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Open AccessArticle

The Minimum Safe Thickness and Catastrophe Process for Water Inrush of a Karst Tunnel Face with Multi Fractures

by Jiaqi Guo 1,2, Yuan Qian 1, Jianxun Chen 2,* and Fan Chen 3
1
School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, China
2
School of Highway, Chang’an University, Xi’an 710064, Shaanxi, China
3
State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou 221116, Jiangsu, China
*
Author to whom correspondence should be addressed.
Processes 2019, 7(10), 686; https://doi.org/10.3390/pr7100686
Received: 29 August 2019 / Revised: 18 September 2019 / Accepted: 20 September 2019 / Published: 2 October 2019
Water inrush of tunnel face is one of the most common geological disasters during tunnel construction in China. Aiming at the rock mass with multi fractures in water-resistant strata ahead of karst tunnel, the compressive-shear cracking property is analyzed by fracture mechanics theory and the change law of rock bridge shear strength with branch crack propagated length under karst water pressure and geo-stress is studied according to Mohr-Coulomb strength criterion. Moreover, the critical water pressure of water-resistant strata with multi fractures under tension-shear failure is deduced. The safe thickness of water-resistant strata with multi fractures ahead of karst tunnel is established based on two band theory and critical water pressure, and the influence of karst water pressure, initial crack length, crack spacing, array pitch of cracks, lateral pressure coefficient and the angle between the crack and the maximum principal stress on the minimum safe thickness of water-resistant strata are discussed. A 3 Dimension Distinct Element Code (3DEC) considering the fluid-solid coupling effect and structural characteristics of rock mass is adopted to study the catastrophe process and the influence of karst cavity scale on displacement and seepage field in water-resistant rock mass ahead of tunnel in the process of sequential excavation. The numerical simulation results show that: The transition from the single effect of unloading on the extrusion displacement of karst tunnel face to combined action of unloading and karst water pressure occurs with the tunnel face advance; The displacement at each measuring point in water-resistant strata continues to increase in the process of tunnel excavation; The extrusion displacement and water flow velocity in tunnel face suddenly increase when the water inrush pathway is about to form; With the increase of karst cavity size, the minimum thickness of water-resistant strata, the displacement of measuring point and pore pressure of crack increase. The study results provide a reference for early warning and prevention of water inrush in karst tunnel face. View Full-Text
Keywords: karst tunnel; water-resistant strata with multi fractures; critical water pressure; minimum safe thickness; catastrophe process; karst cavity size karst tunnel; water-resistant strata with multi fractures; critical water pressure; minimum safe thickness; catastrophe process; karst cavity size
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MDPI and ACS Style

Guo, J.; Qian, Y.; Chen, J.; Chen, F. The Minimum Safe Thickness and Catastrophe Process for Water Inrush of a Karst Tunnel Face with Multi Fractures. Processes 2019, 7, 686.

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