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A closed circulating water conduit of 233 meters wide by 6.25 meters depth is planned to be tunneled through a highway. The highway is expected to carry loads of say 60 MT by 12 meters long trailer. It is planned to have the conduit located 4 meters beneath the highway. I need advise what is the best way of tunneling method without disturbing the traffice on the road.

RE: Tunneling

There was an error on my earlier posting. The conduit is 23 meters wide by 6.25 meter depth. Sorry for the inconvenience.

RE: Tunneling

Dear Helmley

If I understand your problem you have a structure which is 23 metres wide by 6.25 metres deep below a highway? This does seem rather large. Well, if you must do this then I can think of two or three ideas but the risks are very high. One cost effective way may be to temporarily re-route the road by a few metres, build your structure in open cut across the existing road and then re-construct the road and dismantle the diversion.
The tunnelling options assume the road is on an embankment and is in "soft" ground. The options are:-

1. Bridge Jacking. Construct the structure to one side of the road complete with a massive steel cutting edge. Use massive jacks (specialist companies do this) to push the structure into the ground. Then excavate the face inside the cutting edge. This will require experienced miners and intricate face support to the area inside the cutting edge.

2. NATM Tunnel. Construct a sprayed concrete lined tunnel larger than you need and build the structure you require inside then fill in the gap left betweem structure and sprayed lining.

3. Pipe Ramming. If the road is on an embankment you can ram a series of steel tubes through the embankment to form an arch of contiguous steel tubes when viewed in elevation. You then excavate the area below these pipes whilst using insitu or sprayed concrete linings to supplement the strength of the tube arch. Again you need experienced miners.

If the road is in rock then use conventional rock tunnelling methods. Please note that for a structure of such size the settlements of the highway surface will be sufficiently large as to warrant immediate highway repair, and if you have to do this, then you might as well choose the first option of open cut. The tunnelling options outlined become increasingly risky if groundwater is present. Without more info I cannot help you further.



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