Experimental study on mode I fracture characteristics of compacted bentonite clay

Abstract

To explore the pure mode I fracture characteristics of compacted Gaomiaozi bentonite clay, notched semi-circular bend specimens of compacted Gaomiaozi bentonite with different dry densities and moisture contents were prepared by using the self-designed compaction and slitting molds, and then three-point bending tests were carried out, real-time monitoring was also conducted with the help of digital image correlation method. Based on the test results, the effects of dry density (1.5 g·cm−3, 1.6 g·cm−3, 1.7 g·cm−3, 1.8 g·cm−3) and moisture content (6.20%, 9.48%, 13.65%, 16.47%) on the mode I fracture toughness of compacted Gaomiaozi bentonite were analyzed, and the development of fracture process zone (FPZ) was also revealed. The results show that the pure mode I fracture toughness of compacted Gaomiaozi bentonite is in the magnitudes of 30 to 180 kPa·m1/2 within the testing range of dry density and moisture content. The mode I fracture toughness increases with increasing the dry density. At a moisture content of 9.48%, the mode I fracture toughness obtains a peak value, and with the decrease or increase of moisture content, the mode I fracture toughness presents a general decreasing trend. The length of the fully developed fracture process zone and the critical crack tip opening displacement decrease first and then increase with the increase in moisture content, while there is no obvious regularity in the variations of fully developed FPZ length and critical crack tip opening displacement with respect to dry density.