Study On Stability Of Surrounding Rock Of Long Span Tunnel Through Coal Seams

In this year, with the development of our country's highway, the construction scale of highway tunnel is coming larger and larger, which plays important role in decreasing traffic accident rate, shortening driving distance, increasing vehicle speed and enviornmental protection. However, with the construction of Large-span Tunnels through the coal seam, it appeared that there are many unresovled problems in Criterion analysis and theory of stability of surrounding rock.This article aims at the hotspot in Large-span Tunnels through the coal seam research, selects Expressway Circling Chongqing City, Huanshanping Tunnel as the object, basing on definition and analysis Large-span Tunnels and its mechanism of interaction of Rock and Support, simulating Surrounding Rock Deformation and stress distribution after tunnels drugged by software, combining the result of The Monitor Measuring in Natm, studies the stability of surrounding rock of Large-span Tunnels through the coal seam), and puts forward Criterion, and draws conclusions as following:①Max equivalent stress concentration coefficient of Large-span Tunnels varies with flat ratio as inverse ratio, which is close to line relationship. When flat rate is 0.5, Max equivalent stress concentration coefficient of Large-span Tunnels is more than 1.5 times of the same of Circular Chamber.②Sensitivity of equivalent stress concentration coefficient from Vault to abutment is different, surrounding rock nearby the abutment is the most sensitive, while surrounding rock nearby the Vault doesn't vary with flat rate.③Chamber stress concentration of Large-span Tunnels through the coal seam is greater, but the flat rate vary rule is the same. A series or physical phenomenon such as Rockburst, convergent deformation, Deformation of the Tunnel, rockfall, collapse, appears with construction process of tunnel drugging,④During Large-span Tunnels through the coal seam digging, distortion course of surrounding rock lies on the cut surface's moving.⑤Yield approach index of the vault of tunnel across Soft and Weak Surrounding Rock increases with digging forward, and the area which Yield approach index greater than 1 gradually expands to top of the Vault.⑥According to the space convergence analysis on surrounding rock of Huanshanping Tunnel, actual measurement on Representative Sections and Finite Element Analysis result, it proved that surrounding rock is stable and safe. It makes out that digging tunnel in Coal Series Seam Section and mining backfill area among Laminated hard rock be stable and safe as long as under proper protection.⑦Coal Series Seam Section nearby the tunnel, especially mining backfill area influences the stress more. While weak layer cuts the tunnel, the influence area by stress and distortion of weak layer is larger, and is easy to destroy the surrounding rock.The innovation of this study is analyzed stability of surrounding rock in Large-span Tunnels through the coal seam by the numbers, and brings forward the scientific criterion, and has important theory and practice meaning.