Y. Li et alii, Frattura ed Integrità Strutturale, 34 (2015) 599-607; DOI: 10.3221/IGF-ESIS.34.66 599 On the decay of strength in Guilin red clay with cracks Yi Li, Keneng Zhang School of Geosciences and Info-Physics, Central South University, Changsha, 410083, China Baochen Liu College of Civil Engineering and Architecture, Guilin University of Technology, Guilin, 541004, China Zongyuan Pan Institute of Karst Geology, CAGS, Guilin, 541004, China A BSTRACT . In order to research the effect of cracks in red clay on shear strength through dry-wet cycle test, the experimenters used imaging software and a mathematical model to determine fractal dimension and crack ratio of surface cracks in red clay in Guilin, China. After each dry-wet cycle, direct shear tests were carried out on the sample, and such variables as matrix suction on the crack propagation process of red clay were analyzed. The mechanics model was established and obtained the critical condition of soil cracks. The results show that with the increase in the number of dry-wet cycles the shear strength of the samples would decrease. But the rule of shear strength of sample 3 is slightly different from samples 1 and 2. The shear strength of red clay has a good correlation with fractal dimension and crack ratio, which could be an identification index of the strength of red clay. K EYWORDS . Red clay; Dry-wet cycle; Fractal dimension; Crack ratio; Shear strength. I NTRODUCTION uilin is located in the northeast of Guangxi Province, at a low latitude, with a subtropical monsoon climate. It is variably rainy throughout the year, with the rainy season coinciding with high temperatures. The climate easily causes the development of soil fissure of Guilin red clay resulting in a decline in the ultimate strength of the clay. We should pay attention to the influence of red clay cracks on the stability in the area of slope and foundation excavation, as it may lead to free face collapse, ground subsidence and other geological mishaps. Therefore, researching the influence of cracks on the shear strength of red clay will help us to improve the safety of the geo-body. Cracks in soil have been a concern for a long time, however, the research on geotechnical engineering is still relatively insufficient. Until the 1980s, only a few scholars have started the research on the soil cracks [1-6]. A new kind of constitutive model capable of describing the damage of soil structure has been proposed and crack evolution in clay during dry and wet cycles has been simulated [7,8]. The effects of cyclic dry-wet process on the fatigue G