Research On Effect Of Clay Minerals On Pore Structure And Water Absorption Characteristics Of Mudstone

Mudstone has stronger water absorbency,and it would be softness and disintegration after water absorption,which easily causing landslide,water or mud inrush and other major geological disasters.The type and content of clay minerals in mudstone is one of the main influencing factors for its hydroscopicity.The chemical composition of clay minerals in mudstone is similar,mainly composed of silicate aluminate,the changes of pore structure of clay minerals in mudstone will lead to significant differences in its water absorption.Therefore,the research on effect of the type and content of clay minerals in mudstone on its pore structure and water absorption characteristics will provide theoretical support for the further study of water inrush,landslide and other disasters caused by the weakeness of mudstone by water absorption.Clay minerals commonly found in mudstones mainly include montmorillonite,kaolinite and illite,which usually exist in mixed form.In this paper,chemically pure montmorillonite,kaolinite and illite were selected and mixed in a certain proportion to make artificial clay-doped minerals in order to simulate the composition of real mudstone clay minerals.Two mudstone samples were also collected.The essence of the influence of clay composition on the water absorption characteristics of mudstone were revealed through the comparative analysis.X-ray diffraction and low temperature liquid nitrogen adsorption were applied to test the mineral composition and pore structure of the samples.At different relative humidity conditions,water absorption experiments were carried out on the artificially caly-doped minerals and mudstone samples.The pore structure was correlated with the water absorption of the sample.The main results are as follows:(1)The pore structure of kaolinite tends to be narrow and flat,and that of illite tends to be ink-bottle type,while that of montmorillonite and artificial clay-doped minerals has the characteristics of both narrow slab and ink-bottle type.In this paper,the main clay minerals of the two types of mudstone samples,taken from the aquiclude,are kaolinite,illite and a small amount of montmorillonite,and the pore structure characterastics are relatively similar to that of the artificial clay-doped minerals.Because mudstone contain minerals with less developed pore structure such as quartz and feldspar,the specific surface area,pore volume and other pore structure parameters of mudstone samples are relatively smaller than that of the artificial clay-doped minerals.(2)Basing on the fractal FHH model,fractal dimension of clay minerals in the stages of multilayer adsorption and capillary condensation were calculated by the data of low temperature liquid nitrogen adsorption.Since there are no strictly quantified differentiated indicators between the stages of multilayer adsorption and capillary condensation,so there exist many ways to divide phases.The selection of the stage partition point has a relatively great influence on the calculation results of the fractal dimension in the adsorption stage of multilayer adsorption and a relatively small influence on that in the stage of capillary condensation for artificially doped samples and mudstone samples.Compared with the artificial clay-doped minerals,the fractal dimension of the mudstone samples is larger due to its more complex composition.(3)The water absorption of artificial clay-doped minerals and mudstone samples increased with the increase of relative humidity.The water absorption rate of the two kinds of samples at different relative humidity conditions can be fitted by Guggenheim-Anderson-deBoer(GAB)model.According to the single layer adsorption amount obtained by fitting,the interval of the artificial clay-doped minerals and mudstone samples from single layer adsorption to multilayer adsorption is between 11% and 33% of relative humidity.The water absorption rate of artificial clay-doped minerals can be predicted according to that of single minerals basing on the ratio of the minerals.The water adsorption rates of artificial clay-doped minerals are closely associated with the type and proportion of minerals contained,the water adsorption rates of the clay-doped minerals for montmorillonite and kaolinite,as well as montmorillonite and illite increased with the content of montmorillonite increasing,that of clay-doped minerals for kaolinite and illite bibulous rate increased with the content of kaolinite increasing.Therefore,the water absorption rate of mudstone can be predicted according to the corresponding relationships of the water absorption rate of artificial clay-doped minerals,mineral types and proportions.(4)The linear correlation between the specific surface area and water absorption of the artificial clay-doped minerals as well as the mudstone samples is the highest,and the water absorption of the two kinds of samples increases with the specific surface area increasing.There was no significant correlation between pore volume(or average pore diameter)and water absorption.The specific surface area is the main influencing factor for the water absorption.Clay minerals affect the water absorption of mudstone mainly by changing the specific surface area.