Abstract
The influence of water content on mode I fracture toughness (KIc) of mudstones has been studied using semi-circular bend (SCB) specimens subject to three-point bendings. And the mudstone SCB specimens are divided into three types, including Type-A, Type-B and Type-C, corresponding to the three configurations of the bedding planes, including divider direction, arrester direction, and transverse direction, respectively. The test results show that the values of KIc for the three types of specimens are different due to the bedding structure, the Type-A specimens have the largest value of KIc for the same soak period, while the Type-C specimens possess the smallest value. As the soak period increases, the KIc of the three kinds of mudstone specimens decreases, and the fracture mechanisms of the specimens change gradually from the brittle failure form to the ductile failure form. Moreover, the standard deviation was used to quantify the anisotropy degree of the KIc of the mudstone samples. As the water content increases, the standard deviation increases from 0.057 to 0.139, which indicates a significant increase in anisotropy of the KIc of the mudstone specimens. In addition, the acoustic emission (AE) system was used to detect the AE events associated with the fracture initiation and propagation in the mudstone specimens for the different water content, with the raising water content, the cumulative AE events decrease, and the standard deviation of AE events increases, repesenting that the anisotropy of the AE events of the three types of specimens becomes more prominent. Further, the relationship between the tensile strength (σt) and the KIc of the three types of mudstone specimens for different water contents has been proved to be the linear relation.
Highlights
Mudstones widely exist in various engineering geological environments, such as mining [1], hydraulic fracturing [2] and tunnelling
Liu et al [5] confirmed that the anisotropy of the static and dynamic uniaxial compression strength exists in bedded rocks
Numerous experimental methods and specimen types have been designed to test the KIc of rocks, such as the diametral compression specimen with a central crack on the discs [24], the cracked chevron notched Brazilian disk specimen [25, 26] and the semi-circular specimens under three-point bending (SCB) [27, 28]
Summary
Mudstones widely exist in various engineering geological environments, such as mining [1], hydraulic fracturing [2] and tunnelling. As a type of sedimentary rock, mudstones contain bedding structures, which can induce the anisotropy of the physical and mechanical properties. Zhou et al [4] tested the thermal expansion and the P-wave velocity of sedimentary rocks along the different bedding directions, and these physical parameters showed significant anisotropy. Liu et al [5] confirmed that the anisotropy of the static and dynamic uniaxial compression strength exists in bedded rocks. Claessona and Bohloli [6] analyzed the stress field and the tensile strength of anisotropic rocks with bedding by using an analytical solution. Ghazvinian et al.’s [7] experimental research shows that the shear strength is anisotropic because of the existence of the bedding plane in rocks
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