Thickness measurement and distribution law of loose rings of surrounding rock in large cross section semicircle arch seam gateway

in order to study the distribution law of the loose rings in the semicircele arch seam gateway with the vertical sidewalls,the mechanicsanalysis and the stress wave theory were frstly aplied to explain the formation mechanism of the loose rings. Secondliy,based on No.11713 air return gateway of a mine as an engineering case,a Midas/GTS-FLAC~(3D)couping simulation technology was appied to simulate the formation process of the loose rings,the loose rings obtained of the type gateway was in a " butterfly"form and meanwhile the calculation method of the loosering thickness in the numerical simulation was defined. n order to verfy the reliability ofthe simulation results, an ultrasonic wave measuring method was applied to the site measurement on the loose ring thickness of the gateway.The results showed that the actual measured value of the loose ring thickness was 1.8~ 2.0 m and was much closed to 2.0 m obtained from the numerical simulaton.The surrounding rock type was lV,thesupport method of the gateway was changed from the U type shield support to the bolft and steel mesh suppor,the support nethod could effectively control the deformation of the surrounding rock and could be promoted and applied to the engineering