Abstract：Cracks in unsaturated expansive soils influence the engineering properties of soils. The purpose of this paper is to research the tensile crack propagation depth of unsaturated expansive soils. The formula of crack propagation depth based on linear elasticity is put forward，which considers the contributions of effective cohesion and effective internal friction angle at the same time. Then，two expressions are derived from it. One is the expression of the cracking value of matrix suction on ground surface，which can be taken as one of the criteria to estimate the cracking of the ground surface of expansive soils. Another is the expression of the crack propagation depth when the groundwater level has little influence on it. Finally，the relationships between the crack propagation depth and the factors are analyzed，such as effective cohesion，effective internal friction angle，reduction coefficient of effective cohesion，Poisson¢s ratio，matrix suction on ground surface and the groundwater level. The following results can be drawn：(1) With the increase of effective cohesion and effective internal friction angle，the crack propagation depth exhibits a descending tendency. Effective cohesion，however，has a much more serious influence than that of effective internal friction angle. (2) For the different effective cohesions and effective internal friction angles，the crack propagation depth increases as matrix suction on ground surface increases. And with the increase of Poisson¢s ratio and effective cohesion as well as effective internal friction angle，the critical matrix suction on ground surface at crack initiation exhibits an increasing tendency. Effective cohesion has a greater influence relatively. (3) For different effective cohesions and Poisson¢s ratios，the crack propagation depth increases with the increase of the groundwater level. When the groundwater level has minor influence，it increases linearly with matrix suction at the ground surface and decreases as effective internal friction angle and Poisson¢s ratio increase.
