Issue34

Y. Li et alii, Frattura ed Integrità Strutturale, 34 (2015) 599-607; DOI: 10.3221/IGF-ESIS.34.66 602 Number of dry-wet cycles: 1 2 3 4 5 Sample 1 Crack ratio 0 1.65% 2.57% 3.27% 3.63% Fractal dimension 0 0.632 0.783 1.012 1.133 Sample 2 Crack ratio 2.25% 2.77% 3.86% 6.55% 8.03% Fractal dimension 0.688 0.853 1.016 1.193 1.417 Sample 3 Crack ratio 0 2.14% 2.92% 3.37% 3.77% Fractal dimension 0 0.963 1.076 1.167 1.257 Table 3: Number of dry-wet cycles as related to crack ratio and fractal dimension. Tab. 3 shows that sample 1 and sample 3 had no fissures after the first wet-dry cycle, but the crack ratio and fractal dimension were 2.25% and 0.688, respectively. Comparing three groups of crack samples after five dry-wet cycles, the fissure of sample 2 developed earlier and more was more substantial than that of samples 1 and 3. This is because sample 2 was obtained by the large ring sampler while samples 1 and 3 used the small ring. In addition, the fissure ratio and fractal dimension of sample 3 was slightly larger than that of sample 1 due to different humidification methods. Fracture mechanical analysis The red clay is the unsaturated soil under normal circumstances. This soil has the characteristics of shrinkage and the rate of water loss in soil on the surface is greater than internally. After water loss and the matric suction increases, the soil is subjected to tensile stress at first. Assuming that the soil is isotropic and linear elastic bodies, the following constitutive relations can be established:       x a a w x y z a y a a w y x z a z a a w z x y a σ u u u μ ε σ σ 2u E E H σ u u u μ ε σ σ 2u E E H σ u u u μ ε σ σ 2u E E H                               (7) where a u - pore air pressure w u - pore water pressure E - elastic modulus of soil  - poisson ratio H - elastic modulus associated with a w u u  , x  - horizontal strain y  - longitudinal strain z  - vertical strain x  - horizontal stress y  - longitudinal stress z  - vertical stress. Taking the horizontal as the object of study, and there are no cracks in the soil: 0 x   (8) The first combination of the constitutive relation:       a w x a z a u u E μ σ u σ u 1 u H 1 u        (9)