Jack and Bore

[Riggly]

Does any have experience with jack and bore in very loose sandy soils, or have any good reference to jack and bore construction? This is in relation to jack and bore of a 42" pipe under a roadway. Total jacking length is expected to be less than 120ft.

 

[civilperson]

Absolutely the best possible soil conditions, NO BOULDERS. The jacking pit may have to be shored to keep the excavation small. Why such a big sleeve diameter?

 

[msucog]

keep an eye out for surficial settlement of the roadway along the alignment...may take 2 weeks or 2 years to show up...just something to keep in mind. as mentioned, boulders=pain in the rear. don't have any good references on hand though...will keep an eye out for anything good.

 

[jdonville]

Riggly,

Take some intermediate borings if you can. I have been called in to projects where jacking hit unknown buried debris and caused substantial subsidence below mainline railroad tracks. Not a good time for the contractor!

If you anticipate unstable sandy conditions or groundwater problems, I know of a few projects where the soils along the pipe alignment were stabilized using jet grouting ahead of the main excavation activities.

Jeff

 

[Riggly]

Thanks for the responses. Greatly appreciated.

 

[rconner]

Some information in "Horizontal Auger Boring Projects"
(ASCE Manuals and Reports on Engineering Practice No. 106) @

http://www.asce.org/bookstore/book.cfm?book=4561

may be of interest.

 

[cvg]

settlement due to running sand or voids is very likely with loose sandy soils. you will need to use either a pressure balanced TBM or a shield and auger designed to prevent the sand from running. chemical grouting ahead of the bore may help to stabilize the ground. verify that the amount of excavated material matches the theoretical volume of soil to be removed from the bore. If you see larger volumes coming out, expect that you have created a void above the casing that will need to be grouted to prevent settlement. If you expect any boulders at all mixed with the sand, augers or TBM may have a difficult time proceeding. In these cases, ramming may be a better option.

 

[Rjeffery]

I have some small experience with J&B under railroad beds in very rocky conditions. the contractor used low strength grout injection which worked out well. Kept the ballast in place on an active rail line.

 

[DRC1]

A 42 inch pipe can be readily jacked in loose to med sands. You will need a jacking pit in the order of 32 x 10 feet. The reaction required will probably be between 200 & 400 kips. Jackers will probably use a louvered sheild at the face where they can use boards to limit the exposed face. The key to the operation will be grouting of the face with a chemical grout. The grouts are generally enviornmentally friendly except they have a rather basic ph. This sometimes becomes an issue if you are dewatering, as the effluent may need to have citric acid added to it. Prior to jacking, the jacker may pump bentonite or a modern substitute to lubricate the pipe. once the jack is finished, the annulus betwwen the soil and pipe is usually grouted by pumping through the pre installed grout ports. Pipe jacking is a speacilty and if you talk to a pipe jacking contractor, they will tell you more about it than you could ever have imagined.