We investigate the stress-dependent permeability issue in fractured rock masses considering the effects of nonlinear normal deformation and shear dilation of fractures using a two-dimensional distinct element method program, UDEC, based on a realistic discrete fracture network realization.A series of "numerical" experiments were conducted to calculate changes in the permeability of simulated fractured rock masses under various loading conditions. Numerical experiments were conducted in two ways: (1) increasing the overall stresses with a fixed ratio of horizontal to vertical stresses components; and (2) increasing the differential stresses (i.e., the difference between the horizontal and vertical stresses) while keeping the magnitude of vertical stress constant.These numerical experiments show that the permeability of fractured rocks decreases with increased stress magnitudes when the stress ratio is not large enough to cause shear dilation of fractures, whereas permeability increases with increased stress when the stress ratio is large enough.Permeability changes at low stress levels are more sensitive than at high stress levels due to the nonlinear fracture normal stress-displacement relation. Significant stress-induced channeling is observed as the shear dilation causes the concentration of fluid flow along connected shear fractures.Anisotropy of permeability emerges with the increase of differential stresses, and this anisotropy can become more prominent with the influence of shear dilation and localized flow paths. A set of empirical equations in closed-form, accounting for both normal closure and shear dilation of the fractures, is proposed to model the stress-dependent permeability. These equations prove to be in good agreement with the results obtained from our numerical experiments.2

No abstract

No abstract

No abstract

No abstract

No abstract

Objective This study was conducted to investigate the association between depressive symptoms and job stress, as measured by the KOSS, among Korean employees in small-and medium-sized enterprises, and examined which components of stress are involved in the risk for depression among males and females. Methods Data were collected from a work-stress survey of full-time employees of small-and medium-sized enterprises in Incheon, South Korea. A total of 3,013 participants were included in the analysis. Job stress was measured using 24 items (7 sub-scales) of the short form of Korean occupational stress scale (KOSS-SF), and depressive symptoms were evaluated using Center for epidemiologic studies depression scale (CES-D). Results After adjustment for confounding variables, most of subscales of job stress contributed to an increased risk of depressive symptoms, and job insecurity (male; OR = 2.02, 95%CI: 1.61-2.40, female; OR = 1.95, 95%CI: 1.42-2.70) and occupational climate (male; OR = 1.84, 95%CI: 1.49-2.28, female; OR = 1.78, 95%CI: 1.30-2.49) showed strong associations in both male and female. Other subscales revealed diVerent eVects for males and females; for males, job demands (OR = 1.68, 95%CI: 1.43-2.20), inadequate social support (OR = 1.55, 95%CI: 1.23-1.94), and lack of rewards (OR = 1.88, 95%CI: 1.48-2.37) were associated with depressive symptoms, whereas for females, organizational injustice (OR = 1.62, 95%CI: 1.14-2.30) was associated with depressive symptoms. Conclusion These results indicate that job stress may play a signiWcant role in increasing the risk of depressive symptoms, and that further preventive eVorts and research are needed to reduce job stress and address health problems caused by job stress among Korean employees.

Association between Job Stress and Insomnia in Korean Workers: Hwan-Cheol Kim, et al.