Benefits of soil borings for HDD planning

[LearnerN]

In my experience, soil borings are always strongly recommended for any HDD, especially for things like river crossings. But in terms of explaining their value for an HDD to the client, how are soil borings' value best conveyed? (I'm thinking of an example of let's say a 10" steel pipeline crossing a 1000' wide river.)

The things I can think of are:

(1) Will the driller hit rock? This would save time/money for planning for the driller, and could also significantly increase the cost for the client's budget. And for a river crossing, I'm sure any drilling contractor would want to know what to expect for soils when they're bidding on a project.

(2) The soil bore will tell what type of soils will be encountered, and this will affect the type of drilling fluid to be used (or if using air might work on the drill) as well as indicate how stable the bore hole would be in those soils (fine vs coarse-grained, cohesive vs not cohesive, etc).

(3) The soil bore could indicate if an HDD may not be successful, such as if the soils are inconsistent, filled with till, gravel/cobbles/boulders, sandy, too water laden, etc.

(4) Compressive strengths of the sub-surface materials to know how hard it will be to drill through various soil layers.

What are any other benefits of a soil bore for HDD planning? Are there any safety/hazards/concerns related to not having soil boring data for an HDD, like maybe a greater chance of a frac-out if the driller didn't know the soils to best decide on the right type of fluid and how best to execute the drill?

 

[bimr]

The issue can be summed up in higher project risk and less certainty. If you skip the borings, the project will have to have a larger contingency for the unknown included in the project cost. In addition, the project schedule will have to include more time to accommodate the risk of the schedule being delayed.

 

[BigInch]

It's not really optional. In the US, it will be required by PHMSA regulations (you must show that blow out is controllable and proper mitigation plans will be in place).

 

[dicksewerrat]

Many contractors will not bid a project without soil borings.. Or they will double the cost to cover the risk.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[LittleInch]

LearnerN,

your points in the OP are well made, but if you need to put it in non technical language, perhaps something like this might help - You are building a structure, it might be underground, but it's still a structure.

Would you build a 10 story building without knowing what the ground conditions were? - If you do, the risk is the building falls down and you lose all your money or it costs three times as much to build because the builder can't see below ground and hence will simply charge you for anything he finds which isn't perfect.

Borings are not "strongly recommended", they are required and anyone who does a drill that long across a river without doing a number of deep boreholes is simply a fool.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.