On the east coast of Africa, Damen Shipyards is currently constructing a slipway with a lift capacity for ships up to 4000t and a maximum length of 150 m. With these specifications, this will be the largest slipway of East Africa. The slipway will offer the possibility to bring various types of ships on land, which can be cleaned, repaired and / or revised.
With a rail system the ships will be able to be moved, depending on the size and the intended work, to a large or small hangar. In addition to a workshop, the smaller hangar will also offer space for offices, changing rooms and washrooms. Heavier hoisting work with a mobile crane track will be carried out in the larger hangar. For the final design of the facilities, Geobest coordinated the geotechnical soil survey and prepared the geotechnical design. The ship lift is expected to be put into use at the end of 2019.
Drilling and Prospecting International (DPI) has been subcontracted by Damen Shipyards for specific geology and on-site soil research. DPI is a local soil investigation agency that has extensive experience with drilling and sounding all over the African continent. DPI has also been responsible for the implementation of 26 boreholes, 20 of which were carried out on land, and 6 were carried out from the jack-up. In addition to Standard Penetration Tests (SPTs) every 1.5 m, disturbed and undisturbed samples were taken to provide sufficient insight in the stratigraphy and the basic parameters before the start of the design phase. The undisturbed samples were tested in both the DPI laboratory and in the laboratory of Nairobi University, including unit weights, grain distributions and triaxial testing.
Geobest coordinated the execution of the soil investigation for a period of two months on-site to guarantee the quantity and quality of the soil investigation. An integrated geotechnical design was then drawn up on the basis of the soil investigation. In total, approximately 400 meters of shore protection have been analyzed, and approximately 80 meters of (anchored) steel sheet piling screens and approximately 1000 pieces of open steel tubular piles with varying lengths and diameters have been included in the design. In addition to the physical design of the foundation work, drivability analyses were also carried out. Finally, a last but certainly not unimportant part of the design was the overall stability of the excavated hill at the rear of the site. In order to achieve an optimal balance in the required earthmoving, the material retrieved from the hill, which mainly consisted of (silty) sand, was therefore used for land reclamation on the water side of the terrain.
By linking our specific knowledge of the implementation process of foundation techniques and soil behavior to the limited possibilities that the work at such a location entails, an economically responsible and integral geotechnical design has been achieved. The ultimate client and user of the slipway was able to experience how we work with local and international standards, in order to realize a solid and reliable end product.