Dewatering and stress characteristics of stacking geotextile tubes under dry and underwater conditions

By filling and stacking geotextile tubes, cofferdams can be constructed with high efficiency and relatively low economic costs. However, the cofferdam construction at river estuary area may face significant challenges due to the limited time period of tide ebbing (e.g., 4 ∼ 6 h at Qiantang river estuary, Zhejiang, China) and the complexity of construction conditions (e.g., filling and stacking under dry and underwater conditions). First, tensile tests were carried out on the geotextile to obtain the tensile strength and stiffness of the material along the warp and weft, respectively. Subsequently, self-weight and stacking dewatering tests were conducted in a model container under both dry and underwater conditions. During the test, the pore water pressure, the height and strain of geotextile tube, and the volume of water discharge were monitored. Model test data revealed that, using an 80% dewatering degree as the formation criterion, the formation time of a geotextile tube is 4 ∼ 6 times longer for the underwater condition when compared to the dry condition. The earlier the stacking pressure was applied, the greater the final dewatering volume was achieved along with the reduced formation time. However, the early application of stacking pressure rendered higher risk of tensile failure of the geotextile.