Keywords

intermediate geo-materials, weak rocks, strong soils, strength, drilled shafts, ultimate friction, ultimate point pressure, load tests, database

Abstract

Materials intermediate between soils and rocks are referred to as Intermediate Geo-Materials or IGM. They are earth materials that typically have SPT blow counts N between 50 and 200 bpf, unconfined compression strength σCIR between 0.5 and 5 MPa, and pressuremeter limit pressure pL between 2.5 and 55 MPa. Deep foundations in IGM include bored piles (drilled shafts) and, less often, driven piles. The ultimate axial capacity of such deep foundations in IGM is studied in this article. A database of load tests on instrumented single piles with separate measurement of ultimate side shear stress fu and ultimate point pressure pu is assembled and analyzed. In tandem with the load test data, the IGM properties are collected including σCIR and N. Because the pressuremeter is thought to be the best tool for the characterization of IGM, values of pL are obtained from correlation with σCIR. Correlation charts between fu and pu on one hand, and σCIR, N and pL on the other, are generated to help the engineer select appropriate values of fu and pu for IGM. Furthermore, existing guidelines to estimate fu and pu in IGM are reviewed and evaluated against the database.

DOI