A Technique Of Recognizing Mud Pumping In Railway Subgrade On Train-Mounted GPR Profiles

The roadbed diseases of existing railway lines in our country are widespread.Subgrade mud pumping is one of the common roadbed diseases.Mud pumping will cause ballast bed subsidence and hardening,reduce the strength of track bed,and affect the safety and transport capacity of railway transportation.The vehicle mounted ground penetrating radar detection technology is being popularized in the survey of railway subgrade disease,but how to identify the mud pumping on the vehicle ground penetrating radar image is a problem that needs to be solved.In this paper,both of qualitative and quantitative ways to identify the image of mud pumping are proposed,which is of great significance for the identification and classification of mud pumping in future.In this paper,the mud pumping is divided into two different types: ballast powder pumping and mud pumping,and the effects of the mud on the dielectric properties of the ballast and the subgrade are studied.The ballast powder pumping the and mud pumping lead to dirty the ballast and to increases the water content,which makes the dielectric constant of the ballast larger.The water content of the basis bed soil increased and the porosity decreased,and the dielectric constant of the surface layer of the subgrade was greatly enhanced.According to the measured data of the Jiaoliu railway line,the B-scan and A-scan are studied.In B-scan,the gray scale image is found to be more suitable for the layer information of the underground medium,while the red and black Order images can highlight the high energy area of the mud pumping,showing the purple white which is very different from the surrounding soil.In A-scan,the sample point X is converted to the depth information d(cm),and in order to classify the diseases: when the depth of the disease d is less than 5 cm,it can be judged to be mud pumping on the ballast surface;when 5 cm < d < 50 cm,it can be judged to be in the middle of the ballast,and when d is more than 50 cm,it can be judged to be mud pumping on the surface of the base bed.The amplitude of the reflections is obviously higher than that of the normal ballast as mud pumping causes the rise of the dielectric constant of the ballast and base soil rise at the disease.It is suggested a method that is used T,the ratio of the reflected amplitude at the doubtful mud pumping to the reflection amplitude at the normal ballast,to judge whether mud pumping has occurred.According to the principle of electromagnetic wave reflection,a quantitative discriminant formula is derived.After measuring the dielectric constant of various media,the thresholds of mud pumping in the measured area are given: the ballast powder pumping on the surface of the ballast: 1.4036 ? T<2.1667,and the mud pumping up to the surface of the ballast: 1.5834?T<2.5080;the ballast powder pumping at the middle of the ballast layer: 1.2062?T<1.9543,and the mud pumping at the middle of the ballast layer: 1.5537 ?T<2.0452;mud pumping on the surface of the base bed: 1.5537 ?T<2.2928.In the classification of the mud pumping diseases of railway subgrade,according to the grade of S= S1+ S2+ S3+ S4,this paper proposes an index S1 for determining the depth of the mud pumping,and determines the index S4 according to the continuous number of the mud pumping,that is the lengthwise extension.S2(related to subgrade soil type)and S3(extension time)are provided by the administrative department.According to the above indicators,the grading method is used to classify the mud pumping in the roadbed detection data collected in K0~K40 section of the Jiaozuo-Liuzhou railway downline by vehicle mounted ground penetrating radar.In the mud pumping section with a length of 3063 m,grade I is 357 m,grade II is 1956 m,grade III is 750 m.On the ballast track line of the Museum of Xipu campus of Southwest Jiaotong University,the method of identifying mud pumping in this paper is tested and verified.Clay and water are allocated into mud according to the proportion of 3:1,and the mixed mud is divided into two parts evenly,which two kinds of conditions are simulated,including the surface of the ballast and the middle of the ballast.The measured image of mud pumping is the same as that measured on the Jiaoliu line.On the mud pumping up to surface of ballast,T=1.5612,which is coincide with the conclusion in the fourth chapter that the clean ballast bed and the depth of dumping are within the range of 1.5537< T<1.8811.The test results show that this method is effective in the range of T=2.4083 in the mud pumping on the surface of base bed,which is given in the fourth chapter,and the depth of the bed is 2.2772 < T<2.5080.The influence of water evaporation factors on data was also studied in the simulation experiment.As time goes on,the more evaporation of water,the more attenuated the reflection amplitude will be.The attenuation of the reflection amplitude at the surface of the ballast is obviously greater than the attenuation of the reflection amplitude in the middle of the ballast,which is of reference to the determination of the mud and mashed mud by the reflection amplitude method.The research of this paper provides a qualitative and quantitative identification method for the detection of mud pumping in the railway subgrade by vehicle ground penetrating radar,which provides technical support for the application of the vehicle ground penetrating radar detection technology in the survey of railway subgrade diseases.