Impact of second tunnel blasting on the stability of a separated tunnel
The separated highway tunnel was taken as an example to study the stability influenced by the blasting construction of the second tunnel on the first one.In the process of blasting con-struction of the second tunnel,the variation of displacement and vibration velocity of the initial support of the first and second tunnels were studied through theoretical calculation,numerical analysis,and in-site monitoring,and the influence range of blasting vibration was also deter-mined.Results indicated that the blasting construction of the second tunnel has a considerable im-pact on the blasting side of the initial support of the first tunnel than on the back-blasting side,and the impact on the arch waist at the blasting side is the largest.The deformation of the initial support fluctuates within 10 m before and after the monitoring section.The blasting construction of the second tunnel has minimal impact on the stability of the initial support of the first tunnel when the control standard is 10 cm/s.During the blasting construction,the maximum vertical and horizontal displacements occur at the vault and arch waist of the second tunnel,respectively,and the vertical and horizontal displacements are convergent after the 10th excavation step.In this process,the blasting influence of the upper bench on the displacement of the initial support is greater than that of the lower bench.When the control standard is 10 mm/d,the influence range of blasting vibration on the initial support of the second tunnel is 20 m,which is consistent with the safe distance of 19.7 m determined by Saskatchewan theory.In addition,the variation rules of arch waist convergence and vault settlement of the second tunnel obtained from numerical simula-tion are consistent with the in-site monitoring results,but the former is slightly smaller than the latter,reducing by 1.2％and 2.3％,respectively.
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维普
