Experimental Study on the Damage Characteristics and Fracture Behaviour of Rock-like Materials with Weak Interlayer Zones

Liang Zhang,Hongwen Jing,Hanxiang Liu 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.9

To study the effect of the dip angle of the weak interlayer zone (WIZ) on the damage characteristics and fracture behaviours of rock-like samples, a series of uniaxial compression tests were conducted, accompanied by acoustic emission (AE) tests and the digital speckle correlation method (DSCM). The experimental results indicate that the stress–strain curves before the peak can be divided into plastic–elastic–plastic and elastic–plastic curves, and the stress–strain curves after the peak can be divided into plastic failure, transitional failure and brittle failure curves. The relationship between the peak stress and peak strain and WIZ angle can be well described by two linear functions. As the angle increased, the specimen gradually changes from tensile failure to shear failure, and the number of cracks and falling fragments decreases gradually. In addition, it becomes difficult to predict rock mass failure by AE when the WIZ angle is close to 60°. The AE counts decrease with an increasing angle, reach a minimum at 60°, and then increase. Furthermore, the WIZ plays a key role in the deformation of upper hard rock.

Investigation on Mechanical and AE Characteristics of Yellow Sandstone Undergoing Wetting-Drying Cycles

Yaoyao Meng,Hongwen Jing,Qian Yin,Xiaowei Gu 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.11

The cyclic wetting-drying phenomenon is a complicated physical and chemical process. This kind of process will weaken the properties of rock to some extent. Some fundamental physical parameters of sandstone were first tested to study the weakening influence of wetting-drying cycles on the physical characteristics. Then, the water weakening effect on the mechanical and acoustic emission (AE) characteristics of rock on account of wetting-drying cycles was experimentally studied. Laboratory test results showed that when the number of cycles increased from 0 to 25, the density, P-wave velocity, uniaxial compressive strength (UCS), (elastic modulus (E)) and total AE counts of the rock specimens continuously decreased. However, the water absorption would increase as the number of cycles increased. The functional relationships between the total AE counts and the mechanical parameters (UCS and E) of sandstone after each cyclic number were established based on the test results. In addition, the chemical components and microstructure variations of rock undergoing wetting-drying cycles were examined. From the results, it can be concluded that microcrack growth and expansion inside the rocks undergoing wetting-drying cycles are the main reasons for the attenuation of the rock properties. Moreover, with increasing loading rate, the UCS, E and total AE counts of sandstone after each cyclic number would increase.

Experimental Study on Shear Behavior of Bolted Cement Mortar Blocks under Constant Normal Stiffness

Bo Meng,Hongwen Jing,Shengqi Yang,Tao Cui,Biao Li 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.8

In this paper, the influence of bolting on shear mechanical behavior of cement mortar specimens were studied. First, a shear test apparatus which could provide CNS (constant normal stiffness) condition was designed. Then, more than 140 bolted and non-bolted cement mortar blocks (100 × 100 × 100 mm) were prepared. The strengthening effect of bolts with diameters of 0 − 10 mm on cement mortar specimens was studied under different initial normal loads ranging from 20 kN to 60 kN and constant normal stiffness of 420 kN/mm. Two simplified models of shear behavior of reinforced cement mortar blocks were proposed. The most important influence of bolt on the cement mortar blocks was to strengthen the post-peak shear strength rather than the peak shear strength, and the strengthening effect was reduced under high initial normal force. The cohesion of cement mortar blocks was reduced while internal friction angle was increased in residual sliding stage by bolts. The dilation of reinforced cement mortar specimens in postpeak shear stage was significantly reduced due to bolting, and the larger the bolt diameter, the greater the reduction in the block dilation.

Investigation on mechanical behavior and crack coalescence of sandstone specimens containing fissure-hole combined flaws under uniaxial compression

Qian Yin,Hongwen Jing,Haijian Su 한국지질과학협의회 2018 Geosciences Journal Vol.22 No.5

This study focuses on the effect of pre-existing flaw geometry on mechanical behavior and crack coalescence modes of sandstone specimens containing combined flaws with different fissure angle, ligament length and fissure length under uniaxial compression. The flaw geometry is a combination of a single hole and an inclined fissure underneath, which is generated by a high pressure water-jet cutting machine and is different from that reported in previous studies. The effect of flaw geometry on mechanical behavior of sandstone specimens is analyzed. Basically, mechanical parameters including the peak strength, peak axial strain, elastic modulus and secant Young’s modulus for the flawed specimens are lower than those for the intact specimens, with the reduction extent related to the fissure angle, ligament length and fissure length. Variation trends of the crack initiation stress for all tested cases are studied. Initiated crack types and cracking modes also depend on the combined flaws geometry. For the flawed specimens with a small fissure angle, ligament length or fissure length, cracking modes are generally characterized by cracks initiated from the hole-wall and evolved to the specimen boundary. However, when the fissure angle, ligament length or fissure length is increased, cracks initiated from both the hole-wall and fissure tips produce the main failure planes, accompanied by a free-standing “triangular prism structure” within the specimens. Numerical simulations using RFPA2D (Rock Failure Process Analysis in two dimensions) are carried out on the flawed sandstone specimens and agree well with the experimental results in the peak strength and overall cracking behavior.

Study on Mechanical Properties and Fracture Behavior of Granite after Thermal Treatment under Brazilian Splitting Test

Hanxiang Liu,Hongwen Jing,Qian Yin,Zhenlong Zhao,Yaoyao Meng,Liang Zhang 대한토목학회 2023 KSCE JOURNAL OF CIVIL ENGINEERING Vol.27 No.2

In this paper, the effects of thermal treatment on the mechanical properties, fracturecharacteristics, and roughness of the fracture surface of granite under the Brazilian splitting testare studied using an electro-hydraulic servo testing machine with an acoustic emission (AE)and digital image correlation (DIC) system. The test results show that: 1) Thermal treatmentdegrades the physical and mechanical properties. Density, P-wave velocity, and peak load ofgranite decrease with the increase in thermal treatment temperature (T). 2) With the increasing T,the fracture pattern changes from “I” type tensile fractures to “Y” type tensile-shear mixedfailure. The DIC results show that the fracture process changes from transient to progressive. 3) AE counts show that granite gradually changes from brittleness to ductility with the increaseof T. Furthermore, the variations in the RA and AF values of the AE events indicate that theincreasing T leads to an increase in shear cracks in granite. After the test, 4) the roughness ofthe fracture surface of the specimen was analyzed using a spatial digitizer. The results showthat thermal treatment significantly improved the fracture surface's asperity height androughness. 5) Scanning electron microscopy (SEM) results revealed that thermal treatmentleads to the generation of micro-cracks in granite and the desquamation of mineral grains,which influences the macro properties of granite.