Deep cement mixing (DCM) is a popular in situ soil stabilization method, while the investigation on long-term coupled consolidation and contaminant leaching behavior of cement-stabilized contaminated soil is limited. In this study, axisymmetric physical model tests were conducted to investigate the coupled behaviors of a composite ground, which consisted of a central column made of cement-stabilized arsenic-contaminated marine deposits and surrounding untreated marine deposits. The test results revealed the settlement development of composite ground and the mechanism of load transfer between the DCM column and surrounding soils with increasing loading. The presence of arsenic decreased the strength and stiffness of the DCM column through the reaction between arsenic and hydration and pozzolanic reaction products. With the increase of the water/cement ratio in the DCM column, the concentration level of arsenic in the draining-out water of the composite ground increased significantly, while that in the surrounding soil showed no obvious change, indicating that arsenic mainly migrated directly through the DCM column. A theoretical axisymmetric consolidation model coupling solute transport for composite ground was established and subsequently applied to analyze the test data. The numerical model accurately depicted the pore water pressure, settlement, and spatiotemporal distribution of arsenic concentration in the physical model.

The deep cement mixing (DCM) is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay columns. The investigation on the mechanical behaviour of the DCM samples is limited to either laboratory-prepared samples or in-situ samples under unconfined compression. In this study, a series of drained and undrained triaxial shearing tests was performed on the in-situ cored DCM samples with high cement content to assess their mechanical behaviours. It is found that the drainage condition affects significantly the stiffness, peak and residual strengths of the DCM samples, which is mainly due to the state of excess pore water pressure at different strain levels, i.e. being positive before the peak deviatoric stress and negative after the peak deviatoric stress, in the undrained tests. The slope of the failure envelope changes obviously with the confining pressures, being steeper at lower stress levels and flatter at higher stress levels. The strength parameters, effective cohesion and friction angle obtained from lower stress levels (c(0)' and phi(0)') are 400 kPa and 58 degrees, respectively, which are deemed to be true for design in most DCM applications where the in-situ stress levels are normally at lower values of 50-200 kPa. Additionally, the computed tomography (CT) scanning system was adopted to visualize the internal structures of DCM samples. It is found that the clay pockets existing inside the DCM samples due to uneven mixing affect markedly their stress-strain behaviour, which is one of the main reasons for the high variability of the DCM samples. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).