Study on the Hydraulic action Mechanism and Support Measures of Weakly Cemented Muddy Surrounding Rock

Abstract In western China, there are extensive silty weakly cemented strata, whose significant hydraulic effects severely restrict the safe and efficient mining of coal. In order to address the problem of deformation and failure in roadways within weakly cemented muddy surrounding rock, This paper investigates through indoor experiments, theoretical analysis, numerical simulation, and field tests, The study investigated the hydro-mechanical disintegration of clayey weakly cemented rocks, established the constitutive relationship of clayey weakly cemented rocks under hydraulic influence, determined the deformation and failure process of surrounding rock in tunnels of clayey weakly cemented formations, proposed a high-strength bolt (cable) combined support technology, and conducted field tests at the No. 5 Mine of DaNanHu. The research results indicate:①Under soaking conditions, the undried muddy weakly cemented rock blocks begin to absorb water and crumble after 1 hour, and disintegrate into smaller pieces after 1.5 hours. After drying, the clayey weakly cemented rock samples will exhibit muddying and disintegration phenomena after 20 minutes. After 3 hours, the samples disintegrate into larger blocks, completely losing their strength. ②A mathematical model of muddy weakly cemented rock under hydraulic action was established, and its validity was demonstrated through comparison with triaxial compression tests. ③When the rock water content increases from 2% to 6%, the distance from the stress concentration zone in the surrounding rock of the roadway to the roadway surface increases from 3.1 m to 6.7 m. When the moisture content is in the range of 8–12%, the extreme value of the principal stress difference increases significantly with the increase of moisture content, aggravating the deformation and instability risk of the roadway. When the moisture content reaches 12%, the peak values of the principal stress difference in the roof and ribs are approximately 13.0 MPa and 11.8 MPa, respectively. When the moisture content increases from 2% to 12%, the convergence of the roof and floor in the middle of the roadway increases from 410mm to 2110mm, and the convergence of the two sidewalls in the middle of the roadway increases from 374mm to 1020mm. ④The joint support parameters were determined through simulation tests: The roof and side walls use anchor bolts with a diameter of 22mm and a length of 2400mm, with a spacing of 800×800mm between the bolts. The anchor cables have a diameter of 18.9mm and a length of 6300mm, with a spacing of 2400×2400mm between the cables. ⑤The support parameters determined based on simulation tests were field-tested in the return air tunnel of the 1801 working face at DaNanHu No. 5 Mine.Using high-strength anchor (cable) combined support technology, the maximum settlement of the roadway roof is 140mm; the maximum separation measured between base points located 3.5m, 4.5m, and 5.5m from the roadway roof is approximately 25mm; The maximum separation measured between base points at 0.5 m, 1.5 m, and 2.5 m from the tunnel roof was about 30 mm. The axial stable loads of roof bolts 1 and 2 and side bolts were 90 kN, 120 kN, and 60 kN, respectively, all below the failure load of the bolts, effectively controlling the deformation and damage of the mudstone weakly cemented tunnel.