Research On Double Wedge Cutting Technology For Super Large Section Tunnel In Hard Rock

With the rapid process of urbanization, the exploitation and utilization of underground space becomes more and more, and both the difficulty and the requirement on blasting excavation of rock underground space becomes higher. The paper took the super large section tunnel at the top of the oil storage underground structure in hard rock as research objects, and carried out the design of double wedge cutting. Analyze the mechanism of cavity forming from the point of physical mechanics, and the numerical simulation was done on wedge cutting. The blasting effect of the double wedge cutting and the whole section was tested by field test,and comparing the results of numerical simulation at the same time. The main research contents and results are as follows:(1) The simplified model of the middle deep hole wedge cutting was built and the best angle(with free surface) of wedge cutting hole was obtained through analysis of physical mechanics, which was range of65°~ 85°.(2) The numerical model of the middle deep hole wedge cutting wasbuilt, and then the numerical simulation of wedge cutting was carried out.When the wedge cutting hole charge exploded, the stress wave spread around first with circular wavefront, then spread around with columnar wavefront as the stress wave in adjacent hole met and made complex changes, such as superposition. The relief duration of the efficient stress wave in wedge cutting to cutting cavity was about 1000 us, and the peak was more than 500 MPa. It could break most of rock in cutting cavity and throw them, so it could form obvious cavity to create good free surface for follow-up blasting and provide expansion space for rock breaking.(3) Combined with previous construction experience, according to geological conditions, rock properties, used explosive and excavation section, the double wedge cutting was designed on the basis of the theory of blasting. The results of field test verified the results of numerical simulation well. The double wedge cutting was both reasonable and efficient, with great cutting cavity bulk, high hole utilization rate, large footage driving cycle, moderate size of rock broken. It had a good cutting effect, and could solve the cutting puzzle of super large section tunnel.(4) Based on the double wedge cutting, the whole section one-shot smooth blasting was designed. In hard rock blasting of super large section tunnel, the double wedge cutting was reasonable and efficient, the arrangement and parameters of hole chosen reasonably and effectively,the explosive energy used fully, surrounding rock damaged lightly, andwith high hole utilization rate, well-distributed size of rock broken, few bulker, high half-borehole ratio, flat wall. The effect of smooth blasting improved obviously, and solved a series of previous puzzles. It improved the blasting quality and sped up the construction pace. It can provide reference for future super large section underground engineering.The technology of double wedge cutting in blasting excavation of super section hard rock tunnel is reasonable and effective, and can make super large section hard rock tunnel obtain an ideal blasting effect. It can speed up construction pace and improve excavation quality, and have a great significance.