Abstract: To accomplish theoretical calculation and qualitative analysis on the ultimate bearing capacity of the flat foundation of unsaturated soil, the bearing capacity of strip foundation in unsaturated soil are calculated. The matric suction and effective stress coefficient are introduced into the equilibrium equation to obtain the slip line equation containing unsaturated parameters, which is further altered into difference equation using the slip line method. The effects of cohesion, internal friction angle, groundwater level and vertical unsaturated velocity on the bearing capacity of strip foundation of unsaturated soil are discussed comprehensively, and the bearing capacity of strip foundation of unsaturated soil under different conditions is calculated. Results show that the ultimate bearing capacity and the average bearing capacity of unsaturated soil flat foundation are greater than those of saturated soil foundation. The matric suction used in the calculation is not a fixed value, but is more in line with the actual situation, hence providing a reference for the calculation of bearing capacity of unsaturated soil foundation.

Key words: unsaturated soil, strip foundation, bearing capacity, slip line, difference equation