| Freezing sinking technology is widely used in our country,but the freezing pipe fracture problem has been difficult to complete eliminate.The underground freezing pipe has the characteristics of concealment.It is difficult to find the freezing pipe fracture in time.It often takes a period of time to find and check the fracture location.However,during this period of time,the salt water will gradually leak and melt the surrounding frozen soil.In serious cases,it may even cause the freezing wall to open a window laterally,which may induce the gushing water to flood the well.In order to explore the rapid detection method of freezing pipe fracture location,this paper uses the low strain pile testing technology for reference,and adopts the methods of indoor test,numerical simulation and field test to carry out the research on the propagation attenuation of low strain stress wave and the reflection signal characteristics of fracture surface in freezing pipe.Firstly,according to the actual working condition of the freezing pipe,the indoor test of the propagation law of low strain stress wave in the freezing pipe is carried out.By means of model test,the similar relationship between model specimen and prototype specimen is verified,and the model specimen is selected for indoor test.It is found that the duration of excitation signal in the frozen tube is negatively correlated with the frequency of excitation signal,the frequency of excitation signal has nothing to do with the magnitude of excitation force,and the peak value of excitation signal is positively correlated with the excitation force.The rock layer medium has little influence on the stress wave velocity in the pipe,and the average velocity of stress wave is 4850m/s.When the elastic modulus of rock and soil layer increases from 237.8MPa to 453.8MPa,the propagation distance of stress wave decreases from 64.52 m to only 15.61 m.The larger the elastic modulus of rock and soil medium outside the pipe,the greater the transmittance of stress wave on the fracture surface and the smaller the reflectivity.Then,through the comparison of numerical simulation and physical test,the characteristics of stress wave propagation attenuation and reflection signal caused by the existence of joint,fracture surface,salt water filled pipe,frozen soil elastic modulus,soil property change and other factors are studied.The results show that:when there is expansion and contraction joint in the freezing pipe,there is reflection echo at the joint;when the freezing pipe includes the outer liner joint,the reflection echo at the joint is consistent with that at the bottom of the pipe;when the freezing pipe includes the inner liner joint,there is no reflection echo at the joint;the reflection echo at the fracture surface of the freezing pipe has obvious wave direction change.The salt water in the freezing pipe has little effect on the propagation of stress wave.With the increase of elastic modulus of rock and soil outside the pipe,the frequency of excitation signal increases,and the attenuation coefficient increases from 0.0691 to0.0736.When the soil layer changes,the low elastic modulus high elastic modulus soil layer is more conducive to the detection of frozen pipe defects.Finally,the field test of freezing pipe structure characteristics is carried out.The results show that: the frequency of freezing pipe excitation signal is in the range of2900 Hz ～ 4200 Hz,the duration of excitation signal is negatively correlated with the frequency of excitation signal,the peak value of excitation signal increases with the increase of freezing pipe buried depth,and the detection distance of low strain stress wave to freezing pipe is about 70 m.The paper has 86 figures,47 tables and 80 references. |
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