下穿隧道爆破施工对既有隧道的振动影响及对策研究

摘要

依托云南省盐津县白水江三级电站引水隧洞下穿内昆铁路手扒岩隧道的工程实际,采用LS-DYNA显式动力数值模拟及现场爆破振动监测,对既有隧道受下穿新建隧道爆破施工产生的振动影响和对策进行研究.结果表明:全断面起爆中,D(D为下穿新建隧道洞径,下同)＜2.5D0(D0为基准洞径)时,既有隧道的振动速度、振动加速度均随D的增大而增加,且基本呈线性关系;2.5D0≤D＜3.5D0时,振动速度及加速度均急剧增大;D≥3.5D0时,振动速度、加速度随D的增加而减小.随两隧道间距的增加,既有隧道考察点的振动速度和加速度均减小;在距离相等时,掌子面未到达前的振动响应大于掌子面离开后的响应;相同爆破参数时,距离越远,受到的振动越小;同时起爆药量越大,受到的振动越大.随围岩的变差,既有隧道处的振动速度增大,振动加速度变化较小.根据不同影响因素与振动速度关系的规律,推导了包含隧道开挖洞径、进尺长度、上下交叉隧道净距、单位药量等参数的隧道开挖爆破振动速度计算公式,并由现场爆破振动监测验证了数值模拟的正确性.同时,针对不同影响因素,提出分部开挖、分段起爆、干扰减振等减小爆破振动影响的对策措施及选择原则,并指出爆破试验及爆破振动监测在近接隧道工程中的重要性和可操作性.%Based on the practical situation of diversion tunnel for BaiShuiJiang third class power station in Yanjin county of Yunnan province,which passes under the existing Shoubayan tunnel on NeijangKunming Railway,by using methods of LS-DYNA explicit dynamic numerical simulation and in-situ blast vibration monitoring,the vibration influence on existing tunnel by blasting construction of diversion tunnel passing under it in short distance and countermeasures were studied.The result shows:For full-face excavation and D＜2.5D0(D,diameter of newly-built tunnel passing under existing tunnel; D0,reference diameter),vibration velocity and acceleration of existing tunnel induced by blasting construction of newly-built tunnel passing under it increases as D increases and nearly in linear relationship; For 2.5D0 ≤D＜3.5D0 vibration velocity and acceleration increases rapidly; For D≥3.5D0,vibration velocity and acceleration does not increase but decrease as D increases.Vibration velocity and acceleration decrease as the distance of the two tunnel increases; For same distance,vibration influence before excavation face reaches existing tunnel is bigger than vibration influence after excavation face passes under existing tunnel; For same blasting parameters,vibration influence decreases as distance increases;Vibration influence increases as explosive dose increases; Vibration velocity increases and acceleration decreases as surrounding rock becomes worse.Furthermore,according to different relation between influence parameter and vibration velocity,formula to calculate blasting vibration velocity was derived,considering parameters of excavation diameter,footage,clear distance of two tunnels,explosive dose.And then onsite blasting vibration monitoring validated the numerical simulation.Countermeasures to reduce blasting vibration influence (stepped excavation,subsection detonation,interfere damping) were given.For tunnel adjacent to existing one,the importance and maneuverability of blasting test and onsite monitoring were emphasized.