×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Drilled shafts in limestone
3

Drilled shafts in limestone

Drilled shafts in limestone

(OP)
What is a good resource for design and analysis of drilled shafts in limestone?  Or any type of foundation in limestone, for that matter.  A little background - I've been designing foundations (among outher things) for 2 years, and have just moved from Louisiana to Texas, and limestone is a material with which I've not dealt.  Any help would be appreciated.  Thanks...

RE: Drilled shafts in limestone

I've used caissons for end bearing on limestone as well as socketed caissons; the socketed caissons use the skin friction between the concrete and the rock.  Depending on the weathered surface a portion of the socket may be discounted.  It's been so long since I've used socketed caissons, that I don't recollect the friction value used.

The installation I'm familiar with is a matter of drilling the main shaft to the limestone bedrock and then drilling a smaller shaft, approx 6" smaller diameter to provide a bit of a shoulder.  The smaller shaft is drilled to the depth required to provide the necessary surface area.

Sometimes the end bearing is used in conjunction with the friction, but best to check with a local geotekkie to get an opinion due to the differences in moduli for shear and compression.

Also sometime a small 2" drill is used to determine if there is soundness in the limestone to a suitable depth.  Again local practice could dictate this.

RE: Drilled shafts in limestone

2
The best document by far is FHWA Publication No. IF-99-025, Drilled Shafts:  Constuction Procedures and Design Methods by Mike O'Neill and Lymon Reese (two volumes).  It can be obtained thru the ADSC by calling 214-343-2091, or check their website at www.adsc-iafd.com. ; It addresses design of shafts in sands, clays, weak rocks, hard rocks, and intermediate geomaterials.

RE: Drilled shafts in limestone

I agree with KAM on the publication.  However, I have these caveats on the matter.  Here in the Midwest (a little above Texas) Drilled Shafts are not really very common although we're seeing more of them these days.  I think this is mainly due to the amount of construction going on near existing facilities which require a non-intrusive method of constructing a foundation.  On the other hand, another main reasons is cost.  Drilled shafts are expensive and rock sockets are even more expensive.  Yet another is qualified contractors.  A big vicious circle - more shafts, more contractors ultimately lead to lower cost.

I have worked in Texas a little but I am aware that just about everything (in the bridge business) down there is drilled shafts.  This probably keeps the cost down.

RE: Drilled shafts in limestone

I think in limestones you have to be careful abaout cavities

RE: Drilled shafts in limestone

Small diameter grouted piles (mini-piles, micro-piles) can be used in limestone and can be reinforced to achieve relatively high capacities. FHWA also has a manual describing the design procedures for these piles, including bond capacities for the sockets in various types of rock.   

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources