Installation and Monotonic Pullout of a Suction Caisson Anchor in Calcareous Silt

Abstract

This paper reports results from a series of model tests undertaken to provide insight into the behaviour of a stiffened caisson anchor during installation and monotonic pullout in lightly overconsolidated calcareous silt. The tests were carried out in a beam centrifuge, varying the installation process (jacked in or jacked in followed by suction assisted installation), and the consolidation period prior to anchor pullout. The mudline load inclination was also varied to encompass various mooring configurations. The centrifuge data were used to calibrate analytical installation and vertical pullout capacity models, based on conventional bearing and frictional resistance factors but with strain rate dependent and strain softened undrained shear strength for the soil. Piezocone based direct design approaches were also proposed, deriving end bearing and frictional resistance from cone tip resistance and sleeve friction, respectively. Holding capacity of suction caisson under inclined loading was presented as failure envelopes expressed in terms of dimensionless vertical and horizontal components of caisson net resistance, which agreed well with a plastic limit analysis based envelope developed for suction caissons in clay. The regain of anchor capacity was found to be in good agreement with predictions based on the cavity expansion framework.

Model Test of the Pull-up Capacity of Folding Type Ground Anchors in Cohesive Soil

“…Previous studies attempted to predict the behaviour of anchors in the field by simulating laboratory test models and using numerical algorithms or theoretical formulations [18]. During field installation, the researchers encountered issues with the usage of huge plate anchors [19]. This is particularly true if the anchors are put in water regions on saturated cohesive soils, since they must first be dug to the necessary depth, then the anchors installed, and then backfilled [18].…”

Insight into the Behavior of a Caisson Anchor under Cyclic Loading in Calcareous Silt

“…Thus far a very few researchers have focused on caisson anchor response in calcareous soils (e.g. Randolph et al, 1998;Lehane et al, 2014;Koh et al, 2017Koh et al, , 2020. However, there are no corresponding industry standards and guidelines given in ISO (2016).…”

Cyclic response of a stiffened suction caisson anchor in calcareous silt

“…The internal friction angle of  = 38 o was determined from a separate series of triaxial tests. Further details can be found in Koh et al (2017).…”

“…The caisson was installed in-flight by jacking followed by applying suction, and then a reconsolidation period of 12 months (in prototype scale) was permitted before loading. For monotonic loading tests (tests M1 ~ M3; Table 3), as were reported by Koh et al (2017), a constant loading rate of v = 0.4 mm/s was adopted with V = vD/cv ~ 420 > 30, which was sufficient to ensure undrained conditions (Finnie and Randolph, 1994).…”

“…Very recently, Koh et al (2017) presented an extensive series of model testing on a stiffened suction caisson in calcareous silt. Calculation methods have been established for assessing caisson installation, influence of set-up period, and performance under monotonic loading.…”