한국지반공학회논문집 (Journal of the Korean Geotechnical Society)

  • 제30권1호
  • /
  • Pages.37-47
  • /
  • 2014
  • /
  • 1229-2427(pISSN)
  • /
  • 2288-646X(eISSN)
한국지반공학회 (Korean Geotechnical Society)
권호 표지
DOI QR코드

DOI QR Code

불포화 사면의 포화 부근 침투 특성을 고려한 수리전도도 모델

A Hydraulic Conductivity Model Considering the Infiltration Characteristics Near Saturation in Unsaturated Slopes

  • 오세붕 (영남대학교 건설시스템공학과) ;
  • 박기훈 (도담엔지니어링) ;
  • 김준우 (영남대학교 건설시스템공학과)
  • 투고 : 2013.10.08
  • 심사 : 2013.12.20
  • 발행 : 2014.01.31
PDF 다운로드
⟨ 이전 논문 다음 논문 ⟩

초록

불포화 수리전도도는 Mualem 모세관 모델에 의하여 이론적으로 함수특성곡선으로부터 적분된다. 하지만 예측된 수리전도도는 포화 부근에서 모관흡수력의 미소한 변화에도 극도로 민감하다. 원활한 형태의 함수특성곡선에 의한 Mualem 수리전도도는 포화 부근에서 급격하게 감소하며, 수리적 거동을 신뢰할 수 있게 모델하지 못하거나 수치해의 안정성을 저해 한다. van Genuchten-Mualem(VGM) 수리전도도를 개선하기 위하여, 낮은 모관흡수력 수준에 있는 임의의 공기함입치이내에서 van Genuchten 함수특성곡선을 수정하였다. 수정 VG 곡선은 대수축에서 임의의 공기함입치에서 포화상태까지 선형화된다. 수정 VG 함수특성곡선은 실제 함수특성거동의 회귀분석에 영향을 끼치지 않으며 원래의 VG 함수특성곡선의 계수를 그대로 사용한다. 수정 VG 곡선을 이용하여, VGM 수리전도도는 임의의 공기합입치를 기준으로 구간별 적분하여 수정되었다. 수정 VGM 수리전도도가 해석적 해로 제안되었으며, 포화부근 영역에서 수리전도도가 급격하게 감소하는 현상이 제거되었다. 실제 사면의 2차원 침투해석을 통하여 VGM 수리전도도와 제안된 모델에 따른 수리거동을 비교하였다. 제안된 모델은 여러 강우조건에 따른 해의 수렴성을 확보하였지만, VGM 수리전도도를 적용하면, 포화부근의 수리전도도가 급격하게 감소하여 강우량이 많은 경우 해가 수렴하지 않았다. 특히 선행강우에 의한 초기 안전율과 집중강우 후 최종 안전율을 크게 평가할 수 있었다. 제안된 수리전도도 모델은 침투해석과 안정해석을 통하여 실제 사면의 붕괴를 재현할 수 있었다.

Unsaturated hydraulic conductivity (HC) is integrated theoretically from soil water retention curves (SWRC) by Mualem capillary model, but the prediction of HC is extremely sensitive to small variation of matric suction near saturation. Near saturation, the Mualem HC based on smooth SWRC decreases abruptly and has problems in the reliability of hydraulic behavior and the stability of numerical solutions. To improve van Genuchten-Mualem (VGM) HC, the van Genuchten SWRC model is modified within range of low matric suction (arbitrary air entry pressure). At an arbitrary air entry pressure, the VG SWRC is linearized in log scale until full saturation. The modified VG SWRC does not affect the fit of actual retention behavior and either the parameters of original VG SWRC fit. Using the modified VG SWRC, the VGM HC is modified to integrate for each interval decomposed by arbitrary air entry pressure. An analytical solution on modified VGM HC is proposed each interval, to protect the rapid change in HC near saturation. For silty soils, VGM models of HC function underestimate the unsaturated permeability characteristics and especially show rapid reduction near saturation. The modified VGM model predicts more accurate HC functions for Korean weathered soils. Furthermore, near saturation, the saturated HC is conserved by the modified VGM model. After 2-D infiltration analysis of an actual slope, the hydraulic behaviors are compared for VGM and the modified models. The prediction by the proposed model conserved the convergence of solutions on various rainfall conditions. However, the solution by VGM model did not converge since the conductivity near saturation reduced abruptly for heavy rainfall condition. Using VGM model, the factor of safety is overestimated in both initial and final stage during heavy rainfall. Stability analysis based on infiltration analysis could simulate the actual slope failure by the proposed model on HC.

키워드

참고문헌

  1. Kim, Y. K. (2009), Soil slope design and stability evaluation methodology considering hydraulic conductivity and rainfall characteristics, Ph.D. Thesis, Dept. of Civil Eng., KAIST.
  2. Oh, S., Lu, N., Park, Y. M., and Lee, J. (2012)," Analysis of an Actual Slope Failure in the Residual Soil", J. of Korean Society of Civil Engineers, Vol.32(3C), pp.113-120.
  3. Brooks, R. H. and Corey, A. T. (1964), "Hydraulic properties of porous media", Colorado State University Hydrology Paper, Fort Collins, No.3.
  4. Campbell, J. D. (1973), Pore pressures and volume changes in unsaturated soils, Ph.D. Thesis, University of Illinois at Urbana-Champaign, Urbana-Champaign, IL.
  5. Fredlund, D. G., Xing, A., and Huang, S. (1994), "Predicting the permeability function for unsaturated soils using the soil-water characteristic curve", Canadian Geotechnical Journal, Vol.31, No.3, pp.533-546. https://doi.org/10.1139/t94-062
  6. Kunze, R. J., Uehara, G., and Graham, K. (1968), "Factors Important in the Calculation of Hydraulic Conductivity", Soil Science Society of America Proceedings, Vol.32, pp.760-765. https://doi.org/10.2136/sssaj1968.03615995003200060020x
  7. Mualem, Y. (1976), "A New Model for Predicting the Hydraulic Conductivity of Unsaturated Porous Media", Water Resources Research, Vol.12, pp.593-622.
  8. Khalili, N., Geiser, F., and Blight, G. E. (2004), "Effective stress in unsaturated soils: Review with new evidence", Int. J. Geomech., 4(2), 115-126. https://doi.org/10.1061/(ASCE)1532-3641(2004)4:2(115)
  9. Lu, N. and Likos, W. J. (2006), "Suction stress characteristic curve for unsaturated soils", Journal of Geotechnical and Geoenvironmental Engineering, 132(2), 131-142. https://doi.org/10.1061/(ASCE)1090-0241(2006)132:2(131)
  10. Lu, N., Godt, J., and Wu, D. T. (2010), "A closed-form equation for effective stress in unsaturated soil", Water Resources Research, 46, doi:10.1029/2009WR008646.
  11. Lu, N., Oh, S., and Wayllace, A. (2013), "Infiltration-induced seasonally reactivated instability of a highway embankment near the Eisenhower Tunnel, Colorado, USA", Engineering Geology, 162, 22-32. https://doi.org/10.1016/j.enggeo.2013.05.002
  12. Oh, S. and Kim, Y.K. (2014), "A modification of van Genuchten- Mualem model on the hydraulic conductivity to account for numerical stability and empirical connectivity in Korean residual soils", submitted to Unsaturated 2014-The 6th International Conference on Unsaturated Soils, Sydney, Australia.
  13. Oh, S., Lu, N., Y. K. Kim, S. J. Lee, and Lee, S. R. (2012), "Relation between the soil water characteristic curve and the suction stress characteristic curve: experimental evidence from tests on residual soils", Journal of Geotechnical and Geoenvironmental Engineering, 138(1), 47-57. https://doi.org/10.1061/(ASCE)GT.1943-5606.0000564
  14. GEO-SLOPE International, Ltd, GeoStudio 2007, Calgary, Alberta, Canada.
  15. van Genuchten, M. T. (1980), "A closed-form equation for predicting the hydraulic conductivity of unsaturated soils", Soil Science Society of America Journal, Vol.44, 892-898. https://doi.org/10.2136/sssaj1980.03615995004400050002x
  16. van Genuchten, M. T., Leij, F. J., and Yates, S. R. (1991), The RETC Code for Quantifying the Hydraulic Functions of Unsaturated Soils, EPA 600/2-91/065.
  17. Vogel, T., van Genuchten, M. T., and Cislerova, M. (2001), "Effect of the shape of the soil hydraulic functions near saturation on variably-saturated flow predictions," Advances in Water Resources, Vol.24, pp.133-144.