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RE: Expansion Joint in Tunnel

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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. 

Regards,
Harold Sprague



From: ssrinivasan(--nospam--at)lntecc.com
To: seaint(--nospam--at)seaint.org
CC: surendra(--nospam--at)lntecc.com
Date: Tue, 20 Nov 2007 12:30:39 +0530
Subject: Expansion Joint in Tunnel

Dear Sefiant,

 

We are having 50m long tunnel connected between two buildings at raft foundation level. Building sizes are approximately 50m x 50m and building has one basement hence tunnel is connected between basements and entirely buried in soil.   And water table is 3m above bottom of tunnel as per geotechnical report.   We are not providing any Expansion Joint, is it acceptable or not?

 

Also We are having underground car parking structure approximately 500m long, 60m wide and top of roof slab is 1.5m below ground level. We have not provided any expansion joint in raft but expansion joint is provided every 50m c/c above raft.  Request you to comment on the proposal whether it is ok or not?

 

Can anybody having the design experiences share some knowledge?

 

Thanks in advance.

 

Regards,

S.Srinivasan,

J.Surendra

 



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