Study on grease escape law of shield tail brush-grease cavity sealing system
Grease escape leads to the decrease in pressure in a grease cavity,which induces water leakage and slurry leakage in a shield tail sealing system.A unit body test device for grease escape in a shield tail brush sealing system was developed.The grease was injected into the grease cavity of the shield tail seal system with step-by-step pressure,and the pressure of each stage lasted for 420 s.The grease injection pressure at which the seal grease began to escape into the cavity under different shield tail clearances and different grease cone penetration conditions was recorded,and the stable loss rate of the seal grease in the grease storage device after escape was recorded.Finally,the grease escape rule of shield tail sealing system was obtained,and the escape mode of shield tail grease was summarized.The results show that:1)the grease escape rate is mainly affected by the grease cone penetration and grease pressure.According to the grease escape curve,the grease escape rate can be divided into three stages:non-escape,low speed escape and fast escape.The grease pressure from non-escape to low-speed escape is called the grease escape pressure,and the grease pressure value between low-speed escape and fast escape is the control of the pressure difference inside and outside the grease cavity.2)The corresponding relationship between the grease escape rate and the grease consumption in the project was established,and the sealing performance of the shield tail brush could be evaluated in real time in combination with the allowable grease consumption of each ring in the project.3)When the grease cone penetration is less than 286.4(1/10 mm)and the shield attitude and segment attitude are well controlled(the average gap between the shield tail is 75 mm),the maximum grease pressure can be increased by 0.3 MPa based on the soil and water pressure and the synchronous grouting pressure.The proposed pressure difference between the inside and outside the grease cavity can guide the setting of the maximum grease pressure in the shield tail in practical projects.4)The grease escape mode can be divided into three modes:non-escape,non-uniform escape and uniform escape,and its occurrence conditions are obtained.This research is of fundamental significance for guiding the design and construction of shield tail seals.
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