Abstract:

In recent years，with the decrease of land mineral resources，the development of marine minerals has become a global emerging industry，especially the mining of coastal bedrock deposits under the sea，has been the focus of mining development in various countries.For large-scale mining under the sea，the movement and deformation of the submarine rockbody poses a major threat to mining safety.It is important to pay attention to the deformation damage of the surrounding rock，which is important to realize the safe and efficient production of submarine mines. In order to study the deformation and damage characteristics of the surrounding rocks of the underground mine body in the Xinli mining area，the 55 exploration line perpendicular to the mine body was used as the monitoring profile，and the roadway roofs of -200 m，-240 m，-320 m，-400 m，-480 m，and -600 m sublevels were monitored by the underground four-level monitoring system that has been deployed since December 2015.The vertical displacements of the surrounding rocks in sublevels of the roadway at -200 m，-240 m，-320 m，-400 m，-480 m and -600 m were monitored for a long time，and the time series data of the settlement of the roadway roof in each sublevel were obtained.The deformation of the surrounding rock caused by metal ore mining is a complex mechanical problem.By analyzing the multi-year monitoring results，several significant characteristics of underground settlement are revealed.（1）The deformation caused by mining of the orebody in sublevel at different depths of the seabed shows a large influence range on the rock mass of the fault hanging wall，while the influence range on the footwall rock mass is small.（2）The closer to the orebody（or the ore-control fault F₁） the greater the subsidence of the rock body，forming the feature that the slope of the curve to the left of the maximum settlement point in the settlement curve is larger in absolute value，while the slope of the curve to the right is slightly smaller in absolute value.（3）The final subsidence curves of the six sublevels in the line 55 profile have similar shapes and are generally asymmetric funnel-shaped，with the -200 m sublevel and the -240 m sublevel having a gentle bottom of the cumulative subsidence curve，which is similar to a “pot”，while the -320 m，-400 m，-480 m and -600 m sublevels have a “funnel” shaped subsidence curve.This phenomenon is related to the mining activities in the mine area.（4）The single settlement value in any monitoring period in the sublevel at any depth has the characteristics of up and down fluctuation，which reflects the non-linear characteristics of settlement deformation to a certain extent.The practice of seabed mining in Sanshandao gold mine confirms that：Since 2005，with the expansion of mining scale，the increase of mining intensity and the extension of mining years，the deformation of some of the underground tunnels is serious，and the movement and deformation of the underground surrounding rocks may cause seawater to gush into the tunnels along the damaged rocks，thus threatening the life safety of mining personnel.The study concluded that the thickness of the orebody，mining depth，mining intensity，surrounding lithology and rock structure as well as filling effect in the Xinli mining area are potential factors affecting the deformation of the surrounding rock in the mining of the inclined orebody.Among them，the presence of the controlling fault F₁ in the mine area directly affects the shape of the surrounding rock deformation curve，and this deformation feature should be considered in future production work as well as safety maintenance work（roadway repair work） to prevent from affecting productivity or even generating safety accidents.

Key words: Sanshandao gold mine, seabed mining, underground subsidence, levelling, influencing factors