Modified LRFD Method for Drilled Shafts in Intermediate Geomaterials Using the Pressuremeter: Fid-Bau Portal

Modified LRFD Method for Drilled Shafts in Intermediate Geomaterials Using the Pressuremeter

Drumright, Elliott E. / Barnard, Thomas R.

The load resistance factor design (LRFD) method for drilled shafts specifies that the service load multiplied by a load factor typically greater than 1.0, be less than or at most equal to, the sum of the nominal (ultimate) end-bearing and side shear resistances, each multiplied by a respective resistance factor less than 1.0. Some designers are reluctant to design combined end-bearing and side shear drilled shafts, referencing the known larger displacement required to mobilize peak end bearing than side shear. The authors have developed a modified LRFD method that combines the nominal (ultimate) side shear from empirical methods with the maximum allowable end-bearing derived from in situ pressuremeter testing (PMT). The creep pressure (p_f) from the pressuremeter may be taken as the maximum allowable end-bearing value, and is typically greater than can be justified from SPT or other empirical methods. For the cases presented, settlements calculated using the creep pressure in dense strata or intermediate geomaterials were typically on the order of ½-in. or less, which is much closer to the ¼-in. maximum deflection often cited as required to mobilize peak side shear resistance.