The “Human Factor” in Structural Failure in Concrete Water-Holding Structures
Pool Design article by William T. Drakeley, Jr.
While individual scenarios may vary widely, there are two primary factors that contribute to the failure – minor or massive – of water-holding structures produced via the sprayed concrete process, known as shotcrete or gunite.” These vessels may include swimming pools, spas, fountains, and other water features such as trough and runnels, reflecting pools, man-made ponds, etc.
The first factor is departure – intentional or otherwise – on the part of the contractor from standard best practices in shotcrete construction. Beginning with job specification, each phase of the shotcrete process should be primarily governed by guidelines designated by the American Concrete Institute Committee 506 and the American Shotcrete Association position statements. Such publications set the authoritative minimum standards for each component of the construction process, including excavation, forming, steel work, mix design, shotcrete application, finishing, and curing. Adherence to these standards maximizes the contractor’s odds of achieving a high-quality vessel with low risk of failure.
The specifying parties may know these standards for shotcrete construction and may even explicitly incorporate them into the bid documents or construction plans. This does not prevent the contractor from disregarding the higher standard articulated in the specification, contract, or construction plan and opting for an inferior (and likely, less expensive) material or method that could compromise the quality of the structure.
A second factor that can contribute to structural failure is the fracturing of the construction process as different phases of work are bid out to subcontractors. Without uniform project oversight, the risks of “cut corners” and inadequate quality assurance increase the risk of defects in the structure. The reduced accountability inherent to a decentralized construction process gives each subcontractor greater leeway to make decisions that contribute to their own bottom line.
Each phase of construction has its own parameters, minimum requirements, and required materials and methods. Leaving these factors to the personal discretion of multiple subcontractors – who may never have to deal directly with the client – increases the risk of variability in both process and product. This variability may introduce material incompatibilities and physical flaws to the structure that, when taken together, may greatly reduce the strength of the structure.
In sum, when analyzing the underperformance of or defect in a concrete water-holding structure, it is critical to see the failure of the structure as the end result of preceding failures to observe best practices and to approach each phase of construction with the requisite standard for quality in shotcrete construction.
William T. Drakeley, Jr.
Drakeley Pool Company
74 Hickory Lane
Bethlehem, CT 06751
T (203) 263-7919
F (860) 274-7902