冲击载荷下锚杆-围岩结构冲击失效机制的数值分析

针对冲击地压造成大量锚杆支护结构破坏问题,采用动力数值计算方法,研究冲击载荷作用下锚杆-围岩的动力耦合作用与破坏机制。结果表明:(1)冲击载荷作用下锚杆与围岩振动存在明显的"时差效应",导致锚杆与围岩非同步振动,致使锚固剂承受动态剪切作用。随着锚固长度的增加锚杆与围岩的振动呈同步趋势,削弱了振动"时差效应"引起的锚固剂剪切作用,有效避免锚杆的脱粘滑移失效;(2)随着冲击速度的增大,"时差效应"导致锚杆锚固剂承受动态剪切作用被覆盖,锚杆的破坏失效模式由脱粘或杆体屈服断裂转变为锚杆与围岩统一破坏模式;(3)当冲击载荷频率接近锚固围岩体固有频率时,冲击载荷引起锚杆与围岩共振,锚杆与围岩同步振动速度幅值显著增大,可在相对较低的冲击速度下造成锚杆与围岩整体失效。远离锚固围岩体的固有频率对锚杆-围岩动力相互作用影响较小。

Numerical Analysis of the Failure Mechanism of Bolted Rock Structure under Impact Load

To solve the problem about bolt support structure failure caused by rockburst in coal mine, dynamic numerical calculation method was used to study the dynamic coupling effect and failure mechanism of supporting structure of anchor-surrounding rock under impact load. The result shows that: (1) the action of impact load, a phenomena of non-synchronous vibration appears in bolt and rock the phenomena is defined as "time difference effect", which would trigger the synchronous vibration of rock and thesurrounding rock the debonding along bolt and rock interaction appear. With the increase of bond length, the synchronous vibration between bolts and rock occurred, which obviously, and eventually avoids the debonding between bolts and rock. (2) With the increase of velocity of impact load, obviously, and the failure mode of bolted rock from the type of the debonding or shank break into the type of overall failure of bolts and rock. (3) The resonance phenomenon presented as the excitation frequency approaching natural frequency of bolted rock structure, but velocity amplitude of synchronous vibration of bolted rock structure obviously increases, and the bolts or its surrounding rock would be damaged even under the action of impact load with a relative small peak value.For a given bolted rock structure, an excitation load with a critical frequency would cause a half vibration period between bolt and rock, which would result in greater relative vibration velocity between bolt and rock, and finally yield the debonding or shank break. Influence of impact load on the interaction between anchor and surrounding rock is less when the frequency of impact load is away from natural frequency of bolted rock structure.