Effect of water content on strength of unsaturated loess

Loess suction's contribution to its strength was regarded as the increment of minor principal stress.The increment was gained by analyzing the Mohr's circle geometric figure of loess ultimate stress.When loess was in ultimate state at failure, a computation method of loess strength was put forward under the condition that the cohesion and the internal friction angle synchronously changed, the relationship between the strength indexes and water content was obtained, and the relationship curves of major principal stress and water content of unsaturated loess were analyzed at failure.Computation result shows that the changing rules of computation curves and test curves for major principal stress are same, their difference becomes smaller with the increase of water content, the maximum is 11.63%, and the minimum is 1.59%, so the method is credible.With the increase of water content, when the cohesion and the internal friction angle both change, the computation value of major principal stress is larger than the value only when the cohesion changes, their relative error range is 1.26-2.17 times, which indicates that the influence of water content on the strength of unsaturated loess is significant.