• Title/Summary/Keyword: permeable fracture

Search Result 20, Processing Time 0.026 seconds

Transient response of a piezoelectric layer with a penny-shaped crack under electromechanical impacts

  • Feng, Wenjie;Li, Yansong;Ren, DeLiang
    • Structural Engineering and Mechanics
    • /
    • v.23 no.2
    • /
    • pp.163-175
    • /
    • 2006
  • In this paper, the dynamic response of a piezoelectric layer with a penny-shaped crack is investigated. The piezoelectric layer is subjected to an axisymmetrical action of both mechanical and electrical impacts. Two kinds of crack surface conditions, i.e., electrically impermeable and electrically permeable, are adopted. Based upon integral transform technique, the crack boundary value problem is reduced to a system of Fredholm integral equations in the Laplace transform domain. By making use of numerical Laplace inversion the time-dependent dynamic stress and electric displacement intensity factors are obtained, and the dynamic energy release rate is further derived. Numerical results are plotted to show the effects of both the piezoelectric layer thickness and the electrical impact loadings on the dynamic fracture behaviors of the crack tips.

Fresh Water Injection Test in a Fractured Bedrock Aquifer for the Mitigation of Seawater Intrusion (해수침투 저감을 위한 균열암반 대수층 내 담수주입시험)

  • Shin, Je-Hyun;Byun, Joong-Moo
    • Economic and Environmental Geology
    • /
    • v.43 no.4
    • /
    • pp.371-379
    • /
    • 2010
  • Fresh water injection test in a fractured bedrock aquifer was applied as an efficient approach to lower saline concentrations in the saltwater-freshwater transition zone formed by seawater intrusion in a coastal area. The methodology and effectiveness of fresh water injection for hydraulically controlling seawater intrusion is overwhelmingly site dependent, and there is an urgent need to characterize the permeable fractures or unconsolidated porous formations which can allow for seawater flow and transport. Considering aquifer characteristics, injection and monitoring boreholes were optimally designed and completed to inject fresh water through sand layer and fractured bedrock, respectively. We devised and used the injection system using double packer for easy field operation and maintenance. Overall fracture distribution was systematically identified from borehole image logs, and the section of fresh water injection was decided from injection test and monitoring. With fresh water injection, the fluid electrical conductivity of the monitoring well started to be lowered by the inflow of fresh water at the specific depth. And this inflow leaded to the replacement of the fluid in the upper parts of the borehole with fresh water. Furthermore, the injection effect lasted more than several months, which means that fresh water injection may contribute to the mitigation of seawater intrusion in a coastal area.

Numerical simulation of groundwater flow in LILW Repository site:I. Groundwater flow modeling (중.저준위 방사성폐기물 처분 부지의 지하수 유동에 대한 수치 모사: 1. 지하수 유동 모델링)

  • Park, Kyung-Woo;Ji, Sung-Hoon;Kim, Chun-Soo;Kim, Kyung-Su;Kim, Ji-Yeon
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
    • /
    • v.6 no.4
    • /
    • pp.265-282
    • /
    • 2008
  • Based on the site characterization works in a low and intermediate level waste(LILW) repository site, the numerical simulations for groundwater flow were carried out in order to understand the groundwater flow system of repository site. To accomplish the groundwater flow modeling in the repository site, the discrete fracture network(DFN) model was constructed using the characteristics of fracture zones and background fractures. At result, the total 10 different hydraulic conductivity(K) fields were obtained from DFN model stochastically and K distributions of constructed mesh were inputted into the 10 cases of groundwater flow simulations in FEFLOW. From the total 10 numerical simulation results, the simulated groundwater levels were strongly governed by topography and the groundwater fluxes were governed by locally existed high permeable fracture zones in repository depth. Especially, the groundwater table was predicted to have several tens meters below the groundwater table compared with the undisturbed condition around disposal silo after construction of underground facilities. After closure of disposal facilities, the groundwater level would be almost recovered within 1 year and have a tendency to keep a steady state of groundwater level in 2 year.

  • PDF

Development of Failure Criterion of Hot Mix Asphalt Using Triaxial Shear Strength Test (삼축압축시험을 이용한 아스팔트 혼합물의 파괴기준 개발)

  • Kim, Seong Kyum;Lee, Kwan Ho
    • KSCE Journal of Civil and Environmental Engineering Research
    • /
    • v.34 no.3
    • /
    • pp.947-954
    • /
    • 2014
  • In general, Fracture of the material is not occurring of the maximum normal stress or the maximum shear stress failure in the state. Maximum normal stress and maximum shear stress in the state of Critical coupling from being destroyed based on the Mohr-Coulomb theory. Couple of different mixtures, including permeable asphalt pavement, SMA and dense-graded asphalt mixture, were used for compression triaxial test at $45^{\circ}C$ and $60^{\circ}C$. Mohr-Coulomb theory to the analysis of compression triaxial test result of the internal friction angle $38.9^{\circ}{\sim}46.9^{\circ}$ measured somewhat irregularly, but in the case of cohesion, depending on whether the temperature and immersion of the specimen appeared differently. In addition, Indirect tensile test and compression triaxial test of the asphalt mixture to determine the correlation between compression triaxial test results assessed as cohesion and internal friction angle calculated using the theoretical Indirect tensile strength and measured indirectly tensile strength were analyzed. The Measured & Predicted IDT St values tended to be proportional.

Oxygen Permeation and Mechanical Properties of La0.6Sr0.4Co0.2Fe0.8O3-δ Membrane with Different Microstructures (미세구조에 따른 La0.6Sr0.4Co0.2Fe0.8O3-δ 분리막의 산소투과 및 기계적 특성)

  • Lee, Shi-Woo;Lee, Seung-Young;Lee, Kee-Sung;Woo, Sang-Kuk;Kim, Do-Kyung
    • Journal of the Korean Ceramic Society
    • /
    • v.39 no.10
    • /
    • pp.994-1000
    • /
    • 2002
  • Oxygen permeability and the mechanical properties of mixed ionic-electronic conductive $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ perovskite-type membrane, fabricated by solid state reaction, were investigated with regard to microstructure. The microstructure of the membrane was controlled by changing the sintering temperature and holding time. The average grain size and relative density were evaluated as a function of sintering conditions. As the fraction of grain boundary decreased, oxygen permeability showed a tendency to increase. Especially the maximum oxygen flux of 0.37 ml/$cm^2$${\cdot}$min was measured for the specimen sintered at 1300${\circ}C$ for 10 h, which has high density and relatively large grain size. Fracture strength was dependent on the relative density of sintered body, while fracture toughness increased with average grain size.

Defining the hydraulic excavation damaged zone considering hydraulic aperture change (수리적 간극변화를 고려한 수리적 굴착손상영역의 정의에 관한 연구)

  • Park, Jong-Sung;Ryu, Chang-Ha;Lee, Chung-In;Ryu, Dong-Woo
    • Journal of Korean Tunnelling and Underground Space Association
    • /
    • v.9 no.2
    • /
    • pp.133-141
    • /
    • 2007
  • The excavation damaged zone (EDZ) is an area around an excavation where in situ rock mass properties, stress condition, displacement, groundwater flow conditions have been altered due to the processes induced by the excavation. Various studies have been carried out on EDZ, but most studies have focused on the mechanical bahavior of EDZ by in situ experiment. Even though the EDZ could potentially form a high permeable pathway of groundwater flow, only a few studies were performed on the analysis of groundwater flow in EDZ. In this study, the 'hydraulic EDZ' was defined as the rock zone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation by using H-M coupling analysis. Fundamental principles of distinct element method (DEM) were used in the analysis. In the same groundwater level, the behavior of hydraulic aperture near the cavern was analyzed for different stress ratios, initial apertures, fracture angles and fracture spacings by using a two-dimensional DEM program. We evaluate the excavation induced hydraulic aperture change. Using the results of the study, hydraulic EDZ was defined as an elliptical shape model perpendicular to the joint.

  • PDF

A Study on the Applicability of the Hydraulic Test Method Performed at an underground Research Facility in Crystalline Rock (결정질 암반내 지하연구시설에서 수행한 현장수리시험법 적용성 연구)

  • Park, Kyung-Woo;Ko, Nak-Yeol;Ji, Sung-Hoon
    • Economic and Environmental Geology
    • /
    • v.53 no.2
    • /
    • pp.121-131
    • /
    • 2020
  • In this paper, the transmissivities obtained from the pulse test, the slug test and the constant head test were compared each other to assess an applicability and a reliability of the hydrogeological test method, which are commonly used to derive the hydrogeological properties of a crystalline rock at un underground research facility. When comparing the results of the pulse test and the slug test, the transmissivities were very similar in the entire test section of the medium. However, there was a little discrepancy in the results in the areas where the permeability is relatively high. The results of the constant head test on the same section showed the lower transmissivity than the results of the pulse test and the slug test on the highly permeable section. This difference in permeability was considered to be due to the difference in the radius of the hydraulic effect applied in each hydraulic test. When the heterogenetic distribution of fracture affects the hydrogeological properties on crystalline rock, it is believed that the hydrogeological characteristics can be explained through a constant head test or a constant flow rate test with a large hydraulic effective radius, as well as a pulse and a slug test that can identify hydrogeological properties in a relatively short time.

Numerical simulation of groundwater flow in LILW Repository site:II. Input parameters for Safety Assessment (중.저준위 방사성폐기물 처분 부지의 지하수 유동에 대한 수치 모사: 2. 처분 안전성 평가 인자)

  • Park, Kyung-Woo;Ji, Sung-Hoon;Koh, Yong-Kwon;Kim, Geon-Young;Kim, Jin-Kook
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
    • /
    • v.6 no.4
    • /
    • pp.283-296
    • /
    • 2008
  • The numerical simulations for groundwater flow were carried out to support the input parameters for safety assessment in LILW repository site. As the input parameters for safety assessment, the groundwater flux into the underground facilities during construction, flow rate through the disposal silo after closure of disposal silo and flow pathway from the disposal silo to discharge area were analyzed using the 10 cases groundwater flow simulations. From the total 10 numerical simulation results, the statistics of estimated output were similar to among 10 cases. In some cases, the analyzed input parameters were strongly governed by locally existed high permeable fracture zone at radioactive waste disposed depth. Indeed, numerical simulation for well scenario as a human intrusion scenario was carried out using the hydraulically severe case model. Using the results of well scenario, the input parameters for safety assessment were also obtained through the numerical simulation.

  • PDF

Groundwater Flow Analysis around Hydraulic Excavation Damaged Zone (수리적 굴착손상영역에서의 지하수유동 특성에 관한 연구)

  • Park, Jong-Sung;Ryu, Dong-Woo;Ryu, Chang-Ha;Lee, Chung-In
    • Tunnel and Underground Space
    • /
    • v.17 no.2 s.67
    • /
    • pp.109-118
    • /
    • 2007
  • The excavation damaged zone (EDZ) is an area around an excavation where in situ rock mass properties, stress condition. displacement. groundwater flow conditions have been altered due to the excavation. Various studies have been carried out on EDZ, but most studies have been focused on the mechanical bahavior of EDZ by in situ experiment. Even though the EDZ could potentially form a high permeable pathway of groundwater flow, only a few studies were performed on the analysis of groundwater flow in EDZ. In this study, the' hydraulic EDZ' was defined as the rock Lone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation. And hydraulic EDZ (hydraulic aperture changed zone) estimated by two-dimensional DEM program was considered in three-dimensional DFN model. From this approach the groundwater flow characteristics corresponding to hydraulic aperture change were examined. Together. a parametric study was performed to examine the boundary conditions that frequently used in DFN analysis such as constant head or constant flux condition. According to the numerical analysis, hydraulic aperture change induced by the hydraulic-mechanical interaction becomes one of the most important factors Influencing the hydraulic behavior of jointed rock masses. And also from this study, we suggest the proper boundary condition in three-dimensional DFN model.

The Study on the Increased Causes of Chloride ($Cl^{-}$) Concentration of the Samyang 3rd Pumping Station in Cheju Island (제주도 삼양 3수원지의 염소이온농도 상승 원인에 관한 연구)

  • 이성복;김구영;한소라;한정상
    • Journal of the Korean Society of Groundwater Environment
    • /
    • v.4 no.2
    • /
    • pp.85-94
    • /
    • 1997
  • The study is aimed to find out the causes of rapidly increasing chloride (Cl$^{-}$) concentration of the Samyang 3rd pumping station originated from coastal springs of Cheju since January 1996. The study results show that it was caused by following complicated natural and anthropogenic effects. Due to severe draught in 1996 with total rainfall of only 41.7% of annual mean of the last 36 years (1991 to 1995), it creates firstly), significant decrease of the spring discharges as well decline of the groundwater level at the site . Sea water level was in general 4.4 cm to 12.4 cm higher than the groundwater level of the site during 2 to 3.8 hours at each high tide. Those higher potential head of sea water motivates the sea water intrusion into the fresh water lens through the permeable clinkers and fracture zones situated beneath the existing grouted zone which was installed to a maximum 10 m below the ground water surface, The repeated expansion and contraction of the fresh water lens occurred by periodic changes of the sea water level at high and low tide accelerates secondly the enlargement of the transition zone between the fresh and sea water at the site. The decrease of recharge amount by rainfall shortage creates thirdly the reverse flow at the interface of sea water and groundwater. The repeated groundwater extraction of 2790${\pm}$450 $m^3$d$^{-1}$ at the time of low tide, when the fresh water lens of the sire is under the contraction stare, makes additional drawdown of the ground water level and induces the upconing of salt water into the fresh water lens. The duration of spring discharge whose Cl concentration is less than 150 mg/1 at the low tide measured at the nearby springs was about two hours with discharge rate of 532 $m^3$d$^{-1}$ and after that Cl$^{-}$ concentration is increased up to more than 1900 mg/ι.eased up to more than 1900 mg/L.

  • PDF