Receiving pit at EOP

[ACtrafficengr]

I'm looking at a highway work permit for a new water line connection. They are proposing to jack a waterline under the highway. The receiving pit will be 8 wide by 8 feet deep, right at the back of the curb. The waterline is below a 24" CPP storm drain.

I have two concerns - supporting the pavement during the work, and supporting the storm drain.

Would you require driven sheeting, rather than a sheeting box?

I have no doubt the storm drain could support its own weight, but what if it's carrying water? Half full would be ~800#m of water.

Advice would be welcome.

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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[sam74]

I think they will be jacking an encasement pipe under the highway before loading the waterline through the encasement. Therefore I don't see an issue with the pavement or the existing storm line.

If you've never witnessed this before the encasment pipe will be forced into the dirt and an auger in the encasement pipe will carry the dirt through it back to the bore pit. This should be just as stable as the existing earth if not more.

As for the pit being directly behing the curb I guess I could see a possible issue if a heavy storm were to come through and cause some erosion of the earth under the curb or maybe existing waterlogged cohesionless soils sloughing off under the curb. This typically wouldn't be the case where I'm located and the bore pit probably won't be open to long to the weather. If something does happen it should be the contractors understanding that he/she has to replace whatever they destroy.

 

[ACtrafficengr]

I'm not worried about the jacking. In the event of a bank failure, it could damage the road. Also, the storm drain will be hanging out to dry during excavation.

I should have mentioned that this area is known for its fine soft sand and high water tables.

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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[Cosimo]

A high water table may preclude the use of a sheeting box as a jacking pit, unless dewatering is considered. Although with a jacking operation, dewatering may be required in any case. As for tight sheeting (or any support method) against the back face of the curb, assume you will loose the curb, or at the least disturb it to the point of requiring replacemnt. Wouldn't be concerned with the storm sewer because, as sam74 mentioned, the casing will be jacked, thus providing continuous support. As with most such operations, means and methods should remain that of the contractor. As part of his submittal, he should address and/or stipulate replacement/repair for any damage done.

 

[ACtrafficengr]

What I'm trying to say is the storm drain is directly over the main, and will be spanning the pit, completely unsupoorted by anything but itself. I'm not worried about the jacking, I've worried about the unsupported weight of any water that may be flowing through it.

Maybe ascii art will help. This is a cross section of the pit, looking downstation along the road. "O" is the drain, "o" is the main. --- is the casing.

_____ ____________
| |
| O |
| |
-----| o |
| |


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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[ACtrafficengr]

Or should I just take your advice and make any needed repairs a requirement of the permit?

------------------------------------------
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[cvg]

temporary or permanent support of the line is required. temporary might include a couple of I-beams with strapping to support the pipe. Permanent would be concrete encasement.

 

[Zambo]

Where is the waterline going after the reception pit? It seems as if it will either be heading parallel with the drain, in which case you have another problem. Or it is continuing in the direction of jacking in which case why can't you jack further?

 

[DRC1]

I have used boxes for reciving pits w/o a problem, however if the stompipe is perpendicular to the jacked pipe and the jacked pipe in the pit, that would preclude the use of the box as a reciving pit. Putting the pit right behind the curb will make it difficult to retain the curb. If I were doing the work I would pull and Reset the curb. the only problem is that you would need to patch the road at the curb location. If Possible, the best thing to do is to move the recieving pit behid the storm drain so you jack under the curb and the pipe then daylight.