Laboratory Test for Efficient and Cost-Effective Design of CPR Grouting to Improve Soft Soils

CPR grouting is a technique used to improve soft clayey soils through vertical drains and the injection of low mobility grout. CPR grouting still faces limited acceptance among certain practitioners, primarily due to the doubtful process of soil consolidation induced by grout injections. The aim of this study is to investigate the behavior of soft clays subjected to CPR grouting, attempting to enhance the theoretical understanding of the technique and evaluating the related consolidation process. The technique is studied using a special laboratory apparatus, in which a latex membrane is inflated within a soil specimen to simulate the grout injection. In this paper, we introduce the modified equipment, its components, describe the experimental procedure, outline the sample preparation, and present the experimental results. The key findings of this study suggest that injection pressure appears to be unrelated to the expanded volume, the peak injection pressure is similar across all tests, and larger injected volumes does not necessarily produce higher amount of soil consolidation. Although laboratory conditions are not identical to field conditions, laboratory tests indicate that grout injection does lead to consolidation in the soft clay, offering a valuable empirical guidance for a more cost-effective grouting design plan.