Study On Detection Technology Of Back Grouting Defect Of Shield Tunnel Segment

In recent years,the number of tunnels excavated by shield tunneling in China has increased year by year.The grouting defect behind shield segment will not only threaten the safety of tunnel,but also affect the health of ground facilities.In order to ensure the safety of tunnel structure and surrounding buildings,it is necessary to use effective detection methods to quickly and accurately detect the grouting defects behind shield segments,so that the grouting defects behind shield segments can be treated in time.Through consulting the relevant literature,the types and causes of grouting defects behind segments are analyzed and studied.The relevant detection methods are compared and studied.Ground Penetrating Radar(GPR)and Shock Echo(Shock Echo)instruments are selected for comparative study.In the experiment,different types of grouting defects are made behind the solid segments,and the results of the two tests are compared and verified with the actual defects.The experimental conclusions obtained have important guiding significance for the actual engineering detection.In the model test of different void thickness behind the segment,the void thickness can not be detected by both methods.Shock-echo method is more advantageous in detecting smaller void thickness(5 mm).The minimum vertical resolution of ground penetrating radar can reach? /30.In different grouting compactness model tests,the impact-echo method is more advantageous in larger compactness.For ground penetrating radar,900 MHz antenna is superior to 400 MHz antenna.In the model test of different water content of sandy surrounding rock,neither method can identify the specific water content of sandy soil.In the model test of filling water in the cavity behind the segment,neither method can detect the degree of filling water,but ground penetrating radar can distinguish whether the cavity is filled with water or air.In the model test of void behind grouting layer,the impact echo method can not be used to detect this type of defect.Ground penetrating radar method is suitable to detect this type of defect,and 400 MHz antenna is superior to 900 MHz antenna.