Influence of in-situ stress on rock fragmentation by TBM cutters and prediction of TBM performance for deep tunnels

Abstract

In-situ stress is a significant factor influencing TBM tunneling for deep tunnels, especially for the construction of deep repository for radioactive waste disposal. Beishan area of Gansu Province is the first preferred area for high-level radioactive waste disposal repository in China, and the feasibility of using TBM technology in Beishan area is investigated in recent years. In this paper, six levels of in-situ stress related to different depths from ground to 500m at Beishan area were selected and the influence of in-situ stress on rock fragmentation was investigated by linear cutting test. The rock samples were collected from the Jijicao site in Beishan area, with uniaxial compressive strength of 105.6MPa. The test results show that: 1) there is a clear power function correlation between the penetration and the normal cutter force for each stressed condition, and the higher the confining stress, the smaller the gradient of the power function curve, which means slower increase of penetration rate under the same cutterhead thrust; 2) the required normal cutter force increases with the increase of overburden as the corresponding in-situ stress increases. Based on the laboratory testing, the Specific Rock Mass Boreability Index model was modified and further used in the prediction of TBM performance at different depths on Jijicao site. This paper helps better understanding of rock fragmentation mechanism in TBM tunneling in stressed ground, and also provides reference on parameter selection for TBM operation in deep tunnel tunnelling.