Combination Modeling And Zone Partition Study On The Construction Area Along Nanning’s Subway Line No.1

The subway line No.1of the city of Nanning goes across the Nanning basin from east to west, with a total length of32km, and25stops. This tube would mainly run through quaternary overburden, characterized by richness in water, high permeability, and the poor ability to resume stability after disruptions, and tertiary swell-shrink rock formation, characterized by proneness to swelling and shrinking, and sensitivity to water. Different combinations of rock formations and tunnel structures will bring different challenges for the construction of Nanning’s subway system. Unfortunately, relevant researches on similar projects are no more than a handful.This dissertation pooled together all available information and research papers on the engineering geology and hydrogeology of the construction area along the subway line, and studied them. Such study would lead to a modeling of the combination of the rock formations along the subway line. Then, based on this modeling, five distinctive types of zones are madeout. The findings of this dissertation can be summarized as the following:In type-one zones, the upper part of the tube would go through gravel layer, while the lower part would have to go through mudstone and silty mudstone. Underground water could pass the gravel layer to reach the mudstone layer during and after the construction to cause the rocks surrounding the bottom of the tube to swell, and trigger some engineering problems. In type-two zones, the upper part of the tube would go through siltstone and argillaceous siltstone, while the lower part would come into contact with mudstone and silty mudstone. Problems caused by the unique engineering properties of the tertiary swell-shrink rocks would be unavoidable. In type-three zones, the upper part of the tube would go through fill stratum, while the bottom of the tube would come into contact with mudstone and silty mudstone. Protecting the bottom of the tube from swelling up and cracking under the work of the water originating from the till stratum, and passing through mudstone and silty mudstone would be an essential problem faced by the construction team. In type-four zones, the whole tube would be enveloped by the gravel layer. The relative strength and large grain size of this structure can prove to be a hard job for the shield machine and slow down the progress of the project. In type-five zones, the stability of the filling during the excavation requires attention from the construction team.This dissertation also studied the suitable parameters for various rock formations’physical properties to ensure a reasonable accuracy in the modeling of the combination and the zone partition. At the end of this dissertation, an outlook into further follow-up studies was offered.