| The characteristics of soil particles(size,shape,combination and aggregation morphology,surface properties)and the interaction between particles and water determine the physicochemical process of soil particle water air interface,and then affect the water holding capacity,shear strength and other soil and water mechanical properties of soil.At present,the research on particle characteristics,soil hydraulic process and soil mechanical process has been very mature,but the research on the influence of particle characteristics and interaction between particles on Soil and water mechanical characteristics is still very scarce from the macro and micro perspective.In addition,few scholars quantitatively calculate the changes of particle surface electric field,particle physical and chemical stress and soil shear strength caused by pore salt solution The control function of degree.Therefore,in this paper,Shaximiao Formation sandy loam to clay loam series texture purple soil in Chongqing area as the research object,setting different pore fluid environment(pure water,0.5,1.0,2.0 mol / L)The physicochemical stress of saturated / unsaturated purple soil in different pore fluid environments was quantitatively calculated.The particle characteristics,mineral composition,interaction between particles,water holding capacity and shear strength of purple soil with different texture were compared and analyzed,and the mechanism of the effect of soil particle characteristics and interaction between particles on Soil and water mechanical behavior of purple soil was discussed,The mechanical mechanism of interaction between purple soil particles and water is clarified.The main results are as follows:(1)Soil particle characteristics and mineral composition significantly affect the soil and water mechanical properties of purple soilSoil particle characteristics and mineral composition significantly affect the soil and water mechanical properties of purple soil.For the shear strength of purple soil,the difference of mineral composition and particle composition of purple soil makes the shear strength of purple soil in high saturation stage as S6(loam)> S4(silt loam)> S3(sandy loam)> S2(loam)> S5(clay loam)> S1(clay loam),in which the cohesion of S1,S2 and S5 is significantly higher than other soil samples,and the internal friction angle is smaller than other soil samples.In addition,the variation range of internal friction angle and shear strength of S1,S2 and S5 with saturation is significantly larger than that of other soil samples due to the difference of particle composition and mineral composition of purple soil.For the water holding capacity of purple soil,the differences of clay content and pore structure in the middle and low suction stage make the overall performance of water holding capacity as follows: S1>S5 > S2> S4>S6 >S3;in the high suction stage,the differences of mineral composition and surface properties of purple soil make the water holding capacity of different texture purple soil The overall performance is: S1>S5>S2>S6 >S3 >S4.In addition,the fitting results of water characteristic curve model showed that BC model and VG model had the best fitting effect on the water characteristic curve of middle low suction stage and full suction stage;S1specific water capacity increased first and then decreased with the increase of soil water suction,while S2,S3,S4,S5 and S6 specific water capacity decreased with the increase of soil water suction.(2)The internal friction angle of saturated purple soil is increased by pore solution salt solution,and the shear strength of saturated purple soil is improvedCompared with pure water saturated purple soil,the pore salt solution reduces the thickness of the water film between particles,increases the internal friction angle and shear resistance,and increases the shear strength.On the other hand,the pore salt solution will cause the change of surface potential and physical and chemical stress between particles,and the cohesion will also change.The effect is related to the characteristics of particles and mineral composition.The differences of grain characteristics and mineral composition of S1,S2 and S3 make the pore fluid saturated with salt solution.The cohesion of S1 sample increases slightly,while that of S2 and S3 sample decreases slightly.The results show that the shear strength of S1 and S2 saturated samples increases with the increase of ion concentration in pore fluid,while the shear strength of S3 saturated samples has no obvious change with the increase of ion concentration in pore fluid.(3)The effect of pore salt solution on shear strength increases with the decrease of saturationThe results show that the shear strength of unsaturated purple soil with different pore fluid environment is higher than that of unsaturated purple soil with pure water under the same saturation when the pore fluid environment is 1mol / L sodium chloride solution,and the increase range increases with the decrease of saturation.The reason is that in the low saturation stage,the capillary force,surface tension and matrix suction caused by the liquid bridge between particles reduce the particle spacing,and the effect of the change of physicochemical stress caused by the pore solution is enhanced.To sum up,the soil particle characteristics,mineral composition and the type and strength of the interaction between particles will affect the soil and water mechanical properties of purple soil.The effect of particle characteristics and mineral composition on the soil / water mechanical behavior of purple soil is different.The pore salt solution changes the surface potential of particles,the thickness of the water film on the surface of particles,and the physical and chemical stress between particles It shows the change of soil strength.The results of this study can provide data support for soil water management and soil and water conservation in purple soil area,and promote the sustainable development of cultivated land resources. |
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