Unraveling the hydraulic properties of loess for landslide prediction:A study on variations in loess landslides in Lanzhou,Dingxi,and Tianshui,China

Loess has distinctive characteristics,leading to frequent landslide disasters and posing serious threats to the lives and properties of local re sidents.The involvement of water repre sents a critical factor in inducing loess landslides.This study focuses on three neighboring cities sequentially situated on the Loess Plateau along the direction of aeolian deposition of loess,namely Lanzhou,Dingxi,and Tianshui,which are densely populated and prone to landslide disasters.The variations in hydraulic properties,including water retention capacity and permeability,are investigated through Soil Water Characteristic Curve(SWCC)test and hydraulic conductivity test.The experimental findings revealed that Tianshui loess exhibited the highest water retention capacity,followed by Dingxi loess,while Lanzhou loess demonstrated the lowest water retention capacity.Contrastingly,the results for the saturated permeability coefficient were found to be the opposite:Tianshui loess showed the lowest permeability,whereas Lanzhou loess displayed the highest permeability.These results are supported and analyzed by scanning electron microscopy(SEM)observation.In addition,the water retention capacity is mathematically expressed using the van Genuchten model and extended to predict unsaturated hydraulic properties of loess.The experimental results exhibit a strong accordance with one another and align with the regional distribution patterns of disasters.

Experimental investigation into temperature effect on hydro-mechanical behaviours of bentonite

The bentonite barrier of underground repositories for high-level radioactive waste will be hydrated by the groundwater while it is subjected to high temperatures due to the radioactive decay of the wastes. These changes of temperature affect the hydraulic and mechanical responses of bentonite, which has important effects on design and performance of repositories. The temperature influence on the hydro-mechanical behaviour of bentonite was studied in this paper by experiments, which were carried out with the Spanish FEBEX bentonite compacted at dry densities expected in the＇ repository （from 1.5 to 1.8 Mg/m^3）. The dependence of the swelling strains of bentonite on the temperature has been measured from 30℃ to 90 ℃. At high temperatures the swelling capacity of clay slightly decreases. Also, a clear decrease of swelling pressure as a function of temperature was observed for the same dry densities. Nevertheless, the deformation of bentonite is more dependent on the stress than the temperature. An increase in the permeability of water saturated bentonite with temperature has also been detected. The water retention curves of bentonite compacted at different dry densities were determined under isochoric conditions and in the range of temperatures from 20 ℃ to 120℃. For a given density and water content, the suction decreases as the temperature increases at a rate, which is larger than the one predicted on the basis of water surface tension changing with temperature. Mechanisms related to the physico-chemical interactions that take place at microscopic level, in particular the transfer of interlayer water to the macropores triggered by temperature, seem to explain qualitatively the experimental observations.

The soil configuration on granite residuals affects Benggang erosion by altering the soil water regime on the slope

A permanent collapsing gully,locally called Benggang,formed on slopes with deep granite red soil and is a type of unique gully erosion widely prevalent in southern China.Three different soil configurations(SC),ie,red-transition-sandy(SC I,the transition is the soil layer between the red soil and the sandy soil layer),transition-sandy(SC II)or sandy(SC III)are usually present in the soil profile of the Benggang slope.However,little attention has been paid to impacts of SCs on the triggering of Benggang erosion.In this study,we aimed to explore the relationships between soil water content(SWC)and triggering of Benggang erosion under different SC conditions.The soil properties of different soil layers were measured and the SWC at depths of 20,40,60,and 80 cm were monitored at 5-min intervals along a typical Benggang(SC I)during 2016-2018.The SWC of Benggang slopes with different SCs were simulated by VADOSE/W model.Results showed that the red soil layer had a higher water retention capacity and shear strength than the sandy soil layer.Even if the SWC is higher(e.g.,0.42 cm^(3)/cm^(3))at red soil layer or transition layer,the corresponding shear strength is greater than that of sandy soil layer with a lower SWC(e.g.,032 cm^(3)/cm^(3)).Relationships between shear strength and SWC of different soil layers indicate that Benggang erosion is triggered by an increase in the SWC in the deep sandy layer.Results also showed that differences exist in the SWC distribution among the different SCs.The SWC is higher in topsoil than in deeper soil in SC I and SC II,while in SC III,the opposite trend is observed.These results revealed that the presence of the red soil or transition layer can reduce the infiltration of rainwater into the deep sandy layer,thus can reduce the possibility of collapse.Our results show that the SC affects the stability of the headwall,and results provide great significances to guide the mitigation of Benggang erosion.