Abstract
Rockburst disasters frequently occur in deep tunnels excavated by TBM (tunnel boring machine) under complex geological conditions in western China. Using FLAC3D, the characterization of a three-dimensional numerical model of a compound stratum tunnel excavated by TBM is conducted, based on a water transport project in Shanxi Province. Then, the characteristics of rockburst in deep hard and soft compound stratum tunnels excavated by TBM are revealed, and the energy criteria of the rockburst considering the rock brittleness are proposed. In addition, the prevention and control method of drilling pressure relief for rockburst has been investigated. Results show that: (i) the rockburst risk of compound stratum tunnel excavated using TBM is mainly in the upper-hard rock part, while there is no rockburst risk in the soft rock part; (ii) after the excavation of the tunnel, slight rockburst risk occurs first in the hard rock area of the tunnel vault, and then the rockburst risk gradually rises to the strong level at 7 m behind the working face, indicating the hysteresis of strong rockburst; (iii) the rockburst in the vault of the rock surrounding the compound stratum tunnel has the effect of forming the deepest area, gradually narrowing to both sides, showing a “V” shape, and the occurrence of rockburst may not be completed at one time; (iiii) borehole pressure relief can significantly reduce the rockburst risk of surrounding rock in a tunnel. The larger the borehole diameter and depth, the better the effect of rockburst prevention. In addition, the effect of borehole diameter is more significant than depth. The research results provide guiding references for the prevention and control of similar rockburst disasters in underground engineering.
Highlights
With the in-depth implementation of China’s “Western Development” and “One Belt and One Road” strategies, resource mines, water conservancy structures, and traffic tunnels are gradually being transferred to western China [1], which has a topography of high mountains and deep valleys
Rockburst occasionally occurs in TBM construction of deep tunnels in
The rockburst risk of the compound stratum tunnel excavated by TBM mainly occurred in the upper-hard rock part, while in the soft rock part, rockburst risk did not occur
Summary
With the in-depth implementation of China’s “Western Development” and “One Belt and One Road” strategies, resource mines, water conservancy structures, and traffic tunnels are gradually being transferred to western China [1], which has a topography of high mountains and deep valleys In this region, the stratum structure is variable due to the significant burial depth and the effect of regional tectonic activities over multiple periods; the soft and hard strata appear alternately. To reduce the risk of rock explosion in TBM construction of deeply buried tunnels, some scholars [13] have suggested that a combined excavation process consisting of the drill-and-blast method for tunnel guidance and TBM boring under high-stress conditions could be effective; a series of measures were proposed to prevent and control the rock explosion. In the current paper, theoretical analysis and numerical simulation methods were applied to reveal the characteristics of rockbursts in TBM construction tunnels in deep soft and hard composite strata by taking as background a water transmission project in Shanxi. To provide a reference for the prevention and control of rockburst disasters in tunnel TBM construction under similar conditions, methods of unloading and preventing rockbursts in boreholes were developed
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