Case Study: Carsington Dam (United Kingdom, 1984)

The Carsington Dam’s sliding failure in June 1984 as it neared completion resulted in neither flooding nor loss of life but represented the culmination of error-filled design and construction processes. The design team did not meet the geotechnical standard of care, failing to consider progressive shear failure, probable slip surfaces, preexisting shear planes within the core clay, and acid drainage problems (which led to four construction workers dying of CO2 poisoning). The designers also included a sliding-prone “boot” within the clay’s core. The contractor made mistakes during construction, most notably compacting the embankment material well wet of optimum, but had well-founded concerns about the design and even hired an outside consultant to investigate them. However, while the consultant validated these concerns, the designer ignored them. The resulting failure led to an extensive forensic investigation that led to improved design procedures for dams, most notably regarding the brittleness of clays, progressive failure within embankments, and finite element modeling (FEM) analyses. These collectively proved valuable in designing and constructing a replacement Carsington Dam, which stands to this day.