Penetration and Removal of the Mooring Dolphin Platform With Three Caisson Foundations

Abstract

Mooring dolphin platforms (MDPs) with three caisson foundations were installed in the ice-drifting Bohai Sea of China. Before installation, prototype tests of penetration and removal processing were conducted near the design site. To determine the lateral soil pressure and skin friction of the caisson, soil pressure and strain gauge transducers were fixed along the external skirt of caisson B of MDP1. The shaft skin friction was calculated from the strain difference between any two points of the strain gauges. The transducer results indicated that when the soil property determined by unconsolidated and undrained (UU) triaxial tests was used to calculate the unit skin friction resistance, a value of the adhesion factor α of 1.5–2.0 is recommended. The factor α is 1–0.4 during the suction-assisted penetration phase. The lateral earth pressure coefficient K decreased with penetration depth, most likely due to seepage caused by underpressure. In addition, the difference between the measured values obtained from the soil pressure transducers represented the small tilt of MDP1 during the installation phase. The skin friction and lateral earth pressure significantly decreased in the removal phase, 12 h after the penetration phase, mainly due to the soil disturbance caused by suction penetration around the caisson.