| With the rapid development of China's economic construction,a large number of geotechnical engineering projects come out.In recent years,the number of tunnel projects have increased.It is one of the research hotspots to study the correlation between stress waves and joints of rock mass in geotechnical engineering and the identification method of tunnel loose rock zone.So this paper mainly discusses the propagation law of stress wave in monolithic rock masses and combines its relevant theoretical knowledge to detect the thickness of loose rock zones.According to the overall structure,this paper is divided into the theoretical simulation part of the stress wave related exploration,the experimental part of jointed rock masses and the engineering practice part of the measurement of loose rock zones.The propagation of the mass point in the medium caused by external disturbances forms a stress wave,which is a ubiquitous phenomenon in the natural world.According to the propagation modes,different stress waves are divided into longitudinal and transverse waves.The model of jointed rock mass is divided into linear model and nonlinear BB model,BB model is more common in practical application.For the propagation of stress waves in jointed rock masses,the wave function equations and correlation coefficients are generally deduced using elastic mechanics combined with displacement discontinuity theory.Compared with elastic mechanics,time domain recursive method eliminates the complex Fourier transform,it transforms the propagation process into a two-dimensional plane problem and derives a matrix representation of the stress wave equation.This paper sorts out the theoretical formula of the time domain recursive method for elastic mechanics,defines the reflection coefficient and transmission coefficient to express the energy variation of the stress wave through the jointed rock mass,and uses the matlab programming to explore the initial joint stiffness,the stress wave frequency,the influence of stress wave velocity on the anti-transmission coefficient when the longitudinal wave enters the jointed rock mass vertically.The fractures with only slight or no displacement on both sides of the fracture surface are called joints.The corresponding rock masses are jointed rock masses.The related properties of jointed rock masses are very important for the study of stress wave propagation.The Split Hopkinson Pressure Bar device is a commonly used device in the impact test.The impact bar impacts the incident bar at a certain speed under the action of a power source,causes an incident wave in the incident bar,and sequentially transmits the sample to the test sample and the transmission bar.The data of incident wave,transmitted wave,and reflected wave are obtained by deducing the data to explore the variation law of stress wave during propagation.In this paper,a pair of cylindrical granite specimens are combined to form a joint,and the specimen is impacted by a Split Hopkinson Pressure Bar to study the influences of contact area size,the distribution pattern of the contact area,the velocity of the impact end these three factors to the anti-transmission coefficient,and then explored the influences of the above three factors on energy changes,and provide theoretical support for engineering applications.The method for determining loose rock zones can be divided into two major methods: lossy and non-destructive.The acoustic wave method,multi-point displacement meter method and borehole camera method are representative loss detection methods.The geological radar method and refracted wave method are representatives of non-destructive testing methods,the current accuracy of non-destructive testing methods needs further improvement.This paper combines the previous two parts of related knowledge,using the single-hole imaging method and the dual-hole radar method to jointly detect the thickness of loose rock surrounding rock in different depths of Jilin project. |
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