Pipe jacking through sand embankment 4

[jdonville]

Is it possible to jack a pipe through a sand embankment?

Our client wishes to install a 42in RCP (inside a 50in steel casing) through a railway embankment. The embankment (we suspect) is composed of sands, silts and silty sands - We will be performing continuously sampled borings prior to pit design and all that good jazz to confirm or deny. The jacking distance will be a minimum of 110 ft at a 7.5% grade (uphill), and the minimum clearance between the rails and the crown of the pipe will be approx. 5 ft.

GWL is expected to be about 2 ft below lowest point of the pipe invert, based on many borings in the area.

We are naturally concerned about subsidence during jacking, and would love to learn of any case histories involving similar soil conditions or other methods.

I am already thinking about some sort of stabilization methods like jet grouting to add strength to the embankment soils to make jacking/boring possible, but want to learn about others' experiences.

Jeff


Jeffrey T. Donville, PE
Wang Engineering, Inc.

http://www.wangeng.com

 

[VAD]

Interesting problem. I would try to examine if the sand, silty sand is collapsible. Presumably being under a rail tie system this may not be the case as it would have densified somewhat over time.

However, it would be necessary to look at the material obtained from your drilling. If possible a testpit down the side slope of the embankment would perhaps provide some indication of what time interval is possible before any collapse. The horizontal boring procedure could then be tailored to suit the findings.

I would think that if the sand is not fine, loose and dry of optimum then the likelihood of collapse would be minimal.

I see your concerns and thoughts on an alternative stabilization approach, however,I think your geotechnical investigation would be a key component of your final decision making. This is one for the Engineer being on site during the investigation and applying judgement. It would be a good idea to have potential contractors or a known reliable contractor witness the field exploration.

Thats all for now. Others may have their two cents to share.

[Cheers]

 

[DRC1]

You sure can.
The pipe will usually have a short section in the front known as a shield to protect the roof. Although you can have a boring machine, if you are concerned about settlements, it will probably be hand mined. If the soil can run run it is usually stabilzed with a weak chemical grout and broken out with clay spades. If the pipe is jacked, the backwall of the jacking pit must be reinforced to recieve the jacking loads. This load will be passed to the soil behind the walls so any structures or utilities behind the wall must be considered. Once the pipe is in place, the exterior is usually post grouted through ports in the interior of the pipe. You can increase the reinforcing on the 42 inch concrete pipe and jack that directly with out the steel sleeve, unless the steel sleeve serves some other purpose. Your best bet is to look up a local pipe jacking contractor and talk to him. Most are happy to talk about yhe ins and outs of pipe jacking and can probably give you apretty good idea on how to approach the project.

 

[JoeCavey]

Jeff,
This project sounds like an ideal jet grouting or chemical grouting application. Both grouting methods could provide increased stability at the tunnel face, reducing surface settlement. Recently, we jet grouted in similar soils such that a 72-inch RCP could be jacked under the main runway at BWI (see RETC 2003 Proceedings). Jet grouting was performed to construct a soilcrete plug to tunnel through directly below the runway. We have also performed chemical grouting for very similar site conditions (depending on the fines content of the sand). I can provide budget pricing for either system if you are interested. If so, please fax drawings and soil borings to (410) 551-8206, or give me a call at (410) 551-1980. I hope this information helps.

Joseph K. Cavey, P.E.
Sr. Project Manager

Hayward Baker Inc.
1875 Mayfield Rd.
Odenton, MD 21113

(410) 551-1980 (office)
(410) 551-8206 (fax)
(443) 831-5092 (mobil)

 

[jdonville]

All,

Thanks for the good information. JoeCavey, I think that I saw a small presentation on your project at a local ASCE dinner presentation, which is where I think I got the jet grout/soil cementing idea from.

For information, the railroad requires all utilities crossing underground to have a steel casing. Presumably, this reduces corrosion damage and/or improves locating.

I don't know when we will be performing the borings as railroad occupancy permits can take time to process, but I thank everyone for their input.

Jeff

Jeffrey T. Donville, PE
Wang Engineering, Inc.

http://www.wangeng.com