Micro-disturbance Construction Technology of Ultra-deep Caisson for Hard Soil Layers in Marine Areas

To minimize disturbance to the surrounding environment when driving ultra-deep caissons through hard soil layers on an artificially reclaimed island in coastal waters, a full-process non-drainage crawler crane mud-sinking technique was adopted for a 35.4 m-deep bottomless beam multi-step variable cross-section caisson in a North Sea seawater discharge pipeline project. Key technical measures included high-pressure water breaking for deviation correction and assisted sinking, as well as pipe jacking grouting wall protection to reduce resistance. By eliminating the bottom beam, improving grab bucket operation methods, and installing grouting pipes at well wall steps to form a slurry sleeve, the project addressed sinking difficulties, tilt risks, and environmental disturbances caused by uneven soft-hard strata, highly permeable sand layers, and high-strength cohesive soil layers. Results demonstrated that eliminating the bottom beam and adopting improved grab buckets effectively penetrated hard cohesive soil layers under non-drainage conditions. High-pressure water jetting through pre-buried pipes at well walls effectively cut the hard soil beneath the cutting edge, achieving deviation correction and assisted sinking. The combination of multi-step well walls with pipe jacking grouting formed a complete slurry sleeve, effectively reducing lateral friction resistance and minimizing disturbance to surrounding soil. The maximum settlement of the surrounding wave wall was only 8 mm. The research findings provide a reference for the micro-disturbance construction of similar ultra-deep well.