Hydraulic heave at the excavation walls with under-flow of small embedded depth and filter layers at the excavation side of the wall

摘要

Hydraulic heave safety in many cases is a relevant factor for designing the embedded length of excavation walls of deep excavation pits. To reduce the embedded depth, a surcharge filler can be placed on the bottom of the pit. Numerical based analyses show lhat the conventional design of excavation pit with installed surcharge filter according to Terzaghi/Peck and Baumgart/Davidenkoff is not valid. A theoretical approach, which considers the vertical flow forces below the base of the excavation wall was developed by the Federal Waterways Engineering and Research Institute. To verify this theoretical approach, the Institute for Soil Mechanics and Geoteehnieal Engineering of the Bundeswehr University carried out numerous laboratory tests in a specific box to simulate hydraulic heaves. During the series of experiments, the embedded depth of the wall and the thickness of the filter layers were varied. Moreover, the elevations on the excavation side of the wall were detected by displacement transducer, the water pressure around the end of the wall was deteeted by waler pressure sensors and the figure of failure was mapped by Picture Image Veloeimelry {PIV) Method and video camera. The Paper shows the results of the laboratory experiments and the consequences lor the design of the filter layers on the excavation side of the wall by under-flown and small-embedded depth.