1.Applicability to a wide range
of soil types
This method is applicable to diverse soil types because sand, gravel,
silty clay, Shirasu, and alternations thereof can be converted to
muddy soil with plastic fluidity and impermeability using mud making
agent.
2.Minimization of settlement
The face is retained by muddy soil and thus there occurs hardly any
disturbance of the soil. Ground surface settlement can therefore be
minimized.
3.Simultaneous backfilling
Shield perimeter and the kneading chamber are waterproofed by muddy
soil, so no backfill material affects the face. Simultaneous backfilling
is thus ensured.
4.Applicability at great depths and under high water pressure
Tunnel driving tests under a maximum water pressure of 0.7 MPa have
confirmed satisfactory performance of the method under high water
pressure. The method is applicable to great depths exceeding 50 m.
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The DK Shield Method controls muddy
soil pressure in three phases to minimize disturbance to the ground,
and thus controls tunnel driving.
1.Convert excavated soil into muddy soil
Mud making agent is injected into soil that has been excavated from
the tunnel by a cutter. Excavated soil is then kneaded forcefully
with the agent using kneading blades and changed to muddy soil with
plastic fluidity and impermeability.
2.Stabilize the face with muddy soil
Kneading chamber and screw conveyor are filled with muddy soil. Then,
muddy soil pressure is generated by the thrust of a jack to resist
groundwater pressure and earth pressure for providing face stability.
3.Control tunnel driving by muddy soil pressure
Muddy soil pressure is constantly monitored using muddy soil cells
attached to the bulkhead. Tunnel driving is controlled by changes
in the rate of shield advance and the rotational speed of the screw
conveyor so that muddy soil pressure becomes equivalent to the total
of earth pressure at rest and water pressure. |
