Abstract: The physico-mechanical properties of tailings dam material will be changed by capillary water, which will effect on the stability of tailings dam. The research on this field is barely reported at home and abroad. Therefore, in-situ sampling and laboratory geotechnical experiments on tailings dam material are conducted for testing its physical properties, and the rising test of capillary water is carried out about 6 months by the self-designed layered sampling device for capillary fringe; and the physico-mechanical properties of tailings sand in capillary water fringe are gained by layered sampling and soil testing. Furthermore, the variation characteristics of physico-mechanical indexes such as water content, gravity density, cohesion, internal friction angle and shear strength with the height of capillary water have been systematically studied. The results show that water content and gravity density decreased with the height of capillary water. The relationships of cohesion and internal friction angle with the height and water content increases firstly and then decreases. However, the relationship of internal friction angle with water content is different from the traditional conclusion that the relationship is decreasing with water content. This difference is caused by surface properties of the tailings particles which are different from that of sands. The surface of tailings particles is dirtier than that of sands and is covered by mineral and something else which is soluble in water. The research results also show that the effect of capillarity on shear strength is great, and the relationship of shear strength with the capillary height increases firstly and then decreases. As we known, the gravity is one of major causes of tailings dam failure. In a real tailings pond, there is full of industrial wastewater which has bigger surface tension than pure water, and the bigger surface tension will cause higher capillary water in tailings dam. In fact, the capillary water will result in weight gain of tailings dam which is danger to the stability of tailings dam. Therefore, it is more important to analyzing the stability of tailings dam by researching on the physico-mechanical properties of dam body materials in capillary water fringe of tailings dam. This research will put forward a new idea to the dam and slope engineering, and laid a foundation for establishing a new method and theory to analyzing stability of tailings dam by considering the role of capillarity.

Key words: tailings dam, capillary water fringe, Physico-mechanical properties