Naohiro ONOZUKA

Experimental study on rheological resistance of grease in shield tail
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 be increased and then segment damage during construction occurred increasingly
The predominant component of construction loads is tail force. To make clear the rheological resistance of grease for tail force 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, the flow of grease through wire brush, i.e., the piston intrusive speed, the tail clearance, and the hydraulic pressure behind wire brush were adopted as test parameters. 
As a result, the followings were concluded: 
1) The peak and residual of grease pressure increased with the piston intrusive speed increase.
2) The piston intrusive pressure, the grease pressure at face side, and the grease pressure at tail side were in order of decreasing. This is supposed to come from the friction resistance between grease and steel box. 
3) In the case of 35 mm tail clearance, the piston intrusive pressure and the grease pressure in conditions of 100 and 300 mm width of wire brush are almost similar. However, in the cases of 5 mm tail clearance, those in condition of 100 mm width of wire brush is larger than those in condition of 300 mm width of wire brush.
4) The effective piston intrusive pressure and the effective grease pressure show inverse variation with the hydraulic pressure behind wire brush.
5) The piston intrusive pressure and the grease pressure for 5 mm tail clearance is much larger than those for over 15 mm tail clearance.
6) As for the friction force between grease and steel box, the peak value was smaller than the residual value. Since the friction 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 is 1.4 – 2.4 kPa.
7) As for the grease rheological resistance f, the peak value was larger than the residual value. And the peak value increase with the flow volume q of grease. In addition, the convergence tendency is demonstrated when the piston intrusive speed is over 30 mm/min.
8) Based on the above results, the empirical equation about rheological resistance of grease f and flow volume of grease q was proposed.