Prediction method of surface residual subsidence for land resource reuse after low-carbon underground coal gasification

Underground coal gasification (UCG) is an important part of the low-carbon green coal mining technology system. With the implementation of the carbon peaking and carbon neutralization and the maturity of UCG, UCG will inevitably perform large-scale and industrialized production, which will certainly cause some issues such as serious waste of UCG sites caused by large-scale surface residual subsidence and poor foundation of fractured rocks. The key to the reuse of the surface site after UCG is to ensure that the surface residual subsidence does not exceed the design index of the building (structure). However, there is still a lack of methods for predicting residual subsidence on the surface of UCG. Under such background, combined with the characteristics of the UCG process, this paper analyzed the mechanism of the surface residual subsidence after UCG, and concluded that the root resource of the surface residual subsidence after UCG was the stripping and yielding of the hyperbolic coal pillars. Next, a calculation model of the maximum stripping width and yielding zone width of the "hyperbolic" coal pillar for UCG was established by the theoretical analysis method, and a method for predicting the surface residual subsidence with the consideration of coal pillar stripping and yielding was proposed and applied to Ulanqab UCG test site. The research findings have important theoretical and practical significance for the UCG site stability evaluation and land resource reuse.