Abstract: Upon drying,desiccation cracks would occur in expansive soils due to evaporation and volume shrinkage.The presence of cracks may significantly weaken soil engineering properties.Better understanding the characteristics of tensile strength during drying is very helpful to study the essential mechanisms of desiccation crack initiation and propagation.In this investigation,Romainville expansive soil was used and several groups of initially saturated slurry specimens were prepared.The specimens were then dried in room condition to different water content.Direct tensile test was performed on these specimens by employing the modified super mini-penetrometer(SMP-1).The evolution of tensile strength with water content was quantitatively characterized.In addition,vapor equilibrium technique was applied to control the soil suction during drying,and the effect of suction on tensile strength was also studied.The results indicate that,during drying,the specimen tensile strength generally increases exponentially with decreasing water content.Before the water content is lower than plastic limit(40%),the tensile strength and the increase rate is very low; after the water content reaches the plastic limit,a slight decrease of water content can lead to significant increase of the tensile strength.With increasing suction,the specimen water content decreases exponentially as expected,and the tensile strength increases linearly.It is found that the evolution behaviour of soil tensile strength during drying is mainly connected with pore water properties,water-soil interactions,contact behviour between soil particles and soil structure.