A new solution for water-tightening of the cemented sand-gravel (CSG) hardfill dams

摘要

The hardfill dams comprised of the cemented sand-gravel (CSG) mixtures and are widely used in worldwide due to many considerable advantages. As the CSG mixtures in the main body of hardfill dam have a higher permeability, the water-tightening of these dams is a main concern. In this paper, a specific type of the CSG mixture with low permeability was achieved to implement in the impervious zone of hardfill dams. To this end, various types of CSG mixtures were prepared by blending two native sand and gravel soils with different amounts of kaolinite or bentonite additives in the presence of various cement contents. The compaction properties, uniaxial compressive strength, permeability, and scanning electron microscope images of the mixtures are measured. According to the results, when the soil fraction in the cemented mixture 10% kaolinite additive, the maximum strength was attained. On the other hand, the bentonite disturbs the cement hydration in the mixture, and the strength of mixtures, especially in the mixtures with high cement content, decreases with increasing the bentonite content. The permeability of mixtures is related to the amount and interaction between cement and fine additive in the mixture. The permeability of both cemented sand and cemented gravel mixtures considerably decreases with increasing the bentonite additive. However, the kaolinite additive has a limited influence on the permeability of cemented gravel mixtures. For attaining a low permeable CSG mixture to implement for water-tightening the hardfill dams, the mixture involving a higher amount of bentonite (with a weight ratio of 30%) in the presence of adequate cement (higher than 10%) is recommended.