Kengo GOTO

Experimental study on load acting on segment due to grease flow resistance

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 increases.
The predominant construction load is considered to be tail force. To make clear the grease rheological resistance at tail quantitatively when grease passes wire brush, this study carried out the elementary tests on grease and wire brush. In this study, the width of wire brush (300mm), the flow of grease through wire brush, i.e., the piston penetration speed (10, 30, 50 mm/min), the hydraulic pressure behind wire brush (0, 100, 300, 500 kPa), and the tail clearance(35, 25, 15, 5mm) were adopted as test parameters.
As a result, the followings were concluded:
1) The peak and residual of grease pressure increased lineally with the piston penetration speed.
2) The piston penetration pressure, the grease pressure at face side, and the grease pressure at tail side were in order of decrease for both the peak and the residual of grease pressure. This is supposed to come from the frictional resistance between grease and steel box.
3) When the piston penetration speed is within 10กม50 mm/min, as for 35 mm tail clearance, the piston penetration pressure and the grease pressure in conditions of 100 and 300 mm width of wire brush are almost similar. However, as for 5 mm tail clearance, the piston penetration pressure and the grease pressure in 100 mm width of wire brush are larger than those in 300 mm width of wire brush.
4) The effective piston penetration pressure and the effective grease pressure show inverse variation with the hydraulic pressure behind the wire bruth.
5) As for the frictional force between grease and steel box, the peak value was smaller than the residual value. Since the frictional resistance shows full effects in case of the residual, it is better to use the residual friction as a dynamic friction between grease and steel. The cohesion for the residual friction was 0.92 - 1.46 kPa.
6) As for the grease rheological resistance f, the peak value was larger than the residual value. And the peak value increase with the flow q of grease. In addition, the convergence tendency is found when the piston penetration speed is over 30 mm/min.
7) Based on the above results, the empirical equation about the rheological resistance of grease f and the flow of grease q was proposed.

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