Abstract: Hydrophobic soils have drawn extensive attention due to their properties of waterproofing,seepage resistance,and evaporation inhibition.However,conventional methods for preparing hydrophobic soil require drying and mixing with water-repellent agents,which can damage the clay structure and limit its application.This study employed a technique where octadecylamine (ODA) powder was applied to the soil surface.When the surface temperature reached the melting point of ODA,the powder melted and infiltrated the surface soil to form undisturbed hydrophobic modified clay.Investigations into the hydraulic properties of the modified soil demonstrated that a higher initial moisture content prolonged the time required for hydrophobization but did not affect the final modification effect.The surface hydrophobic modification effectively prevented soil disintegration,although the measured soil disintegration rate could exhibit negative values due to the influence of internal trapped air.Beyond the water-repellent nature,the undisturbed modified clay exhibited a dual water-blocking mechanism comprising a surface coating by molten ODA and pore clogging by crystals.The findings provide a valuable reference for the hydrophobic modification of intact soils and easily weathered rocks.