Study On The Effect Of Clay Mineral Composition On The Strength Of Unsaturated Net-like Red Soil

Net-like red soil is widely distributed in the Southern China.There were few researches in the relations among the component and microstructure and strength.The microstructure and strength were seriously influenced by the clay minerals component,therefore,it is significant to study on the effect of clay mineral composition on the strength of unsaturated net-like red soil.Element and clay mineral composition of net-like red soil were first analyzed by X-ray diffraction and X fluorescence spectra experiments.Then two distinctive kinds of clay minerals were selected as additives to study the strength of net-like red soil.In the end,scanning electron microscopy and digital image technology were used to study the microstructure of soil samples,to study on the effect of clay mineral composition on the strength and microstructure of unsaturated net-like red soil.(1)The XRD results showed that net-like red soil was composed of red matrix and white vein,the types of clay minerals between them were almost same,besides,the major clay minerals were illite,chlorite,muscovite and kaolinite.The content of illite in red matrix and white vein was 64% and 56%.Respectively,chlorite,muscovite and kaolinite in white vein were more than that in red matrix.(2)The XRF results showed that the elements of red matrix and white vein were mainly consisted of oxygen,silicon,aluminum and iron,whose content were greater than 95%.The content of potassium,titanium,magnesium,zirconium,calcium,sodium and manganese was less.Iron in red matrix was greater than that in white vein.(3)Different clay minerals had diverse effects on the strength of net-like red soil.The strength of the soil reduced and the moisture content increased with the incorporation of montmorillonite,illite behaved the opposite effect.The shear strength of net-like red soil mixed with 7%,14% and 21% montmorillonite reduced by 3.8%,13.1% and 16.9%,and the moisture content increased by 0.85%,1.63% and 3.07%.The shear strength of net-like red soil mixed with 7%,14% and 21% illite was 199 kPa,191 kPa and 193 kPa,respectively the strength of soil without incorporation was 183 kPa.The shear strength of samples mixed with illite increased by a small margin,while the moisture content reduced by 1.74%,2.46% and 2.96%.The cohesion and internal friction angle of the samples mixed with 14% montmorillonite changed from 69 kPa and 35.56° to 77 kPa and 28.23°,for illite,they changed to 138 kPa and 24.77°.(4)The results of microstructure experiment showed that lumpy and lamellarstructure were the main structure form of net-like red soil,point to surface connection and surface to surface connection were the main fabric among soil particles.Clay minerals had no significant effect on the fabric among soil particles,but had some effect on the spatial distribution of soil particles.The average value of the pore radius,the perimeter and the proportion of the soil sample mixed with 14% montmorillonite were larger than those of the soil mixed with illite.The distribution of pore radius,perimeter and area of the soils mixed with two kinds of clay minerals were similar,the small pore whose area was less than 0.01μm2accounted for about 50% of the total pore.The average value of pore radius,perimeter and area of the soil mixed with 14%montmorillonite were 0.25μm,0.95μm and 0.41μm2,the average value changed to0.23μm,0.72μm and 0.27μm2when the soil was mixed with 14% illite.Under the condition of incorporation of illite,the porosity decreased,the contact area between soil particles increased,the moisture content reduced and the shear strength of soil increased.While the soil was mixed with montmorillonite,the moisture content increased and the shear strength of soil reduced.