horizontal driling under a dam 1

[thatdamengineer]

I need to develop specifications for horizontal drilling underneath a 50ft tall flood control dam. We expect to drill approximately 35 ft below the toe of the damn and emerge approximately 300 ft upstream and downstream of the structure. Does anyone have any information on the allowable pressures in clay soils? Us Army Corps of Engineers has some information but not really for specifications.

I am under the gun on this as the project was to be completed 3 days ago. Just got involved.

http://WWW.thatdamengineer.com

 

[bimr]

Somewhat surprised that you will be allowed to drill under a dam. What size pipe are you planning to drill and what is the purpose of the project?

 

[cvg]

good luck with the 3 days thing. I dont see this going anywhere quickly. you will need a permit from the state and that will take at least 3 months.

 

[thatdamengineer]

Dsm is operated by a state/federal agency. We have been allowed to do this if they approve our specifications and procedure. USACE has some guidelines for HDD under levees and embankments. Mississippi river levee is much taller and higher hazard potential than this dam. State has deferred to the Fed. I retired from the state agency in charge of this in 2007 after 30 years. We can do this if we stay in the foundation, not into the core or the embankment. A 10inch HDPE pipe will be pulled through the bore to serve as a conduit for the electric line. The bore will be approximately 30 ft below natural grade and 20 ft below the core of the dam. Foundation material is a red shale & heavy clay. 12inch bore with a 10in ID HDPE pipe. I need to develop specifications for the procedure. The Corps has issued a guideline from research on conduits installed for fiber optic line borings.

http://WWW.thatdamengineer.com

 

[rconner]

While I guess I understand the reasons for wanting a tight fit, "12inch bore with a 10in ID HDPE pipe" sounds AWFUL tight (with any reasonably small DR)!

 

[thatdamengineer]

I am really looking for some guidance on the allowable soil pressures that a discussion of the merits of the installation.

http://WWW.thatdamengineer.com

 

[bimr]

A good start may be a geotechnical boring. Would think that a project of this nature would benefit greatly. Perhaps some boring information is already available.

 

[dicksewerrat]

Talk to the HDD Contractor and look around for engineers familiar with HDD. NASTT.org may be helpful. UCT 2015 may still have lists of contractors ,engineers and equipment suppliers.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[BUGGAR]

You could start the Specs with the requirements for an adequate geological investigation, even if you have to put that in the construction specs. Kind of a design build spec.

 

[thatdamengineer]

The foundation is in a red shale that is very prevalent in this area. The route will traverse an old creek channel that was filled during construction of the dam, but the depth of the drilling will be below the bottom of the old flow line of that channel. we have borings that were done 40 years ago indicating the shale foundation. Other borings within 1/4 mile of the dam verify the shale foundation. USACE has the most experience with this method and application. Thanks for the reference to NASTT.org

http://WWW.thatdamengineer.com

 

[thatdamengineer]

The fed design center overseeing this project does not want us to bore in the area. Boreholes within 50 ft of the drilling path could create a path for piping during the drilling. This appears to be one of those operations that cannot really be spec'd because of the art of this procedure not the science. We will monitor pressures in the annular area and keep them as low as possible. Probably in the 5-6 psi range.

http://WWW.thatdamengineer.com

 

[rconner]

As to the issue I believe you are really grappling with, you may be interested if you have not seen same in the paper at

http://www.stahelitrenchless.com/pdf/hydrofracture.pdf

or its references, with some quite detailed perspectives on what the authors say may influences frac-outs that some might worrry about. As others have indicated, it is clear this would in even theoretical analyses require some quite detailed information or assumptions about the soil/stratas and water levels you are dealing with - have a good weekend.

 

[thatdamengineer]

Thank you I have read this paper. I have determined that if the boring does not exceed 8psi there should be no danger of hydrofracking. Contractor has agreed to install a pressure sonde at the borehead to monitor pressure. Also sonde has an output that can be recorded and made a part of the boring log.

http://WWW.thatdamengineer.com