Dynamic Response Analysis Of Anchor System In Different Surrounding Rocks With Low Strain

Anchorage technique has been widely used in railway, highway, mine and hydraulic tunnel engineering. It is important for geotechnical reinforcement engineering to find out the anchorage integrity, the consistency between anchorage length and design length, the mortar plumpness of anchorage system and so on. However, because of the effect of construction technology, working environment and other factors, large area out of control phenomena of surrounding rock often happen caused by the problem of anchorage integrity. Therefore, the damage identification, integrity diagnosis, real-time detection and reinforcement of anchorage engineering are extensively concerned and emergent problem for geotechnical engineering field. As a result of various reasons, destructive pull-out test also holds a leading position in the testing of anchorage integrity and forced state. The pull-out test is time-consuming, costly and destructive inaccurate, especially it causes disturbance for reinforced rock and soil mass with bolts and reduces the reinforcing function, so it is restricted to individual spot check. The nondestructive testing of anchorage system is emergent problem need to be solved for geotechnical engineering field.Based on theoretical analysis, the low-strain dynamic response analysis of anchorage system with different defects in different surrounding rock was studied through interior model experiment and modern signal processing. Because the nondestructive testing of anchorage system is based on the principle of the dynamic testing of pile foundation, the two dynamic testing methods can be confused and this can cause the misjudgment of testing results in practice. The comparative study on both is need to be carried out. The main contents and conclusion are as follows:(1) At different curing time, the waveform characteristic of acceleration response curves for integrated and defective bolts in different surrounding rocks and anchorage media was studied. The results show that the fixed end reflection signals of integrated bolts are very strong and the bottom reflection signals are weak for the effect of the fixed end reflection and stress wave attenuation, and that the fixed end reflection signals of defective bolts are also strong and the bottom and defect reflection signals are weak for the same reason.(2) The stress wave velocity in anchorage system (SWVAS) is a basic parameter for evaluating the anchorage quality. The theoretical analysis shows that SWVAS ranges from wave velocity in anchorage medium to that in free bolt, and this is verified by experimental result in this paper. The experimental results also show that SWVAS decreases with the increasing of curing time and anchorage medium strength in the early stage but gently increases in the late stage, that SWVAS has a negative correlation to anchorage quality, and that SWVAS and stress wave velocity in anchorage medium (SWVAM) vary in exponential law and are mutually symmetric with curing time and anchorage medium strength. The study provides the basis for the real-time detection of anchorage, and brings a new idea for the determination of SWVAS.(3)Based on the low strain reflected wave method, the comparative study between SWVAS and stress wave velocity in pile(SWVP) was performed. The theoretical analysis of SWVP shows that the SWVP is bigger than SWVAM because of the effect of three-dimensional effect, and this is verified by experimental result in this paper. The experimental results also show that SWVP and SWVAM increase with the increasing of curing time and anchorage medium strength and vary in exponential law, and that SWVP and SWVAM are symmetric to SWVAS.(4)In accordance with SWVAS of integrated bolts, anchorage quality of bolts with different defects and compactions was evaluated. The results show that the evaluation is well accord with the design, and this further verifies the veracity of SWVAS in this paper.(5) The dynamic testing signals of anchorage system are discrete, and they can not be accurately expressed with analysis formula. The analysis and processing of the signals need clarify the frequency spectrum distributed rule of these signals. First, the Fast Fournier transformation (FFT) was used to analysis these signals. The analysis results show that the FFT of the signals only can overall analyze various frequency component included in the signals, and that the frequency range curves of integrated and defective bolts are different, the FFT amplitude curves of defective bolts have obvious multi-peak phenomena and the energy spreads in frequency band, and that the FFT of the signals has not time domain information, it is to say the happening time of a certain frequency in frequency domain is not known.(6)In order to obtain obvious bottom reflection signals and provide basis for the determination of SWVAS, the Short-time Fourier transformation (STFT) was used to analysis the signals. The analysis results show that the STFT of the signals can express the intensity size of the signals in the phase plane, the bottom reflection signals are obvious, the defect reflection signals can not be reflected, the more the detects, the bigger the energy of reflection signals, and that although the STFT overcome the partial analysis ability flaw which the FFT does not have, the determination of defects need adopt other signal processing technology such as Wavelet analysis, Wavelet packet analysis and so on.