Case study: Engineering of a EPC 3km jetty fast track project
Hubert VANDER MEULEN1 and Loic VAN DURMEN2
1 BESIX Engineering Department, BELGIUM.
email: hvandermeulen@besix.com
2 BESIX Engineering Department, BELGIUM.
Keywords: Jetty, EPC, In-house engineering, tight schedule, remote location.
Introduction
In the Red Sea, the BESIX-Orascom Joint Venture has constructed the Ain Sokhna Product Hub, a 3 km F-shaped jetty. The project consists of three berths, including berthing furniture and M&E works (firefighting systems, CCTV and control building). The construction time was less than one year.
The paper will focus on the engineering aspects related to this EPC contract. The mains challenges of the project where:
Extremely tight construction schedule
Absence of trustable geotechnical investigation at start of the works
Top side equipment and layout not fully defined at the start of the detailed design
The paper will consist in a case study about the fast track engineering study in the framework of a challenging EPC contract with limited information at start of the detailed design.
The project includes:
- 3km of Trestle
- 3 Loading Platforms
- 3 Service Platforms
- 18 Mooring Dolphins
- 12 Berthing Dolphins
- 530 piles driven in 9 months
- 16,000 m³ offshore concrete poured in 9 months
Engineering Schedule
The schedule of engineering woks presented in this section. The sequence on work in relation with the available input data and the strategy to allow early procurement will be detailed. A basic design stage with some tangible targets has been undertaken immediately after kick-off. Its results with the associated limitations was provided to the procurement tem to enable market enquiries while the detailed design was progressing
Geotechnical investigation and consequences on design
The 7 CPT logs for the 3 km jetty provided during tender where not sufficiently detailed to undertake a detailed design for permanent works. Hence, a dedicated soil investigation campaign was specified. The mobilization of state of the art floating equipment in a remote area was challenging. Hence a sub-campaign, land based and requiring the construction of a temporary bund was undertaken.
The land-based campaign has allowed the early identification of a liquefiable layer in the first 300meters of the jetty where a causeway was originally planned in tender. An additional engineering team has been mobilized to design a mitigation measure for this issue. The stability of a traditional rubble mounted causeway was jeopardized by the presence of this layer. Hence, it has been proposed to cast vertical concrete piles through a temporary bund with land based equipment. This solution was to be provided up to a depth where the steel piles of the remaining part of the jetty could be driven through this layer with marine equipment. Both concrete and steel piles reduce drastically the sensitivity to the weak layer.
The CPT preformed by the JV indicated an soil profile constituted of alternating weak sand and soft clay layers. The interpretations of the results of the soil investigation lead to very long steel piles to be installed for the jetty (up to 75m). The design has been confirmed by two static load pile test at two different locations. At each location, 4 piles where installed: two reaction piles, 1 compression test pile and 1 tension test pile. Pile test have demonstrated that the design was adequate.
Structural design
Pile design was mainly governed by geotechnical bearing capacity and by the combination of axial force and bending moment. The installation of the piles with jack-up barges was also carefully designed. The very long piles where having an long stick up portion of their length above the driving gates before start of driving. Finite 3D models where undertaken to check the risk of local buckling inside the gate supports under the combined effects of: self-weight of the pile; weight of the driving equipment and compression wave during driving.
The crosshead beams joining the piles have been designed to work properly in absence of piperack, with 1 or with 2 piperacks. As the jetty has a particular F shape, piperacks are crossing the roadway at some locations. Particular crossheads have been designed to support the piperack bridges at these locations.
The roadway spanning from Crossheads to crossheads has been designed as simply supported on a 36m span. It is made of a composite deck. On top ow welded steel beams, precast planks are installed which are connected to the main beams via in-situ concrete and pockets of shear studs. This choice of structural solution has allowed procurement near the site, ensuring guarantee on the delivery.
The services platforms are supported on vertical piles. The deck is composed of precast slabs connected through in-situ stiches. This structural solution has allowed very quick installation with all the concrete prefabricated on site. This has allowed optimized usage of the marine fleet. The loading platform are supporting berthing fenders. For these 3 platforms, an engineered pile layout has been proposed, match with the two main requirements: distribute efficiently vertical and horizontal loads within the pile group while offering regular supporting mesh to precast pieces. These platforms are split in two zones: the front part where heavy elements are to be embedded are deep in-situ sections while the rear part, supporting lighter equipment, is composed of precast planks connected with in-situ stiches.
M&E requirements
In order to allow early exploitation of the terminal, requirement has been raised during design to support water piping and gas piping along the jetty. It has been proposed to extend the bracing of the roadway steel beams outside of the footprint of the roadway in order to use them as support for the piping.
Conclusion
This case study will demonstrate how the detailed design by an in-house engineering department of an EPC contractor has allowed to build the jetty in the required time frame with the selected equipment. Focus will be set on the constructability of the different parts of the project, showing the interconnections between: design; procurement and construction, resulting in a safe and efficient project.