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

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.

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Theoretical Analysis of Safety Thickness of the Water-Resistant Rock Mass of Karst Tunnel Face Taking Into Account Seepage Effect

10.21203/rs.3.rs-384740/v1 ◽

2021 ◽

Author(s):

Jiaqi GUO ◽

Wenlong Wu ◽

Xiliang Liu ◽

Xin Huang ◽

Zhengguo Zhu

Keyword(s):

Rock Mass ◽

Influencing Factors ◽

Water Pressure ◽

Water Inrush ◽

Surrounding Rock ◽

Karst Water ◽

Seepage Force ◽

Karst Tunnel ◽

Tunnel Face ◽

Safety Thickness

Abstract This paper took into account the adverse influence of the karst water seepage effect on the water-resistant rock mass. Based on the upper-bound theorem of limit analysis and the Hoek-Brown failure criterion, through a series of formula derivation, the expression of critical safety thickness of water-resistant rock mass of karst tunnel face was finally obtained. The paper carried out a feasibility analysis, an analysis of influencing factors and a comparative analysis with previous related research achievements of this method. The results showed that: (1) With the decrease of surrounding rock grade, the safety thickness of water-resistant rock mass gradually increased, and the safety thickness of surrounding rock at all grades remained within a reasonable range. (2) The safety thickness decreased as the compressive strength, the tensile strength and parameter A increased, and it increased as the karst water pressure, the tunnel excavation height, and parameter B increased. (3) The change trend of the safety thickness with the influencing factors was completely consistent under the two conditions of considering and without the seepage effect, and the safety thickness with considering the seepage force was greater than that without considering the seepage force. Taking the Yunwushan tunnel of Yiwan railway as an example, the critical safety thickness of the water-resistant rock mass was calculated and the calculated value was in good coincidence with the safety thickness adopted in the actual project. The research results are of great significance to prevent the occurrence of high pressure filling karst geological disasters such as water inrush in tunnels.

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Study on Safe Thickness of Comparatively Intact Rock Ahead of Karst Tunnel Face

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.90-93.2456 ◽

2011 ◽

Vol 90-93 ◽

pp. 2456-2459 ◽

Cited By ~ 1

Author(s):

Jia Qi Guo ◽

Lian Wei Ren ◽

Xi Liang Liu

Keyword(s):

Mechanical Model ◽

Water Pressure ◽

Water Inrush ◽

Intact Rock ◽

Tensile Fracture ◽

Karst Tunnel ◽

Tunnel Face ◽

Rock Wall ◽

Safe Thickness ◽

Tension Strength

Under the effect of water pressure in karst cave before tunnel face, water inrush happens when excavation face enters into the minimal value of safe thickness. Aiming at comparatively intact rock ahead of karst tunnel face, rock wall often appears to be tensile fracture. With some hypotheses, a mechanical model of water inrush for tunnel face instability has been established, furthermore, the analytical expression to calculate safe thickness of rock wall has been given based on the criteria of tension strength through elastical theories. Combined with Maluqing tunnel in Yiwan line, applicability and reliability of formula is discussed.

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Analysis of Seepage and Displacement Field Evolutionary Characteristics in Water Inrush Disaster Process of Karst Tunnel

Geofluids ◽

10.1155/2021/5560762 ◽

2021 ◽

Vol 2021 ◽

pp. 1-20

Author(s):

Yongbiao Lai ◽

Shuo Li ◽

Jiaqi Guo ◽

Zhengguo Zhu ◽

Xin Huang

Keyword(s):

Numerical Simulation ◽

Rock Mass ◽

Lateral Pressure ◽

Water Pressure ◽

Water Inrush ◽

Pressure Coefficient ◽

Karst Tunnel ◽

Seepage Pressure ◽

Lateral Pressure Coefficient ◽

Tunnel Depth

Water inrush of tunnel is one of the most common geological disasters in the karst strata in China. Aiming at the rock mass with a quasi-masonry structure in the water-resistant strata between karst cavity with high pressure water and tunnel and the shortcomings of theoretical analysis, traditional numerical simulation, and physics model test for describing and reflecting this special structure of rock mass, a Discrete Element Method considering the fluid-solid coupling effect and structural characteristics of rock mass is employed to study the disaster process of water inrush and the evolutionary characteristics of catastrophe information like seepage pressure and displacement under condition of different karst water pressure, tunnel depth, and lateral pressure coefficient. Research results show the following: (1) the seepage pressure and displacement increase with the increase of kart water pressure. The seepage pressure demonstrates a decreasing state from top to bottom in water-resistant strata, and the time of arrival to a stable value for the seepage pressure shows the time effect. (2) The larger the tunnel depth, the greater the coalescence and distribution scope of fracture and the more likely the water inrush to occur in a short time. The stability of water-resistant strata decreases on the whole with the growth of tunnel depth. (3) The increase of lateral pressure coefficient can restrain the fracture development and strengthen stability. The fracture state is significantly influenced by a lateral pressure coefficient. The results of numerical simulation are consistent with those obtained by a model test. Research and analysis based on energy are a promising train of thought for studying the disaster process of water inrush in a karst tunnel.

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Evolution Pattern and Matching Mode of Precursor Information about Water Inrush in a Karst Tunnel

Water ◽

10.3390/w13111579 ◽

2021 ◽

Vol 13 (11) ◽

pp. 1579

Author(s):

Jie Song ◽

Diyang Chen ◽

Jing Wang ◽

Yufeng Bi ◽

Shang Liu ◽

...

Keyword(s):

Rock Mass ◽

Stress Field ◽

Displacement Field ◽

Water Inrush ◽

Seepage Field ◽

Karst Tunnel ◽

Rock Mass Structure ◽

Evolution Pattern ◽

Water Blocking ◽

Precursor Information

The water inrush of the Shangjiawan karst tunnel is used to study the evolution pattern of precursor water inrush information in water-filled caves and to further reveal the matching mode of the information. The three-dimensional numerical method FLAC3D was used to simulate the evolution process of water inrush after damage to a water-blocking rock mass structure in a water-filled cave and to obtain the evolution pattern of precursor water-inrush information caused by the damage. The results show that the multifield response to the characteristic precursor information of the water-inrush pattern after the fracture of the water-blocking rock mass follows the order of stress-field displacement-field seepage-field. Further, the matching pattern of the information shows that the stress field increased first and then decreased, the displacement field always increased, and the seepage field increased first and then decreased.

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Numerical Analysis of the Mud Inflow Model of Fractured Rock Mass Based on Particle Flow

Geofluids ◽

10.1155/2021/5599748 ◽

2021 ◽

Vol 2021 ◽

pp. 1-16

Author(s):

Yongjian Pan ◽

Huajun Wang ◽

Yanlin Zhao ◽

Qiang Liu ◽

Shilin Luo

Keyword(s):

Rock Mass ◽

Pressure Gradient ◽

Flow Direction ◽

Fractured Rock ◽

Water Pressure ◽

Water Inrush ◽

Quadratic Function ◽

Particle Flow ◽

Fractured Rock Mass ◽

Particle Flows

Water inrush and mud outburst are one of the crucial engineering disasters commonly encountered during the construction of many railways and tunnels in karst areas. In this paper, based on fluid dynamics theory and discrete element method, we established a fractured rock mass mud inflow model using particle flow PFC3D numerical software, simulated the whole process of fractured rock mass mud inflow, and discussed the effect of particle size and flow velocity on the change of pressure gradient. The numerical simulation results show that the movement of particles at the corner of the wall when the water pressure is first applied occurs similar to the vortex phenomenon, with the running time increases, the flow direction of particles changes, the vortex phenomenon disappears, and the flow direction of particles at the corner points to the fracture; in the initial stage, the slope of the particle flows rate curves increases in time, and the quadratic function is used for fitting. After the percolation velocity of particles reaches stability, the slope of the curve remains constant, and the primary function is used for fitting; the particle flow rate and pressure gradient are influenced by a variety of factors, and they approximately satisfy the exponential function of an “S” curve.

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Effect of Wetting-Drying Cycle on the Deformation and Seepage Behaviors of Rock Masses around a Tunnel

Geofluids ◽

10.1155/2020/4237163 ◽

2020 ◽

Vol 2020 ◽

pp. 1-14

Author(s):

Qingzhen Guo ◽

Haijian Su ◽

Hongwen Jing ◽

Wenxin Zhu

Keyword(s):

Rock Mass ◽

Principal Stress ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Water Inrush ◽

Surrounding Rock ◽

Tunnel Excavation ◽

Cycle Number ◽

Simulation Results

Water inrush caused by the wetting-drying cycle is a difficult problem in tunnel excavation. To investigate the effect of the wetting-drying cycle on the stability of the tunnel surrounding rock, physical experiments and numerical simulations regarding the process of tunnel excavation with different wetting-drying cycle numbers were performed in this study. The evolutions of stress, displacement, and pore water pressure were analyzed. With the increase in cycle number, the pore water pressure, vertical stress, and top-bottom approach of the tunnel surrounding rock increase gradually. And the increasing process could be divided into three stages: slightly increasing stage, slowly increasing stage, and sharply increasing stage, respectively. The failure process of the surrounding rock under the wetting-drying cycle gradually occurs from the roof to side wall, while the baseplate changes slightly. The simulation results showed that the maximum principal stress in the surrounding rock mass of the tunnel increases, while the minimum principal stress decreases. Furthermore, the displacement of the rock mass decreases gradually with the increasing distance from the tunnel surface. By comparing the simulation results with the experimental results, well consistency is shown. The results in this study can provide helpful references for the safe excavation and scientific design of a tunnel under the wetting-drying cycle.

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Karst Water Pressure’s Varying Rule and Its Response to Overlying Strata Movement in Coal Mine

Advances in Civil Engineering ◽

10.1155/2020/8848924 ◽

2020 ◽

Vol 2020 ◽

pp. 1-7

Author(s):

Jian Hao ◽

Hua Bian ◽

Anfa Chen ◽

Jiahui Lin ◽

Dongjing Xu

Keyword(s):

Water Level ◽

Water Column ◽

Coal Mine ◽

Simulation Experiment ◽

Water Pressure ◽

Water Inrush ◽

Column Height ◽

Karst Water ◽

Working Face ◽

Water Column Height

Karst water is widespread throughout China and is heavily influenced by complex geological conditions, and floor inrush of karst waters associated with coal seams is the second most common coal mine disaster in China. Due to the limitation of precision and cost of geophysical exploration technology, the volume and pressure of karst water are challenging to measure, especially during the mining process. Therefore, predicting karst pressure’s response to mining is critical for determining the mechanism of water inrush. Here, closed karst water pressure (CKWP) response to mining was studied in an innovative physical simulation experiment. In the simulation experiment, a capsule and a pipe were designed to reflect CKWP and the water level. In the experiment, the vertical stress and karst water level were monitored throughout the process of an advancing coal panel. Monitoring results show that the range of the abutment pressure was about 40 cm, and the peak coefficient value was about 2. When the working face is far away from the water capsule, the stress and water column near the water capsule have no obvious change. With the working face 10 cm from the water capsule, the stress and water column height increased significantly. When the working face was right above the water capsule, the stress and water column rose sharply and reached the maximum value. When the working face advanced beyond the water capsule, the stress and water column height declined. Through establishing a structural mechanics model, the karst water system underneath the working face is assumed to be a hydraulic press. Accordingly, the compressed area was assumed to be a piston. The karst water pressure increases sharply, while the piston is compressed, increasing water inrush risk. This discovery may help determine the water inrush mechanism from a novel point of view.

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