• Title/Summary/Keyword: In-situ Stress

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The Inflence of Excavation Damaged Zone around an Underground Research Tunnel in KAERI (한국원자력연구원 내 지하처분연구시설 주변의 암반 손상대 영향 평가)

  • Kwon, S.;Kim, J.S.;Cho, W.J.
    • Explosives and Blasting
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    • v.26 no.2
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    • pp.11-19
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    • 2008
  • The development of an excavation damaged zone, EDZ, due to the blasting impact and stress redistribution after excavation, can influence on the long tenn stability, economy, and safety of the underground excavation. In this study, the size and characteristics of an EDZ around an underground research tunnel, which was excavated by controlled blasting, in KAERI were investigated. The results were implemented into the modelling for evaluating the influence of an EDZ on hydro-mechanical behavior of the tunnel. From in situ tests at KURT, it was possible to determine that the size of EDZ was about l.5rn. Goodman jack tests and laboratory tests showed that the rock properties in the EDZ were changed about 50% compared to the rock properties before blasting. The size and property change in the EDZ were implemented to a hydro-mechanical coupling analysis. In the modeling, rock strengths and elastic modulus were assumed to be decreased 50% and. the hydraulic conductivity was increased 1 order. From the analysis, it was possible to see that the displacement was increased while the stress was decreased because of an EDZ. When an EDZ was considered in the model, the tunnel inflow was increased about 20% compared to the case without an EDZ.

Behavioral Mechanism of Hybrid Model of ABG: Field Test (현장시험을 통한 ABG 하이브리드 공법의 거동 메커니즘 분석)

  • Seo, Hyung-Joon;Kim, Hyun-Rae;Jeong, Nam-Soo;Lee, In-Mo
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.03a
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    • pp.523-534
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    • 2010
  • A hybrid system of soil-nailing and compression anchor is proposed in this paper; the system is composed of an anchor bar (installed at the tip) with two PC strands and a steel bar. After drilling a hole, installing proposed hybrid systems, and filling the hole with grouting material, prestress is applied to the anchor bar to restrict the deformation at the head and/or to prevent shallow slope failures. However, since the elongation rate of PC strand is much larger than that of steel bar, yield at the steel bar will occur much earlier than the PC strand. It means that the yield load of the hybrid system will be overestimated if we simply add yield loads of the two - anchor bar and PC strands. It might be needed to try to match the yielding time of the two materials by applying the prestress to the anchor bar. It means that the main purpose of applying prestress to the anchor bar should be two-fold: to restrict the deformation at the nail head; and more importantly, to maximize the design load of the hybrid system by utilizing load transfer mechanism that transfers the prestress applied at the tip to the head through anchor bar. In order to study the load transfer mechanism in a systematic way, in-situ pullout tests were performed with the following conditions: soil-nailing only; hybrid system with the variation of prestress stresses from 0kN to 196kN. It was found that the prestress applied to the anchor system will induce the compressive stress to the steel bar; it will result in decrease in the slope of load-displacement curve of the steel bar. Then, the elongation at which the steel bar will reach yield stress might become similar to that of PC strands. By taking advantage of prestress to match elongations at yield, the pullout design load of the hybrid system can be increased up to twice that of the soil-nailing system.

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A Study of the Laboratory Scale Measurement Technique of P-Wave Velocity for the Assessment of the An isotropy of Engineering Property of Rock (암석의 공학적 이방성 측정을 위한 실험실내 P파 속도 측정기법에 대한 연구)

  • 박형동
    • The Journal of Engineering Geology
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    • v.5 no.3
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    • pp.237-274
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    • 1995
  • This study was focused on the improvement of the measurement technique of P-wave velocity for the assesment of the anisotropy of the engineering property of rock. Samples used were collected from a working quarry within the Carnmenellis granite area on which series of engineering geological data have been accumulated. This study mainly concerned the development of measurement technique at the curved surface of rock, the use of natural honey-based coupling agent and the drying method for rock specimen over $P_2O_5$. According to the results, the range of the P-wave velocity anisotropy in two dimensional plane, fell between 0 and 4.68 (%). The direction where maximum velocity occurred was parallel to the orientation of the maximum in-situ stress. The result showed that P - wave velocity is a useful measure to asses the anisotropy of the engineering property of rock and it is suggested that the improvements adopted here can be applied to the experimental work on the rocks in Korea.

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Prediction of Ground-Condition Ahead of the Tunnel Face by Using 3-Dimensional Absolute Displacements (3차원 절대내공변위를 이용한 터널 막장전방의 지반면화 예측기법)

  • Lee, In-Mo;Gang, Gi-Don;Park, Gwang-Jun
    • Geotechnical Engineering
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    • v.14 no.4
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    • pp.17-32
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    • 1998
  • has been much progress in theories and construction techniques to secure the stability of the underground structures. Recently, several studios have shown that it is possible to predict the existence of discontinuities ahead of a tunnel face by analyzing 3-dimensional absolute displacements measured during tunnel excavation. This paper concentrated on the development of a methodology to predict the existence and location of the discontinuities, or the void space(abandoned mine) , by performing 3-dimensional FEM analysis and considering the stress relocation caused by arching effect during excavation. Also, this study tried to verify deformation for choosing the most suitable support system. The results of this study might provide a way of safer and economical tunnel construction by utilizing the in-situ monitoring data.

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Application of flat DMT and ANN for reliable estimation of undrained shear strength of Korean soft clay (국내 연약지반의 신뢰성있는 비배수 전단강도 추정을 위한 flat DMT와 인공신경망 이론의 적용)

  • Byeon, Wi-Yong;Kim, Young-Sang;Lee, Seung-Rae;Jeong, Eun-Taeg
    • Proceedings of the Korean Geotechical Society Conference
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    • 2004.03b
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    • pp.154-161
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    • 2004
  • The flat dilatometer test(DMT) is a geotechnical tool to estimate in-situ properties of various types of ground materials. The undrained shear strength is known to be the most reliable and useful parameter obtained by DMT. However, the existing relationships which were established for other local deposits depend on the regional geotechnical characteristics. In addition, the flat dilatometer test results have been interpreted using three intermediate indicesmaterial index($I_p$), horizontal stres index($K_p$), and dilatometer modulus($E_p$) and the undrained shear strength is estimated only by using the horizontal stress index($K_D$). In this paper, an artificial neural network was developed to evaluate the undrained shear strength by DMT and the ANN, based on the $p_0,\;p_1,\;p_2,\;{\sigma}'_v_0$, and porewater pressure. The ANN which adopts the back-propagation algorithm was trained based on the DMT data obtained from Korean soft clay. To investigate the feasibility of ANN model, the prediction results obtained from data which were not used to train the ANN and those obtained from existing relationships were compared.

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A Study on the 3D Analysis of Driven Pile Penetration Based on Large Deformation Technique (Coupled Eulerian-Lagrangian) (대변형 해석기법(Coupled Eulerian-Lagrangian)을 이용한 항타 관입성 모사의 3차원 해석)

  • Ko, Jun-Young;Jeong, Sang-Seom;Lee, Seung-Yeon
    • Journal of the Korean Geotechnical Society
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    • v.31 no.8
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    • pp.29-38
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    • 2015
  • This paper presents the application of the Coupled Eulerian-Lagrangian (CEL) numerical technique to simulate the driving of open-ended piles into sandy soil. The main objective of this study was to investigate the applicability of CEL technique to the behavior of the driven pile penetration. Comprehensive studies to verify the behavior of driven pile penetration are presented in this paper. Through comparison with results of field load tests, the CEL methodology was found to be in good agreement with the general trend observed by in situ measurement, and the CEL approach accurately simulated the behavior of driven pipe piles.

Undrained Creep Rupture of an Anisotropically Normally Consolidated Clay (이방정규압밀점토의 비배수크리프 파양)

  • Kang, Byung-Hee;Hong, Eui
    • Geotechnical Engineering
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    • v.9 no.4
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    • pp.55-64
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    • 1993
  • The Undrained creep tests on the normally consolidated clays with four different consolication ratios(c3c'/clc': 1.0, 0.7, 0.5, 0.4) were performed to investigate the effects of avisotropic consolidation on the undrained creep rupture behavior. The elapsed time to a certain minimum strain rate is decreased with decreasing the value of the consolidation pressure ratio, and the elapsed time to rupture for a certain minimum strain rate is also decreased with decreasing the ratio. The upper yield strength obtained from the equation suggested by Finn and Shead(1.) is coincided well with the creep strength irrespective of the magnitude of the consolidation pressure ratio, and the normallised upper yielding strength by mean confining pressure is decreased with increasing the consolidation pressure ratio. The critical strain for creep rupture, the strain at min. strain rate, is constant irrespective of the magnitude of creep stress, but it increased exponentially with increasing the ratio, It accordingly is dangerous that the potential of in-situ creep rupture is estimated only by the creep rupture test on the isotropically consolidated clay in case of K0-value below 1.0.

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Velocity-effective stress response of $CO_2$-saturated sandstones ($CO_2$로 포화된 사암의 속도-유효응력 반응)

  • Siggins, Anthony F.
    • Geophysics and Geophysical Exploration
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    • v.9 no.1
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    • pp.60-66
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    • 2006
  • Three differing sandstones, two synthetic and one field sample, have been tested ultrasonically under a range of confining pressures and pore pressures representative of in-situ reservoir pressures. These sandstones include: a synthetic sandstone with calcite intergranular cement produced using the CSIRO Calcite In-situ Precipitation Process (CIPS); a synthetic sandstone with silica intergranular cement; and a core sample from the Otway Basin Waarre Formation, Boggy Creek 1 well, from the target lithology for a trial $CO_2$ pilot project. Initial testing was carried on the cores at "room-dried" conditions, with confining pressures up to 65 MPa in steps of 5 MPa. All cores were then flooded with $CO_2$, initially in the gas phase at 6 MPa, $22^{\circ}C$, then with liquid-phase $CO_2$ at a temperature of $22^{\circ}C$ and pressures from 7 MPa to 17 MPa in steps of 5 MPa. Confining pressures varied from 10 MPa to 65 MPa. Ultrasonic waveforms for both P- and S-waves were recorded at each effective pressure increment. Velocity versus effective pressure responses were calculated from the experimental data for both P- and S-waves. Attenuations $(1/Q_p)$ were calculated from the waveform data using spectral ratio methods. Theoretical calculations of velocity as a function of effective pressure for each sandstone were made using the $CO_2$ pressure-density and $CO_2$ bulk modulus-pressure phase diagrams and Gassmann effective medium theory. Flooding the cores with gaseous phase $CO_2$ produced negligible change in velocity-effective stress relationships compared to the dry state (air saturated). Flooding with liquid-phase $CO_2$ at various pore pressures lowered velocities by approximately 8% on average compared to the air-saturated state. Attenuations increased with liquid-phase $CO_2$ flooding compared to the air-saturated case. Experimental data agreed with the Gassmann calculations at high effective pressures. The "critical" effective pressure, at which agreement with theory occurred, varied with sandstone type. Discrepancies are thought to be due to differing micro-crack populations in the microstructure of each sandstone type. The agreement with theory at high effective pressures is significant and gives some confidence in predicting seismic behaviour under field conditions when $CO_2$ is injected.

Prediction of Brittle Failure within Mesozoic Granite of the Daejeon Region (대전지역 중생대 화강암 암반 내 취성파괴 예측연구)

  • Jang, Hyun-Sic;Choe, Mi-Mi;Bae, Dae-Seok;Kim, Geon-Young;Jang, Bo-An
    • The Journal of Engineering Geology
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    • v.25 no.3
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    • pp.357-368
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    • 2015
  • Brittle failure of Mesozoic granite in the Daejeon region is predicted using empirical analysis and numerical modeling techniques. The input parameters selected for these techniques were based on the results of laboratory tests, including damage-controlled tests. Rock masses that were considered to be strong during laboratory testing were assigned to "group A" and those considered to be extremely strong were assigned to "group B". The properties of each group were then used in the analyses. In-situ stress measurements, or the ratio of horizontal to vertical stress (k), were also necessary for the analyses, but no such measurements have been made in the study area. Therefore, k values of 1, 2, and 3 were assumed. In the case of k=1, empirical analysis and numerical modeling show no indication of brittle failure from the surface to1000 m depth. When k=2, brittle failure of the rock mass occurs at depths below 800 m. For k=3, brittle failure occurs at depths below 600 m. Although both the Cohesion Weakening Friction Strengthening (CWFS) and Mohr-Coulomb models were used to predict brittle failure, only the CWFS model performed well in simulating the range and depth of the brittle failure zone.

Distribution and Statistical Analysis of Discontinuities in Deep Drillcore (심부시추코어를 활용한 불연속면의 분포 특성 및 통계학적 해석)

  • Junghae Choi;Youjin Jung;Dae-Sung Cheon
    • The Journal of Engineering Geology
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    • v.34 no.3
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    • pp.415-427
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    • 2024
  • This study undertook a quantitative analysis of the distribution of fractures in deep drillcore from a Precambrian metamorphic complex on the north face of Hongcheon-gun, Gangwon-do, Korea. The fracture distribution with depth, inclination of fractures, and grain size in the fracture zone were measured and statistical techniques applied to derive probability distributions of fracture intervals. Analysis of the inclination angles of fracture planes showed that sub-horizontal fractures are dominant, and fracture spacing is mainly ≤0.5 m, with a median of 0.09 m, first quartile of 0.04 m, and third quartile of 0.18 m, indicating very dense fracture development. Statistical analysis of joint properties was undertaken with fitting using five probability density functions (double Weibull, exponential, generalized logistic, gamma, and lognormal). The lognormal distribution (sum of squared errors, SSE = 2.80) yielded the best fit based on the sum of residual squares. Quantitative characterization of the fracture characteristics of deep bedrock in the Hongcheon area is important for various geotechnical applications such as groundwater flow modeling, slope stability assessment, and underground structure design. In future studies, it will be necessary to combine in situ stress measurements and geophysical surveys to determine the relationship between fracture development and the local stress field.