Experimental And Numerical Analysis On Vibration Signal Characteristics Of Freezing Pipe Fracture

In the process of shaft sinking with freezing method,the freezing pipe often breaks,which endangers the safety of engineering construction.If the vibration signal generated by the pipe break can be captured and identified in time,it will provide valuable emergency rescue time for the construction on site.Therefore,in this thesis,combined with indoor model test,numerical simulation and field test,the characteristics and attenuation law of freezing pipe fracture vibration signal under different working conditions are studied,in order to provide theoretical basis for the establishment of freezing pipe fracture field monitoring and early warning system.First of all,aiming at the complex working condition of freezing pipe fracture,this thesis carried out the indoor test method research of freezing pipe fracture.Based on the prototype of "frozen soil + frozen pipe(including lining pipe)" form,the similar model test is carried out,which is simplified to the model specimen of "frozen soil similar material + steel pipe(using slotted pipe joint)" form,and the similarity criterion is verified through the test.On this basis,the model size optimization design is carried out,and the reasonable size of the model specimen is obtained.Secondly,in view of the shortcomings of previous experimental studies on the influence factors,through the similar model test,the pipe specification,frozen soil elastic model,pipe peripheral pressure,pipe fluid pressure and pipe breaking mode are comprehensively studied,and the variation rules of characteristic parameters such as vibration signal amplitude and dominant frequency are obtained.The results show that the variation trend of characteristic parameters such as amplitude is in good agreement with the load history curve of the model freezing pipe,which shows that the variation range of each characteristic parameter before the pipe breaking is small,and it suddenly increases to the maximum value at the moment of pipe breaking,which has obvious characteristics of pipe breaking signal.The main frequency is less affected by external factors and has good regularity,which can be used as a key research index.Within the research scope of each factor,with the increase of pipe diameter thickness ratio,frozen soil elastic modulus and pipe peripheral pressure,the main frequency of broken pipe vibration signal shows a decreasing trend;With the increase of the fluid pressure in the pipe,the main frequency of the signal changes slightly and basically remains stable;in the bending tensile joint loading test,with the increase of the proportion of the axial tensile force,the main frequency of the signal presents an upward trend.Then,using numerical simulation method,the propagation and attenuation law of freezing pipe vibration signal under different frozen soil elastic modulus,salt water inlet pressure and pipe peripheral pressure are studied.The results show that frozen soil elastic modulus and salt water inlet pressure have little influence on signal attenuation,while pipe peripheral pressure will cause serious dispersion and large attenuation of signal.In order to simplify the content of field test,this paper continues to use numerical simulation method to study the influence of excitation force and its action time on the main frequency of signal,and verifies the feasibility of using artificial excitation approximation to replace freezing pipe fracture excitation.Finally,through on-site detection,the vibration signal characteristics of freezing pipe under different salt water conditions are studied.It is found that whether there is salt water in the pipe or whether the salt water flows has no effect on the signal.Through the surface detection of frozen pipe fracture signal in the process of inclined shaft excavation and construction,it is found that: under the condition of shaft buried depth of about 80 m,the vibration signal induced by underground frozen pipe fracture can be effectively captured and identified at the end of surface freezing pipe;the main frequency of broken pipe vibration signal is basically in the frequency range of prototype freezing pipe fracture vibration derived from indoor test.In addition,through the artificial vibration test on the ground pipe end,the effects of different excitation methods,pipe specifications and soil layer constraints on the vibration signal of freezing pipe are studied.The results show that the greater the excitation force is,the greater the dominant frequency of vibration signal is;the dominant frequency of signal under transverse excitation force is greater than that under longitudinal excitation force;the larger the diameter thickness ratio of pipe is,the lower the dominant frequency is;the stronger the soil constraint is,the lower the dominant frequency is.In this thesis,the laboratory test,numerical calculation and on-site detection research further reveal the characteristics of freezing pipe fracture vibration signal under complex working conditions,and confirm the feasibility of detecting broken pipe vibration signal under the conditions of actual engineering and certain buried depth,which provides a basis for further research and development of frozen pipe fracture detection technology.There are 125 figures,55 tables and 125 references in this thesis.