Acoustic Wave Detection Of Large Boulders And Safely Tunneling Technology During The Shield Construction

The large boulders widely distributed in sandy cobble stratum and other soil layers have brought great security risks in shield construction,and there are dozens of shield construction accidents caused by large boulders at home and abroad.Because the boulders have high strength,good hardness and poor stability,and it is different from the surrounding strata.It is not easy to be broken by the shield,and it is not easy to be found by drilling.Because of it’s distribution and separation and it affects the safety of the shield.By referring some materials,the paper has stated in detail about the reasons why the boulders formed and the characteristic of distribution and the engineering,the harm of the boulders on safety operation of shield.The solution of the boulders is to “start with detection,and then deal with.” From some reference,the main methods including drilling method,electric method,geological radar method and seismic wave method.The advantages and disadvantages of various detection methods used to detect large boulders in shield construction are analyzed,and a method of detecting large boulders by using low frequency sound waves in the drilling is put forward.Because the low frequency sound waves will reflect when it detects the boulders.The devices of boulder acoustic detection used in the borehole is developed.By using the vibration of the mechanical spring,the incompressibility of the water and the expansion of the latex film,it will transfer the vertical vibration into horizontal vibration in the drill hole wall and it solved the problem that horizontal vibration can not be implemented.What’s more,through the engineering geological drilling can be dome in any soil with any depth in the boulders detection.By using the self-developed low frequency acoustic detective devices have done the test on the boulders in the laboratory.Building a hole with the length is 10 meters,the width is 2 meters and the depth is 2 meters by the bricks.The hole should be filled with compacted soil,and buried two sizes of the boulders in it.The devices of detection placed in the borehole,and it will detect the boulders from the vicinity from distance.Through the experiment,it is found that the self-developed low frequency sound wave sounding device is not ideal for the large boulder with a particle size of 0.21 m in the soil with the velocity of 322m/s,and no obvious reflection wave signals are received.The detection effect of the large boulder with a particle size of 0.42 m is better,and the reflected wave signal is received.At last,from the reference,it has introduced the technology of the pretreatment and safety shield tunneling.The pretreatment technology of hand piles,broken impact plies,blasting the piles and dealing with the slip casting.The applicable conditions of various pretreatment technologies are introduced to achieve the purpose of safe and economical treatment of large crus.Safe driving technology and shield cutting large boulders are the main technical points of the boulder shield machine selection.Shield selection is introduced for earth pressure balance shield,slurry shield and shield cutter layout.The main technical points of shield cutting large drifters are mainly introduced in the analysis of large drifters in shield tunneling,the inspection and replacement of cutting tools in shield construction and the operation of standard personnel.