Chinese karst geology and measures to prevent geohazards during shield tunnelling in karst region with caves

Abstract

Karst landscapes are widely distributed in China, and buried karst is widespread in Guangdong. This study mainly focuses on buried karst or karst caves which are underground at depths of up to 50 m and can significantly affect engineering construction activity. The karst caves, which are widely distributed in Guangdong Province, have the following features: high fissure water content, high rock permeability, prone to collapse, variable shapes, and irregular distribution. When a shield tunnel is constructed in this kind of environment, hazards, such as sink holes, the ingress of water or stones, and damage to the constructed tunnels may occur. Thus, karst caves need to be treated before tunnel construction. This paper presents a procedure for karst cave treatment to mitigate possible hazards during shield tunnelling in karst regions. The construction procedure includes field investigation, judgment, treatment, and effectiveness check. The treatment criteria, grouting material, construction steps, and effectiveness check for the karst cave treatment are introduced in detail. A field test on shield tunnelling excavation was conducted using the karst cave treatment in the karst region of Guangzhou, China. Field investigations include testing the unconfined compressive strength (UCS) of borehole samples of grouting materials, standard penetration test (SPT), core recovery (CR), ground surface settlement and building settlement. All of the UCS values of the borehole samples are greater than 0.2 MPa, the modified SPT values are more than ten, and the CR values are greater than 90 %. The measured values of ground surface settlement and building settlement are all within the allowable ranges. All of the test results demonstrate the applicability of this treatment process in karst regions.