The Layout of the Combustion Cavity and the Fracture Evolution of the Overlying Rock during the Process of Underground Coal Gasification

Table 1

Numerical model parameters.

Parameters	Roof strata	Coal strata	Floor strata
Young’s modulus, , GPa	16	10	18
Poisson’s ratio,	0.3	0.33	0.3
Internal cohesion, , MPa	3.5	2.5	3.6
Internal frictional angle, , °	35	26	37
The proportion of damaged elements, , %	20%	30%	20%
Specific heat, , J/(kg·°C)	890	1760	1650
Thermal conductivity, , (J/h)/(kg·°C)	4320	1810	3240
Thermal expansion, , (/°C)