隧洞开挖重复爆炸荷载作用下围岩累积损伤特性

Accumulated damage in surrounding rocks due to repeated blasting loads during blasting excavation of tunnels

隧洞毫秒爆破开挖推进过程中，预留岩体在重复爆炸荷载作用下产生不可逆的损伤叠加。而现有的岩体爆破损伤数值模拟基本都是针对单孔装药和单段爆破，很少涉及实际工程中的重复爆炸。基于LS-DYNA程序的用户自定义材料接口，将统计损伤演化模型嵌入到弹塑性本构材料中，模拟圆形隧洞全断面毫秒爆破过程中重复爆炸荷载作用下的岩体累积损伤效应，并考虑地应力对岩体爆破损伤的影响。计算结果表明，围岩损伤范围和损伤程度随重复爆炸荷载次数而增加，在一个爆破进尺内，围岩损伤的临界峰值质点振动速度较单段爆破降低了12%；爆炸荷载作用下，围岩主要表现为拉损伤，围岩地应力对爆破张拉效应起到非常敏感的“抑制”作用，在2～10 MPa应力水平时，围岩爆破累积损伤范围随着应力增加而明显减小，围岩损伤的临界峰值质点振动速度增加24%～57%。

During tunnelling works with the method of drill and blast, millisecond delay blasting technique is always employed to reduce charge weight in a single fire for safety. Under the repeated blasting loads, cracks are propagated in quantity and extent, or connected gradually to main cracks or collective cracks, leading to irreversible accumulation of damage in remaining rock masses. However, considerable numerical calculations are directed towards a single-hole charge and a single blasting, and they rarely get involved in the repeated blasting. In the present study, the millisecond delay blasting in a circular tunnel is simulated to find out the effect of repeated blasting on the rock mass damage, where in-situ stress in surrounding rock masses is also considered. The numerical simulation is implemented by embedding a statistical damage model into the commercial software LS-DYNA through its user-subroutines. According to the simulation results, rock masses subjected to the repeated blasting loads in a blasting footage result in relatively excessive damage than a single blasting. The peak particle velocity （PPV） threshold for initiation of damage is reduced by 12%due to repeated dynamic loading. The blasting load mainly induces tensile damage to surrounding rock masses. However, this tensile effect is very easily inhibited by the in-situ stress in surrounding rocks. When the in-situ stress reaches a magnitude of 2 to 10 MPa, the accumulated damage extent is significantly reduced with the increasing of the stress, and the PPV threshold for initiation of damage increases by 24%to 57%.