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RE: Expansion Joint in Tunnel[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Expansion Joint in Tunnel
- From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
- Date: Wed, 21 Nov 2007 17:35:47 +0000
I do not like expansion joints either if avoidable. I have just designed several miles of critical tunnel structures that have to remain in service in a 2,500 year seismic event. |
I presume that you are using an open trench, placing a foundation slab, casting the walls and then casting the roof structure. Regardless of what you assume, concrete will shrink and soil will settle. Casting the walls after some finite time of curing of the foundation slab will assure residual differential stresses due to constraint of the foundation slab relative to the shrinkage of the walls.
If my assumptions hold, I would suggest that you use expansion joints at about 20m in the walls and roof only. I would design the floor as a continuous slab / mat on grade and allow some degree of hinge action at the wall / roof expansion joint location (20m). This will reduce the differential shrinkage and when the soil settles, the tunnel will have the capacity to flex and hinge without imparting large stresses on the tunnel.
The multiple small well spaced shrinkage cracks in the slab on grade will accommodate any expansion due to thermal growth especially considering that the earth will act as a large heat sink and help mitigate thermal growth.
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