Kenji YOSHIZAKI

Study on Water-Sealing by Wire Brush for Construction at ¡ÈGreat Depth¡É Underground by Pneumatic Caisson

Mitsutaka SUGIMOTO

Pneumatic caisson method can be widely applied to various ground and has high reliability, while its applicable depth is restricted due to the work under high pressure. To overcome the problem, the pneumatic caisson method employing an unmanned excavation method with helium mixed gas has been developed, which enables the work under pressure up to 0.7MPa. However, the new technology of the pneumatic caisson method for ¡Èultra-great depth¡É underground space with a groundwater level of 100m will be required to construct infrastructures in urban areas.
Therefore, applying water-sealing technologies at shield tail, a method to reduce work atmospheric pressure for pneumatic caisson has been proposed. This research carried out the element tests to improve the water-sealing performance of wire brush and made clear the influence of some propeties on water-sealing performance and its mechanism.
The obtained results are as follows.
1) If ground surface in rough, the maximum grease pressure using the wire brush without a protection cloth is just less than or equal to 400kPa. However, in this study, this pressure is 1.5MPa when the wire brush is equipped with the protection cloth. Therefore, the waterproof performance can be improved by installing a protection cloth to wire brush.
2) The influence on the maximum grease pressure caused by the roughness of the ground surface is following order. The existence or nonexistence of roughness > the height of roughness > the distance between two adjacent roughness points.
3) When the size of the wire brush is larger, the leakage possibility of grease is lower, since the pressing force by it on the ground surface increase.
4) The wire brush proposed in this study can keep the grease pressure at 1.0MPa for an hour. In the other hand, when the grease pressure is maintained at 1.0MPa, the pumped grease flow rate is almost 0 L/min/m.
5) The cause of leakage grease is due to the gaps between the protection cloth of the wire brush and the step on the surface.

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