Study On The Mechanical Properties And Mechanisms During Soil Reconstruction Of Red Soil Complex In Yunnan

Red soil is a special soil formed by leaching during high temperature and rainy climate conditions.It has the properties of high plasticity,high void ratio,high water content,low compressibility,heavy viscosity,easy caking,slightly acidic soil,poor water and fertility conservation and poor shear strength.Red soil is one of the most widely distributed soil types in China,with a total area of 569000 km~2,mainly distributed in low mountains and hills to the south of the Yangtze River.It is also a typical soil type distributed in Yunnan Province of China.However,rainfall,irrigation,high-temperature evaporation,and disturbances in production and construction projects cause during dry-wet alternation,leading to shrinkage of red soil during drought,surface subsidence,and the formation of cracks.During rainfall,the soil expands,the surface moves up,and the cracks gradually close,the changes of soil and water properties are exceptionally severe.The spatiotemporal differences during dry-wet alternations are significant.Therefore,it is urgent to carry out soil reconstruction in red soil areas.Soil reconstruction has become a key technology in land remediation projects and a hot topic in research on land reclamation,ecological restoration,and high standard farmland construction in industrial and mining areas.In view of this,this dissertation focuses on the main technical and scientific issues faced by land remediation projects in red soil areas,such as how to stabilize loose slopes,how to improve soil water holding and water conservation performance,how to maintain scarce soil water resources,how to quickly restore plant community,and how to respond to the impact mechanism during soil reconstruction process.Therefore,this dissertation based on the perspective of soil reconstruction,constructed theoretical framework of improving soil,regulating water,and restoring plants.This dissertation adopts theoretical analysis,indoor experiments,numerical simulation and other research methods to study the soil water performance of red soil in Yunnan Province.Four types of added amounts(0,0.5%,2.5%,5.0%)of wood fiber,glutinous rice glue,and mixture(wood fiber/glutinous rice glue),as well as two types of herbaceous plants(white clover,ryegrass),are set to reconstruct the soil water performance of red soil,Conducting research on the mechanical properties and impact mechanisms of red soil composite soil based on soil reconstruction.The results can improve the theoretical and methodological system of land consolidation,and provide theoretical basis and technical guidance for ecological engineering practices such as land remediation,ecological restoration,and soil and water conservation in ecologically fragile areas.The main conclusions of this dissertation are as follows:(1)Adding an appropriate amount of glutinous rice glue,wood fibers,or mixed reconstructive materials can enhance the shear strength of red soil,while inhibiting the attenuation effect of dry-wet alternation of the shear performance of the soil.During the two cycles of dry-wet alternation,the shear strength and parameters of red soil and composite soil will decrease and tend to a stable value;As the content of reconstituted materials increases,the various shear indicators of composite soil are enhanced to varying degrees,among which the shear strength and cohesion enhancement are the best with 5.0%wood fiber;The initial addition of glutinous rice glue increases the shear strength and cohesion rapidly,but as the number of dry-wet alternations increases,the shear strength and cohesion decrease rapidly;After adding a mixture(wood fiber and glutinous rice glue),there is a significant effect of dry-wet alternation attenuation between 0.5%and 2.5%,and the inhibition effect is not significant when the content is less than 0.5%.5.0%mixed composite soil has the best effect of inhibiting dry-wet alternation attenuation.(2)The addition of appropriate amount of reconstructive materials can enhance the water retention and retention performance of red soil,while decelerate the hysteresis effect of dry-wet alternation on the hydraulic properties of red soil.The degree of influence of the addition of reconstructive materials on the suction of red soil matrix ranges from wood fiber,glutinous rice glue,mixture,and plain soil.Among them,the decrease in 2.5%wood fiber composite soil is the smallest,indicating that it is less affected by the alternation of dry-wet conditions.Adding it can increase the suction value of the red soil matrix and effectively improve the water holding capacity of the red soil;During the alternation of dry-wet conditions,the hysteresis of 5.0%wood fiber composite soil gradually decreases,and it is least affected by hysteresis effect,that is,the change in volume moisture content is also the smallest.The addition of 2.5%and 5.0%glutinous rice glue can significantly increase the volumetric moisture content of soil,but at the same time,its water absorption and loss rates vary greatly,which does not promote long-term water retention.In the stage of medium and high moisture content,the mixed composite soil is greatly disturbed by water,resulting in a significant change in matrix suction.The logistic model was utilized to simulate changes in SWCC of four treatments(plain soil,glutinous rice glue,wood fiber,and mixture),with a coefficient of determination ranging from 0.987to 0.999.(3)White clover and ryegrass can enhance the reinforcement and soil fixation ability of red soil composite soil.The increase in shear strength of ryegrass root soil is higher than that of white clover root soil composite,and compared to white clover,ryegrass has stronger reinforcement and soil fixation ability.With the increase of plant RAI and R_V,except for the decrease in shear strength of 0.5%glutinous rice glue+white clover root soil and 5.0%wood fiber+ryegrass root soil,the other experimental groups showed an overall increasing trend.After adding glutinous rice glue,as the plant RAI increases,the increase in cohesion changes as follows:white clover root soil complex>rye grass root soil,while the increase in internal friction angle is opposite;After adding wood fibers,the cohesion and internal friction angle of the wood fiber+white clover root soil showed an increasing trend with the increase of RAI.When RAI>1 or above,the change in internal friction angle tended to be gentle,and the increase in cohesion of the 5.0%wood fiber+white clover root soil composite was the largest;After adding a mixture(glutinous rice glue+wood fiber),as the plant RAI increases,the cohesive force shows an increasing trend,and the change in internal friction angle is relatively small.(4)Adding the optimal ratio of glutinous rice glue composite soil can improve the aboveground and underground biomass of herbaceous plants.The aboveground biomass increment(13.15g)is noticeably higher than the underground biomass increment(1.16g),and the biomass increment of ryegrass is better than that of white clover.Glutinous rice glue composite soil can increase the biomass of herbaceous plants.As the addition amount increases,the biomass of ryegrass and white clover shows a trend of first increasing and then decreasing,with 2.5%glutinous rice glue composite soil having the greatest increase in herbaceous plant biomass;Adding medium to high content wood fibers and mixed composite soil will have an inhibitory effect on herbaceous biomass and affect the normal growth of herbaceous plants.(5)Herbal plants can enhance the water holding capacity of red soil composite soil.The matric suction of ryegrass root soil increased with the increase of root surface area index(RAI),root volume ratio(R_V),leaf area index(LAI)and underground biomass(UB)of herbaceous plants,and the relationship between them was generally linear function.The matric suction of white clover root soil increases with the increase of RAI,R_V,LAI and UB,and the relationship between them is generally linear function;However,the 2.5%wood fiber root soil shows a trend of first increasing and then decreasing,and the two satisfy a second-order polynomial function relationship.As the amount of composite soil added increases,the overall increase in matrix suction of ryegrass root soil complex is greater than of white clover root soil complex,and the difference gradually increases,indicating that ryegrass has better water retention performance than white clover.The logistic model was utilized to simulate the SWCC changes of white clover and rye grass root soil at different growth stages.The curve changes showed a nice"S"shape,and the correlation coefficient R~2 of the fitting curve was above 0.99.With the increase of plant height of herbaceous plants,the SWCC of both white clover and rye grass root soil shifts upwards,indicating that plant planting can improve the water holding capacity of red soil composite soil.The SWCC increase of 2.5%glutinous rice glue+white clover root soil is the best,while the SWCC increase of 5.0%glutinous rice glue+ryegrass root soil is the most worrying.There are 82 figures,37 tables,and 258 references in this dissertation.