Study On Characteristics Of Red Layer Weathering In Danxia Landform Area,Chishui City

In this paper,the weathering conditions of the red layer in Danxia landform area,Chishui city,are analyzed from the perspectives of geological conditions,stratigraphic lithology,hydrogeological conditions and ecological environment.The basic properties of the red layer such as water content,water absorption,disintegration resistance,uniaxial compressive strength and shear strength were determined,and the basic characteristics of the red layer such as chemical composition,mineral composition and microstructure were analyzed by means of X-ray fluorescence spectrometry?XRF?,scanning electron microscope?SEM?and polarizing microscope.Combined with the lithology of the red layer and the weathering environment,the characteristics of the main weathering types,the formation reasons,the failure modes and the protection measures were analyzed.The influencing factors of red layer weathering in the study area were discussed by laboratory test and field in situ monitoring.The chemical weathering index was established to quantitatively analyze the weathering degree of sandstone.The main contents and research conclusions are as follows:?1?High temperature,abundant rainfall,air humid climate characteristics in the Chishui city Danxia landform areas,K_2Sand K₁w are different form stratum structure,the study area experienced multiple tectonism,the red layer's differences of basic properties,chemical composition,microstructure,in addition,the local vegetation and biological,are produced different degrees'impact for red layer weathering processes.?2?The basic differences in physical properties,such as water content,water absorption,coefficient of resistance.The Si O₂?Al₂O₃?TFe₂O₃?K₂O differences in chemical composition,quartz particle size,roundness,particle contact way,cementation types in the difference of the microstructure,lead to the difference of weathering resistance between red sandy rock and argillaceous rock,in the Danxia landform areas,Chishui city.The higher the hydrophilicity,the higher the clay mineral composition and the smaller the quartz particle size of the red layer,the worse the mechanical properties and the weaker the weathering resistance of the red layer.The red sandstone layer in Danxia landform area,Chishui city,are divided into four types:feldspar quartz sandstones,lithic quartz sandstones,lithic sandstones and argillaceous sandstones.?3?The weathering types in the study area are mainly affected by climate and meteorology,stratigraphic lithology and landform,and mainly include differential weathering dominated by physical weathering,surface lamellar stripping and rock trough.Dissolution weathering,honeycomb weathering and spherical weathering dominated by chemical weathering;Biological weathering dominated the root splitting,organic acid corrosion,artificial excavation,etc.Differential weathering,trough weathering and spheroidal weathering are the most common weathering phenomena in the study area.?4?Damage,fissure proliferation,expansion,particle differential expansion,hydration reaction and so on in the red layer lead to the gradual degradation of the red layer structure and the increase of the mass loss rate,which has a significant impact on the deterioration of the red layer strength.The weathering of the soft and hard interbedded slope is mainly dominated by the collapse of the strongly weathered mudstone and the block dropping of sandstone,with the retreat rate of 0.4?3.5 cm/a and the average rate of 1.0 cm/a.?5?Nine commonly used chemical weathering indexes such as CIA,CIW,MWPI and LOI are reflected in the sandstone depth.The Fe²⁺/Fe³⁺established in this paper is basically consistent with the classification results of the weathering degree of sandstone on the vertical depth by the above nine chemical weathering indexes.The weathering zone of sandstone in the Danxia landform areas,Chishui city,can be divided into:0?5 cm is surface strong weathering zone;5?15 cm is medium weathering zone;and breezy zone is larger than 15 cm.?6?Through the analysis and discussion of the key steps such as dosage,dissolution and color development,a chemical analysis method for the determination of trace Fe²⁺and total iron in red sandstone by o-filloproline spectrophotometry was established.This analysis method has high accuracy and operability for the determination of trace Fe²⁺and total iron in red sandstone.The multiobjective determination of the same solution was achieved,and the problems of complex experimental operation and reagents were solved to a large extent.By using this method,the total iron content of sandstone in the Danxia landform areas,Chishui city,was measured between 0.7%and 1.5%.The Fe²⁺mass content ranges from 0.01%to0.1%.Fe³⁺is between 0.7%and 1.5%.