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August 5, 2021

Breaking Rocks: Quality Control Issues in Coastal Structures

The start of numerous coastal protection projects across the Caribbean has seen traditional civil works contractors venturing into coastal works construction. It often comes as a surprise to the client and contractors that when dealing with coastal projects, the requirements are unlike the typical road and retaining wall construction. Simple things like armour stone quality and size, environmental considerations, surveying, setting out and packing become major hurdles initially. There is often a steep learning curve to get the contractor up to speed on the specifications and fine details required to make revetments and breakwaters functional and sustainable. CEAC Solutions has monitored the construction of coastal structures across the Caribbean, and found that a combination of detailed pre-construction briefings, quarry surveys, and close monitoring helps to alleviates the common issues.

Armour stone size and quality are often first hurdle as contractors try to source the cheapest supplies. This is the first requirement to be met for breakwater and revetments to be functional. An initial quarry survey with the contractor usually helps to guide this aspect of the works, along with regular monitoring to check sizes. Nonetheless, often there is the temptation or incidence of smaller stones “slipping in”, primarily because they are perceived to be cheaper. Encouraging the contractor to put in quality control at the quarry before delivery of stones is often very helpful and breaking rocks on site is not. Quality issues are less pervasive once the geology is identified and tested to verify water absorption and density. A monthly check along with “drop tests” usually helps to verify or identify these issues.

Turbidity along the coastline or on adjoining reefs is a major concern in the placement of fill and armour. The usual requirement of not more than 5 NTU above background level is easy to meet with both clean stones and turbidity barrier. This is not a usual requirement of traditional civil works, and often contractors are faced with learning how to construct, deploy and maintain barriers in place for the duration of the works. Independent and internal water quality monitoring also helps to routinely keep track of the potential issues and fulfil regulatory requirements.

The land surveyor’s role in marine works is key to both function, and profitability for the contractor. Steep nearshore slopes and wider than required bases can quickly consume expensive armour stones. Here, the surveyor who is specialized in coastal surveys plays a critical role in setting out toe and alignments for the work. The routine monitoring of cross sections at foundation, fill, secondary and primary armour levels using the Rock Manuals recommendations, helps to verify the construction quality of slope and material thickness. Thinner than required armour and steeper slopes are some of the typical issues that need to be addressed initially.

Armour stone packing is probably the biggest hurdle that most contractors face. The temptation to put down loosely packed stones that rock when stepped on and to not select stones during placement for tighter packing is often met with many discussions and reminders of the specification’s requirements for tight packing. Visually, an experienced contractor’s work is easy to identify versus a newcomer.

Beach stabilization and coastline protection works have similar but different quality control issues from traditional civil engineering works. Close attention has to be paid to armour stone size and quality, turbidity, surveying and packing. Our experience at CEAC points to the importance of pre-construction activities and routine monitoring to alleviate the common issues.

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