Experimental Platform Development of Similar Simulation and Mechanical Test for Undersea Metal Mining

With the depletion of shallow metal resources in the land, the development of seabed resources has become a new direction. In order to achieve safe and efficient exploitation of seabed metal mineral resources, a similar simulation test platform was established for seabed mining of metal minerals in this paper. Similar simulation materials and the best material ratios were selected to make simulated specimens. A series of mechanical pressurization devices and model sample were prototyped and submarine simulation mining test was conducted. During the simulation mining test, stress and strain changes and microscopic observations of crack evolution were monitored by the static strain test system. These indicators revealed the characteristics of ore-rock mechanical change in the development of submarine mental resources. By exploring the best safe thickness of seabed resource mining, it provides effective data reference for subsequent seabed resource development, so as to realize safe and efficient mining.

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.