Study On Wear Mechanism And Rock Breaking Characteristics Of TBM Disc Cutters

Full face tunnel boring machine(TBM)has the advantages of fast driving speed,high safety,low labor intensity,high construction quality and environmental protection.It is widely used in traffic,municipal,hydropower,mineral,civil and other tunnel projects.With the increasing investment in infrastructure construction,the accelerating development of tunnel and underground space construction,the demand for TBM is also increasing.As the core component of TBM,the disc cutter directly contacts and breaks hard rocks in the process of tunneling construction.The service condition is very complex,which leads to huge consumption of disc cutters,affects the efficiency and cost of construction.It becomes one of the main problems restricting the overall tunneling construction.Therefore,it is of great theoretical and practical significance to reduce the wear failure and improve the service life of disc cutters.The failure of disc cutters is mainly affected by mechanical factors(driving speed,cutter head thrust and rotating speed)and geological factors(rock strength,hardness and abrasiveness,etc.)in the process of excavation.Since natural rock is a mixture of different types of mineral particles,cements and local defects,it is a complex material formed through long-term geological changes in nature.The mechanical properties of rocks show great discontinuity,which seriously affect the accuracy of service life prediction of disc cutters.In addition,the contact form between disc cutters and rocks is complex in the process of rock breaking,which has a negative impact on the study of the damage mechanism of disc cutters.In view of the huge wear consumption of TBM disc cutters under complex service conditions,the rock breaking characteristics of disc cutters and the interaction between disc cutter and rock are studied in this paper.Based on the principle of tribology,the damage mechanism of disc cutter is revealed and the wear amount is predicted.The main contents of this paper are as follows(1)According to the feedback from the construction site,the local blackening phenomenon on the surface of the partially failed cutter ring caused by the friction heating,resulting in the abnormal failure of the disc cutters.In order to study the causes of abnormal failure and performance changes of disc cutters,the mechanical and thermal coupling properties of typical disc cutter materials close to service conditions are studied.The change trend of mechanical behavior,hardness and elastic modulus at different temperatures are also obtained.Finally,the suitable service temperature range of disc cutter materials is determined.In this paper,the high-temperature friction and wear performance tests and studies on the disc cutter material and four typical rocks are carried out.Based on the friction coefficient,wear weight loss and wear morphology of disc cutter material,and the change trend of rock wear depth,the friction and wear characteristics of disc cutter material with rocks at different temperatures are analyzed.The results show that the wear behavior becomes more and more serious with the increase of temperature.When the temperature rises to 400?,the surface of disc cutter material appears oxidation phenomenon.The main wear mechanism of disc cutter material is abrasive wear from room temperature to 300?,and the main wear mechanisms are abrasive wear and oxidation wear at 400?,the disc cutter is not suitable for excavating rock at this temperature.To improve the service life of disc cutter at high temperature,the optimization scheme of material composition and preparation process of disc cutters is proposed.(2)In TBM excavation,the parameters,geological conditions,the structure and properties of the disc cutters directly affect the cutter life.A set of rock breaking test device with rotating disc cutter is developed in this paper.It has the characteristics of simple structure,economical application and convenient operation.At the same time,according to the practical application of the disc cutters,two kinds of disc cutter models with different blade shapes are designed,and the rock breaking tests are carried out for four typical rock blocks to study the matching relationship between cutter and rock.The paper studies the rock breaking efficiency of the disc cutters by analyzing the vertical load,the depth and morphologies of the rocks,and the information about the rock chips.The damage mechanism of the disc cutters in the process of rock breaking is revealed by analyzing the wear weight loss and wear behaviors of the disc cutters.Finally,the matching relationship between the disc cutter and the rock is analyzed and summarized.That is,when TBM is excavating soft rocks,the blade width of disc cutters can be appropriately increased to improve rock breaking efficiency with higher service life;when TBM is excavating high strength rock,the blade width of disc cutters can be appropriately reduced,the excessive arc of blade can be increased to reduce wear,and improve rock breaking efficiency while keeping the blade angle unchanged.The results provide a certain reference for the structural design and the selection of disc cutters in TBM tunneling construction.(3)After determining the cutter-rock matching relationships,the rock breaking characteristics and wear mechanism of disc cutters are studied.The cutter-rock interaction mechanism and the wear mechanism of disc cutters are analyzed,through the analysis of the rock breaking efficiency and wear behavior of the disc cutter after adding different cooling medium.Furthermore,the damage mechanism of the disc cutters under service conditions is revealed.After adding the cooling medium,especially the surfactant in the cooling medium,it can effectively alleviate the wear behavior of disc cutter in the process of rock breaking,thereby increasing its service life,and playing a positive role in improving construction efficiency and reducing construction costs.The results are of great significance for the selection and development of cooling medium in TBM tunneling constructions.(4)Based on the abrasive wear calculation model and CSM rock breaking load prediction model,a TBM disc cutter wear prediction model is proposed.The model is verified by the measured data of disc cutter wear in four tunnels from 400 m to 1.4 km during the excavation,and the error range of predicted wear is obtained,The research results have a certain guiding significance for the wear prediction of TBM disc cutter and the selection of tool changing time.