QA/QC plan and evaluation of field strength and permeability value for deep cement mixing

Abstract

Deep Cement Mixing (DCM) is widely used to improve the strength and stiffness of soil by mixing it with cement. When DCM is used as a low permeability barrier for water cut off, permeability must be tested in addition to the usual strength values. One concern in DCM construction is the quality assurance and quality control (QA/QC) of this technique to ensure uniformity along the DCM column. It is even more crucial when low permeability is required for the DCM column to be used as a seepage cut-off in an earth bund, in addition to its strength requirement. In this application, the DCM columns require low permeability and adequate strength. In this paper, two QA/QC aspects will be evaluated: the operational control and the evaluation of the treated DCM column. The operational control in terms of mixing time, cement content, rotation speed and mixing energy will be studied to gain an understanding of how strength and permeability changes with the variability of the soil with depth. A rational QA/QC plan will be briefly proposed to ensure a consistent and rational method is developed for the evaluation of the strength and permeability variation of the treated soils over the area and the depth. These will help in the development of acceptable characteristic value for the geotechnical parameters of soils treated with DCM (in line with Eurocode 7).