Suitability Evaluation Of Foundtion Of High-rise Buildings Above Multi-level Goaf And Treatment

With the urbanization process in China and the transformation and development of mining cities,the demand for land construction and ecological utilization of abandoned coal mines is increasing.In order to promote the utilization of land resources and ensure the safe use of buildings and structures in mining subsidence areas,it is necessary to evaluate the stability of the goaf scientifically,reasonably and objective.This paper takes the Xuzhou Rong Sheng Cheng project as an example.The Rong Sheng Cheng project is located in the minefield of the Wo Niu Shan coal mine of Xuzhou Mining Group.The main coal seam is 2,3,7,9,10,20,21 coal.This coal mine closed in 2008.The proposed building above the site are mainly 4F,11 F,18F,24 F,34F residences(with 1-2 floors of basement)and multistorey commercial building.Therefore,this paper comprehensively uses geophysical exploration,drilling and borehole imaging to carry out the survey of goaf detection.Based on the analysis of the extent of goaf,overburden deformation and surface movement and deformation,the stability of the mining subsidence area is evaluated and partitioned.Then the corresponding grouting treatment program is put forward.The main research results are as follows:(1)Quantitative analysis of the distribution of goaf and the development of fractures in the site.According to the collected data,the detection results of the transient electromagnetic line,the results of the drilling exposure and the borehole imaging,there are localized voids in the 3,7,9,10,20 coal goaf under the site,the whole goaf has been filled with water and the water level of the goaf is 56.1-63.9m.In addition,the statistical results of the fracture zone according determined that the height of the fracture zone of the 7 coal with the gentledip is 51.5m,and the height of the fracture zone of the 7 coal with the steep dip is 59.0m.According to the observed borehole water level,the height of the fracture zone of the 7 coal with the gentle-dip is 35-48 m,the development height of the fault zone of the 7 coal with the steep dip is 64 m.(2)The stability of the pillar-type,strip-type mining goaf and long-wall mining goaf under the site is respectively is evaluated by using the coal(rock)column stability analysis method and the goaf condition feature identification method.According to the comprehensively evaluate results,the stability of the site is divided into stable zone,basic stable zone and unstable zone.(3)Using the goaf feature discriminant method,the activation influencing factor analysis method,the surface residual deformation discriminant method,etc.to analyze and evaluate the influence degree of the goaf on the project.In addition,using the load influence depth discriminant method and the additional stress analysis method to analyze and evaluate the influence degree of the construction project on the goaf.According to the stability of the site of the goaf,the degree of mutual influence of the goaf and the proposed project,the difficulty of the technical measures to be taken against the mining,and the project cost,the suitability of the site construction of the goaf is divided into suitable area,basic suitable area,and unsuitable area.(4)According to the environmental conditions of the proposed building and site,the grouting plan is refined.The range of the grouting treatment,the arrangement of the grouting hole and the process of grouting construction are clarified.The results of comprehensive testing methods,including drilling,wave velocity test,water injection test,borehole imaging,and stone body strength test,show that the effect of ground collapse disasters in the goaf has been basically eliminated through grouting treatment.Meanwhile,the effect of residual deformation of the ground settlement is reduced,the engineering quality of the site after grouting treatment has reached the design requirements.