Piezocone Penetration Testing in Atlantic Piedmont Residuum

Piezocone soundings were performed in residual silts and fine sands of the U.S. Atlantic Piedmont geologic province to investigate penetration pore-water pressures and subsequent dissipation characteristics in these "nontextbook" geomaterials. Piedmont residuum has been formed by the in-place weathering of Paleozoic schist, gneiss, and granite. Pore-water pressures were measured at two positions: midface of the cone tip u1 and at the shoulder or behind the tip u2. At the standard rate of 2 cm/s, penetration pore-water pressures on the midface element are fairly high positive values (u1 = +600 kPa ± 200 kPa), yet readings at the shoulder element were negative (u2 ≈ −90+ kPa). At an increased penetration rate of 20 cm/s, midface and shoulder readings increased in magnitude and were positive (u1 ≈ +800 kPa and u2 ≈ +200 kPa); however, measured tip resistance qc exhibited an unusual decrease, per comparisons with data available in the literature. Upon halt of penetration, both u1 and u2 decayed quickly and reached hydrostatic values u0 within 1–2 min.