Boshan No.2 tunnel is a 4-lane continuous-double-arch tunnel, it was constructed by drill and blast with three pilots, the middle pilot was firstly excavated, followed by the bilateral pilots which would be enlarged after the middle wall had been built. Because the column between the pilots is small (which is 5.3meter), the blasting effect on the middle pilot caused by bilateral pilot excavation is very large. This effect was analyzed by means of FEM in this paper. At last, the relation between velocity, displacement and time at the top of arch, the foot of arch, the middle of wall and the foot of wall are given as well as its largest value and time. The results show that blasting parameters are reasonable.
Boshan No.2 tunnel, situated in Boshan-Laiwu highway to the southwest of Boshan district, Zibo City, is a 4-lane continuous double- arch tunnel. The clear width of single arch is 10.61m, and is 23.12m for double arch, the clear height of the lining (top of arch) is 7.24m, and the thickness of middle wall is 1.90m. The structure of the tunnel is illustrated in figure 1 The tunnel passes through the alternation of the dolomite and limestone. The tunnel was constructed by drill and blast with three pilots: The middle pilot was firstly excavated, followed by the bilateral pilots, which would be enlarged after the middle wall had been built. Because the rock pillar between the pilots is small (which is 5.3meter), the blasting effect on the middle pilot caused by bilateral pilot excavation is large. This effect was analyzed in this paper.
the calculation can be more accurate with larger demarcated area. But it cannot be too large since the memory capacity of computers is limited. In general, five to six times span of the tunnel lateral could be accepted as calculation range. In this paper, six times span is used. 2.2 Treatment of boundary condition Among dynamic analysis of tunnels and underground structures. the result largely depends on the way to deal with boundary conditions.
The vibration caused by blasting is random, it depends on many factors such as dynamite and its quality and quantity, charging structure, arrangement of shot holes, sequence and span of blasting, loading time of blasting exciting force, the specialty of surrounding rock and support. 3. 1 Calculation of blasting exciting force In this paper, the theory in which shock wave and expanded gas work simultaneously are considered to blast rocks is adopted. The initial peak pressure of shock wave is the blasting exciting force acting on the surrounding rock. Its magnitude depends on specialty of explosives and rock as well as coupling between them. When the decoupling index is up to 1.0, the value is calculated by equation (2). in other condition, it is obtained by equation (3). All parameters used in equations.