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Evaluation of Capacity of Micropiles Embedded in Dolomite
A Final Report to the Infrastructure Technology Institute
by:
Professor Richard J. Finno
Department of Civil and Environmental Engineering
Northwestern University
September 20, 2002
1. Report No. A433, A438 |
2. Government Accession No. |
3. Recipient's Catalog No. |
4. Title and Subtitle Evaluation of Capacity of Micropiles Embedded in Dolomite |
5. Report Date September 20, 2002 |
6. Performing Organization Code |
7. Author/s Richard J. Finno |
8. Performing Organization Report No. |
9. Performing Organization Name and Address
Department of Civil and Environmental Engineering, Northwestern University , 2145 Sheridan Road, Evanston, IL 60208
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10. Work Unit No. (TRAIS) |
11. Contract or Grant No. DTRS98-G-0016 |
12. Sponsoring Organization Name and Address U.S. Department of Transportation
Research and Special Programs Administration
400 7th Street, SW
Washington, DC 20590-0001 |
13. Type of Report and Period Covered Final Report, August 2000 – December 2001 |
14. Sponsoring Agency Code |
15. Supplementary Notes |
16. Abstract
Axial load tests were conducted on four micropiles installed from the floor of a quarry southwest of Chicago. The micropiles consisted of 178 mm diameter steel drill casing with a wall thickness of 13 mm. The piles were drilled into dolomite with sockets that varied in length from 0.3 to 2 m, were tremie filled, and then grouted with pressures of about 140 kPa. The tests were conducted on piles instrumented with strain gages to determine axial load distributions and load transfer characteristics. The non-linearity of the response of the composite pile was considered when determining the axial load distribution in the piles. Results of the tests suggest the current practice based on structural considerations can be quite conservative, if the rock is competent. Load transfer through side friction is governed by the interface shear strength between the steel casing and the surrounding grout. Due to the relatively high compressibility, the allowable axial loads of full-scale micropiles, installed in the same manner as described herein and founded on competent rock, are determined more rationally from allowable deformation considerations, rather than code-specified allowable stresses in the pile. |
17. Key Words Dolomite, Piles, Axial loads, Bearing capacity, Testing, Infrastructure |
18. Distribution Statement No Restrictions |
19. Security Classification (of this report) Unclassified |
20. Security Classification (of this page) Unclassified |
21. No. Of Pages 80 |
22. Price |
Table of Contents
Acknowledgements
1.0 Introduction
2.0 Technical Background
2.1 Design Methods
2.2 Design Considerations
2.3 Typical Load Test Data
2.4 Summary
3.0 Axial Load Test Section
3.1 Overview
3.2 Rock Conditions
3.3 Instrumentation
3.4 Testing Procedures
4.0 Results of Axial Load Tests
4.1 Axial Load Deflection Response
4.2 Axial Load Transfer
4.3 Unit Side Resistance
5.0 Discussion of Results
5.1 Computed Design Loads and Observed Capacities
5.2 Comparison of Results with Full Scale Load Tests
5.3 Suggested Design Approach
6.0 Conclusions
Appendix
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