Jack Tunnel Design and Construction Flashcards
(37 cards)
What does tunnel jacking refer to?
The installation of tunnels by pushing them into the ground while excavating from an open face.
Where is tunnel jacking most often used?
In soft ground and at shallow depth.
In what ground and length conditions is tunnel jacking generally used?
Soft ground for relatively short lengths of tunnel where a tunnel boring machine is not appropriate.
What tunnel method is tunnel jacking an alternative to for shallow tunnels?
Cut-and-cover method.
What is a secondary application of tunnel jacking?
Used to install relatively small tunnel sections within which concrete foundations can be constructed in readiness to receive a bridge superstructure.
How can tunnel sections be installed with minimal disruption?
Jacked into position with no disruption or slid into position during a limited possession of the overlying facility.
Once Tunneling has started?
It should be a continuous ‘around the clock’ operation.
What is the first step in constructing a pedestrian subway using tunnel jacking?
The tunnel is first fabricated on a jacking base.
What is provided at the front of the tunnel during tunnel jacking?
A shield
What is the function of the shield in tunnel jacking?
To allow the contractor to excavate the open face of the tunnel as jacking proceeds.
How does the shield enter the ground?
Through an opening formed in the headwall.
What is used to push the tunnel forward into the soil face?
Hydraulic jacks.
Where are the jacks located?
At the rear of the tunnel and can either push-off the jacking base or off a rear thrust wall.
How is the shield driven upon completion of the jacking?
Through the reception pit of steel sheet piles.
How can the shield be compartmentalized?
Into cells from which hand excavation can be carried out.
How is jacking force reduced for long tunnels?
** intermediate jacking station** (IJS).
How can abutments be constructed using tunnel jacking?
Using jacked-in rectangular tunnels to support bridge superstructures.
What does the full-size monolithic tunnel section method involve?
Constructing tunnel sections in-situ on a high tolerance casting slab adjacent to the final position.
How can the tunnel be jacked into position?
While excavating the tunnel face or within an open excavation during a brief possession.
What tends to happen at shallow depths of cover?
The prism of soil above the tunnel moves along as the tunnel is jacked forward.
How is a rail track supported?
On a grillage of steel beams.
What can be used to separate moving tunnels and stationary ground at shallow cover?
Flat sheet material or a system of closely spaced steel cables.
At greater depths of cover, how is separation from stationary ground achieved?
By a drag reducing laminate, such as rubber or polyester sheets, steel cables, or injected lubricating material.
What provides the motive force to the tunnel units?
Hydraulic rams.
