Abstract
Muzhailing Highway Extra-long Tunnel in Lanzhou, Gansu Province, China, belongs to the soft rock tunnel in the extremely high geostress area. During the construction process, large deformation of the soft rock occurred frequently. Taking the no. 2 inclined shaft of Muzhailing tunnel as the research object, an NPR (negative Poisson’s ratio) constant resistance and large deformation anchor cable support system based on high prestress force, constant resistance, and releasing surrounding rock pressure was proposed. The characteristics of the surrounding rock under the steel arch support and NPR anchor cable support were compared and analyzed by using 3DEC software. A series of field tests were conducted in the no. 2 inclined shaft, and the rock strength, displacement of the surrounding rock, deep displacement of the surrounding rock, internal force of steel arch, and axial force of anchor cable were measured to study the application effect of the NPR anchor cable support system in tunnel engineering. Moreover, the 3DEC numerical simulation results were compared with the field test results. The research results show that the application of NPR constant resistance and large deformation anchor cable support system in tunnel engineering has achieved good results, and it plays a significant role in controlling the large deformation of the tunnel surrounding rock.
Highlights
With the rapid development of tunnel engineering in the modern world, the construction of railway and highway tunnels in China has developed by leaps and bounds in recent years
E traditional tunnel support measures cannot adapt to the special thin-bedded slate surrounding rock of the Muzhailing tunnel, and a new support system needs to study urgently. is paper introduced the application of negative Poisson’s ratio (NPR) constant resistance and large deformation anchor cable support system in tunnels. e steel arch support and NPR anchor support were compared and analyzed using the 3DEC numerical simulation software. e results of the field monitoring test show that the NPR constant resistance large deformation anchor cable has achieved good results in controlling the surrounding rock deformation
Muzhailing tunnel is located in Lanzhou, Gansu Province, China. It is a key control project of the Lanzhou-Haikou national expressway. e length of the tunnel is 15.226 km. It is the longest tunnel on the whole line with a maximum depth of 629.1 m. e excavation area is larger than 133.8 m2, and some parts of the tunnel are deeper than 500 m over 60% of the total length. is paper relies on the no. 2 inclined shaft of Muzhailing tunnel to explore the supporting measures of the soft rock tunnel. e inclined shaft is 1813.43 m in length and 591 m in maximum depth
Summary
With the rapid development of tunnel engineering in the modern world, the construction of railway and highway tunnels in China has developed by leaps and bounds in recent years. Researchers have done a lot of research on the deformation and support methods of the tunnel surrounding rock. Hoek et al [1] studied rock strength and rock mass strength, as well as the deformation characteristics of tunnels at different depths. Meguid and Rowe [2] used a three-dimensional numerical simulation method to study the deformation law and stress distribution law of the tunnel surrounding rock under different stresses. Merlini et al [6] studied the deformation mechanism of the soft rock in the Ceneri Base extra-long tunnel and proposed a combined support scheme of deformable bracket + anchor net shotcrete + shotcrete reinforced with fibers + steel arch, which could effectively control the tunnel surrounding rock subsidence. E relationship between surrounding rock stress, tunnel depth, and bolt support strength was analyzed. E traditional tunnel support measures cannot adapt to the special thin-bedded slate surrounding rock of the Muzhailing tunnel, and a new support system needs to study urgently. is paper introduced the application of NPR constant resistance and large deformation anchor cable support system in tunnels. e steel arch support and NPR anchor support were compared and analyzed using the 3DEC numerical simulation software. e results of the field monitoring test show that the NPR constant resistance large deformation anchor cable has achieved good results in controlling the surrounding rock deformation
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