Performance assessment of a newly developed and highly stable sandy cementitious grout for karst aquifers in China

Grouting operation in karst aquifers is difficult due to the rapid underground water flow in large karst voids, which may scour and destroy the integrity of the slurry before solidification and, therefore, lead to a grouting curtain of poor quality. An important aspect of using grouting material in karst aquifers is to ensure that the slurry has a strong scour resistance and stability. For this purpose, a highly stable sandy cementitious grout is developed for karst aquifers, and the main components of this grout are cement, water, well-graded natural river sand, and sodium metaaluminate (NaAlO₂, as the additive). The sand can improve the grain size distribution of the slurry and further enhance its scour resistance. To assess the mechanical performance of the newly presented grout, the bulk shrinkage rate, water-bleeding rate, setting time, weight retaining ratio, rheological properties, compressive strength and permeability are obtained by a series of indoor experiments. The results show that grout with an additive content of 1.0% has a very low bulk shrinkage rate of nearly 0% and a high weight retaining ratio of 85% under water scouring. All the physical and mechanical properties of the grout meet the requirements of curtain and consolidation grouting, including the requirements that the 28-day compressive strength of the grout reaches approximately 5–10 MPa and the permeability of the grout stone is less than 7.7 × 10^–7 cm/s. Compared with clay–cement paste and cement–water–glass paste, using sandy cementitious grout can reduce the material costs by at least 43.1%. Finally, engineering applications in a dam foundation surrounded by karst aquifers are conducted, and the seepage problem is solved.