Multiscale characteristics of the wetting deformation of Malan loess in the Yan’an area,China

Loess is prone to collapse upon wetting due to its open metastable structure,which poses a considerable threat to the environment,construction processes and human life.In this study,double oedometer tests and scanning electron microscopy and mercury intrusion porosimetry analyses were conducted on loess from Yan’an to study the macroscopic and microscopic characteristics of loess wetting deformation and the underlying mechanism.The wetting collapse of loess under loading depends on the changes in different microstructure levels and elements.This collapse chain reaction is manifested by the dissipation,scattering and recombination of the cementation,deformation and reorganization of the particles,blocking of the pore channels,decrease in the dominant size and volume of unstable macropores(>14μm)and abundant mesopores(2.5-14μm),increase in the volume of small pores(0.05–2.5μm),and volume contraction at the macroscale.This process is dependent on the initial water content,stress level and wetting degree.These findings can facilitate collapsible loess hazard prevention and geological engineering construction.

Model test study on the formation and development of underground erosion ground fissures in the Kenya Rift Valley

The Kenya Rift Valley is relatively prone to underground erosion ground fissures and associated disasters,which gravely hinder local engineering construction and economic development.In this research,we performed field and experimental studies on ground fissures in the Kenya Rift Valley area,and determined the structural characteristics of underground erosion fissures.Based on a geological survey of the area,we generalized a geological model for typical ground fissures and reproduced the intermediate process of ground fissure propagation using a large-scale physical model test.Further,the development process of underground erosion fissures were categorized into four stages:uniform infiltration,preferential infiltration,cavity expansion,and collapse formation stages.During the development of underground erosion fissures,water content was distributed symmetrically along the fissures,and these fissures acted as the primary infiltration paths of water.When the ground collapsed,the increase in negative pore water pressure was greater,whereas the increase in positive pore water pressure was less in the shallow soil;moreover,in the deep soil,the increase in positive pore water pressure was greater than that of negative pore water pressure.Additionally,the earth pressure increment initially increased and then decreased with the development of erosion.During underground erosion collapse,the water content and pore water pressure appeared to increase and decrease rapidly.These results can be employed to predict the occurrence of underground erosion ground fissures and the resulting soil collapse.