Optimization design and characteristic of retarding and low-early-strength grouting material for capsule grouting technology: laboratory and field evaluation

Abstract

Capsule grouting technology (CGT) is developed to control the deformation of underground structures induced by the adjacent underground construction. Meanwhile, multiple grouting is necessary for CGT to achieve the desired effect as the heterogeneity and complexity of the soil. This study proposed a retarding and low-early-strength grouting material (RLGM) to realize the multiple grouting of CGT. Response surface methodology (RSM) was applied to study the effects of formulation on the workability and mechanical strength of RLGM, then the microstructures of optimal RLGM were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Moreover, the analysis of variance (ANOVA) models were developed to predict the performance of RLGM. Results show that different formulations lead to significantly different contributions to RLGM performance, and each factor shows positive or negative synergistic effects with others. Etidronic acid retarder (EAR) plays a dominant role in the initial setting time, and the correlation between the initial setting time and compressive strength presents an obvious negative correlation. Based on the multi-objective optimization considering the multi-performance requirement of grouts for CGT, the optimized RLGM mix proportion is obtained that water-cement ratio of 1, bentonite (B) of 27.5%, polycarboxylate superplasticizer (PCE) of 0.28%, EAR of 0.75%. Accordingly, the initial setting time and 10 days compressive strength of the optimal RLGM achieve a highly desirable goal, that is, 124.1 h and 0.2 MPa, respectively. Finally, the field trial result confirms that RLGM for CGT shows good working performance during grouting construction.