Key Techniques For Construction Of Shallow Buried Under-biased Tunnel Entrance Through S-type Highway

With the China’s railway and highway construction continues to expand,in some newly-built or rebuilt railway and highway projects,in order to reduce land occupation and mutual influence on existing traffic,meet the requirements of lines,slopes,etc.,and in order to reduce the impact on the surrounding environment,tunnels are used to cross existing routes.Or more and more projects of buildings(structures),and in such projects,if the construction techniques used and selected are unreasonable,it will seriously affect the safety of existing buildings(structures),causing unnecessary losses.Based on this article,the key technology of tunneling under the shallow buried tunnel is discussed through the engineering background of the existing section of the exit section of the Xueshanliang tunnel combined with theoretical analysis,field monitoring measurement data and numerical simulation.The main contents and results of the study are as follows:(1)Combined with on-site construction conditions,monitoring and measurement data,numerical simulation and theoretical analysis,the construction technology adopted by the Xueshanliang tunnel under Chuanhuang Highway is reasonable and feasible.(2)Through numerical simulation analysis,the structural stress of the tunnel under the shallow buried undisturbed tunnel underneath the existing highway and the road settlement law were studied.It was concluded that the stress was greatest when using the reserved core soil method for the lining structure.The area is located near the left and right sides of the lower excavation face and shoulders of the excavation face and the support of the rock mass;the shallow buried pressured tunnel excavation has a greater impact on the surface of the tunnel,which is approximately 2.5 to 3.0 times the diameter of the hole directly above the vault of the tunnel.(3)Based on the analysis and optimization of the reinforcement technology of micro-composite steel pipe piles,the results show that under the conditions of single-row pile spacing of 1m and 2m and double-row staggered arrangement of pile spacing of 2m,the ground and slope reinforcement is obtained when the distance between single-row piles is 1m.The minimum value of displacement settlement value control in the area,the distance between two rows of staggered arrangement of piles is 2m,and the support range of the slope support area is the largest.When double-row piles are arranged,the bending moment of the first row of piles is much larger than that of the second row of piles,and the maximum value of the bending moment is distributed at the end of the pile.(4)According to the design and calculation of blasting parameters,when the velocity of particles on the up highway structure is controlled at 1.5 cm/s,the maximum amount of explosive charge designed for single-stage blasting parameters is 2.43 kg,which is less than the calculated maximum allowable explosive charge 5.52 kg The control method of blasting excavation can be applied theoretically to the main tunnel of the Xueshanliang tunnel heading through the highway section.(5)According to the numerical simulation of the influence of the blasting vibration of the main tunnel of the Xueshanliang tunnel on the existing Chuanhuang highway and the guided tunnel,the Xueshanliang tunnel should be dominated by mechanical excavation at 5 meters before and after the highway section,and the blasting construction should be strictly controlled.The influence on the leveling tunnel meets the design control value requirement.The difference between the detonation interval and the detonation time of the second detonation section is increased by 9%-15% when the interval between 50 ms and 75 ms.Therefore,it is effective to reduce the mutual influence of the blasting vibration effects of two adjacent sections when the millisecond difference between blasting intervals is more than 50ms~75ms.