A Non-Linear Fluid-solid Coupling Mechanical Model Study for Paleokarst Collapse Breccia Pipes Under Erosion Effect

 

Banghua Yao

State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221008, China; e-mail:yaobanghua@126.com

Xianbiao Mao

State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221008, China

Kai Zhang

State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221008, China

Wei Cai

Department of Civil Engineering, The University of Nottingham, University Park, Nottingham NG7 2RD, UK; e-mail: Caiwei3594967@126.com

ABSTRACT

In this research the seepage characteristics of Paleokarst collapse breccia pipes under particles erosion effect, and their water inrush mechanism were studied. In this paper, based on the seepage theory of pores media and the nonlinear mechanics theory, we deduced the transport equation of particles in Paleokarst collapse breccia pipes, obtained the seepage field equation for Paleokarst collapse breccia pipes, and investigated the porosity evolution equation under the effect of particles transport, building a nonlinear fluid-solid coupling model for Paleokarst collapse breccia pipes. Furthermore, we took the relationship between fluid and particle velocities as well as the effect of particle concentration on fluid property into account, and assumed the porosity in Paleokarst collapse breccia pipes obey Weibull distribution. Finally, we lead the model equations into the COMSOL Multiphysics to solve, obtaining the parameters including porosity, seepage velocity, particle concentration, water inflow evolution law as the time. The research results indicate that: (1) particles in Paleokarst collapse breccia pipes will be eroded and transport under the effect of fluid movement as the time, the concentration of particles behaved rapidly increased and then sharply decreased, and the porosity and seepage velocity grew quickly until reached the maximum value; (2) the seepage capacity for Paleokarst collapse breccia pipes initially grows slowly, while seepage velocity increases at an increasing rate with the growth and connectivity of porosity; (3) the porosity evolution under erosion effect in Paleokarst collapse breccia pipe is an important reason for Paleokarst collapse breccia pipe water inrush.

Keywords: Paleokarst collapse breccia pipe; fluid-solid coupling model; erosion effect; numerical simulation.

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