• Geomechanics and Engineering
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• 제7권3호
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• pp.233-246
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• 2014

Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

• 대한금속재료학회지
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• 제47권8호
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• pp.466-473
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• 2009

Our group previously observed the intrinsic stress evolution of Cu thin films during deposition by changing the deposition rate. Intrinsic stress of Cu thin films, which show Volmer-Weber growth, is reported to display three unique stress stages, initial compressive, broad tensile, and incremental compressive stress. The mechanisms of the initial compressive stress and incremental compressive stages remain subjects of debate, despite intensive research inquiries. The tensile stress stage may be related to volume contraction through grain growth and coalescence to reduce over-accumulate Cu adatoms on the film surface. The in-situ intrinsic stresses behavior in Cu thin films was investigated in the present study using a multi-beam curvature measurement system attached to a thermal evaporation device. The effect of substrate surface roughness was monitored by observed the in-situ intrinsic stress behavior in Cu thin films during deposition, using $100{\mu}m$ thick Si(111) wafer substrates with three different levels of surface roughness.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.244-251
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• 2003

A two-dimensional BEM code, $FRACOD^{2D}$, was applied to simulate fracture initiation and propagation processes in a rock pillar during an in situ heater test of a rock pillar planned at the $\"{A}sp\"{o}$ Underground Rock laboratory of SKB, in Southern Sweden. To take the advantage of conventional BEM for simulating fracturing processes, but without efforts for domain integral transformation, a hybrid approach is developed to simulate the fracturing processes in rock pillar under coupled thermo-mechanical loading. The code FRACOD was used for simulating the fracture initiation and propagation processes with its boundary tractions reflecting the effects of the initial and redistributed thermomechanical stresses in the domain of interest at multiple excavation and heating steps were produced by a special algorithm of stress inversion, based on resultant thermo-mechanical stress fields at each excavation and heat loading step by a FEM code without considering fracturing processes. This hybrid approach can take the advantages of both types of numerical methods and avoids their shortcomings for fracturing process simulation and domain effects, respectively. In this paper, we present the hybrid approach for the stress, displacements, and fracturing processes at sequential excavation and heating steps of the in situ heater test as a predictive modelling, the formulation of the fracturing models and the predictive results. Two sections of borehole depth, 0.5 m and 1.5 m below the tunnel floor are considered. The pillar area is modelled with the FRACOD and the stress field produced by excavation and heating is transferred with corresponding boundary stresses. From the modelling results, the degree of fracturing and damage are evaluated for 120 days of heating. Dominated shear fracturing in the vicinity of the central pillar was observed from the models at both sections, but spalled area appears to be limited. Based on the modelling results, a sensitivity study for the effect of pre-existing fractures in the vicinity of the holes is also conducted, and the initiation and evolution of EDZ around the deposition holes are investigated using this particular numerical technique.

• 지질공학
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• 제10권3호
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• pp.225-236
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• 2000

웨스터리 화강암과 베리아 사암 시료에 지하 심부에 상당하는 현장 응력을 가한 후 시추를 함으로써 시추공벽 파쇄를 발생시켰으며, 이를 통하여 현장 응력의 크기를 추정할 수 있는지 연구하였다. 실험은 삼축압축 및 시추공벽 파쇄시험 등 두 단계로 나뉘어 수행되었다. 삼축압축 시험 결과로부터 모아-쿨롱, 나다이, 그리고 모기파괴 기준을 구하였다. 각 파괴 기준을 공벽 파쇄 경계 지점에서의 응력 상태와 비교한 결과, 모아-쿨공 파괴 기준은 공벽에서의 파쇄 응력과는 전혀 일치하지 않았다. 반면, 베리아 사암에서는 나다이기준, 그리고 웨스터리 화강암에서는 모기파괴 기준과 같은 다축(혹은 진 삼축) 파괴 기준이 공벽 주변에서 파쇄를 일으키는 응력 상태와 잘 일치하였다. 적당한 파괴 기준 및 시추공벽 파쇄 크기를 이용하여 두 개의 현장 수평 주응력 중 하나가 알려졌을 경우 다른 하나를 비교적 신뢰할 수 있는 정도로 추정할 수 있다는 것이 밝혀졌다.

• Molecules and Cells
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• 제20권2호
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• pp.247-255
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• 2005

Three different catalase cDNA clones (CaCat1, CaCat2, and CaCat3) were isolated from hot pepper (Capsicum annuum L.), and their expression patterns were analyzed at the levels of mRNA and enzyme activity. Northern hybridization showed that the three catalase genes were differentially expressed in various organs, and that expression of CaCat1 and CaCat2 was regulated differently by the circadian rhythm. In situ hybridization revealed different spatial distributions of CaCat1 and CaCat2 transcripts in leaf and stem. In response to wounding and paraquat treatment, CaCat1 mRNA increased at 4-12 h in both paraquat-treated and systemic leaves. In contrast, wounding had no significant effect on expression of the catalase genes. The increase of catalase activity in the paraquat-treated and systemic leaves paralleled that of CaCat1 mRNA, but did not match that of CaCat1 mRNA in paraquat-treated stems. Our results suggest that CaCat1 may play a role in responses to environmental stresses.

• International Journal of Railway
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• 제3권1호
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• pp.1-6
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• 2010

The steel plate-girder bridges with concrete gravity piers have possibilities of overturning by lateral inertial force which can be reproduced by sudden earthquake attack. This paper explores an overturning mechanism of existing concrete gravity pier onto the sandy soil in the event of lateral push-over load by in-situ experimental observation. The in-situ push-over experiment for pier with earth anchors between spread footing and rock beds exhibits a reasonable enhancement of ductility against overturning. In unanchored system, a flexural crack at cold joint of concrete pier is not developed because of the over-turning of the pier. This leads a global instability (rotation) of pier-footing system with relatively low stresses in pier itself. While a lateral load is persistently increased in anchored system, the successive flexural cracking failure at cold joint is observed even after the local shear failure of soil due to redistribution of stress equilibrium between soil and pier structure as long as a tensile action of anchor cable is active.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.431-438
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• 2005

In this paper, the characteristics of excessive horizontal stress components in Korea were studied using the in-situ hydraulic fracturing stress measurement data over five hundred in 110 individual test boreholes. Based on the in-situ testing data, the magnitude and orientation of the horizontal stress component and variation of stress ratio (K) with depth were investigated. And also horizontal stress magnitude versus depth relationships and distribution limits of stress ratio components were suggested. For the subsurface space above 310 m depth in the entire territory, the stress ratio has a tendency to diminish and be stabilized with depth, but for some areas, it was revealed that the excessive horizontal stress fields with stress ratio close to 3.0 below 200 m in depth have formed. The result of investigation for excessive horizontal stress regions indicates that there exist several regions above 300 m in depth where localized excessive horizontal stresses enough to induce potentially brittle failure around future openings have formed.

• 한국자기학회지
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• 제5권5호
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• pp.470-473
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• 1995

We have constructed an apparatus for in sity measurement of stress of the film prepared by sputtering using an optical noncontact displacement detector. A Change of the gap distance between the detector and the substrate, caused by stress of a deposited film, was detected by a corresponding change of the reflectivity. The sensitivity of the displacement detector was $5.9\;{\mu}V/{\AA}$ and thus, it was turned out to be good enough to detect stress caused by deposition of a monoatomic layer. The apparatus was applied to in situ stress measurements of Co/X(X=Pd or Pt) multilayer thin films prepared on the glass substrates by dc magnetron sputtering. At the very beginning of the deposition, both Co and X sublayers have subjected to their own intrinsic stresses. However, when the film was thicker than about $100{\AA}$, constant tensile stress in the Co sublayer and compressive stress in the X sublayer were observed, which is believed to be related to a lattice mismatch between the matching planes of Co and X.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 연약지반처리위원회 학술세미나
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• pp.71-78
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• 2000

SHANSEP method involves the consolidation to stresses in excess of the preconsolidation pressure in order to overcome sample disturbance effect. The concept of SHANSEP is based on an approach to laboratory test which attempts to reproduce the in-situ conditions more closely than is possible in routine tests and evaluates normalized strength parameters for the soil as a function of OCR. But SHANSEP method can be applied only to fairly uniform clay deposits, and is unsuitable for a random deposit. In this study, CK/sub o/U triaxial compression test and incremental loading consolidation test were performed for the application of SHANSEP method on Yangsan clay. During the K/sub o/-consolidation, triaxial specimens were consolidated to stress equal to two times the in-situ vertical effective stress. And for overconsolidated condition, the specimens were swelled to a known vertical effective stress in order to have the desired OCR. With the results of CK/sub o/U triaxial compression test using the block samples, the relationship between c/sub u//σ/sub vc/' and OCR on Yangsan clay was established. For evaluating the undrained shear strength of Yangsan clay with depth, CK/sub o/U triaxial compression test was performed using the piston samples taken from Yangsan site. And also undrained shear strength was analyzed from the in-situ test such as Cone Penetration Test(CPT), Dilatometer Test(DMT), and Field Vane Test(FVT) and was compared with that of CK/sub o/U triaxial compression test.

• 지질공학
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• 제5권2호
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• pp.139-153
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• 1995

현장시추코어를 이용한 역학적, 수리학적 분석을 수행하여 거제지역 화강암체의 공학적 특성을 산정하였다. 코어분석시에 현장응력의 영향이 고려될 수 없어서 암반불류에 의거하여 산정된 공학적 성질들이 현장실험결과와 상이하게 도출되기도 하였다. 암반분류, 공내실험 및 실내실험 결과에 근거하여 지하공동 설계에 대한 경험적 계수들을 산정하였다. 거제도 남단에 분포하는 화강암체의 경우, 비록 균열대가 존재하지만, 상당히 양호한 암반상태를 나타내고 있으며, 대규모 지하시설도 용이하게 건설될 수 있을 것으로 기대된다.