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 u(1) and at the shoulder or behind the tip u(2). At the standard rate of 2 cm/s, penetration pore-water pressures on the midface element are fairly high positive values (u(I) = +600 kPa +/- 200 kPa), yet readings at the shoulder element were negative (u(2) approximate to -90+ kPa). At an increased penetration rate of 20 cm/s, midface and shoulder readings increased in magnitude and were positive (u(1) approximate to +800 kPa and u(2) approximate to +200 kPa); however, measured tip resistance q(c) exhibited an unusual decrease, per comparisons with data available in the literature. Upon halt of penetration, both u(1) and u(2) decayed quickly and reached hydrostatic values u(0) within 1-2 min.