Hydraulischer Grundbruch : zur erforderlichen Einbindetiefe bei Baugruben in nichtbindigem Baugrund

摘要

These days ground water lowering is rarely applied in urban areas as it results in settlements and thus as the case may be results in damages of the surrounding buildings. Instead of this complex civil works like grouting works or underwater concrete bottoms are applied. Otherwise the retaining walls have to be embedded deep enough to avoid hydraulic heave caused by the ground water flow and the vertical seepage force. For the determination of the embedded length, which is required for the safety against hydraulic heave, flow nets can be analyzed. For this purpose an iterative process is normally necessary including several 3D ground water flow calculations. Hence, a couple of approximate solutions exist. However, these solutions are iterative itself or can lead to unsafe results as they do not consider fundamental boundary conditions. Thus within the framework of this thesis numerous ground water flow calculations have been carried out. From these calculations relations between the required embedded length and several boundary conditions have been identified. Especially the width of the construction pit B has an important influence as the required embedded length increases disproportionally for narrow construction pits. Furthermore, the position (corner, front side, long side) inside the construction pit is crucial as due to the spatial ground water flow the required embedded length is higher at the corner as at the front side or at the long side. Next dimensionless design charts have been generated based on these results. By using the design charts the required embedded length T related to the difference of the ground water table H can be determined quick and easy considering different boundary conditions (B, L, S, gamma‘, anisotropy, soil stratification) as well as the safety level according to Eurocode 7-1 and DIN 1054 respectively. Furthermore, it is differentiated between the corner and the front side and the long side of rectangular construction pits. In Addition investigations on the economic design of large construction pits have been carried out. By a stepping along the side walls a more economic but still safe design is possible. Finally, in addition to the design charts an approximate formula has been developed step by step. By the use of this approximate formula the required embedded length can be determined analogous to the design chart considering the different boundary condition. The influence of anisotropic as well as stratified soil can be considered by additional terms. At last a design factor was added to get an overall formula for the determination of the embedded length required for the safety against hydraulic heave in homogenous, isotropic soil. This formula can be implemented into software solutions so that the time-consuming switch over between software for the static and flow calculation becomes lapsed.