Research On The Investigation And Prevention Technology Of Old Mined-out Area Under Buildings

Mined-out areas problem,which is a special geological engineering problem under building basement,brings serious hidden risk to the stability of building.In recent years,with the development in the technology of administration mined-out areas administration and the surface deformation theory,many old mined-out areas have been disposed and a lot of industrial or civil buildings have been constructed on the surface successfully.It is the insufficient of the mined-out areas' survey and treatment that leads to many geological hazards,such as the settlement,cracking and collapse of the existing buildings over the gob.This passage explores the prospection,stability evaluation and control technology of mined-out areas based on the reconstructed project of Dongshan subsidence area in Xihu,Benxi and the stability of mined-out areas under buildings,which has important practical significance and application value.The underground mined-out areas,backfilling areas and mining roadways where the Dongshan subsidence area is located resulted from the random mining during the period of puppet Japanese(1940s).As it has experienced natural and human factors for more than 70 years,the stress relief and rock mass deformation are almost stable.This paper summarizes and analyses appropriate conditions of different exploration methods to study the mined-out areas,and optimizes the exploration method of gob under buildings—geophysical method of prospecting based on shallow seismic reflection and Rayleigh wave,supplemented by drilling verification of gob.It is concluded that the surface stability is fairly poor in the area where the depth burial of goaf roof is less than 10m and the thickness of top rock(intermediary weathered sandstone)is less than 6.0m,which leads to high possibility and dangerousness of land subsidence;when the depth burial of goaf roof is more than 10m and less than 50m and the thickness of top rock(intermediary weathered sandstone)is more than 6.0m,the surface stability is also poor.With well surface stability in the area where the depth burial of goaf roof is more than 50m,there are also possibility and risk of land subsidence when constructing high-rise residential buildings.According to the engineering geological conditions,structure characteristics and the actual situation of the mined-out areas,the paper adopts the project of drilling and backfilling grouting control,atmospheric pressure perfusion of high water consolidation materials.Also,the technological parameters and working system that suit the project are established.After research and engineering practice,the paper presents a set of suitable technology system for mined-out areas prospecting,mined-out areas control and the quality monitoring and evaluation after construction,which can provide referential engineering practice for other similar projects.