Effects of Creep on Grout Efficiency in Clay

Existing structures can deform and damage due to newly constructed underground structures, which induces surrounding soil deformation due to ground loss and stress relief. Compensation grouting is an active control method widely used in practice due to its advantages of using readily accessible material, a convenient construction process, and the ability to make real-time adjustments compared with passive control methods. However, in current studies, consolidation settlement is commonly considered the primary factor causing the gradual loss of the grouting effect. In this study, a numerical model exhibiting an elastic viscoplastic behavior was established using the finite-difference method to investigate the influence of creep on grout efficiency. The model parameters were first calibrated by comparing them with the measured and computed results of the grouting tests conducted in a consolidometer. Then, the model was used to perform parametric studies, to investigate the influences of initial overconsolidation ratio (OCR) and grout volume. The results show that the grout efficiency, defined as the ratio between total displacement and ideally anticipated heave displacement after grouting, is lower than that when only consolidation is considered. It can decrease up to 2.5 times over 3 years when the OCR is set to 1.00 and the grout volume is 1 mL. This implies that neglecting creep behavior may lead to a nonconservative design for compensation grouting in the long term. The creep control efficiency, defined as the ratio between the settlement induced by creep and that induced by consolidation, has been newly proposed to evaluate the influence of soil creep. It is found that the creep control efficiency of OCR = 1.00 serves as an upper limit under different OCRs because of the significant consolidation settlement in underconsolidated soil and the small creep settlement in overconsolidated soil. Therefore, the creep control efficiency value of OCR = 1.00 can be recommended for conservative design estimates when determining the final grout efficiency.