Support optimization of ultra-large cross-section chamber in underground coal mine based on numerical simulation

The combined support of bolts and cables and concrete masonry is suitable for the large-section chamber in underground coal mine. However,the role of anchor rods and cables and concrete masonry in support is not clear. Specific support parameters need to be determined based on engineering experience,which often results in insufficient support or excessive support.In order to solve the supporting problem of large-section chamber in underground coal mine,an initial support scheme of“bolts and cables + concrete masonry”was proposed for a hydraulic support dismantling and assembling chamber with a super large section based on engineering experience. The support effects under four conditions of no support,support with bolts and cables only,support with concrete masonry only and combined support were analyzed by numerical simulation,respectively.An improved support scheme was proposed based on the numerical results,and was applied to engineering practice for verification. The results show that:the reasonable support of ultra-large cross-section chambers in underground coal mine can be realized by means of combining engineering experience and numerical simulation.An initial support plan can be proposed based on engineering experience,then the support parameters can be optimized by numerical simulation to avoid insufficient support or excessive support. Both bolts and cables and concrete masonry have good supporting effects for the ultra-large cross-section chambers in underground coal mine and the supporting effect of concrete masonry is much better than that of bolts and cables. Bolts and cables are suitable as preliminary support to reduce the severe deformation in the initial stage of excavation,and concrete masonry is suitable as permanent support and plays the main supporting role. The combined support of bolts and cables and concrete masonry should be adopted for ultra-large cross-section chambers. When the surrounding rock is relatively broken,grouting reinforcement should be supplemented.In this case,the supporting density of bolts and cables can be appropriately reduced to speed up the construction speed and the concrete masonry support should be carried out in time.