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Ningxia University (2022)

Study on the Influence of Dry-Wet Cycle on Gravel Degradation in the Arid Zone of Central Ningxia

安文举

Titre : Study on the Influence of Dry-Wet Cycle on Gravel Degradation in the Arid Zone of Central Ningxia

Auteur : 安文举

Grade : Master 2022

Université : Ningxia University

Résumé
Aiming at the unclear mechanism of soil coarse particle degradation in dry far mLand in the central arid zone of Ningxia,through field investigation,sampling,and field and indoor dry-wet cycle experiments,from microscopic pore growth to mineral composition changes,the macroscopic In order to provide a data reference for the rapid deterioration of soil coarse particles in the arid zone of central Ningxia,we systematically studied the effect of drying and wetting cycles on the deterioration of soil coarse particles.The main conclusions are :(1)In the initial state,the degradation degree of soil coarse particles of different particle sizes is generally low,the surface of the coarse particles is relatively flat,and the pore connectivity is poor ;after the drying and wetting cycle,the degradation degree of soil coarse particles is generally higher than the initial state.Pass length up to 40μm.The number of pores of coarse particles has increased significantly compared with the initial stage,but the average pore area has decreased compared with the initial stage.There were significant differences in porosity under different treatments,and the average shape coefficient decreased to varying degrees after drying-wetting cycles,and the pore shape between treatments had no obvious fractal characteristics.The water absorption rate of soil coarse particles decreased with the increase of particle size before and after cycling.(2)The content of quartz in the coarse particles of the initial soil is the largest,and the content of quartz is more than 50%except for the particle size of 15~10 mm,and has a decreasing trend with the increase of particle size ;the content of albite has a trend of increase with the increase of particle size.,the content of calcite is only 2%when the largest particle size is 10~15 mm.The evaluation score of quartz weathering in the initial state is 2~3 points,and the grade is slightly weathered.After the dry-wet cycle,the quartz weathering evaluation score is between[-1,1],and the weathering degree is mild weathering or moderate weathering.Dry-wet cycles lead to increased mica content.The content of soil coarse-grained clay minerals increased in different ranges from the initial stage.The growth rates of soil coarse particles with the smallest particle size of 0.5-2 mm were 24.16%,1.49%,8.18%,and-6.32%,respectively,while the maximum particle size of soil coarse particles of 10-15 mm were increased by 24.1 6%,1.49%,8.18%,and-6.32%.The increments of clay mineral content are 10.60%,85.25%,51.61%and 62.21%,respectively.(3)The stage mass loss rate of coarse soil particles in both field experiments and laboratory experiments was inversely proportional to the particle size.In the field test with 125 mL of water,the stage mass loss rate was 497.46%higher than that of the 10-15 mm particle size at 60 cycles,and the indoor test with 250 mL of water was the lowest when the particle size was 10 to 15 mm in 80 cycles,is 0.32%.(4)The temperature difference has a great influence on the deterioration of soil coarse particles.The minimum particle size of 0.5-2 mm coarse particles reaches the maximum value when it is cycled 60 times in the field test,which is 2.562%,and reaches the maximum value when it is cycled 60 times in the indoor test,which is 3.18%,the cumulative mass loss rate of soil coarse particles increased gradually with the increase of cycle times.The maximum mass loss of different grain grades before and after the drywetting cycle occurred in the field at 2-5 mm of the grain size under the 250 mL treatment,which was 21.84 g,and the mass loss of other grain grades under the four treatments was all about 10 g.within a reasonable range.

Mots clés : coarse soil particles ;degradation;porosity ;fractal;clay minerals ;mass loss ;PCAS;

Présentation (CNKI)

Page publiée le 20 octobre 2022