Issue34

Y. Li et alii, Frattura ed Integrità Strutturale, 34 (2015) 599-607; DOI: 10.3221/IGF-ESIS.34.66 604 ratios of samples 1, 2 and 3 are over 1.65% 、 2.77% and 2.14% respectively, the cohesion drops rapidly, which indicates that there is a threshold quantity that makes the cohesion of red clay change. The cracks of sample 2 appears earlier than those of samples 1 3. After five dry-wet cycles, the cohesion of samples 1 and 2 are about 19kPa, but the cohesion of sample 3 is only 13.77kPa. (2) Number of dry-wet cycles: 1 2 3 4 5 Sample 1 Cohesive force / kPa 39.38 38.21 36.14 29.57 19.05 Internal friction angle /° 8.82 8.56 8.49 7.88 7.26 Sample 2 Cohesive force / kPa 38.57 37.89 34.77 30.09 18.66 Internal friction angle /° 9.76 9.29 9.03 8.56 7.12 Sample 3 Cohesive force / kPa 38.04 33.05 27.39 19.33 13.77 Internal friction angle /° 9.06 8.66 7.69 7.13 6.68 Table 4 : The relationship between the number of dry-wet cycles and shear strength of test results. Figure 1 : The relationship between the number of dry-wet cycles and cohesive force. Figure 2 : The relationship between the number of dry-wet cycles and internal friction angle. (2) The relationship between the crack ratio and the internal friction angle is shown in Tab. 5 and Fig. 4. Changes in the internal friction angle in different crack ratios are familiar to cohesive force, both having a threshold quantity. After two dry-wet cycles, the internal friction angle of sample 3 is slightly higher than that of sample 1, but after the forth wet-dry