Borehole intervals for design of undergroung gas pipeline 4

[pipe72]

Hi everybody,

I'm preparing a scope of work for geotechnical investigation for a gas pipeline project. The problem is that nobody has any idea how many boreholes ( boreholes intervals) should be drilled for 8 km gas pipeline. They are 4 pipe in the trench and the smallest one is a 4 inch and biggest one is 10 inch. The pipe is buried about 1.5 m in the ground. Do anybody has any idea or a reference to find the criteria about number of boreholes.

I highly appreciate your comments.

Regards

 

[SlideRuleEra]

The way we would approach a green field site was to plan a two stage investigation:

1. Considering accessibility and what is known about the site, plan a manageable number of samples, ...say 17 or so in your case (one every 0.5 km).

2. Based on what is found (mainly variability between samples) your geotech firm will be able to make an informed recommendation on what to do next.

For general information see "GeoGuide 2, Guide To Site Investigations" at this link

http://www.cedd.gov.hk/eng/publications/manuals/index.htm

This is written specifically for use in Hong Kong, but has informative generic information, too.

http://www.SlideRuleEra.net

 

[fndn]

I would also add borings to any elevation changes, bends and road crossings and change in geological formations.

 

[jdonville]

pipe72,

You might want to include a geotechnical consultant to help you identify potential problem areas and develop the scope. They can then (if you choose) bid on the scope as well. Please note that this will likely involve some additional work when reviewing bids for the recommended scope, as the other geotech firms bidding on the scope may provide modifications to it which will need to be considered.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[GeoPaveTraffic]

pipe72,

Why not let the Geotechnical professional determine the number of borings needed? Why should you prepare the scope? Did the owner prepare your scope? What are you trying to do, get the geotechnicals to bid the investigation?

 

[looksatstars]

If you are only going down 4 feet, it would be very easy to drill that with a truck mounted small drilling unit. Of course this depends on terrain and conditions.
I would be on site (if possible) and do a wide spacing of boreholes to complete the drilling in a day. If the results are fairly consistent, I would probably end there but if the results are varied then drill intermediate distances till you are satisfied.
You will also get more information when the ditchwitch goes in and starts its digging for the line.

 

[jdonville]

pipe72,

I worked on a pipeline soil survey a few years back for a steel natural gas transmission pipe about 4 or 5 feet in diameter. The big concern (at least for the portion of the work I was involved with) was having the pipe float out of the ground, so most of the focus was on the soils above the pipe crown. The borings were performed using hand augers just to record the soil profile using a visual classification. No tests were performed since the soil would be disturbed (excavated) and backfilled over the pipe. Hand augers were performed at areas of greatest concern (wetlands, creek crossings). In order to be sure that these areas were demarcated accurately, we actually drove or walked the entire alignment, making corrections to the limits of wetlands and areas of weights for the pipe as we went.

Hope this helps.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.