Study On Wear Law Of Earth Pressure Balance Shield Cutters In Sandy Soils

The shield machine has been widely used in underground rail transit and tunnel projects.A large number of shield tunnel construction will inevitably face a variety of geological conditions,and the sand layer is one of them.Sand generally has large frictional resistance,good permeability,high soil strength,and large quartz content,it is very serious to the wear of cutting tool.Shield parameters,including cutter parameters,cutting tool parameters and construction parameters,are direct parameters for controlling the tunneling efficiency and have a strong internal relationship to the wear of cutting tool.Studying the wear law between the Sandy soil layer earth pressure balanced shield parameters and the cutting tool is of great significance for preventing and controlling the wear of the cutting tool and ensuring the long distance safe tunneling of the shield.In this paper,the common tool cutters for sand-concrete earth pressure balance shields are used as research objects.The theoretical derivation,indoor wear test and discrete element numerical simulation method are used to respectively shield cutter cutter speed,cutter depth,shield thrust,and knife.The wear control law of the cutter is analyzed by the disc support pressure,the cutter opening ratio,the cutter rake angle,the cutter back angle and the sand moisture content.The main work is summarized as follows:(1)The classification and characteristics of shield cutters and tools are summarized.The cutting process,failure mode and wear mechanism of the cutting tool are analyzed.Based on this,the force model of the cutting tool and the calculation formula of the wear are derived.The control variable method was used to analyze the wear law between the cutting tool and the cutter disc rotation speed,shield propulsion speed,earth chamber pressure,tool depth,cutter rake angle,rear angle,shield thrust and other parameters respectively.(2)The indoor wear test materials and devices were introduced.The control method was used to test the wear law of the cutters on the cutter disc rotation speed,the cutter front and rear angle and the sand moisture content.It is found that the cutter wear increases linearly with the increase of cutter speed and cutter rake angle,and decreases linearly with the increase of the cutter back angle,which is consistent with the trend of the derived wear calculation formula;for the gravel sand used in this test For example,when the moistxire content of the sand is zero,the wear amount of the cutter is relatively large.When the moisture content of the sand is not zero,the wear amount of the cutter is reduced,but the reduction is not very large,at 20%.The amount of wear of the inner cutter in the water content is not significantly affected by the moisture content.(3)The discrete element numerical simulation method and discrete element numerical software EDEM are introduced.The principle and method of discrete element parameter calibration are described.The calibration parameters required in this paper are divided into two categories:particle-particle basic contact parameters and particle-wear specimen contact parameters,and indoor and virtual tests are designed for inversion calibration.The calibration results are relatively accurate,which lays a foundation for the study of tool wear using discrete elements.(4)Using the discrete element numerical simulation software EDEM,the control law was used to study the wear law between the cutting tool and the cutter speed,formation pressure and cutter opening ratio respectively.Comparing the simulation results with the results of the wear calculation formula and the results of the indoor wear test,the corresponding wear laws of the soil pressure balance shield cutter in the sand layer are obtained,and the corresponding measures to prevent and control the cutter wear under the condition are proposed.The reliability of using the discrete element method to study the wear of the cutting tools and the effectiveness of the theoretical calculation of the wear calculation formula are pointed out.