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Frequent occurrence of landslides induced by rainfall or irrigation has seriously threatened the urban and rural development in the Loess Plateau, China. The increase in pore water pressure has been identified as a key factor for understanding wetting-induced loess slopes failures. However, experimental studies are limited regarding the increase in pore water pressure of the collapse loess from an initial negative value until failure occurs under constant total stress condition. An old landslide with progressive retreat development at an early stage of the construction of the Lvliang Airport was selected as a case study. Field surveys including exploration wells and boreholes revealed very fresh sliding shear planes and clearly visible cracks, suggesting the creeping movement of the old landslide. In case of heavy rain or long-term rainfall, this old landslide may be resurrected, threatening the stability of the airport site. To examine the mechanism of the failure induced by wetting for this unsaturated loess landslide, loess specimens were taken from the field, followed by performing a series of laboratory tests, including triaxial shear tests at constant matric suctions and wetting tests at constant deviator stresses. The test results revealed that the wetting-induced deformations of the loess included volume and shear deformations, reflecting compression and shearing behaviour induced by wetting. The failure behaviour of the loess along a wetting path was dependent on the stress level and the loss degree of matric suction as well as the hydro-mechanical path, and could be well described by the linear form of the Mohr-Coulomb strength theory. On this basis, the threshold value of the stress level was identified, which could be used to judge whether the wetting-induced failure of the loess occurs. The threshold value of matric suction at failure was also identified to analyse the loss degree of matric suction from stable conditions to failure. The mechanism of the failure of the soil due to wetting revealed from the present study could interpret the rainfall-induced landslide in unsaturated loess. [ABSTRACT FROM AUTHOR]

The effect of deterioration on the reliability of slopes of various service periods has seldom been considered explicitly in the current reliability approach in slope engineering. Constant annual failure probabilities, that are commonly used in practice to evaluate reliability of a slope over a given expected service period, may not be capable of capturing the deteriorating characteristics of slopes. This paper presents a procedure to model probabilistically the deteriorating effect on the failure probability with time. Past performance of geotechnical systems of similar nature is systematically analyzed to evaluate the failure probabilities for systems of different ages and for different expected service periods. The method was applied to the stability performance of soil cut slopes in Hong Kong. Through this exercise, the reliability of slopes of different ages for different future service periods can be reasonably estimated. As such, a planner can benchmark a design standard and plan a slope improvement program in a more effective and defensible way. [ABSTRACT FROM AUTHOR]