process of construction is known, so that a real comparison can be made. The slope of approximately 50m height belongs to an exception in the area of applications to the subway construction. Higher slopes are known from tailing dams (deposits of open pit mines), for example, attaining up to 80m. In the latter case, measurement equipment can be installed in the slope to observe its behavior. This is not the case in our study; the slopes have to be designed in the correct way in order not to fail.