Behavior of Large Geotextile Mat Cofferdam with a New Arrangement of Geotextile Reinforcement Stiffness Lying on Soft Sediments

This paper proposes a new arrangement of geotextile reinforcement stiffness for large geotextile mat cofferdams that often suffer from the failure of the bottom layer mat. Cofferdams using this new reinforcement method are poorly understood and require a thorough study to explore their behavior lying on soft sediments which is the prevailing situation for land reclamation projects. This paper investigates the performance of large geotextile mat cofferdams with this new type of reinforcement using a systematic numerical study. The numerical finite element models (FEM) were validated against experimental observations and field test data, where the soil flow mechanism and the cofferdam deformation were investigated. Through discussion of the failure mechanism, limiting stack height, and geotextile tension distribution in a systematic parametric study, it was concluded that the effects of the geotextile stiffness of the base mat of the cofferdam, the strength of soft clay, and the width of cofferdam base were significant, and the negligible parameters include the strength of sand fill and cofferdam slope. Based on the results, it was found that large geotextile mat cofferdams with this new type of reinforcement demonstrate two types of failure mechanisms: so-called local and global failures. An equation is proposed to identify these two different failure mechanisms, which consider the properties of the sand fill, the underlying soft sediment, and the geotextile material. A general guideline is proposed to help design large geotextile mat cofferdams with this new reinforcement, using which both the limiting stack height and the safety factor of cofferdam can be evaluated. (c) 2020 American Society of Civil Engineers.