Thursday, November 22, 2012

Verification of Design: Foundation Quality.

Construction can cause defects in driven piles or drilled shafts.

Unfortunately, an installed deep foundation is mostly below the ground  surface and cannot be seen.  The quality of the foundation  should be verified to ensure adequate structural integrity, to carry the required load without a bearing capacity failure,  to limit displacements of the structure to within acceptable levels, and to avoid unnecessary overdesign of the foundation.  This chapter describes methods commonly used to verify  the capability of the foundation to support a structure.

These methods are nondestructive and usually permit the tested piles or drilled shafts to be used as part of the foundation.

a.    Indicators of problem with driven piles.  Piles driven into soils  with variable stratification that show driving records containing  erratic data, which cannot be explained by the construction method, indicate possible pile damage.  Failure to reach  the prescribed tip elevation or penetration rate also indicates pile damage.  Other indicators include drifting of the pile  off location, erratic driving unexplained by the soil stratification,  and a sudden decrease in driving resistance or interference  with nearby piles as indicated by sound or vibration.  A pile can also be damaged during extraction.

b.  Indicators of problems with drilled shafts.  Most problems  with drilled shafts are related to construction deficiencies  rather than design.  Such problems result from inadequate information of the subsurface soil and groundwater conditions  provided to the contractor, inadequate clean-out including  the presence of water in the excavation prior to concrete  placement, inadequate reinforcement, and other
complications during concrete placement.  Drilled shaft failures may  result from neglecting vertical dimensional changes in shrinking and swelling soil as those described in TM 5-818-7.

No comments:

Post a Comment