Fluid–structure interaction in underwater blasting demolition of cofferdam structures: a case study of three gorges phase III RCC cofferdam

A matter of considerable interest and urgency is the mechanical mechanism that controls the motion of fragmented blocks in the underwater explosive demolition of cofferdam structures. Given that the demolition of the Three Gorges Project’s Phase III RCC cofferdam employed a blasting scheme primarily based on "pre-set concentrated charge chambers for toppling blasting, supplemented by drilling and fragmentation blasting at both ends," the cofferdam blasting with pre-set concentrated charge chambers and the movement process of the dam body in water are of significant research value. Through the development of a Fluent-EDEM coupling program based on the UDF interface, a numerical simulation is conducted on the blasting demolition process of the Three Gorges Project’s Phase III RCC cofferdam. The study involves the simulation of the fragmentation zone induced by the designed sequential detonation of pre-planted charge chambers, an analysis of the complete structural motion from loss of stability to ground contact, and a revelation of the mechanical mechanism governing the coupled interaction between blasted blocks and water. Analysis of field vibration monitoring data from the blast reveals that the simulated impact time of the cofferdam’s toppling aligns with the actual recorded time. This validates the successful application of the Fluent-EDEM coupled model in analyzing the blasting effects for the Three Gorges Project’s Phase III RCC cofferdam. The methodology demonstrated herein offers positive implications for the design, construction, and safety protocols of similar future engineering projects. (1) The Fluent-EDEM coupled program developed based on the UDF interface was used for numerical simulation of RCC cofferdam demolition blasting, verifying that this numerical method can be applied to large-scale underwater demolition projects. (2) The simulation modeled the fragmentation range of the cofferdam under sequential detonation of pre-set charge chambers according to the designed initiation sequence, and analyzed the motion process from structural instability to ground impact. (3) The mechanical mechanism of the coupled interaction between blasted fragments and water flow was revealed.