Characteristics Of Soil Salt Crust Formed By NaCl,Na₂SO₄ And Its Mixed Salt With Aeolian Soil From Gurbantunggut

Sandy desertification is an important part of desertification,which has caused serious damage to the ecological environment in northwest China.Moving sand dunes will not only lead to the inundation of villages,farmland and roads,but also cause large-scale sandstorms,which will cause great harm to the transportation of sand areas and to the agriculture of oasis areas.Therefore,the prevention of sandy flow is an urgent ecological problem.Soil salt crust can change the loose structure of sandy soil,improved the resistance of sandy soil to wind erosion,contained the flow of sandy soil.Three kinds of ions(Na⁺,Cl^-,SO₄^2-)with higher content in sandy soil were selected for this salt crust experiment.It was set six salt concentration gradients,which was 0.1,0.5,1,1.5,2,2.5 mol/L in the experiment,and set eleven salt mix ratios(NaCl:Na₂SO₄),0:10,1:9,2:8,3:7,4:6,5:5,6:4,7:3,8:2,9:1,10:0,respectively.The following conclusions were obtained:1)The compressive strength of NaCl,Na₂SO₄and mixed salt crust were affected by salt concentration,salt type and crystal morphology.When the salt concentration was low,the volume of crystals deposited on the sandy soil particles was small,and the crystals spoted on the surface of aeolian soil particles.The compressive strength of the salt crust was increased by the increasing friction force between aeolian soil particles caused by salt crystals deposited on the sandy soil particles.When the salt concentration was?1.5 mol/L,the compressive strength of three salt crusts had different trend curves with the salt concentration increasing.The compressive strength of NaCl crust increased with the salt concentration increasing,and NaCl crystals deposited in the salt crust were cubic or cluster;the compressive strength of Na₂SO₄crust decreased with the increasing of salt concentration,and Na₂SO₄crystals in the salt crust were needle,rod,hairy globular and other,crystals destroyed the salt crust;the compressive strength of mixed salt crust is a waving curve with the salt concentration increasing,the crystal's shape was more complex in the mixed salt crust.2)The surface morphology of the salt crust was influenced by salt specie and salt concentration,and the Na₂SO₄crystals would destroy the salt crust surface.There were obvious differences in the surface morphology between NaCl crust,Na₂SO₄salt crust and the mixed salt,and the morphology of mixed salt crusts were complicated.The shape of NaCl crust on the soil surface was crusty,and it became a rough salt layer when the concentration exceeded 2 mol/L;the shape of Na₂SO₄crust surface was a half-moon patch,and it was a transparent crystals layer when the concentration exceeded 2 mol/L.The surface of the NaCl salt crust will not be broken.The surface of the Na₂SO₄salt crust is usually broken,however,when the salt concentration was?1mol/L,the surface of the Na₂SO₄salt crust wouldn't be broken too.Damage degree of mixed salt crust was affected by the salt concentration and salt mixing ratio.3)The toughness of salt crust was affected by salt concentration and mixing ratio.The number of salt crust layers is independent of salt concentration and mixing ratio.Under NaCl,Na₂SO₄single salt and salt mixing ratio between 1:9-5:5,with the increase of salt concentration,the toughness of salt crust increased firstly,then decreased and then increased,.Under other salt mixing ratio,the toughness of salt crust increased and then decreased with the increase of salt concentration.Mixed salt crust had one or two salt layers,only when the salt mixing ratio was 5:5,the salt crust had three salt layers.4)The crystals'shape of mixed salt formed in sandy soil were complex,and two kinds of salt crystals were fused each other.The crystals of mixed salt had several kinds of shapes on the aeolian soil,such as rod,ladder,sheet and cauliflower.Different kinds of salt crystals adsorbed and fused each other,and the irregular edges of large salt crystals provided deposition points for the small crystals.5)Comprehensive analysis of the results of crust compressive strength,crust thickness,salt distribution,mass of large particle cement,the salt crust with the best wind corrosion resistance was the condition of 1.5 mol/L and salt mixing ratio 5:5.