Abstract: The completely decomposed granite is widely distributed. In deep foundation engineering, slurry is often used to prevent bore-hole caving in soil. However, the strength of mud cake is low, which will lead to the reduction of pile axial capacity. To improve the axial resistance of the pile in the completely granite stratum, post grouting is used to reinforce the soil around the piles. The direct shear tests were used to study the influence of mud cake effect, soil around piles with different cement content and the roughness of the shaft on the shearing behavior of the pile-soil interface. The results show that the interface strength between pile and soil is greatly reduced due to the lubrication of the mud cake. Grouting reinforcement can effectively improve the shear strength of pile-soil interface, but the behavior becomes brittle. Both the internal friction angle and the cohesion of the interface increase with an increase of the roughness of shaft.

Key words: Completely Decomposed Granite, Direct Shear Test, Mud Cake, Cemented Soil, Shaft Roughness