PILE LOAD TEST IN KOOTENAI SHALE

The Cretaceous age Kootenai shale of Central Montana is commonly used for support of shallow and deep foundation systems. Allowable unit loads have been historically low due to the lack of load test data. The Northside Parking structure in Great Falls provided the opportunity for a load test on a high-capacity end-bearing pile. An HP 12 x 53 was driven to refusal (20 blows per inch) in the shale and statically load-tested to 200 tons without failure. An attempt was made to economize on the system by shortening the piles approximately 5 feet for an 80 ton design capacity. Calculations based on previous data (driving records for several other jobs in the area) indicated that, in fact, no economy was available as the result of shortening. That is, the 80 ton pile capacity was reached just inches before a 100 ton capacity. This appears to be the result of extremely uniform weathering of the shale. It did indicate that 50 to 65 ton friction piles are feasible, and that there may be a freeze phenomenon which would allow a higher capacity. However, the latter would require considerably more investigation. (Author)

Media Info

  • Features: Figures; References;
  • Pagination: p. 167-178

Subject/Index Terms

Filing Info

  • Accession Number: 00334064
  • Record Type: Publication
  • Files: TRIS, STATEDOT
  • Created Date: Sep 16 1981 12:00AM