Colorado's Axial Load Tests on Drilled Shafts Socketed in Weak Rocks: Synthesis and Future Needs

Details

• Creators:
  Abu-Hejleh, Naser ; Attwooll, William J.
• Corporate Creators:
  Colorado. Department of Transportation
• Corporate Contributors:
  United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  • Load and resistance factor design
  • Design methods
  • Geology
  • Construction
  • Compressive strength
  • Soil penetration test
  • Axial loads
  • Geotechnical engineering
  • Penetration resistance
  • Sedimentary rocks
  More +
• Publication/ Report Number:
  CDOT-DTD-R-2005-4
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States ; Colorado
• Edition:
  Final Report
• Corporate Publisher:
  Colorado. Department of Transportation
• Abstract:
  Drilled shaft foundations embedded in weak sedimentary rock formations (shale bedrocks) support a significant portion of bridges in Colorado. Since the 1960s, empirical design methods based on the blow counts of the standard penetration test (SPT) have been used to design drilled shafts in Colorado that deviate from the AASHTO LRFD design methods. The most accurate design method is to conduct load tests on test shafts, which are very expensive to perform. CDOT's strategic objective is to identify the most appropriate LRFD geotechnical axial design methods for Colorado's drilled shafts socketed in weak rocks that use test data obtained from cheaper and simpler geotechnical tests (e.g., SPT and unconfined compression test). To fulfill this objective, the measured resistance and settlement results of an adequate number of load tests on drilled shafts socketed in Colorado's shale bedrocks should be obtained and compared with predictions from design methods that use data of simpler geotechnical tests on the same bedrocks. In this report, Colorado's typical geological formations and construction methods for drilled shaft foundations are documented and discussed. Available information on Colorado's past axial load tests performed in the last 35 years on drilled shafts socketed in shale bedrocks are documented (e.g., test results from the load tests and from the simpler geotechnical tests, construction, materials, and layout of the test shafts). The load test results are analyzed and evaluated using Colorado SPT based design methods and methods recommended in CDOT Research Report 2003-6 and AASHTO/FHWA. The influence of conditions of the test shaft hole during construction (roughness and presence of water) on the measured resistances in the load tests is investigated. Based on the lessons learned from the work described above and the recommendations of CDOT Research Report 2003-6, Colorado's future needs for axial load tests on drilled shafts were established.
• Format:
  PDF
• Funding:
  80.18
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/93190/dot_93190_DS1.pdf
• File Type:
  [PDF - 8.90 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:496479bd4542f00a39d8fbfb3536a119b24f35e5101f6c104829373f5cbbebe9c6d4d3d38a2afc2382835384e91ca1b54e56d1161e3f8b7dc963d366303cb0d9