Forensic Study of an Earth Retaining System Failure

Forensic civil engineering can be considered as “The investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property." This paper presents a case history of analysis and review of a touch pile system failure during deep excavation for a commercial building (3 basements, ground floor and 8 floors) near Metro Station Kaloor, Kerala. An excavation to a depth of 10 m from ground level was required to reach up to foundation level of the structure and to retain soil to facilitate the excavation; a retaining wall formed using touch pile system, where in multiple piles almost touching each other to support a change in elevation along with strutting was adopted. As the excavation was in progress, the shoring system collapsed at 9.30 pm on April 19, 2018. A technical expert committee was formed by District Disaster Management Authority, which comprised of authors to evaluate the reasons of failure. The immediate restoration steps adopted, various tests conducted to analyze the reasons for collapse, temporary measures adopted and precautions to be taken for future construction are presented. From the study, it was found that the strutting system was inadequate to take up the lateral thrust from the touch piles and soil at the dredge line has turned out to be very soft and has caused considerable loss of strength of the interface soil. Subsequent increase in unsupported length of pile is also a reason for the failure of retaining system.