Numerical simulation of wave propagation in grouted rock bolts and the effects of mesh density and wave frequency
Numerical simulation of wave propagation in grouted rock bolts and the effects of mesh density and wave frequency
复制标题
DOI：
10.1016/j.ijrmms.2005.09.006
复制
发表时间：
2006-06
影响因子：
7.2
通讯作者：
Chuanda Zhang;D. Zou;V. Madenga
中科院分区：
文献类型：
--
作者：
Chuanda Zhang;D. Zou;V. Madenga
注浆锚杆被广泛应用于岩质边坡及巷道、矿山等露天地下构筑物周围的加固。然而，可用于现场测试浆液质量的技术非常有限。传统的灌浆质量测量方法是拔浆试验和复盖；这两种方法都是破坏性的、耗时的和昂贵的。因此，研究工作可以追溯到20世纪70年代末，一直致力于开发无损检测方法，例如，使用超声波来评估原位锚杆的灌浆质量和其他参数。该仪器被称为[1]的发展是早期研究中最成功的成果。但该装置只能显示整体注浆质量，不能给出定量信息，也不能在不均匀注浆中找到不良注浆的位置。主要的限制是它的渗透深度有限，受到一定长度的良好灌浆的限制。因此，近年来开展了进一步的研究活动。如Beard and Lowe[2]和Beard et al.[3]提出使用引导超声波对注浆锚杆进行检测。从以往的研究中可以看出，波的衰减和能量的弥散是锚栓超声检测的主要技术难点。在灌浆锚杆中，波的衰减不仅与灌浆质量有关，而且与波的频率有关。此外，浆液质量好，能量分散度高；一种叫做能量泄漏的现象。对于自由螺栓，由于没有能量泄漏导致的波衰减，在测试过程中很容易拾取到许多来回反射的清晰回波。然而，对于灌浆锚杆，波衰减和能量色散使问题复杂化。因此，确定合适的频率和波型，使其在注浆锚杆中产生较低的衰减和较少的能量色散，从而增加超声波试验的穿透范围是非常重要的。数值模拟已被作为一种研究工具应用于注浆锚杆的超声研究。Pavlakovic等人（[4]）开发了一个程序，在假设结构在轴向不发生变化（即仅对全注浆锚杆）的情况下，使用连续谐波输入信号计算锚杆试验的无漏模态。然而，在现场试验中，仅使用瞬态信号进行激励，并且大多数锚杆仅部分注浆。因此，通常不可能将模拟结果与实验结果相匹配，并且模拟波形和测量波形之间几乎没有可比性。Ivanovic et al.[5]使用低于10 kHz的频率模拟地面锚固。
Grouted rock bolts are widely used to reinforce rock slopes and the area surrounding underground open structures such as tunnels and mine workings. However, technology available for field-testing of the grout quality is very limited. Conventionally, grout quality is measured by pullout test and over-coring; both methods are destructive, time-consuming and expensive. As a result, research efforts dating back to the late 1970s have been directed towards developing non-destructive testing methods, for example, using ultrasonic waves to evaluate the grout quality and other parameters of rock bolts in situ. The development of the instrument known as the Boltometer [1] was the most successful outcome from the earlier researches. However, this device can only indicate the overall grout quality and cannot give quantitative information or find the location of bad grouting in non-uniform grout. The main limitation is its limited penetration depth, restricted by the presence of a length of good grout. Therefore further research initiatives have been conducted in recent years. For example, Beard and Lowe [2] and Beard et al.[3] proposed to use guided ultrasonic waves for inspecting grouted rock bolts. From the previous researches, it is clear that the wave attenuation and energy dispersion pose major technical difficulties for the ultrasonic testing of grouted rock bolts. In a grouted bolt, wave attenuation is not only related to the grout quality but also to the wave frequency. In addition, good grout quality results in higher energy dispersion; a phenomenon called energy leakage. For a free bolt, where wave attenuation due to energy leakage does not occur, it is easy to pick up many clear echoes reflecting back and forth during tests. For a grouted bolt, however, wave attenuation and energy dispersion complicate the problem. It is therefore very important to identify suitable frequencies and wave modes, which would incur low attenuation and less energy dispersion in grouted rock bolts so as to increase the penetration range of the ultrasonic wave test.Numerical simulation has been used as a research tool for the ultrasonic study of grouted rock bolts. Pavlakovic et al.[4] developed a program to calculate the non-leaky mode for rock bolt tests using continuous harmonical input signals, while assuming that the structure did not change in the axial direction (ie, for fully grouted rock bolts only). However, in field tests, only transient signals are used for excitation and most rock bolts are only partially grouted. Thus, it is often not possible to match the simulated results with those obtained experimentally and there is little comparability between the simulated and measured waveforms. Ivanovic et al.[5] simulated ground anchorage using frequencies less than 10 kHz.