Experimental Research On Detecting Cement Mixing Pile Anti-seepage Wall By Ground Penetrating Radar

The use of ground penetrating radar(GPR)technology for non-destructive detection of cement mixing pile anti-seepage wall in hydraulic engineering has been widely applied,but research on basic detection parameters selection and detection methods is still insufficient.The paper uses indoor model test and field in-situ test method to carry out GPR detection of cement mixing pile under slope,explore the principle of detection method,and derive relevant empirical formula,which has theoretical significance and practical value for in-depth study of GPR detection technology.In this paper,the GPR is used to measure the shallow soil moisture content of the upper overburden layer buried with the target body.The physical model of the relationship between the moisture content of the overlying layer and the dielectric constant of the silt is established,and the buried cement column is used as the electromagnetic wave velocity.The calibration was carried out to analyze the relative dielectric constant of the calculated silt and the silt body with a certain water content gradient.The relationship between the water content and the dielectric constant of the silt was studied.The results show that the relative dielectric constant of silt increases with the increase of water content,and the growth trend is exponential function.This trend indicates that the relative dielectric constant of water is much larger than that of soil,with the soil moisture content of the prepared soil.When the soil moisture content increases,the relative dielectric constant of the soil increases.Comparing the two existing soil moisture content-dielectric constant empirical formulas,combined with the measured results,gives the empirical formula between the measured moisture content and dielectric constant of the silt.The slope physical model of the buried cement mixing pile was established.The slope ratio of the slope was controlled by manual filling.The method of detecting the anti-seepage wall of the GPR on the slope was analyzed and summarized.The multi-antenna array combined with the multi-line method was used to stir the cement on the slope.The pile is continuously probed.Through the theory combined with image recognition technology,the measured results are compared with the design indicators to demonstrate the feasibility of the test method.The results show that the position of the pile body can be defined according to the polar direction of the radar reflection wave,the shape of the same phase axis and the intensity of the reflected signal.The antenna with the main frequency of 900MHz is used for the detection error and the precision is high.The formula for calculating the position coordinates and length of the radar antenna of the cement mixing pile under the slope is derived.This formula can be used to determine the position of the radar line.Based on the anti-seepage project of multi-head small-diameter cement mixing piles,the method of orthogonally arranging radar lines is used to detect the uniformity,continuity and effective depth of the anti-seepage wall,and the detection results are compared with the drilling results.The results show that the detection error range is between-0.5%and-1.33%.It is feasible to use the original data and cross-section radar to determine the position of the line on the slope and then to detect the line continuously.