Research On Shield Cutter Wear Evaluation And Its Influence Based On Discrete Element Modeling

With the acceleration of the urbanization process,cities on the earth where human settlements are becoming more and more crowded,land resources are becoming increasingly tense,more and more cities are accelerating the pace of underground space development.In China,large-scale underground infrastructure projects in major cities such as subways,underground highways,underground commercial complexes and integrated pipe corridors are experiencing or are about to enter the peak of construction.The new structural form supported by the new construction method and the use of new technologies to implement innovation and upgrade of the traditional construction method have become the trend of the “new infrastructure”.Shield method has become one of the most important construction methods for tunnel and underground engineering construction in China in the past two decades because of its advantages of rapidity,economy,environmental protection,and automation.However,the shield machine will encounter various stratums during underground tunneling,especially in the high-abrasive sand composite stratums,due to the characteristics of uneven hardness and high wear resistance,the shield cutters wear extremely fast and the wear distribution on the cutter is uneven.If the cutters are not replaced in time,it will lead to the accelerated wear of the surrounding cutter,shield tunneling efficiency will reduce,and even the shield has to stop working.How to quickly and accurately assess the wear state of the cutter,and how to make scientific and efficient decisions on the timing of cutter change,has become a problem in shield tunneling control.At present,the methods and technologies that can achieve rapid and accurate assessment of the wear of shield cutters are still lacking,and the influence of worn cutters on other service cutters still needs further study.In view of this,based on the three-dimensional digital reconstruction of in-service cutters and the discrete element numerical analysis method,this paper conducted a preliminary quantitative study on the impact of worn cutters on other in-service cutters.The main research results include:(1)Using the Microsoft Kinect depth camera and the self-developed analytical algorithm,around the shield wear cutter sample obtained on the site of a shield tunnel project,in this paper,the rapid three-dimensional digital model reconstruction of the shield wear cutter is realized.The point cloud model of the cutter is compared with the digital model of the new cutter to realize the full surface quantitative evaluation of the shield cutter wear.The results show that the cutter wear of shield is very different on different areas in a single cutter surface.In terms of the wear,only a small part area is large,and the wear of most areas is less than 10 mm.(2)Based on the combined use of 3DMax,EDEM and other commercial modeling and numerical analysis software,firstly,a 3D digital cutterhead model in shield construction is established;secondly,aimed at the highly abrasive sand stratums,the discrete element method was used to establish a shield tunneling 3D discrete element numerical model,and get a preliminary simulation of the abrasion process of cutters during cutting of abrasive sandy soil.For the first time,realized the discrete element simulation of the arbitrary mixed knitting condition of the existing wear cutter and the new cutter in the numerical model.(3)The numerical simulation results of discrete element show that the shield is in the bulk material medium,especially in the sandy stratum with high quartz mineral content.Under the same constraints,the presence of worn cutters will cause increased wear of other in-service cutters on the cutterhead.And the cutters with the same radius installed on the cutterhead will have a greater increase in wear than the cutters with different radius installations.As the number of worn cutters on the cutterhead increase,the marginal effect of increased wear on other in-service cutters gradually decreases.But overall,although the presence of worn cutters will increase the wear of other in-service cutters,the increase is not significant.In addition,in addition to accelerating the wear of other in-service cutters,the presence of worn cutters will also greatly increase the energy required for shield tunneling.Through comparison with the theoretical wear formula,the results of the numerical simulation verify the effectiveness of the discrete element method in simulating shield tunneling in such sandy formations.