Abstract: Dyke intrusion is a relatively common geological phenomenon. The intrusive dykes and their weathered layer have great effect on the seepage field and stability of the slope. However, few studies have been reported on this aspect. The intrusive volcanic dykes and their weathered crust are widely distributed in the volcanic rocks in areas of about 500,000 km2 along the southeastern coast of China, which greatly affect the stability of the residual soil slopes in this area. In this paper the Zhonglin landslide was chosen as the object to study the impact of dyke and its residual soil on seepage and stability of residual soil slope. Zhonglin landslide is mainly composed of tuff and its residual soil and intrusive granite dyke and its residual soil which was found at the crest of a slope. Firstly, by soil column tests we obtained the difference between two types of residual soils with regard to their infiltration property and rules of two in the rainfall. Then the Seep/W in Geo-studio software was applied to retrieve soil column rainfall experiment to obtain the unsaturated seepage parameters of both types of soil to apply it to the numerical analysis of the whole slope seepage field. At last, Slope/W in Geo-studio software was used to analyze the slope stability, which revealed the impact of weathered crust of granite dyke on slope stability. The results showed that the permeability of the granite residual soil in weathered layer of intrusive dykes was better than tuff residual soil. Under the effect of weather conditions like typhoon and rainstorm, the rain water infiltrated rapidly through weathered layer of the intrusive granite dyke and flew along the strong weathered-residual soil interface into the tuff residual soil layer, which resulted in the rapid rising of the groundwater level at the junction of the intrusive granite dyke and the tuff residual soil layer and the pore-water pressure grown from negative to positive rapidly so that the slope was more likely to lose stability at this location. The results in this paper may provide theoretical background for the stability evaluation and treatment for the residual soil slope invaded by granite dykes and weathered crust in the China southeast coastal region.

Key words: residual soil slope, dike intrusion, soil column tests, unsaturated seepage field, stability