Abstract
Radial cracks may exist around tunnel edge, and these cracks may propagate and weaken tunnel stability under nearby blasting operations. In order to study the blast-induced fracture behavior of radial cracks emanating from a tunnel spandrel, a tunnel model containing a spandrel crack (TMCSC) with different inclination angles was proposed in this paper. Crack propagation gauges (CPGs) and strain gauges were used in the experiments to measure crack initiation moment and propagation time. Finite difference models were established by using AUTODYN code to simulate crack propagation behavior and propagation path. ABAQUS code was used to calculate dynamic stress intensity factors (SIFs). The results show that (1) crack inclination angles affect crack initiation angles and crack propagation lengths significantly; (2) critical SIFs of both mode I and mode II decrease gradually with the increase of the crack propagation speed; (3) the dynamic energy release rates vary during crack propagation; and (4) there are “crack arrest points” on the crack propagation paths in which the crack propagation speed is very small.
Highlights
Blasting method is often used in rock engineering, such as in mining and tunneling. ere are many cracks emanating from tunnel edge which could be either induced by the tunnel blasting excavation or naturally existing. ese cracks under nearby blasting operations may propagate and coalesce, damaging tunnel strength and weakening tunnel stability, which could cause some catastrophes, such as rockburst and coal-gas outburst
To study fracture rules of the cracks under blasting, the pressure curve obtained in the test was used in the AUTODYN3D code simulation. e simulation parameters are derived from Table 1
When the crack tip extended 8 mm, the fth wire of the Crack propagation gauges (CPGs) was broken, and the stress intensity factors (SIFs) K0(t) curve at the crack tip could be calculated by the ABAQUS code, and the results are shown in Figure 15
Summary
Blasting method is often used in rock engineering, such as in mining and tunneling. ere are many cracks emanating from tunnel edge which could be either induced by the tunnel blasting excavation or naturally existing. ese cracks under nearby blasting operations may propagate and coalesce, damaging tunnel strength and weakening tunnel stability, which could cause some catastrophes, such as rockburst and coal-gas outburst. Using dynamic load generated by explosives on the supporting system, Shirzadegan et al [10] carried out the fracture study in the LKAB Kiirunavaara mine in Sweden and pointed out that the level of induced damage was limited to the fracture zone behind the supporting system and the crack propagation in the shotcrete. Liu et al [14] studied the dynamic fracture toughness and other fracture parameters of type I crack under the explosive load and pointed out that there was an in ection point on the propagation path and the obvious crack arrest at the in ection point. Some unknown or partly unknown aspects have not been studied, such as the measuring method of critical dynamic SIFs and the fracture rule of mode I-II crack under blasting. In terms of the calculation of crack dynamic stress intensity factors (DSIFs) and combining with the measurement results of crack initiation time, ABAQUS code will be used, and the critical DSIFs will be calculated
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