Rock Revetments: Unique Requirements in the MENA Region
The design and construction of rock revetments in the region are based on standards that have developed and evolved from many engineering research facilities. However, the MENA region has established a unique requirement for these structures, in which design and construction elements need to be carefully assessed to ensure a proper and well-constructed coastal protection system.
When assessing the vast number of revetments on the UAE coastline, it can be seen that rock finish of these structures is extremely smooth. Coastal structures in the region typically use locally sourced, naturally occurring Gabbro rock, due to its hardness, lack of fissures, which leads to an extremely durable material. The majority of revetments designed and constructed are based on the CIRIA Rock Manual, in which placement of rock can be implemented in four ways: random, standard, dense, specific. All methods of placement aim to construct these structures using minimum orientation control. Based on experience in this region, operators take great lengths to select and orientate the rocks for placement to allow this revetment finish to be achieved.
Contractor’s assessment of the construction schedules of rock revetments needs to be done so with care. Clients and Consultants with experience outside the Middle East may review a Contractor’s schedule with the experience of Contractors utilising minimum orientation control whilst placing rocks. Construction of rock revetments in other regions is more functional-based with little thought or Client demand towards the overall finish. This also needs to be considered in the tendering stage. Extra time is generally required to place and orientate the rocks, which leads to extended programmes or additional machine and labour requirements. It must also be considered that rework may occur, in which the rate must reflect or include related contingencies.
Consultant needs to be aware of typical Contractor practices such as “packing”, which is an incorrect method to produce this finish. Small rocks are placed to level the smooth rock face to the design slope angle, to speed up the placing of rock. This method produces possible instabilities within the structures that, if a storm or high wave conditions occurred, could dislodge these “packing” rocks. This could lead to substantial weakening or failures within the structure.
Consultants need to be aware of this particular Client requirement, so it is possible to incorporate into the design. However, adopting a conservative approach may be beneficial due to the finish required of the overall structure. This conservative approach must also be considered when reviewing overtopping values, especially in case of pedestrians traffic in close proximity to the crest of the structure.
However simple the request for the overall finish may seem, the Client must recognize that this can have potentially dramatic effects on the performance and durability of a structure. Client pressures and demands for low priced design and construction may lead to some companies taking shortcuts that could lead to negative consequences to all stakeholders; Client, Consultant, Contractor, and in the worst case, a detriment to users' safety.
By Matthew Sheppard, Project Engineer at Ecocoast