Axial resistance of open-ended pipe pile driven in gravelly sand

Abstract

A full-scale, double-wall, open-ended pipe pile with a diameter, B = 660 mm was densely instrumented with a combination of electrical-resistance and vibrating-wire strain gauges. The test pile was driven into a gravelly sand soil profile to a depth of 30·48 m and then statically and dynamically load tested. The double-wall instrumentation allows independent measurements of the outer shaft, inner shaft (plug) and annulus resistances during a static load test. The residual loads locked in the pile after driving were measured and considered in the correction of the resistance components. The load–settlement curve, load transfer curves and the profile of the unit limit shaft resistance were obtained from the static load test measurements. Two cone penetration test-based methods were used to estimate the resistance of the test pile, which was compared with that obtained from the static load test. Both methods provide good estimates for the unit shaft resistance in sandy layers with low gravel content (<20%), but significantly overestimate the unit shaft resistance mobilised in soil with high gravel content (>30%). The estimated base resistances by both methods match well that measured in the static load test.

Experimental Study of the Load Response of Large Diameter Closed-Ended and Open-Ended Pipe Piles Installed in Alluvial Soil

“…The axial force at cross section A (at the top of the outer pipe) is balanced by the outer shaft resistance Q s . The axial force at cross section B (at the top of the inner pipe) is balance by the summation of Q ann and the inner shaft resistance, Han, Ganju, Prezzi, Salgado, & Zaheer, 2019. ) which is in balance with the compressive stress at the base of the plug, known as the plug resistance Q plug .…”

“…After surface preparation at the desired locations, the closed-ended test pile was instrumented with electricalresistance strain gauges (Tokyo Sokki Kenkyujo Model FLA-6-350-11-3LT) and vibrating-wire strain gauges (Geokon Model 4000) following recommended gauge installation procedures (Han, Prezzi, Salgado, & Zaheer, 2017). All the steps required for proper installation of the electrical-resistance strain gauges were described by Han et al (Han, Prezzi, Salgado, & Zaheer, 2017;Han, Ganju, Prezzi, Salgado, & Zaheer, 2019). Mineral wool was carefully wrapped around the gauge cables collected along the length of the pile so that the welding of steel angles onto the pile (see Figure 3.3) could proceed without risk of excessive heat damaging the gauges and cables.…”

“…Figure 5.4 Setup of the loading system and settlement measurement for the static load test. (Modified after Han, Ganju, Prezzi, Salgado, & Zaheer, 2019. ) In order to obtain a complete, realistic and welldefined load-settlement curve, a slow-maintained static load test was performed with small load increments, in contrast to the four equal increments prescribed in ASTM (2013) or the eight equal increments prescribed in EUROCODE-7 (Selig, 1985).…”

“…In contrast, the lightweight electrical-resistance strain gauges are not affected by inertial forces. Therefore, they are more suitable for the measurement Han, Ganju, Prezzi, Salgado, & Zaheer, 2019. ) of residual loads (Hajduk & Paikowsky, 2000;Han, Prezzi, Salgado, & Zaheer, 2017).…”

“…In empirical pile design methods, the unit shaft resistance is often directly related to the initial vertical effective stress s9 v0 by: q sL 5 bs9 v0 ; this is known as the b method. Figure 5.9 shows the back-calculated b values (5 q sL /s9 v0 ) for the outer surface of the test pile Han, Ganju, Prezzi, Salgado, & Zaheer, 2019. ) at the ultimate load level after correction for the residual loads.…”