Experimental investigation into the salinity effect on the physicomechanical properties of carbonate saline soil

For engineering structures with saline soil as a filling material,such as channel slope,road subgrade,etc.,the rich soluble salt in the soil is an important potential factor affecting their safety performance.This study examines the Atterberg limits,shear strength,and compressibility of carbonate saline soil samples with different NaHCO3 contents in Northeast China.The mechanism underlying the influence of salt content on soil macroscopic properties was investigated based on a volumetric flask test,a mercury intrusion porosimetry(MIP)test,and a scanning electron microscopic(SEM)test.The results demonstrated that when NaHCO3 contents were lower than the threshold value of 1.5%,the bound water film adsorbed on the surface of clay particles thickened continuously,and correspondingly,the Atterberg limits and plasticity index increased rapidly as the increase of sodium ion content.Meanwhile,the bonding force between particles was weakened,the dispersion of large aggregates was enhanced,and the soil structure became looser.Macroscopically,the compressibility increased and the shear strength(mainly cohesion)decreased by 28.64%.However,when the NaHCO3 content exceeded the threshold value of 1.5%,the salt gradually approached solubility and filled the pores between particles in the form of crystals,resulting in a decrease in soil porosity.The cementation effect generated by salt crystals increased the bonding force between soil particles,leading to a decrease in plasticity index and an improvement in soil mechanical properties.Moreover,this work provides valuable suggestions and theoretical guidance for the scientific utilization of carbonate saline soil in backfill engineering projects.

Mapping of geomorphic dynamic parameters for analysis of landslide hazards:A case of Yangbi river basin on the upper Lancang-Mekong of China

Landslides are common hazards in orogenic belt areas.However,it is difficult to quantitatively express the driving effects of tectonic uplift and stream erosion on the occurrence of landslides on large spatial scales by conducting field investigations.In this study,we analyzed a relatively large region that extends over the Yangbi River basin on the upper Lancang-Mekong in China.A series of quantitative indices,including kernel density of the landslide(KDL),hypsometric integral(HI),steepness index(ksn),stream power(?),and stream power gradient(ω)were used to explore the promoting effects of tectonic uplift and stream action intensity on landslides by mapping geomorphic dynamic parameters combined with actual landslide data.The analysis showed that the HI value in the highest landslide risk area was approximately 0.47,and that the KDL in the region can be expressed as a function of steepness or stream power gradient of the channel network,namely,KDL=0.0127 Ln ksn-0.0167(R2=0.72,P<0.001)and KDL=0.0219 Lnω-0.0558(R2=0.21,P<0.02).Therefore,the lower reach of the Yangbi River basin,with higher steepness and stream power gradient,usually has a high uplifting rate and stream incision that drives landslides and causes the entire river network system to be in a stage of longterm active erosion.Furthermore,the results suggest that sediments were being rapidly discharged from the steep tributary channels to the mainstream.This practical situation highlights that the downstream area of the river basin is a high-risk area for landslide hazards,especially in association with heavy rainfall and earthquakes.