• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.313-318
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• 2004

When plan breakdown by permeation of fill dam, bank by original decision scale model test of sound, original decision scale model test of sound that destroy having used water was carried out. And original decision scale model test of sound that use viscous fluid is carried out, but doubt remains in experiment result in state that verification of law of similarity is not achieved. In this study, verified according to Modeling of Models' method effecting law of similarity to use n ship horoscope solution of water.

• Tunnel and Underground Space
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• v.27 no.4
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• pp.243-252
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• 2017

Since the failure behavior of transversely isotropic rocks is significantly different from that of isotropic rocks, it is necessary to develop a transversely isotropic rock failure function in order to evaluate the stability of rock structures constructed in transversely isotropic rock masses. In this study, a spatial distribution function for strength parameters of transversely isotropic rocks is proposed, which is based on the Cassini oval curve proposed by 17th century astronomer Giovanni Domenico Cassini to model the orbit of the Sun around the Earth. The proposed distribution function consists of two model parameters which could be identified through triaxial compression tests on transversely isotropic rock samples. The original Mohr-Coulomb (M-C) failure function is extended to a three-dimensional transversely isotropic M-C failure function by employing the proposed strength parameter distribution function for the spatial distributions of the friction angle and cohesion. In order to verify the suitability of the transversely isotropic M-C failure function, both the conventional triaxial compression and true triaxial compression tests of transversely isotropic rock samples are simulated. The predicted results from the numerical experiments are consistent with the failure behavior of transversely isotropic rocks observed in the actual laboratory tests. In addition, the simulated result of true triaxial compression tests hints that the dependence of rock strength on intermediate principal stress may be closely related to the distribution of the microstructures included in the rock samples.

• Explosives and Blasting
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• v.39 no.2
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• pp.1-14
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• 2021

Recently, with the development of high-performance processing devices such as GPGPU, a three-dimensional dynamic analysis technique that can replace expensive rock material impact tests has been actively developed in the defense and aerospace fields. Experimentally observing or measuring fracture processes occurring in rocks subjected to high impact loads, such as blasting and earth penetration of small-diameter missiles, are difficult due to the inhomogeneity and opacity of rock materials. In this study, a three-dimensional dynamic fracture process analysis technique (3D-DFPA) was developed to simulate the fracture behavior of rocks due to impact. In order to improve the operation speed, an algorithm capable of GPGPU operation was developed for explicit analysis and contact element search. To verify the proposed dynamic fracture process analysis technique, the dynamic fracture toughness tests of the Straight Notched Disk Bending (SNDB) limestone samples were simulated and the propagation of the reflection and transmission of the stress waves at the rock-impact bar interfaces and the fracture process of the rock samples were compared. The dynamic load tests for the SNDB sample applied a Pulse Shape controlled Split Hopkinson presure bar (PS-SHPB) that can control the waveform of the incident stress wave, the stress state, and the fracture process of the rock models were analyzed with experimental results.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.246-246
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• 2019

점착성 유사는 비점착성 유사보다 작은 입자 크기를 가지며 전자기적 점착력에 의해 연속적인 응집과 파괴의 과정인 응집현상을 겪는다. 응집현상에 의해 생긴 유사 덩어리를 플럭(Floc)이라고 하며 유사의 응집현상은 점착성 유사가 가지는 입자 크기, 침강속도, 밀도를 변화시킨다. 유사의 이동은 크기, 침강속도, 밀도에 영향을 받는다. 따라서 점착성 유사의 여러 특성에 관여하는 입자의 크기에 대한 충분한 이해는 점착성 유사의 이동을 파악하는 데에 필수적이다. 본 연구에서는 점착성 유사의 여러 특성 중, 입자 크기 분포에 대한 특성을 분석하는 것을 수행하였다. 일반적으로 점착성 유사의 연구에서 입도 분포는 Log-normal 분포로 가정하여 사용되고 있다. 그러나 그 적합성에 대해서는 검증된 바가 없다. 따라서 과거 연구에서 조사된 점착성 유사의 입도 분포 자료를 현장에서 측정된 자료와 실험실에서 측정된 자료로 나누어 수집한 후, 표본에 통계학적인 방법인 적합도 검정을 사용하여 실제 어떠한 분포를 모사하는지 살펴보았다. 적합도 검정은 Kolmogorov- Smirnov (K-S)검정을 이용하였으며 K-S 검정의 결과가 유의수준 5%를 통과하는 경우 가정된 분포가 실제 표본을 잘 모사하는 것으로 판단하였다. 적합도 검정 결과, 점착성 유사의 입도 분포는 현장 실험과 실험실 실험에서 다른 특징을 나타내었다. 현장 실험의 경우 입도 분포의 형태가 지수 분포의 형태를 나타내는 경우가 많았으며 Gamma 분포가 우수하게 모사하였다. 실험실 실험의 입도 분포는 일반적인 양의 왜곡도를 가지는 분포를 그렸으며 GEV 분포와 Gamma 분포가 우수하게 모사하였다. 두 경우 모두 Log-normal 분포가 적합하다고 판단되는 경우는 많지 않았다. 그러나 Log-normal 분포에 위치 매개변수를 추가하여 3 매개변수의 분포로 모사한 경우 유의수준 5%를 통과하는 경우가 크게 증가하였다. 향후에는 점착성 유사의 입도 분포를 모사하고 사용함에 있어 Log-normal 분포를 무조건적으로 이용하는 것은 지양해야할 것으로 판단된다. 2 매개변수의 분포를 점착성 유사의 입도분포로 사용할 경우, Gamma 분포를 추천하며, 기존에 사용되던 Log-normal 분포를 사용할 경우 위치 매개변수를 추가하여 3 매개변수의 Log-normal 분포를 이용할 것을 추천한다. 또한 점착성 유사의 입도를 모사하는 분포를 개발하여 사용한다면 점착성 유사의 이동과 특성을 연구할 때 가장 중요한 크기 특성에 대한 많은 정보를 제공할 수 있다고 판단된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.757-764
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• 2014

In this study, the effect of shape parameters on the J-R curves of curved CT specimens was evaluated using the limit load method. Fracture toughness tests considering the shape factors L/W and $R_m/t$ of the specimens were also performed. Thereafter, the J-R curves of the curved CT specimens were compared using the J-integral equation proposed in the ASTM (American Society for Testing and Materials) and limit load solution. The J-R curves of the curved CT specimens were also compared with those of the CWP (curved wide plate), which is regarded to be similar to real pipe and standard specimens. Finally, the effectiveness of the J-R curve of each curved CT specimen was evaluated. The results of this study can be used for assessing the applicability of curved CT specimens in the accurate evaluation of the fracture toughness of real pipes.

• Tunnel and Underground Space
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• v.21 no.2
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• pp.93-102
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• 2011

In spite of being unable to take into the effect of intermediate principal stress, Mohr-Coulomb and Hoek-Brown criteria are very popular as rock failure criteria. The recent researches reveal that the influence of intermediate principal stress on the failure strength of rock is substantial, so that 3-D failure criteria in which the intermediate principal stress could be considered is necessary for the safe design of the important rock structures. In this study, the likely application of the 3-D failure criterion proposed by Jiang & Pietruszczak (1988) to the prediction of the true triaxial strength of rock materials is discussed. The failure condition is linear in the meridian plane of principal stress space and it is represented by the smooth surface contacting the corners of the Mohr-Coulomb surface. The performance of the Jiang & Pietruszczak's criterion is demonstrated by simulating the actual true triaxial tests on the rock samples of three different rock types.

• International Journal of Highway Engineering
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• v.1 no.1
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• pp.97-106
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• 1999

This study was conducted to develop a test system for evaluating resistance against reflection cracking in shear mode caused by wheel load in asphalt concrete overlaid on the deteriorated cement concrete pavement. Reflection cracking resistance of selected polymer modified asphalt(PMA) mixtures with and without reinforcement was evaluated using this test system. It was shown that the test results accounted for the effectiveness of materials and reinforcement characteristics in terms of the difference in the resistance against reflection cracking. A shear failure life of a certain mixture was estimated with a high coefficient of determination. when the test results were used in a well known prediction model. Therefore, it seemed to be possible to use this technique for predicting a relative service life of on overlay.

• Explosives and Blasting
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• v.22 no.4
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• pp.7-15
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• 2004

An explosion modeling technique was developed by using the spherical discrete element code, PFC3D, which can be used to model the dynamic stress wave propagation phenomenon. The modeling technique is simply based on an idea that the explosion pressure should be applied to a PFC3D particle assembly not in the form of an external force (body force), but in the form of a contact force (surface force). According to this concept, the explosion pressure is applied to the wall particles by the scheme of radius expansion/contraction of inner-hole particles. The output wall force is compared to the input hole pressure in every time step, and a correction routine is activated to control the radius multiplier of the inner-hole particles. A comparative blast simulation far a cement mortar block of $80\times90\times80mm$ was conducted by using the conventional explosion modeling method and the new one. The results of the simulation are presented in a qualitative fashion.

• Tunnel and Underground Space
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• v.14 no.4
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• pp.248-260
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• 2004

Damage in brittle rock due to stress increase starts from initiation of microcracks, and then results in failure by forming macro failure planes due to propagation and coalescence of these discrete cracks. Conventionally, continuum approaches using macro-failure criteria or a number of elasto-plastic models have been major solution to implement rock damage and failure. However, actual brittle failure processes can be better described in phenomenological approach if initiation and propagation of discrete fractures are explicitly considered. This study presents damage and failure process of rock using a boundary element code, FRACOD, which has been developed to model fracturing process of rocks. Through a series of numerical uniaxial compressive tests, the feasibility of the developed model was verified, and realistic rock failure process was reproduced considering scale effects in rocks. In addition, the fracturing process and the corresponding rock damage in the vicinity of deep shaft in rock mass were presented as an application of this approach. This approach will be expected to contribute to finding better engineering solutions for the analysis of stability problems in brittle rock masses.

• Journal of Korean Society of Disaster and Security
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• v.16 no.1
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• pp.91-103
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• 2023

This study aims to investigate the dynamic fracture characteristics of rocks and rock-like materials subjected to the Nonex Rock Cracker (NRC), a vapor pressure crushing agent that produces vapor pressure by instantaneously vaporizing a liquid mixture crystallized through the thermite reaction. Furthermore, the study seeks to develop an analytical technique for predicting the fracture pattern. A dynamic fracture test was performed on a PMMA block, an artificial brittle material, using the NRC. High-speed cameras and dynamic pressure gauges were employed to capture the moment of vapor pressure generation and measure the vapor pressure-time history, respectively. The 2-dimensional Dynamic Fracture Process Analysis (2D DFPA) was used to simulate the fracture process caused by the vapor pressure, with the applied pressure determined based on the vapor pressure-time history. The proposed analytical method was used to examine various fracture patterns with respect to granite material and high-performance explosives.