Research On Large Deformation Control Technology Of Soft Rock Tunnel Based On Active-Yielding Support Theory

In recent years,with the continuous and rapid development of domestic railway and highway construction,a large number of deep,long,dangerous,and large tunnels passing through high geo-stress areas have appeared especially in the western region of our country since there is a wide range of weak and fractured rock formations in “Hexi Corridor-Qilian Mountain-West Qinling-Longnan-Wenchuan” zone,represented by slate,mudstone,carbonaceous slate,phyllite,etc.Since this type of stratum generally has the characteristics of low rock strength,high degree of fragmentation,and easy softening in contact with water,the problem of large deformation disasters in soft rock during the construction of tunnels under high geo-stress is extremely prominent.Therefore,relying on the construction of the Muzhailing extra-long highway tunnel on the Weiyuan-Wudu Expressway,based on literature and field research and analysis,comprehensive methods including theoretical analysis,numerical simulation,laboratory testing,and field testing are adopted to study the large deformation control technology of soft rock tunnel based on active-yielding support method.The main work and results are as follows:(1)Based on the analysis of the support design scheme of the Muzhailing highway tunnel and the damage of the surrounding rock-support system,the main controlling factors of the large deformation disasters occurring in the high stress soft rock tunnel are explored.From the perspective of the accordance between the mechanical properties of the supporting structure and the displacement of the surrounding rock,the deformation,and failure mechanism of the surrounding rock-support system of the soft rock tunnel under the strong-passive support is analyzed.From the perspective of the gradual release of the surrounding rock stress,it is revealed that the main load-bearing body of soft rock tunnel is the surrounding rock and it is proposed that the suitable support method should be able to actively strengthen the surrounding rock and rapidly increase or utilize the bearing capacity of the rock mass.(2)Based on the triaxial compression test of carbonaceous slate and the mechanism of active support and yield support,the active-yielding support method of "resistance before yield and combination of resistance and yield" in soft rock tunnel with rapid active support as the core is proposed.Furtherly,Based on the numerical simulation,the effectiveness of active support,the necessity of fast support and the rationality of yielding support are analyzed.Finally,the appropriate form of active-yielding support technology and the suitable composition of active-yielding support system are put forward.(3)A constitutive model of surrounding rock that can realize the confining pressure effecthas been developed,named the constitutive model with active support effect.And based on this,select test section,the key parameters of active support including the amount of prestress,the length,space,and the combination type of cable have been studied.Further,based on the Cvsic creep model of carbonaceous slate,the study on the design of yielding deformation and the mechanical behavior of the active-yielding support system is carried out.(4)A new high-strength prestressed anchor cable system with large yielding deformation is developed,which has the function of strong support and appropriate release of deformation energy in the process of large deformation control of soft rock tunnel.The structural advantages and anti-corrosion characteristics of yield pressure anchor cable are analyzed.And,its control mechanism of surrounding rock deformation have been analyzed.The key parameters of cable that affect the yielding force are analyzed,and the theoretical calculation model(process)of yielding force is established.The rationality and accuracy of the theoretical calculation model are verified by the indoor static tensile test of the yield anchor cable,and the constant resistance stability of the yield anchor cable is verified.Further,the applicability of the yielding cable in soft rock tunnel is tested by the field static tensile test.(5)In the test section,the field test is carried out to study the active-yielding support system according to the key design parameters.Through monitoring and analysis of the surrounding rock deformation characteristics,structural force characteristics,and yielding-slip characteristics during the test,the surrounding rock-support stability and support safety of large deformation section in the Muzhailing tunnel under active-yielding support are verified.The applicability and reliability of the active-yielding support system in soft rock tunnels are revealed.