Abstract
The TBM tunneling at the Jinping II hydropower station in Southwest China has received extensive concerns around the world because of its large engineering scale and the high rockburst risks faced in the tunnel advancement. The associated energy changes of rockbursts and control method for safe TBM tunneling are to be further investigated. A movable microseismic (MS) monitoring system was established to capture the MS events and rockbursts when the TBM excavated the headrace tunnel #1 at the Jinping II hydropower station. The spatial and temporal patterns of the energy changes in the tunnel rock masses were studied. Meanwhile, the evolution of a rockburst encountered in front of the TBM excavation face was revealed, and the performance of the top pilot tunnel method on the reduction of the rockburst risks in the headrace tunnel #1 was evaluated based on the energy changes of the surrounding rock masses. It can be concluded that energy accumulation and energy release firstly occurred in the surrounding rock masses at the southern end of the top pilot tunnel section of the headrace tunnel #1. Then, energy transference of the rock masses took place from the southern end to northwest of the top pilot tunnel giving rise to the occurrence of a moderate rockburst about 30 m in front of the tunnel. However, no rockbursts appeared when the TBM excavated through the top pilot tunnel section of the headrace tunnel #1. Therefore, the top pilot tunnel method really works in reducing the risks of rockbursts during the TBM tunneling in deep tunnels.
Highlights
IntroductionRockbursts are engineering disasters normally induced by the excavation of the deep-buried tunnels with highstress, hard, brittle rock zones [8, 9]
Spatial Distribution of MS Events. e MS monitoring system was installed and tested for the monitoring of the tunnel boring machine (TBM) excavation before May 20, 2010. e mileage of the top pilot tunnel ranged from chainage 11 + 976 m to chainage 12 + 125 m in the headrace tunnel #1
Two schemes of sensor arrays, called the following sensor array and the neighbour sensor array, were proposed to adjust the sensor locations with the TBM advancing. e spatial patterns of the MS events and energy changes in the surrounding rock masses during the TBM tunneling through the top pilot tunnel section of the headrace tunnel #1 were revealed
Summary
Rockbursts are engineering disasters normally induced by the excavation of the deep-buried tunnels with highstress, hard, brittle rock zones [8, 9]. During the tunneling of the headrace tunnels at the Jinping II hydropower station, a large amount of intense rockbursts occurred causing casualties and equipment troubles, and resulting. A series of studies concerning the evolution mechanisms of rockbursts in the deep-buried tunnels have been carried out for decades in many countries [14,15,16]. Chen et al [24, 25] investigated the effect of high temperature on the rockburst proneness of rocks and found that the degree of rockburst is increasing with rising temperature, which is important to understand the mechanism of rockbursts in deep-buried tunnels at high ground temperature. Great achievements have been made, which help understand the evolution processes and occurrence mechanisms of rockbursts
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