Numerical Analysis of the Hydraulic Fracturing of Pressure Tunnel Lining Based on the 2P-IKSPH Method

In order to investigate the fracture mechanisms of the pressure tunnel lining under water-stress coupling, based on the traditional smoothed particle hydrodynamics (SPH) method, the solid-water particle interaction method, and the particle damage conversion algorithm are proposed to realize the hydraulic fracturing process, which is called the 2P-IKSPH method. The “particle domain searching method,” the “birth-and-death particle method,” and the “group discrimination searching method” have also been proposed to realize the simulations of complex processes of excavation, lining, and operation of the hydraulic tunnel. Taking the Guzeng hydraulic tunnel as an engineering example, the hydraulic fracturing of tunnel lining under different conditions is numerically simulated. Results show the following: (1) the 2P-IKSPH method can dynamically reflect the stress wave propagation processes of surrounding rock and the damage process of tunnel lining. (2) The lining damage mainly occurs on the vault and the arch foot. (3) The critical internal water pressure increases with the increase of the tunnel buried depth and the thickness of lining, but increases first and then decreases with the increase of the surrounding rock mass grade. The research results can provide some references for the optimization designs of tunnel lining and reinforcement of similar projects. Meanwhile, developing 3D parallelization program based on 2P-IKSPH will be the future research directions.

Effect of Overburden Height on Hydraulic Fracturing of Concrete-Lined Pressure Tunnels Excavated in Intact Rock: A Numerical Study

This study investigated the impact of overburden height on the hydraulic fracturing of a concrete-lined pressure tunnel, excavated in intact rock, under steady-state and transient-state conditions. Moreover, the Norwegian design criterion that only suggests increasing the overburden height as a countermeasure against hydraulic fracturing was evaluated. The Mohr–Coulomb failure criterion was implemented to investigate failure in the rock elements adjacent to the lining. A pressure tunnel with an inner diameter of 3.6 m was modeled in Abaqus Finite Element Analysis (FEA), using the finite element method (FEM). It was assumed that transient pressures occur inside the tunnel due to control gate closure in a hydroelectric power plant, downstream of the tunnel, in three different closure modes: fast (14 s), normal (18 s), and slow (26 s). For steady-state conditions, the results indicated that resistance to the fracturing of the rock increased with increasing the rock friction angle, as well as the overburden height. However, the influence of the friction angle on the resistance to rock fracture was much larger than that of the overburden height. For transient-state conditions, the results showed that, in fast, normal, and slow control gate closure modes, the required overburden heights to failure were respectively 1.07, 0.8, and 0.67 times the static head of water in the tunnel under a steady-state condition. It was concluded that increasing the height of overburden should not be the absolute solution to prevent hydraulic fracturing in pressure tunnels.