Experimental Study on Grease Rheological Resistance as Tail Force and Its Application
Supervisor Mitsutaka SUGIMOTO
Today, shield tunnels have been constructed in deeper underground with sharp curve, as underground structures in urban area become congested. Furthermore, segment become thinner and wider for saving its cost. Consequently, stress in segment during construction tends to increase and then segment damage during construction is increased.
The predominant force of construction loads is tail force. To make clear the grease rheological resistance among tail force quantitatively when grease pass wire brush, this study carried out the elementary tests on grease and wire brush. In this study, the width of wire brush (10, 30cm), the flow of grease through wire brush, i.e., the piston penetration speed (10,30,50 mm/min), and the hydraulic pressure behind wire brush (0, 100 kPa) were adopted as test parameters.
As a result, the followings were concluded:
1) The peak and residual of grease pressure increased as the flow of grease increased lineally.
2) The pressure by piston, the grease pressure at face side, and the grease pressure at tail side were in order of large pressure for both the peak and the residual of grease pressure. This is supposed to come from the friction between grease and steel box.
3) The pressure by piston with 10cm wire brush width was larger than that with 30cm wire brush width. This is because the friction between grease and steel box, which is one part of the piston force, become less, as the wire brush width increases.
4) The effective pressure by piston and the effective grease pressure do not depend on the hydraulic pressure behind wire brush.
5) The dependency of the friction between grease and steel box to confining stress can not be cleared. Further tests are required by changing the hydraulic pressure behind wire brush.
6) As for the friction between grease and steel box, the peak value was smaller than the residual value. Since the friction is mobilized more in case of the residual, it is better to use the residual friction as a dynamic friction between grease and steel. The residual friction is 1.9 ? 2.6 kPa as cohesion and 0.042 ? 0.056 as friction constant (2.4 ? 3.2 degree as friction angle).
7) As for the grease rheological resistance f, the peak value was larger than the residual value. And the peak value increases as the flow of grease through wire brush q increases, but the residual value is almost constant. The empirical equation as for q vs. f was proposed.
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