Movement and control of strata and surface during UCG without shaft

Underground coal gasification (UCG) is one of the important research directions in advanced energy field, and is also an important part of the fluidized mining technical system of coal resources. At present,the completed small-scale UCG industrial experiments haven’t caused significant fractures and surface subsidence. However,with the application and large-scale production of UCG,how to carry out UCG production design for controlling fracture devel-opment and surface subsidence under different geological conditions is the bottleneck problem that greatly hinders the site selection and large-scale production of UCG and urgently needs to be solved. To overcome the problem,the numer-ical simulation method was adopted in this paper to study the strata and surface movement characteristic of UCG with-out shaft and the relationships between development height of water flowing fractures and gasifier parameters. At the same time,the stability evaluation method of hyperbolic coking coal pillar was proposed by the theoretical method. The results indicate that:① The curve shapes of strata and surface movement under UCG without shaft are similar with those under conventional strip mining. Therefore,the strata and surface subsidence calculation of UCG without shaft can refer to that in strip mining,but the prediction parameters need to be revised. ② The stability evaluation of hyper-bolic coal pillar can be divided into bending part and rectangular part. On which basis,the stability evaluation method of hyperbolic coal pillar was proposed,which could provide a technical support for UCG design and production under various geological conditions. ③ The development height of water flowing fractures due to UCG without shaft is directly related with the gasifier parameters. When the gasifier height has a certain value and the isolated coal pillars are sta-ble,the gasifier width has a linear positive correlation with the development height of water flowing fracture. When the gasifier and the isolated coal pillar has certain width,a linear positive correlation also exists in the gasifier height and the development height of water flowing fracture. Therefore, the implementation of UCG under overburden aquifer needs to consider the relationships between the development height of water flowing fracture and gasifier parameters. The research results could provide a scientific basis for large-scale UCG production and site selection.