| In loess region, most of accidents may be rooted in water content variation of ground soils, and the stress and deformation of loess vary dynamically with its water content, so the reserch on properties of loess under the condition of given water content or wetting does not meet the need of engineering practices. In the area where the stratum of loess is thicker and the possibility of flooding is little, the design employing collapse deformation of loess in a state of saturation will be extravagant, so it is reasonable that compressive deformation and moistening deformation are comprehensively taken into consideration.The cause of loess collapse is attributed to stress and water. Loess in a steady of deformation at a certain stress level, when the stress or its water content is increased, the deformation of loess will increase, or even loess will be failed. Hence, as for as the result of its deformation is concerned, collapse loess upon wetting at a state of certain stress is equivalent to that with applied extra load.Through analysis of the similarity of moistening state, moistening level, moistening history and moistening path to stress state, stress level, stresshistory and stress path of loading, the author introduces a technical term---equivalent moistening stress at the first time and sets up its theoretical foundation. Based on the equivalent deformation principle and compressive, shear and triaxial tests, variation of equivalent moistening stress with initial dry density, initial water content, moistening stress, and moistening water content of loess are probed. The equation to calculate equivalent moistening stress is established. Finally, some comprehensive tests were carried out to prove quantitatively and qualitatively the reasonableness of equivalent moistening stress. So, it lays a solid ground to bring water sensibility of loess into stress-strain research and design theory involving possible collapse potential and possible moistening shear potential.
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