Research On Early Monitoring And Early Warning Of Tunnel Bolting Failure Based On Coda Wave Interferometry

With the sudden progress in the field of tunnel engineering in China,breakthroughs have been made in underground engineering fields such as urban rail transit,highway tunnels,underground hydropower stations,deep mines,etc.The complex geological environment brings new challenges to the traditional anchor support system,and timely monitoring and detection of early damage location and size of the surrounding rock is an important proposition for the sustainable development of modern structural engineering.Tunnel surrounding rock is regarded as a strong scatterer due to pore space and developmental texture,and the traditional detection means has limitations for monitoring early small disturbances.In this thesis,the coda wave interference technology,which is sensitive to multiple scattering media,is used as the main research tool to study the propagation law of coda wave under different working conditions of the surrounding rock through simulation and similar tests,write a Python script to put in the surrounding rock scatterer model,and study the propagation law of coda wave under working conditions such as sensor position optimization,local damage of the model,and local failure of the support structure;the anchor support specimen is designed using similar methods The objective of early damage monitoring and localization in the tunnel surrounding rock with anchor support was successfully achieved by using sparse reconstruction algorithm for 2D inversion imaging,and the research results showed that:(1)The waveform should have a high signal-to-noise ratio within the time window selected for the coda wave interference,for the same sensor receiving pair with the time window after the relative increase in its tail wave indicators;sensor placement location has a certain impact on the imaging effect,the actual surrounding rock support engineering applications can increase the sensor density at key structures to improve imaging efficiency;(2)It is feasible to establish a fine-looking perimeter rock model with good fit by Python language and Boolean operation,and the P-wave wave velocity is consistent with the theory by calculation,and the two-dimensional wave field distribution is consistent with the theory;(3)The study on the coda law in the process of local damage development of surrounding rock shows that with the increase of the development size of the damage area,it mainly affects the path of various scattered waves in the later stage of wave propagation,and the wave speed becomes smaller,leading to the change of decorrelation coefficient and travel time offset,which has linear correlation.The law of change can be fitted by the linear function curve and the quadratic function curve respectively,and the coefficient mainly depends on the physical parameters of the medium;(4)For the study of the coda law during the local failure process of surrounding rock support,it was found that the relative wave velocity increases when the anchor length of the anchor rod support gradually decreases.However,compared to the development conditions of local damage,it does not show obvious linear characteristics,and it still shows a unidirectional trend of change.That is,compared to local damage,the coda index correlation of local support failure is weak,but it still changes unidirectionally and tends to be stable;(5)In indoor experiments,some sensors have experienced an increase in relative wave velocity followed by a decrease,which may be due to the increase in compressive density of the concrete matrix or the acoustic elastic effect of the medium;(6)The two-dimensional imaging results of the tunnel surrounding rock supported by sparse reconstruction reverse acting anchor bolts are consistent with the experimental results,and can be monitored and located in the early stages of disturbance and damage.This thesis consists of 78 figures,11 tables,and 119 references.