• Journal of Plant Biology
• /
• 제25권2호
• /
• pp.83-99
• /
• 1982

In this study, thirty-two stands in Kwangnung forest located in the central part of Korea were preferentially selected. In each stand, all stems for trees and shrubs were recorded by species and their girths were measured down to 5cm. In addition, several enviromental factors such as field soil pH, field soil moisture, soil compressibility, depth of soil, thickness of litter layer, elevation and basal area were measured. Three soil cores were sampled and various physical and chemcial properties was determined. The vegetational data were subjected to three kinds of multivariate ordination(PO, PCA, RA). The results suggested that Kwangnung forest was consisted of three forest types: coniferous, mixed and broad leaved forest communities. The relation between the stand scores of ordination and several environmental factors were investigated in terms of correlation analysis in order to examine the relationships between the vegetation and certain environmental factors. As a result of this analysis, the amount of sand content in A1 horizon decreased frm the coniferous to broad leaved forest, while maximum field capacity, pore space, exchangeable cations, loss on ignition, soil pH nad the amount of total nitrogen had a tendancy to increase significantly. However, easily soluble phosphorus appeared to have little to do with the forest types. The result of species ordination of centered-standardized PCA suggested that the major successional pathway in Kwangnung forest was; Pinus densifloralongrightarrowQuercus mongolica, Q. serrata, Q. alienalongrightarrowCarpinus laxifloralongrightarrowC. erosa in sequence. This trend is in good agreement with the past studies. In three kinds of ordination (centered PCA, centered-standardized PCA and RA) based on nineteen species and twenty-five stands, the total variances accounted for the first three axes were 77%, 46% and 63% respectively. The estimated beta diversity in Kwangnung forest assumed as a coenocline, was 1.5~1.8 HC. Increasing the effect of the sampling errors on ordination perfermance, this low heterogeneity seems to cause the poor concentration of the total variance. The results from the four kinds of ordination were in good agreement with each other, especially between PO, centered-standardized PCA and RA appeared robust. It seems to be worthy of applying multivariate method for analyzing other forest communities in Korea.

• 한국지반환경공학회 논문집
• /
• 제20권5호
• /
• pp.39-46
• /
• 2019

준설점토를 활용한 연약지반은 장비주행성 및 진입로의 확보를 위해 시멘트 계 고화재 및 무기질 고화재 등을 활용한 표층고화처리공법이 사용되고 있으나 환경에 유해한 물질의 용출로 인한 문제가 제기되고 있어 환경과 기능성을 모두 만족하는 표층고화처리 공법의 개발이 필요하다. 표층처리 공법으로는 조기강도와 장기적인 안정 등을 고려하여 시멘트계 고화재를 이용한 표층고화처리공법이 많이 활용되고 있으며, 지반개량 효과가 크고 경제적 효율성으로 인해 국 내외에서는 시멘트계 고화재를 이용한 표층개량에 대한 연구과 수행되어 지고 있다. 그러나 최근 환경과 기능성의 문제가 제기되어 시멘트에서 발생되는 6가크롬(Cr6+), 수은(Hg) 등의 유해물질로 인해 지반오염과 환경문제가 발생되어 다양한 친환경적인 공법의 개발이 요구되고 있는 실정이다. 따라서 이 연구에서는 자연함수비의 준설점토를 시멘트와 친토양고화재를 혼합한 혼합토를 대상으로 동일한 배합조건 및 양생조건에 따른 일축압축강도를 분석하고 이 결과를 기준으로 표층개량범위 적용 및 실내모형토조시험을 수행하여 초연약지반의 강도특성 및 지지력 특성을 검토하고자 한다.

• Structural Engineering and Mechanics
• /
• 제68권6호
• /
• pp.747-760
• /
• 2018

In the present study, a methodology for developing fragilities of arch concrete dams to assess their performance against seismic hazards is introduced. Firstly, the probability risk and fragility curves are presented, followed by implementation and representation of the way this method is used. Amirkabir arch concrete dam was subjected to non-linear dynamic analyses. A modified three dimensional rotating smeared crack model was used to take the nonlinear behavior of mass concrete into account. The proposed model considers major characteristics of mass concrete. These characteristics are pre-softening behavior, softening initiation criteria, fracture energy conservation, suitable damping mechanism and strain rate effect. In the present analysis, complete fluid-structure interaction is included to account for appropriate fluid compressibility and absorptive reservoir boundary conditions. In this study, the Amirkabir arch concrete dam is subjected to a set of 8 three-component earthquakes each scaled to 10 increasing intensity levels. Using proposed nonlinear smeared crack model, nonlinear analysis is performed where the structure is subjected to a large set of scaled and un-scaled ground motions and the maximum responses are extracted for each one and plotted. Based on the results, fragility curves were plotted according to various and possible damages indexes. Discrete damage probabilities were calculated using statistical methods for each considered performance level and incremental nonlinear analysis. Then, fragility curves were constructed based on the lognormal distribution assumption. Two damage indexes were introduced and compared to one another. The results indicate that the dam has a proper stability under earthquake conditions at MCE level. Moreover, displacement damages index is more conservative and impractical in the fragility analysis than tensional damage index.

• Geomechanics and Engineering
• /
• 제18권5호
• /
• pp.535-543
• /
• 2019

Building on/with expansive soils with no treatment brings complications. Compacted expansive soils specifically fall short in satisfying the minimum requirements for transport embankment infrastructures, requiring the adoption of hauled virgin mineral aggregates or a sustainable alternative. Use of hauled aggregates comes at a high carbon and economical cost. On average, every 9m high embankment built with quarried/hauled soils cost $12600MJ.m^{-2}$ Embodied Energy (EE). A prospect of using mixed cutting-arising expansive soils with industrial/domestic wastes can reduce the carbon cost and ease the pressure on landfills. The widespread use of recycled materials has been extensively limited due to concerns over their long-term performance, generally low shear strength and stiffness. In this contribution, hydromechanical properties of a waste tyre sand-sized rubber (a mixture of polybutadiene, polyisoprene, elastomers, and styrene-butadiene) and expansive silt is studied, allowing the short- and long-term behaviour of optimum compacted composites to be better established. The inclusion of tyre shred substantially decreased the swelling potential/pressure and modestly lowered the compression index. Silt-Tyre powder replacement lowered the bulk density, allowing construction of lighter reinforced earth structures. The shear strength and stiffness decreased on addition of tyre powder, yet the contribution of matric suction to the shear strength remained constant for tyre shred contents up to 20%. Reinforced soils adopted a ductile post-peak plastic behaviour with enhanced failure strain, offering the opportunity to build more flexible subgrades as recommended for expansive soils. Residual water content and tyre shred content are directly correlated; tyre-reinforced silt showed a greater capacity of water storage (than natural silts) and hence a sustainable solution to waterlogging and surficial flooding particularly in urban settings. Crushed fine tyre shred mixed with expansive silts/sands at 15 to 20 wt% appear to offer the maximum reduction in swelling-shrinking properties at minimum cracking, strength loss and enhanced compressibility expenses.

• Geomechanics and Engineering
• /
• 제17권5호
• /
• pp.453-464
• /
• 2019

Soft marine soil has high fine-grained soil content and in-situ water content. Thus, it has low shear strength and bearing capacity and is susceptible to a large settlement, which leads to difficulties with coastal infrastructure construction. Therefore, strength improvement and settlement control are essential considerations for construction on soft marine soil deposits. Biopolymers show their potential for improving soil stability, which can reduce the environmental drawbacks of conventional soil treatment. This study used two biopolymers, an anionic xanthan gum biopolymer and a cationic ${\varepsilon}-polylysine$ biopolymer, as representatives to enhance the geotechnical engineering properties of soft marine soil. Effects of the biopolymers on marine soil were analyzed through a series of experiments considering the Atterberg limits, shear strength at a constant water content, compressive strength in a dry condition, laboratory consolidation, and sedimentation. Xanthan gum treatment affects the Atterberg limits, shear strength, and compressive strength by interparticle bonding and the formation of a viscous hydrogel. However, xanthan gum delays the consolidation procedure and increases the compressibility of soils. While ${\varepsilon}-polylysine$ treatment does not affect compressive strength, it shows potential for coagulating soil particles in a suspension state. ${\varepsilon}-Polylysine$ forms bridges between soil particles, showing an increase in settling velocity and final sediment density. The results of this study show various potential applications of biopolymers. Xanthan gum biopolymer was identified as a soil strengthening material, while ${\varepsilon}-polylysine$ biopolymer can be applied as a soil-coagulating material.

• 한국지반환경공학회 논문집
• /
• 제12권6호
• /
• pp.43-51
• /
• 2011

국내의 동 서 남해안에는 해성점토층이 폭넓게 분포되어 있으며, 해안지역에서 기반시설물을 설계할 때 압축성이 큰 해성점토로 구성된 연약지반의 공학적 특성을 파악하는 일은 매우 중요하다. 본 논문에서는 인천, 목포, 광양 및 부산지역 해성점토의 물리적 압축특성을 분석하여 각 지역 및 우리나라 서 남해안 점토특성을 비교하였다. 이를 위하여 114구역 1,471개 샘플의 실험결과를 이용하였다. 비교결과, 인천점토의 경우 중국 황하로부터 유입된 세립실트 및 높은 조수간만의 차로 가장 낮은 소성 및 높은 단위중량을 보였고, 광양점토는 광범위한 준설매립의 영향으로 압축성이 가장 컸다. 그와 비교할 때 목포 및 부산의 경우는 부분적으로 비슷한 수준의 특성을 나타내었다. 목포와 부산점토의 압축지수는 인천에 비하여 2배 이상, 광양점토의 경우는 목포 및 부산에 비해 70% 이상 높게 나타났다.

• 한국지반환경공학회 논문집
• /
• 제12권8호
• /
• pp.39-50
• /
• 2011

흙막이 가시설 공사에 사용되는 H-pile은 철거의 어려움으로 공사 완료 후 그대로 지중에 사장되거나 사용 후 인발된다. 이때 H-pile 외부에 공동이 있을 경우 지반 변형을 일으키게 된다. 본 연구의 목적은 H-pile을 이용한 흙막이 구조물 조성 시 천공 후 공동 충진을 용이하게 할 수 있고, H-pile 회수 시 마찰을 최소화하는 채움재 개발에 있다. 일차시험에서는 연구 목적을 만족하는 배합비를 선정하기 위해 수행되었고, 이차시험에서는 사용재료와 철판의 전단시험으로 인발 시 적용성을, 압밀시험을 통해 공동 충진 시 적용성을 평가하였다. 시험결과 유동화 채움재로서 우수한 성질을 보이는 배합은 벤토나이트를 기준으로 물 350%~450%, 시멘트 70%~100%, 모래 70%~100%가 포함된 배합으로 나타났다.

• Geomechanics and Engineering
• /
• 제27권6호
• /
• pp.551-560
• /
• 2021

Due to the low strength and high compressibility characteristics, the loess deposits tunnels are prone to large deformations and collapse. An accurate stability evaluation for loess deposits is of considerable significance in deformation control and safety work during tunnel construction. 37 groups of representative data based on real loess deposits cases were adopted to establish the stability evaluation model for the tunnel project in Yan'an, China. Physical and mechanical indices, including water content, cohesion, internal friction angle, elastic modulus, and poisson ratio are selected as index system on the stability level of loess. The data set is randomly divided into 80% as the training set and 20% as the test set. Firstly, principal component analysis (PCA) is used to convert the five index system to three linearly independent principal components X1, X2 and X3. Then, the principal components were used as input vectors for probabilistic neural network (PNN) to map the nonlinear relationship between the index system and stability level of loess. Furthermore, Leave-One-Out cross validation was applied for the training set to find the suitable smoothing factor. At last, the established model with the target smoothing factor 0.04 was applied for the test set, and a 100% prediction accuracy rate was obtained. This intelligent classification method for loess deposits can be easily conducted, which has wide potential applications in evaluating loess deposits.

• Geomechanics and Engineering
• /
• 제27권6호
• /
• pp.583-594
• /
• 2021

The gas permeability behavior of unsaturated bentonite-based materials is of major importance for ensuring effective sealing of high-level radwaste repositories. This study investigated this by taking a sample of Granular Bentonite Material (GBM) at the end of the Engineered Barrier Emplacement (EB) experiment in the Opalinus Clay, placing it under different humidity conditions until it achieved equilibration, and testing the change in the gas permeability under loading and unloading. Environmental humidity is shown to have a significant effect on the water content, saturation, porosity and dry density of GBM and to affect its gas permeability. Higher sensitivity to confining pressure is exhibited by samples equilibrated at higher relative humidity (RH). It should be noted that for the sample at RH=98%, when the confining pressure is raised from 1 MPa to 6 MPa, gas permeability can be reduced from 10^-16 m² to 10^-19 m², which is close to the requirements of gas tightness. Due to higher water content and easier compressibility, samples equilibrated under higher RH show greater irreversibility during the loading and unloading process. The effective gas permeability of highly saturated samples can be increased by 2-3 orders of magnitude after 105℃ drying. In addition, cracks possibly occurred during the dehydration and drying process will become the main channel for gas migration, which will greatly affect the sealing performance of GBM.

• 한국분말재료학회지
• /
• 제29권2호
• /
• pp.99-109
• /
• 2022

Powder flowability is critical in additive manufacturing processes, especially for laser powder bed fusion. Many powder features, such as powder size distribution, particle shape, surface roughness, and chemical composition, simultaneously affect the flow properties of a powder; however, the individual effect of each factor on powder flowability has not been comprehensively evaluated. In this study, the impact of particle shape (sphericity) on the rheological properties of Ti-6Al-4V powder is quantified using an FT4 powder rheometer. Dynamic image analysis is conducted on plasma-atomized (PA) and gas-atomized (GA) powders to evaluate their particle sphericity. PA and GA powders exhibit negligible differences in compressibility and permeability tests, but GA powder shows more cohesive behavior, especially in a dynamic state, because lower particle sphericity facilitates interaction between particles during the powder flow. These results provide guidelines for the manufacturing of advanced metal powders with excellent powder flowability for laser powder bed fusion.