Mitigation of geohazards during deep excavations in karst regions with caverns: A case study: Fid-Bau Portal

Mitigation of geohazards during deep excavations in karst regions with caverns: A case study

Cui, Qing-Long

Karst landscapes are widely distributed and different characteristics are displayed in different regions due to the effect of various natural environmental factors which occur throughout China. Buried karst cavern systems covered by sandy strata, which are widely distributed in Guangdong Province, possess the following features: high fissure water content, high rock permeability, susceptibility to collapse, variability in shape and an irregular distribution. Socket diaphragm walls are usually adopted to retain soil and to cut-off groundwater during deep excavations in Guangdong Province, for the safety of the excavation and to reduce the impact on the surroundings. However, geohazards often occur during the construction of diaphragm walls in karst regions, causing problems such as diaphragm wall collapse, water or mud ingress, ground collapse and long-term instability. An eight-step treatment technique is proposed, which involves filling the karst caverns before the construction of diaphragm walls. A case study using the treatment technique in Maanshan Park Station on Guangdong Metro Line 9 is also presented. Leakage of the diaphragm wall was observed during the excavation, and grouting failed to seal the leakage. The mechanism of the leakage process was analysed and countermeasures were undertaken.