Image-based investigation of deformation and clogging behavior of dredged soil under varying vacuum pressure gradients

Step vacuum preloading, an enhanced vacuum preloading method, has been developed to mitigate clogging-induced poor improvement of dredged soil. However, the deformation and clogging behaviors under varying vacuum pressure gradients remain insufficiently understood. This study investigates the deformation and clogging behavior of dredged soils under varying vacuum pressure gradients (10, 20, 40, and 80 kPa) through four model tests. Particle image velocimetry technology was employed to capture soil displacement fields and analyze strain evolution. The test results indicate that during the first vacuum stage, all tests exhibited horizontal compression near the prefabricated vertical drain and vertical compression in the far field. At a gradient of 10 kPa, deformation shifted to vertical compression with horizontal extension in subsequent stages, whereas higher gradients largely preserved the initial pattern. The clogging zone primarily developed during the first vacuum preloading stage, with its thickness correlated with the initial vacuum pressure. Lower pressure gradients effectively reduced horizontal soil particle migration and compression, thereby mitigating clogging. In addition, empirical equations were proposed to describe the development of the clogging zone under different vacuum pressure gradients. These findings provide direct visual evidence of the spatiotemporal evolution of clogging and offer references for optimizing theoretical consolidation analyses.