Study On Mechanical Properties And Test Methods Of Shield Tail Sealing Grease

Shield tail sealing system is an important safety protection system for shield tunneling.In recent years,China’s urban subway construction has entered a peak period,and the mileage under construction has increased significantly.With the development of shield tunnel construction,the engineering safety problems caused by the failure of the shield tail seal have become increasingly prominent.The sealing performance of shield tail sealing system mainly relies on the high-pressure barrier formed by the shield tail brush and sealing grease.Once the shield tail seal fails,it will cause insufficient grouting pressure,increased ground subsidence and other hazards.In severe cases,it may even cause major safety accidents such as tunnel collapse.Therefore,it is of great significance to develop high-performance sealing grease and improve the reliability of shield tail seal for shield tunneling.At present,there are many domestic sealing grease brands,but the quality is uneven.The evaluation method of sealing grease is incomplete,and the sealing performance of sealing grease cannot be accurately evaluated.It is urgent to establish the relationship between the mechanical properties of sealing grease and sealing performance,so as to improve the sealing performance of sealing grease.In response to these problems,this paper has studied the mechanical properties of sealing grease,high-efficiency modifiers,sealing mechanism and test methods.(1)The effects of the main components of the sealing grease on mechanical properties,including fibers,base oils thickened with petroleum resin,thickeners and fillers,were studied through experimental tests.The sealing grease samples were prepared by the controlled variable method.The fluidity,cone penetration and dynamic rheological characteristics of the samples were analyzed.The control method of basic mechanical properties of sealing grease was proposed.(2)Through experiments,the dioctyl phthalate(DOP)was selected as high-efficiency modifier for sealing grease.The liquid EPDM was proposed as a tackifier for sealing grease.The modification rules of DOP and EPDM on the mechanical properties of sealing grease are analyzed.The modification mechanism of two modifiers on sealing grease is revealed.(3)Environmentally friendly sealing grease was prepared using vegetable oil and animal oil.And mineral base oil was used to prepare sealing grease as a control.The differences in microstructure,thermal stability and mechanical properties of the two sealing greases were analyzed.It is confirmed that the environmentally friendly sealing grease prepared with vegetable oil has better thermal stability and viscosity-temperature characteristics.(4)A variety of sealing grease samples were tested using the Matsumura sealing test method.The sealing mechanism of sealing grease is analyzed: fibrous aggregates close the micropores by accumulation to play a sealing role.Based on the sealing mechanism,the multi-aperture test method was proposed,and the test process and evaluation method of the Matsumura test were modified.(5)The test device of sealing grease consumption rate was designed and developed according to the shield tail sealing structure.Through the tests with the device,it was found that increasing the pressure of the sealing cavity and the driving rate will increase the consumption of sealing grease.