Research On The Detecting Technique Of Rock-socketed Depth And Loosening Circle Of Surrounding Rock Based On Acoustic Method

With the development and utilization of underground space in China,Various forms of underground building structures are becoming increasingly.Uplift piles are widely used in projects with uplift demand,in which the rock socketed depth is an important factor affecting the ultimate uplift bearing capacity of pile foundation.Tunnel excavation is bound to redistribute the stress of surrounding rock and form a loose circle.It is of great significance to accurately determine the thickness of the loose circle for the stability and safe operation of the project.Due to the concealment and complexity of rock socketed pile and tunnel surrounding rock,its quality can not be judged by direct observation after construction.Acoustic logging is a kind of in-situ testing method.Through the acoustic logging method,the time-domain signals under different test depths are compared and analyzed,and the signal characteristic parameters are extracted to evaluate the internal condition of the structure.In this paper,the change rules of echo energy between uplift pile and different strata and the change rules of transmitted wave energy under different depths of surrounding rock after excavation are studied from the perspective of acoustic dynamic characteristics Law.The main research contents and results are as follows:(1)The interface echo propagation characteristics of rock socketed pile structure in different strata was studied.The finite element model of single hole logging of rock socketed pile structure is established by means of finite element simulation.The stress propagation nephogram of different models and the received simulation signals are compared and analyzed.The influence of different strata on echo characteristics is observed.The characteristic parameters are extracted from the time-domain signals and defined as the interface echo energy to detect the rock socketed depth of rock socketed pile structure.The results show that when the test depth is within the range of strongly weathered stratum(the pile does not enter the rock),α decreases with the increase of depth and shows a linear change trend;when the test depth is within the range of rock socketed depth,α fluctuates with the increase of sounding.(2)The influence of rock socketed pile structure on the detection of rock socketed depth with mud inclusion defect was studied.Through the finite element simulation,the finite element model of rock socketed pile structure with mud inclusion defect is established.The stress propagation nephogram of different models and the received simulation signal are compared and analyzed,and the influence of different mud inclusion size on echo characteristics is observed.The results detected that the larger the size of mud inclusion is,the larger the echo energy is and the shorter the first arrival time is.(3)The propagation characteristics of transmission wave in different failure zones of rock mass during tunnel excavation were studied.According to the properties of actual core rock samples,the finite element model of cross hole logging of surrounding rock loose zone is established.The stress propagation nephogram of different models and the received timedomain signals are compared and analyzed.The influence of different test depths on the characteristics of transmitted wave is observed.The characteristic parameters are extracted from the time-domain signals and defined as the transmitted wave energy β to detect the thickness of surrounding rock loose zone.The results show that when the test depth is within the range of loose zone,the β value decreases with the increase of sounding and shows a linear change trend;when the test depth is within the range of plastic zone,the β value fluctuates with the increase of sounding;the model of surrounding rock loose zone is made and the cross hole logging acoustic test is carried out.The results show that when the test position is at the boundary of two kinds of media,the transmission of the test point is stable The wave energy curve shows a fluctuating trend.Based on the local model,the long-span cross hole acoustic logging test is carried out,and the results show that the larger the span is,the more media information is represented.At the same time,the more interference waves received,we need to filter through certain signal processing methods.