• Geomechanics and Engineering
• /
• 제30권5호
• /
• pp.401-411
• /
• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• 한국지역지리학회지
• /
• 제9권4호
• /
• pp.481-492
• /
• 2003

본 연구는 1993년과 2002년의 위성영상의 비교분석을 통해 북한 만포 강계 지역의 9년간의 경지확대에 따른 산림경관 변화를 정량적으로 분석한 것이다. 연구 대상지역에서의 농경지는 9년 동안 49.9% 증가하였고, 산림지는 16% 감소하였다. 농경지 개간의 공간적 분포 특성을 보면, 경작지의 평균고도는 1993년의 381m에서 412m로, 경사도는 $10^{\circ}$에서 $13^{\circ}$로 상승하였다. 9년 동안 확대 개간지 자체만을 보면 평균고도 455m, 경사도 $15^{\circ}$ 이르며, 최대 경사도는 $70^{\circ}$에 육박하였다. 파편화에 따른 패치 경향을 보면, 1993년에서 2002년 동안 패치수 394에서 1,241개로 증가하였으며, 패치의 증가와 함께 패치의 형태지수와 프랙탈 차원도 약간 증가하였다. 경작지 개간 고도는 $450{\sim}750$에서 가장 많이 진행되었다. 북한 농업 생산성은 정치 및 사회구조의 개건, 농업 발전을 위한 외부지원, 산지삼림의 복원이 동시에 이루어져야 개선될 것으로 보인다.

• Geomechanics and Engineering
• /
• 제16권1호
• /
• pp.85-95
• /
• 2018

Water affects the mechanical properties of coal and stress wave propagation. To comprehensively investigate the effect of water content on the properties of coal, laboratory tests including X-Ray Diffraction (XRD) analysis, P-wave test, S-wave test, static and dynamic compression test with different water contents were conducted. The compressive strength, elastic modulus and failure strain and their mechanism of coal specimen under coupled static-dynamic load with the increased water content were observed. Meanwhile, energy transmission and dissipation characteristics of a stress wave in coal specimens with different water contents under dynamic load and its relation with the failure features, such as fragmentation and fractal dimension, of coal was analyzed. Furthermore, the dynamic interpretation of water infusion to prevent coal burst based on water infusion model of coal seam roadway was provided.

• The Korean Journal of Ecology
• /
• 제23권5호
• /
• pp.359-368
• /
• 2000

Landscape change is the modification and replacement of landscape elements in accordance with human management and natural disturbance on land mosaics. During landscape change, changes in patterns such as heterogeneity, diversity and shape, and juxtaposition of spatial elements are also accompanied. For the sustainable landscape system, therefore, spatial characteristics of the landscape should be considered in implementation of landscape conservation and restoration planning. Short-term changes of land-use and landscape pattern during the 10 years of 1980s and 1990s were investigated in the agriculture-forestry dominated landscape system through the statistics and the analysis of landscape-vegetation map. Study area is Yangdong-myon, Yangpyung-gun (37°27′30"N, 127°46′50"E), Kyonggi-do, in central Korea. Landscape change of this region was significantly related to the recent industrialization according to socio-economic development. Analyses of landscape pattern show that the area of secondary forest sustained by human activity decreased and it was replaced with large exotic plantations during this period. Area of paddy field was also extended. Fractal dimension of the total landscape increased, but that of paddy field area decreased due to rearrangement for mechanized farming. Moreover, the area of landscape management regimes such as plantation and cultivation increased in land mosaics during this period.