Measured Horizontal Capacity of Suction Caissons

Abstract

Laboratory tests were conducted to study the behavior of suction caissons when loaded horizontally below the mudline. The experiments were performed using a 4-in. diameter caisson installed to a depth of 32 in. in normally consolidated kaolinite clay. The test prototype is representative of caisson geometries commonly used in mooring systems for deep offshore locations with soft seafloor sediments. Nine horizontal load tests were conducted with the loading cable attached at different points along the lower half of the prototype caisson. In each test, the caisson was installed to half its length using dead weight, followed by the application of suction to achieve full penetration. The loading cable was then pulled to a horizontal position and excess pore water pressures on the caisson exterior were allowed to dissipate. The caisson was loaded rapidly to failure under undrained soil conditions. Data are presented showing the horizontal load capacity, top cap displacement, caisson tilt, and excess pore water pressure on the caisson wall during loading. The results indicate that the maximum horizontal capacity occurs when the load is applied to the caisson between two-thirds (21 in.) and three-quarters (24 in.) of the embedded length. The failure mechanism and the developed pore pressures depend on the position of the load application.

Evaluation of Undrained Bearing Capacities of Bucket Foundations Under Combined Loads

“…Yun and Bransby (2007b) reported the undrained vertical bearing capacities of skirted strip foundations in non-homogenous soft clay using 100 g centrifuge model tests. Coffman et al (2004) conducted a series of 1 g model tests to study the horizontal bearing Tables 3 and 4 show the comparisons of the vertical and horizontal bearing capacities, respectively. The error between the capacities from the FE analyses and previous studies was only 0.0%À5.5%.…”

Experimental investigation of reverse end bearing of offshore shallow foundations

“…A gap has greater potential to be formed and remain open the higher the soil strength ratio su/γ'z (Britto and Kusakabe 1982;Coffman et al 2004;Supachawarote et al An experimental investigation of Mana/Gourvenec/Randolph reverse end bearing of offshore shallow foundations 6 2005). Analytical solutions (Britto and Kusakabe 1982) indicate that the minimum strength ratio necessary for the stability of an axisymmetric excavation in soft clay varies from around 0.25 to 0.18 for unsupported excavations with an excavation depth to diameter ratio of 0.1 to 0.5.…”

Effect of Gapping on the Transient and Sustained Uplift Capacity of a Shallow Skirted Foundation in Clay

“…Although no literature is available regarding gapping along shallow skirted foundations, various authors have reported that large displacements are required for a gap to form along laterally loaded caissons (similar to skirted foundations but with larger embedment depth to diameter ratio, d/D) in normally consolidated soil, while for lightly and over consolidated soils a gap may appear immediately after lateral or inclined loading (Clukey et al, 1995;Randolph et al, 1998;Clukey et al, 2003;CoŠman et al, 2004). Clukey et al (1995) report results from a centrifuge study of the eŠect of gapping on the capacity of suction caissons in typical Gulf of Mexico normally consolidated soft clay under cyclic loading, but did not observe a critical load at which the caisson suddenly failed from gapping.…”

“…For this case, they proposed an intermediate mode of failure, between pure shearing along the skirt and the full reverse end bearing. CoŠman et al (2004) investigated the horizontal capacity of suction caissons in normally consolidated clay at 1 g and did not observe a distinct gap in the back side of the caisson after lateral displacements up to several times the caisson diameter, but observed a scarp on the back side of the caisson and a wedge of soil that slid downwards, maintaining contact with the caisson. Supachawarote et al (2005) reported three-dimensionalˆnite element analysis investigating the eŠect of gapping on the inclined pullout capacity of suction caissons and for an embedment ratio d/D＝1.5 showed an average reduction in inclined undrained pullout capacity of 27z in lightly over consolidated soil.…”