Estimation of tunnel stability and optimization of support parameters for tunnel below gob pillar in closely-spaced coal seams

摘要

After the upper coal seam mining, stress concentrations under the residual pillar generate an inhomogeneous stress field and the stress on the tunnel increases. This can lead to tunnel destruction if the external forces exceed the strength of the composite rock-bolt bearing structure (CRBBS). The Weibull distribution function was introduced to modify the calculation formula of the CRBBS strength and stress distribution of the CRBBS. The radial stress within the CRBBS under the inhomogeneous stress field was calculated. The tunnel instability coefficient (η) was derived to quantitatively describe the relationship among the tunnel position, tunnel parameters, support parameters, and rock mechanical properties. The coefficient is the ratio of the maximum radial stress within CRBBS to the CRBBS strength;;the CRBBS is stable only when rj20m), abutment pressure influence edge method (14.6m), and rateo fstress change method (> 16.2m). Since the resistance of the bolt support is quantified, the tunnel position evaluated by the tunnel instability coefficient is more practical.