The Research Study Of Grouting Effect Evaluation Of The Defect Rock Mass Based On Ground Penetrating Radar

GPR is an efficient, fast, convenient, continuous detection physical detection method of non-destructive testing and an advanced high-frequency electromagnetic exploration technology and it has good detection results to shallow goal body. Therefore, GPR has been widely used in the engineering structures detecting, engineering geology, hydro geological survey, advanced prediction and detection of tunnel construction, archaeological surveys and ecological environment testing. As the high-frequency characteristics of the electromagnetic waves propagation, environmental conditions of dissemination with big interference and complex detection conditions, which makes the GPR having the defect in the detection of cavity and hollow grouting, such as the low points cutting rate of the data and the identification of radar images main stay on the basis of the artificial eye and hand, etc. So, carrying the physical forward modeling work of rocks defect detection and grouting defect detection and studying electromagnetic wave propagation in the defect and grouting are conducive to understand the radar image and the analysis of radar data collection and accumulating experience for identification of underground structure; by using physics model to verify quickly and effectively, it has improved the accuracy of ground penetrating radar echo signals largely and has important sense for the interpretation and identification of underground media or target body.In this paper, through physical model, numerical forward simulation, Hilbert transform and wavelet transform de-noising have more system-depth study to detection technology of grouting effect of the rock mass defect. Using the LTD-2100ground-penetrating radar measurement systems and GprMax2D software conducts the test and simulation and in the radar processing software IDSP6.0and MALAB numerical analysis platform computing environment, using the proposed method conducts data processing and analysis of probe. The main contents and results are as follows:First, the content of the study(1) Where by MATLAB numerical analysis platform which compiles MATLAB language to have achieved ground-penetrating radar system data import procedures of LTD-2100, that is, the information read in stored files of raw radar data and the information*.LTE format, it can be more convenient to ground penetrating radar data to conduct secondary development, analyzing, processing and imaging.(2) According to the theory of electromagnetic wave propagation, that is, the frequency electromagnetic waves propagate in the medium obey the Maxwell equations, it has analyzed the two-dimensional finite-difference time-domain equation, and whereby the GprMax2D software as numerical simulation platform, it selected the radar excitation source of the actual probe antenna----Ricker, which has built the ground penetrating radar wave propagation model in the rock defect structure of air, water, concrete, wet sand as the filling medium.It has simulated two-dimensional ground penetrating radar field different sizes of different shapes and different filling state and on this basis, the impact of the characteristics of the rock caves grouting effect to radar reflection (echo) signal has been study.(3) Different rock defect structures (shape, size, filling) propagation model tests have been conducted and based on using radar post-processing software IDSP6.0,such as increased regulation,horizontal filtering and vertical filtering, has conducted the analysis of Hilbert transform to radar data,has extracted "three instantaneous" properties of instantaneous amplitude, instantaneous phase and instantaneous frequency,has used property to conduct radar data analysis and explanation and has verified the validity of the method.(4) Based on the features of non-stationary nature of acquisition signal of the original ground-penetrating radar data acquisition signal and nonlinear attenuation of high-frequency pulse signal,it has explored the wavelet transform theory in the de-noising technology of ground penetrating radar echo signals. Based on MATLAB Software, it has analyzed the algorithm of the decomposition, reconstruction and de-noising of two-dimensional wavelet transform in the ground penetrating radar echo signal processing and the analysis of experimental data showed that the two-dimensional wavelet transform has a good effect in terms of-the radar echo signal de-noising.Second, the main results(1) In the same detection environment, using water, concrete, dry sand, wet sand for the filling media to conduct the grouting simulation of the filling level of the defect rock mass. The research results show that using the water, wet sand, silt and clay and other media filling can see the fuzzy vertex waveform vaguely, Among all the media, wet sand and silt in the deep signal can form a strong secondary waveform reconstruction, but it is more difficult to distinguish between concrete and dry sand, It is because that the smaller of the difference of the relative dielectric constant between filling medium and detection environment, the more difficult to distinguish waveforms; In the case of half-filling degree, waveform cross-section can be easily distinguished vertex small form defects, compared to the deep waveform information, we can find that water, wet sand, silt and clay filled have deeper diffracted wave than concrete, dry sand and air filled.(2) Numerical simulation in the different detection environment, The research results show that in the case of full filling degree, we can find that air, water, concrete, wet sand, silt and clay containing the amount of deep Information from more to less is the dry environment, layered environment and humid environment, but dry sand is the opposite; In the case of half-filling degree, the degree of difficulty to distinguish from easy to difficult is moist environment, layered environment and dry environment. Simulated environment which has water, wet sand, silt and clay is easier to distinguish.(3) Numerical simulation of concrete in different shapes and different filling level, I established a comparison model between theoretical exploration and detection test on the spot, indicating that in the on-the-spot simulation test theory, there are obvious differences between the radar waveform when the semicircle with full grouting and semi-grouting and the triangle have some flaws.(4) By the processing and analysis of radar test data, the defect rock is filled with water, wet mud, wet sand, dry sand. Compared with instantaneous amplitude wave diagram, it uses strong white area and layered mutation lines to distinguish the half grouting and full grouting. there is strong white area or layered mutation lines, and it shows that grouting defects have air and filling medium to form another defect and the result of grouting detection show that rock defect is half grouting or not full grouting; If there is no layered mutation lines, it shows the result of grouting detection is full grouting.(5) The research results show that half grouting or no full grouting can form layered mutation lines but no strong white area and the reason is that the filling concrete is not vibrated and compacted and the table level of grouting is not to form a thin film of water; Recommendation:the detection after grouting should be completed as soon as possible. According to this feature to combine them with detection site environment and geological data, it can conduct the detection and evaluation of the grouting effect of the construction site. This is provided the technology for using the ground-penetrating radar to conduct the site monitoring of grouting effect.(6) The research results show that the instantaneous amplitude using the nature of strength and attenuation of the echo can be easier to distinguish the dielectric layers, that instantaneous phase using the coaxial continuity of the echo signal section can be easier to distinguish the top position of rock mass defect and using the deep signal characteristics can be easier to distinguish the degree of rock mass grouting,and that instantaneous frequency using the changing nature of media can be more difficult to distinguish the defects in shape, while combining with instantaneous phase can distinguish the shape of defect grouting. Synthesizing "three instantaneous" attribute to analyze each filling media comparatively can know that radar detect the sensitivity factor of grouting effect is water including moisture content of the filling medium and high water content show the result of detection is sensitive.(7) Using wavelet2D window to choose the db1wavelet function as the number of layers in level2to decompose and conduct the de-noising, select soft threshold and dimensions of white noise from horizontal, diagonal and vertical directions to conduct quantized coefficients debugging, de-noising and restructure and gain clear distinguishable shape of rock mass defect and effect image of defect grouting.(8) Comparing with wavelet de-noising and Hilbert transform analysis, the research shows that radar echo signal in de-noising aspects of two-dimensional wavelet transform has a good effect and can be easier to distinguish the shape of defect rock mass, the top defect and bottom position, which reflect defect rock mass and the grouting effect of the defect in concrete more elaborately and intuitively than Hilbert transform and at the same time, reflect the two small defect holes waveform formed by the inverted triangle and semicircular containers grouting, but under the condition of defect holes detection, the two containers cannot be easier to be distinguished in no full-filled.