Research On Pressure-relief Support Technique For High Initial Stressed Tunnel At Depth

With the development of traffic construction and energy exploration having reached deep mining, high initial stressed tunnel effective support is one of the issues which underground engineerings must face. With high initial stress, the ordinary reinforced support not only wastes plenty of manpower, material and financial resources, but as well results in poor performance of support. Frequently, supporting structure is seriously destroyed and has high repair rate. Therefore, it is urgent to seek methods of high initial stressed tunnel effective support, which can ensure long-term security and stability of tunnel, and improve tunnel support effect, and also reduce tunnel support structure repair rate and support cost, which has important theoretical and practical significance.Based on zonal disintegration theory and blasting damage theory of the mass, this article studies pressure-relief support technique for deep-buried high initial stressed tunnel with theoretical analysis and numerical simulation method. The concrete research contents and main achievements are as follows:(1)Based on zonal disintegration theory of the mass, the charging location and region of pressure-relief by blasting are determined according to the location and width of zonal crack zone, the formulas of radius and width of the corresponding fracturing area are used to calculate some parameters of pressure-relief by blasting. After calculating, the depth of blast hole is 9.0m; the explosive charges are 0.55kg, 0.45kg, 0.40kg, 0.35kg; the stemming lengths of blasting hole are 8.12m, 8.27m, 8.35m, 8.43m.(2)The blast hole spacing and surrounding rock stress after pressure-relief are calculated according to blasting damage theory, the blast hole spacings are 0.7m, 0.8m, 0.9m, 1.0m.And then, considering material mechanics knowledge and tunnel support theory, the tunnel lining thickness and internal forces are determined. After pressure-relief by blasting, the iniaial lining thickness of 1.5m is reduced to 0.9m, 0.75m, 0.6m, 0.8m, and that the moment and axial force of lining structure are also reduced more than 37% after pressure-relief by blasting, which show that pressure-relief by blasting leads to anticipative effect.(3)The ANSYS/LS-DYNA of dynamic finite element software is used to build simulation numerical model to simulate support of pressure-relief by loosening blasting and study the relationship between parameters and effect of pressure-relief by blasting. The simulate analysis results, which is generally agreed with the theoretical achievements, show that the lining structure deformation and internal forces are reduced in various degrees. Deformation is reduced more than 47%, and internal forces are reduced more than 35%,which show that pressure-relief by blasting achieves the purpose of improving supporting condition of surrounding rock. The pressure-relief by loosening blasting could transfer the tunnel high initial stress to the depth rock, which can reduce surrounding rock stress and protect the tunnel.The research achievements in this thesis is of certain guiding significance and reference value in engineering for the construction of deep-seated high initial stressed underground engineerings and energy development.