采礦外文翻譯---頻率和錨固長度對超聲波在錨桿中傳播行為的影響

1、英文原文 英文原文Effects of frequency and grouted length on the behavior of guided ultrasonic waves in rock boltsD.H. Zoua, Y. Cui, V. Madengaa, C. ZhangAbstractExperiments were conducted to study the behavior of guided waves in

2、 free and grouted rock bolts. Ultrasonic waves with frequencies from 25 to 100 kHz were used as excitation inputs. Tests were first conducted on free bolts to help understand the behavior of guided waves in non-grouted

3、bolts. The effects of wave frequency and grouted length on the group velocity and attenuation of the guided ultrasonic waves were then evaluated. The test results indicated clear but different trends for the group veloc

4、ity in the free and the grouted bolts. The attenuation in free bolts was not affected by bolt length and frequency. However, in grouted bolts it increased with frequency and grouted length. It was also found that the two

5、 main sources of attenuation are the setup energy loss, which has a fixed quantity for a specific type of test setup, and the dispersive and spreading energy loss which varies with frequency and bolt length.2007 Elsevie

6、r Ltd. All rights reserved. Keywords: Rock bolts; Guided waves; Attenuation; Amplitude; Group velocity1. IntroductionRock bolts are widely used in underground and surface excavations in mining and civil engineering for g

7、round reinforcement and stabilization. In many applications, rock bolts are grouted in the ground with cement or resin. Testing of the grout quality and monitoring of the bolt tension of rock bolts has long been a challe

8、nge in the field. Conventionally, grout quality is assessed by pull-out test and over-coring. Both methods are destructive and time consuming. The usefulness of pull-out test results as a measure of the grout quality c

9、an be limited by the critical length of grout beyond which the steel bolt will fail first. Therefore, other methods, such as non-destructive testing methods using ultrasonic waves have become attractive. In recent years

10、, research in this area has been very active. It is noticed that properties of guided waves, such as velocity and attenuation, are functions of the input wave frequency. Although the guided ultrasonic wave seems to be

11、a promising method for monitoring rock bolts, research in this area is still in the early stage and many technical problems remain to be solved. In a grouted bolt, wave behavior is not only related to the grout quality

12、 but also to the wave frequency. The grouted length and the properties of materials surrounding the bolt may all play an important role.One of the important characteristics of a guided wave is that its velocity not only

13、 depends on the material properties but also on the thickness of the material and the wave frequency. Unlike a bulk wave, the guided wave propagates as a packet, which is made up of a band of superimposed components wi

14、th different frequencies. It is the group velocity that defines the speed at which the ‘envelope’ of the packet moves where is the total attenuation coefficient. t ?According to the cause, attenuation may be grouped int

15、o the following categories:(a) Dissipative attenuation: An energy loss due to non-elastic resistance of the medium. It increases with thewave travel distance and may become profound over a long distance depending on the

16、 material property. This type of attenuation in steel is generally very low compared to that in rocks. As shown later, it can beignored in practice for guided waves traveling in rock bolts due to the low resistance of s

17、teel and the short bolt length (1–3 m).(b) Dispersive attenuation: An energy loss due to deforma-tion of waveform during wave propagation, a char-acteristic that distinguishes guided waves from bulk waves. The phenomenon

18、 of wave deformation is calledenergy dispersion.(c) Spreading attenuation: An energy loss which occurs at the interface between the bolt and the grouting material. As a guided wave reaches the interface, not all of the w

19、ave energy can be reflected at the interface. Part of the energy passes through the interface and is transmitted into the grouted material, a phenomenon called energy leakage.Therefore, it can be reasonably assumed that

20、 attenuation in grouted rock bolts consists of two major components;dispersive and spreading attenuation, both of which are frequency-dependent. The total attenuation in grouted rock bolts should thus be the sum of the t

21、wo components and in future will be referred to as DISP attenuation.It should be pointed out however, that as observed during our laboratory tests, the amplitude decay and the energy loss of guided waves recorded during

22、tests of rock bolts in laboratory are not solely from the DISP attenua-tion. Another important component is the energy loss due to refraction at the contact surfaces between the bolt sample and the equipment. Theoretica

23、lly, when a wave reaches an interface adjoining a medium which does not transmit mechanical waves (e.g., vacuum or air), no refraction occurs and all energy is reflected back.Ina rock bolt test, transducers are attached

24、to the bolt sample, which is in contact with the testing frame (e.g., a table or a rack). It is at these contact surfaces that some energy is inevitably refracted, causing energy loss. This type of energy loss, as shown

25、 later, is expected to be constant and is of a fixed quantity for a specific type of test setup. In future it will be called setup energy loss. As a result, the recorded amplitude decay and energy loss during rock bolt

26、 tests will be greater than what is actually caused by the DISP attenuation.An ongoing research program at Dalhousie University is aimed at studying the characteristics of guided waves in grouted rock bolts. Effects of

27、wave frequency and grouted length on the behavior of guided ultrasonic waves in free bolts and grouted bolts have been studied. The achieved results are strikingly convincing. The details are given below.2. Experiments

28、 of guided ultrasonic wave testsAn understanding of the ultrasonic wave characteristics in free bolts (non-grouted bolts) is essential to the study of the behavior of guided ultrasonic waves in grouted bolts. In this r