Abstract
The effect of water on fracture toughness in various modes of mudstones was investigated using semicircular bend (SCB) specimens exposed to three-point bendings. Natural mudstone specimens are obtained using a special coring method and are then classified into three types (A, B, and C) corresponding to three directions/configurations of bedding planes (divider, arrester, and transverse). The results show that the Type A (divider configuration) specimens possess the largest fracture toughness value for all tested modes and same soaking time, whereas the Type C (transverse configuration) specimens have the smallest one. By increasing soaking time, the fracture toughness in all three modes decreases and the fracture mechanism changes from brittle failure to ductile failure. Among them, the Type C specimens have the highest degree of degradation for each soaking time period. Regarding the fracture modes, the degradation degree ofKIcis higher than that ofKIIcfor all three types of mudstone specimens. In addition,KIIc/KIcratio increases when soaking time is extended. Furthermore, in the initial and short soaking time stages, the experimentalKIIc/KIcresults are consistent with theoretical findings from modified MTS criterion. However, after being soaked 300 minutes for three types of specimens, the test curves deviate from the theoretical curves. Analogously, the mixed-mode I/II ratio ofKefftoKIcis consistent with the theoretical values in the initial stage when the degree of damage is low. With soaking time increasing, the experimental curve is gradually deviated from the theoretical curve. When soaking time reaches 300 minutes, the deviation is substantial. And the test data for the Type-A specimens are observed to provide better agreements with theoretical predictions by modified MTS criterion than those for the other two types of specimens.
Highlights
Mudstones, a sort of sedimentary rocks containing clay minerals, are found extensively in a variety of engineering geological environments, such as mining, hydraulic fracturing, tunneling, blasting, and geological CO2 storage
Eoretical results and experimental findings according to the modified maximum tangential stress (MTS) criterion are compared here. e following conclusions are drawn in this work: (1) is test used a special coring method to obtain native mudstone semicircular bend (SCB) specimens, which are classified into three types corresponding to the three bedding directions. e fracture toughness of Type A specimens has the largest value for all tested modes and same soaking time and that of the Type C specimens is considerably smaller than the other two types
(3) e degree of degradation of pure mode I fracture toughness is slightly higher than pure mode II, proving that the water sensitivity of pure mode I fracture toughness is higher
Summary
A sort of sedimentary rocks containing clay minerals, are found extensively in a variety of engineering geological environments, such as mining, hydraulic fracturing, tunneling, blasting, and geological CO2 storage. Under these natural conditions, water is a significant factor that alters the physical and mechanical properties of argillaceous swelling rocks [1, 2]. Gautam and Shakoor [6] observed that rocks containing higher amounts of clay slake more extensively and rapidly under natural climatic conditions and that the water content plays a key role in reducing the strength of clay-bearing rocks. Several experimental studies on wave velocities in clay-bearing rocks with rock-water interaction have been conducted [7]
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