Lateritization Evaluation Of Residual Soils Overlying Limestone And Basalt In The Central And Eastern Part Of Yunnan Provinc

Residual soil is the accumulation of rock debris and soil left after rock weathering.The residual soil over limestone and basalt studied in this paper is mainly laterite.Laterite is the most common red soil in tropical and subtropical areas,which is formed by rock weathering and contains iron,aluminum oxide and hydroxide.Compared with other soil types,there are disputes in their genesis,definition and classification,which makes the research of laterite a continuous concern.The geotechnical and engineering properties of laterite mainly depend on the cause and degree of laterite weathering（i.e.decomposition,laterization,dehydration and hardening）.The important effects of weathering on the chemistry,mineralogy and morphology of laterite have been reported in the literature related to the study of laterite.Therefore,it is of great significance to study the laterization degree of residual soil overlying different bedrock.Taking the residual soil overlying limestone and basalt as the research object,this paper finds out the particle size,mineral composition and chemical elements of the residual soil overlying limestone and basalt by using the method of investigation,sampling,analysis,test,comparison and comprehensive evaluation,and makes a comprehensive comparative study on the degree of laterization of the residual soil overlying limestone and basalt based on different quantitative indexes of laterization degree.The main conclusions are as follows:（1）The micron d₁₀and d₉₀of residual soil overlying limestone and basalt show that the permeability of the residual soil is very low,and the low permeability is obviously unfavorable to the recharge of karst water and the development of karst.（2）Clay minerals and oxides of laterite control 13μm of laterite,accounting for more than90%For the part below,also contains some quartz.clay minerals mainly contain chlorite,kaolinite and illite,and oxides mainly contain gibbsite,limonite（hematite）and anatase.（3）Chemical composition of residual soil overlying limestone and basaltl,the contents of active components such as K₂O、Na₂O、Ca O and Mg O are low,while inactive components such as Al₂O₃,TFe₂O₃and Ti O₂tend to be enriched,and the contents of Al₂O₃and TFe₂O₃are high,indicating that residual soil overlying limestone and basalt has experienced strong weathering and leaching in the formation process,resulting in a large loss of alkali and alkaline earth metals of active components and the accumulation of oxides of inactive components.（4）The calculated laterization degree of 6 different quantitative indexes of laterization degree is:T₂g^blimestone overlying residual soil>P₁q+m limestone overlying residual soil;Basalt overlying residual soil>basalt saprolite>fresh basalt.The results show that the leaching loss of active components such as Ca O,Na₂O,K₂O and Mg O of residual soil overlying P₁q+m limestone is weaker than that of residual soil overlying T₂g^blimestone,indicating that the leaching effect of infiltration water on active components in Dabanqiao study area,that is,the runoff alternation of groundwater in unsaturated zone is weak,which should be unfavorable to the dissolution of carbonate rocks;The residual soil with high lateritization degree in Gejiu research area is beneficial to adsorb heavy metal pollutants in tailings pond.The residual soil overlying limestone and basalt in this study area can be defined as laterite,and the residual soil overlying T₂g^blimestone can be called true laterite.（5）The six quantitative indexes of lateritization degree have referential significance for the quantitative trend of lateritization degree,but CIA and CIW prefer the quantitative indexes in the early and middle stages of weathering.In the late stage of weathering and lateritization degree,chemical indexes with Si,Al,Fe and other elements should be used for quantification,such as SA,SAF and IOL.Loss on ignition can also be used as parameters to evaluate the lateritization degree.