• The Journal of Engineering Geology
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• v.29 no.4
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• pp.405-415
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• 2019

The cracks induced by hydraulic rock splitting technique are formed in the direction parallel to the free plane, which is perpendicular to the minimum principal stress of the ground, or is affected by the pre-existing microcracks. In this study, the hydraulic rock splitting experiments were conducted in which the guide slot was engraved in the direction parallel to the borehole axis on the biotite granite slope, and the hydraulic pressure was injected through the double packer pressure and interval section. The test results show that the cracks along with the guide slots were induced either by the double packer pressurization or the injection of hydraulic pressure into interval section, some cracks extended across the boreholes. Therefore, the hydraulic rock splitting test is expected to control efficiently the induced cracks if the guide slots are engraved in the direction of splitting and a big flow rate is applied.

• Geomechanics and Engineering
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• v.14 no.3
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• pp.225-231
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• 2018

In this paper, in order to explain the splitting of cylindrical rock specimen under uniaxial loading, cracks in cylindrical rock specimen are divided into two kinds, the longitudinal crack and the slanting crack. Mechanical behavior of the rock is described by elastic-brittle-plastic model and splitting is assumed to suddenly occur when the uniaxial compressive strength is reached. Expression of the stresses induced by the longitudinal crack in direction perpendicular to the major axis of the crack is deduced by using the Maxwell model. Results show that the induced stress is tensile and can be greater than the tensile strength even before the uniaxial compressive strength is reached. By using the Inglis's formula and simplifying the cracks as slender ellipse, the above conclusions that drawn by using the Maxwell model are confirmed. Compared to shearing fracture, energy consumption of splitting seems to be less, and splitting is most likely to occur when the uniaxial loading is great and quick. Besides, explaining the rock core disking occurred under the fast axial unloading by using the Maxwell model may be helpful for understanding that rock core disking is fundamentally a tensile failure phenomenon.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.04a
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• pp.74-79
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• 1992

The confinement of concrete from splitting bond failure is studied with the experiments and finite element models. The cracks in the test beam-end specimens containing various covers show a typical splitting failure with a dominant fracture surface. The finite element model includes representation of the splitting cracking using Hillerborg's fictitious crack model. The increase in bond strength from addition of covers are consistant for both test bars and numerical models. The numerical solution agrees well with results and also with the test results and also with the empirical equations. The splitting crack in the numerical models generally matches the crack surface observed in the laboratory. The confinement of concrete from splitting is one of the governing factors in the ultimate bond force.

• Tunnel and Underground Space
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• v.27 no.5
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• pp.263-270
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• 2017

Hydraulic rock splitting is a technique which leads to failure of rockmass by means of water injection with a pressure higher than the tensile strength of rockmass, using straddle packer installed in boreholes drilled from free surface. Field tests were conducted in this study for several slopes of biotite granite according to various designs for borehole layout and water injection. Test results showed that new cracks were generated to connect to adjacent holes or that pre-existed cracks were propagated by injection, finally leading to failure. In particular, this study suggests the possibility of controlling the direction of generated cracks with guide slot, since new cracks were generated parallel to the guide slots carved on a borehole wall before injection. Various types of borehole layout and injection methods should be further developed for the practical uses, considering the factors influencing on crack generation.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.719-730
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• 2021

An improved packer and injection system was developed to improve the efficiency of excavation by hydraulic rock splitting by reducing vibration and noise. Field testing of the system found hydraulic fractures limited in expansion and extension due to the loss of injection pressure by leackage from the cracks, and then the single packer applied to injection hole allowed to produce a sufficient tensile displacement for rock excavation. Numerical analysis based on the field test data could explain the development of cracks in the field experiments.

• Explosives and Blasting
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• v.27 no.2
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• pp.1-11
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• 2009

Abstract By investigating the stress redistribution caused by the preceding cut blasting when applying the pre-splitting method to tunnel round, an attempt was made to find conditions that were favorable for the propagation of cracks in contour holes. The investigation of the direction of minor principal stress in the numerical analysis revealed that the most significant factor affecting the change of the direction was the loading condition, while the core shape, rock type, and tunnel depth seemed to be less important in determining the direction of minor principal stress. Moreover, the number of cracks tended to increase with the increase of deviatoric stress. Through the model test of pre-splitting, it is confirmed that the pre-splitting method taking the stress field into account can reduce the extent of yield zone and has advantage in controlling the direction of crack than the conventional one.

• Geomechanics and Engineering
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• v.14 no.5
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• pp.499-507
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• 2018

In this paper splitting failure on rock pillars among the underground caverns has been studied. The damaged structure is considered to be thin plates and then the failure mechanism of rock pillars has been studied consequently. The critical load of buckling failure of the rock plate has also been obtained. Furthermore, with a combination of the basic energy dissipation principle, generalized formulas in estimating the number of splitting cracks and in predicting the maximum deflection of thin plate have been proposed. The splitting criterion and the mechanical model proposed in this paper are finally verified with numerical calculations in FLAC 3D.

• Structural Engineering and Mechanics
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• v.36 no.4
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• pp.447-461
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• 2010

Fiber reinforced polymer (FRP) bars have been widely used as reinforcement for concrete structures. However, under elevated temperatures, the difference between the transverse coefficients of thermal expansion of FRP rebars and concrete may cause the splitting cracks of the concrete cover. As a result, the bonding of FRP-reinforced concrete may not sustain its function to transfer load between the FRP rebar and the surrounding concrete. The current study investigates the cracking resistance of FRP reinforced concrete against the thermal expansion based on a mechanical model that accounts for the tensile softening behavior of concrete. To evaluate the efficacy of the proposed model, the critical temperature increments at which the splitting failure of the concrete cover occurs and the internal crack radii estimated are compared with the results obtained from the previous studies. Simplified equations for estimating the critical temperature increments and the minimum concrete cover required to prevent concrete splitting failure for a designated temperature increment are also derived for design purpose.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.197-200
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• 2005

This paper presents an analytical model for evaluation of Tension Stiffening Effect by actual Bond-Slip relationships between the reinforcement and the surrounding concrete. The presence of longitudinal splitting cracks was found to significantly after the tension stiffening. The model is applied to the longitudinal splittings cracks and derived to Tension stiffening model. The predicted values are shown to be in good agreement with the experimentally measured data.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.171-178
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• 2003

Wing and secondary cracks are unique types of cracks observed in rock masses subjected to uniaxial and biaxial compressive loading conditions. In this study, morphological features of wing and secondary cracks developed in gypsum specimens are investigated in the macro and micro scales. Along the path of wing crack, microtensile cracks are observed. Microtensile cracks coalesce with pores and show branch phenomenon. From the onset of the wing crack, multiple initiations of microtensile cracks are observed. Microtensile cracks show tortuous propagation paths and relatively constant aperture of the cracks during the propagation. It is shown that microtensile cracks propagate by splitting failure. At the micro scale, microfsults are observed in the path of the secondary cracks. Along the path of the secondary cracks, separation of grains and conglomerate grains, oblique microfaults, and irregular aperture of microfault are observed. These features show that the secondary cracks are produced in shear mode. The measured sizes of fracture process zone across the propagation direction near the tip of wing and secondary cracks range from 10$\mu{m}$ to 20$\mu{m}$ far wing cracks and from 100$\mu{m}$ to 200$\mu{m}$ for secondary cracks, respectively.