To solve the problem that the traditional construction method of offshore vibro-flotation with stone column by floating barge with vibro-equipment could hardly meet the schedule and tolerance requirements of ground improvement specification under the extreme wave condition especially from Mediterranean sea, this paper proposes a solution as a jack-up used for offshore vibro-flotation with stone column based on the overall structural stability calculation and foundation settlement calculation. Based on the successful application of offshore vibro-flotation with stone column by jack-up for the construction of Hadarom port in Israel, with its advantage of stability and effectiveness for offshore ground improvement under extreme wave condition, this solution of jack-up has a broad promotion prospect as a reference for similar projects.
As an extension of Ashdod port and Hayovel port in Israel, Hadarom port is designed for Maersk Triple E-class container vessel, comprising a 60-hectare container terminal formed by the hydraulic reclamation, which is shielded by the 600-meter extension of the existing main breakwater as shown in the following Fig. 1 and Fig. 2.
Since the upper layer of ground foundation under the main breakwater extension is mostly soft and loose silty sand with a piezocone penetration test (PCPT) value less than 5 MPa, the vibro-flotation with an Area Replacement Ratio (ARR) of 13% is proposed for ground improvement as an anti-liquefaction measure with the consideration of reducing settlement and increasing load-bearing capacity as well (Degen, 2006).
The major design issues considered for foundation treatment of main breakwater extension are moderate levels of earthquake accelerations, and associated potential for liquefaction of poor soils under breakwater foundations (Mohab , 2013 and Buddhima, 2015).
According to the liquefaction assessment at main breakwater extension, the loose silty sand was determined to be liquefiable based on a PGA value of 0.12g and M value of 7.5, while the silt was determined to be susceptible to strength reduction. Furthermore, analyses were then carried out assuming that the silty sand is: 1) replaced; and 2) improved. As a result, the maximum earthquake induced displacements were on the order of 60 to 80 centimeters, which is considered acceptable for this type of rubble mound breakwater structure with a 50-year design life in combination with a 100-year return period, as it can accommodate lateral deformation (DHV, 2011).