Abstract
When the deep tunnel is excavated, the pressure of the confined water is relatively high, causing the water inrush to have a hydraulic fracturing effect. The method of theoretical analysis was adopted to study this effect. A mechanical model for fracturing water inrush under blasting excavation conditions was established. The water inrush under this condition is the result of the combined action of static load (water pressure and in situ stress) and dynamic load (explosive stress wave). According to whether the normal stress on the hydraulic crack surface was tensile stress or compressive stress, two types of water inrush were proposed: water inrush caused by tensile-shear damage and water inrush caused by compression-shear damage. These two types of critical water pressures were calculated separately. The relationship between critical water pressure, in situ stress, and blasting disturbance load was given, and a pore water pressure splitting factor was introduced in the calculation process. The theoretically obtained critical water pressure had been verified in the case of water inrush in a deep-buried tunnel. The established theory can guide field practice well.
Highlights
After mining or tunnel engineering enters deep [1,2,3], the rock mass often has the characteristics of high water pressure and high in situ stress [4], which is prone to water inrush geological disasters. e water inrush of these rock mass projects has a hydraulic fracturing effect [5, 6]
High water pressure is the basic condition for water inrush channel, and excavation disturbance is the inducing factor of water inrush [7]
If the hydraulic cracks extend to the surface of the floor, water inrush occurs [13]. e relationship between the damage variable and the permeability coefficient was established, and the dangerous area of the floor water inrush was determined [14]. e splitting effect of water pressure on the floor water-resistant layer was analyzed, and the length formula of the split zone at both ends of the crack under the water pressure was given [15]
Summary
After mining or tunnel engineering enters deep [1,2,3], the rock mass often has the characteristics of high water pressure and high in situ stress [4], which is prone to water inrush geological disasters. e water inrush of these rock mass projects has a hydraulic fracturing effect [5, 6]. E water inrush under such geological conditions was caused by the fracturing of the secondary stress field formed by the excavation and the static and dynamic hydraulic pressure in the collapse column. E minimum safe thickness of the rock wall in the case of hydraulic fracturing of water inrush occurs in the tunnel under the disturbance of blasting excavation [24, 26]. These studies failed to consider the pore water pressure gradient effect of hydraulic fracturing, so the established theory has certain limitations. An example was used to verify the correctness of the theoretical derivation
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