| Red soil is mainly distributed in hilly areas in southern China.In case of heavy rainfall,water infiltration leads to the decrease of soil suction,and landslide is easy to occur under the condition of self-weight.The laterite is chemically modified with octadecyl primary amine(CH3（CH2）16CH2NH2,referred to as octadecyl amine)as a water repellent and covered on the slope surface to reduce water infiltration during rainfall,slow down the decay rate of laterite cohesion,and improve the stability and safety of the slope.In order to study the mechanical properties and impervious properties of the modified soil,a total of five soil samples were prepared:hydrophilic laterite（NS）,hydrophobic laterite（RS）,hydrophilic laterite+30%hydrophilic sand（NSS）,hydrophobic laterite+30%hydrophobic sand（RSS）,hydrophilic laterite+30%hydrophobic sand（NRS）.CU test and constant head permeability test were carried out for different soil samples,and slope simulation was carried out using Auto Bank.The results are as follows:（1）In terms of basic physical properties:modifying laterite and adding sand make the liquid-plastic limit and plasticity index of soil sample decrease,NS and RS are clay,NSS,RSS and NRS composite soil are silty clay,NS optimal moisture content is the largest,NSS maximum dry density is the largest,NS,NSS and NRS are hydrophilic no matter how the moisture content changes,RS and RSS are serious water repellent when the moisture content is 30%;The relationship between water content and water repellency of RS and RSS is quadratic parabola.（2）In terms of mechanical properties,modified soil and composite soil RS,RSS,NSS and NRS4 are relatively less affected by water content than NS,which is due to the water repellent forming an envelope on soil particles,and water molecules are difficult to penetrate into soil particles.When the water content increases,the matrix suction changes less,and the shear resistance of soil samples is reduced by water content;Secondly,the water content of sand is low when it is completely saturated,so when the water content of composite soil exceeds the saturated water content of sand,the change of the water content of composite soil within a certain range has little impact on the sand.No matter how the water content changes,NS and NSS are completely destroyed at about 2%strain,reaching the ultimate strength.RS and RSS will be completely destroyed when the strain is far greater than 2%,indicating that the ductility of soil samples modified by octadecylamine is improved.Cohesion c internal friction angleφWithin a certain range of water content,it decreases with the increase of water content,and the formula of water content and mechanical parameters is obtained by fitting.The mechanical properties can be known without measuring the soil suction,which is convenient for practical engineering application.（3）In terms of imperviousness:with the same water content,RS and RSS are less affected by water head,and the cumulative seepage volume is almost constant when the water infiltration is stable,and the cumulative seepage volume and time relationship curve is horizontal and linear;The seepage rate of NS,NSS and NRS is greatly affected by the water head.The greater the water head,the greater the hydraulic gradient,and the faster the seepage rate.The RS permeability coefficient of the modified soil is the smallest among the five soils under the natural moisture content,and the permeability coefficient is extremely low,which fully meets the waterproof requirements of the project;The permeability coefficient of RSS is the most sensitive to water content among the five kinds of soil,and changes most obviously with water content.The permeability coefficient is the largest when the water content is dry,and the permeability coefficient is the smallest when the water content tends to be saturated.Use composite soil RSS in areas with high daily water content to reduce project cost;Modified soil RS can be selected in areas with low water content to achieve better anti-seepage effect.（4）Auto Bank slope stability simulation:the appropriate thickness of soil cover will significantly improve the stability safety factor of the most unfavorable side of the slope.The stability safety factor of the most unfavorable side of rainfall increases first and then decreases with the decrease of the thickness of the soil cover.When the overburden thickness is too thick,the most unfavorable landslide surface is likely to appear from the inside of the overburden,which will reduce the safety of the slope;When the overburden is too thin,the expected anti-seepage effect cannot be achieved.When the overburden thickness is 10 cm,the anti-seepage effect is the best,and the slope stability is the best. |
