Jacked-in pipe reinforcement of a deep excavation in soft soil

摘要

Soil nailing is an in-situ ground improvement method which has gained increasing acceptance in this region, but is not generally recommended for clayey and organic soils. This restriction is empirically based, and little information exists on the performance of soil nails when the method is applied in these soil conditions. To address this gap, a deep excavation for the construction of a 3/12 storey deep basement carried out using a novel technique, which combines Contiguous Bored PIles and Jack-in pipe reinforcements, was instrumented to monitor its performance. This paper will highlight briefly the instrumentation program, which was set up mainly as a safety control and to monitor the interaction of this retaining system with the surrounding soft soil. In addition, numerical analyses were conducted to study the soil-structure interaction of this new construction technique. Data from the field monitoring and FEM analyses will be presented with regard to the effectiveness this system particularly the jacked-in pipes in supporting the deep excavation. It follows from this comparison that the field instrumentation and numerical analyses have proved to be valuable tools in assessing the deformations to be expected at critical stages of the excavation. The project shows that jacked-in pipe in soft clayey soils is possible, at least for short term and can be effectively used as temporary support in deep excavation.