Criteria for number of soil borings required? 1

[eureka]

What is the recomended criteria for how many soil borings should be taken verses the size of the project plot (acres)?

 

[SirAl]

There is no universal answer to your question. The number of borings should be based upon the requirements of the project at hand and will depend upon the geological complexity and land use history of the site. Please provide more details of your project.

 

[BigH]

SirAl is correct that the number of borings will depend on the factors noted - and also on how well you know the site. Still, many agencies do have minimum borehole requirements - see HUD in the States. Many times these are "outlandish" but they are there. Now are the "requirements" always followed; unlikely so long as it based on the geotechnical engineer's knowledge of site and other SirAl factors!

 

[gandersen]

eureka:

I agree with the points made by SirAl and BigH. Another factor that will affect the criteria on the number of soil borings is the "Standard of Practice" in the particular region and the type of construction that is being planned. As geotechnical engineers, we do not operate in a vacuum and often find pressure (in competitive bidding environments) to cut the number of borings to be in line with other competitors.

In various regions of the country there are rules of thumb for standard practice.

 

[hotgas]

The US Department of Housing and Urban Development (HUD) Directive Number 4460.1 "Architectural Analysis and Inspections for Project Mortgage Insurance" para 1-4M4c suggests, "At least one boring must be made for every 2500 sq. feet of foundation area. For buildings supported on pilings, one boring must be made for every 1600 sq. ft. of foundation area."

para 1-4M4d says, "Borings must be at least to the bottom of proposed footings and deep enough to locate bearing strata that will support the proposed structure. When rock is encountered, depth of drilling into rock shall be at least 5 feet or enough to establish rock quality regarding voids, fissures and strength, or whether it is a bolder."

para 1-4M6 says, "Additional information must be required when unusual soil conditions may effect foundation design."

 

[BigH]

Thanks hotgas - I knew it was around but didn't want to quote since I don't have the standards with me.