Disturbance to adjacent marine deposit by offshore DCM construction

Abstract

During deep cement mixing (DCM) construction, the ground adjacent to the DCM operation zone could be affected due to lateral soil movements and construction disturbances. For offshore DCM construction, multiple mixing shafts arranged in parallel at the DCM barge allow DCM panels to be constructed in a single operation but may disturb the surrounding marine soil. In this study, the degree of disturbance and the potential disturbance zone are characterized using cone penetration tests with porewater measurement (CPTu). The CPTu test results in marine deposits adjacent to offshore DCM panels before and after construction were used to evaluate the impact of DCM construction on CPTu raw measurements, soil type and soil parameters. By interpreting the in-situ soil states, the impacts on deformation and strength characteristics and the impact range were evaluated. A theoretical solution is also developed to examine the lateral displacement and stress increments caused by DCM construction. DCM construction in general caused adverse disturbance to the surrounding marine soils, decreasing the overconsolidation ratio while increasing the permeability. A more substantial decrease in sleeve friction and increase in pore water pressure was observed in coarse-grained soils.