[논문]강우시 국내 불포화 풍화토 사면에서의 습윤영향 분석

정삼성; 김재홍; 박성완

강우시 국내 불포화 풍화토 사면에서의 습윤영향 분석
Influence of Rainfall-induced Wetting on Unsaturated Weathered Slopes 원문보기

韓國地盤工學會論文集 = Journal of the Korean geotechnical society, v.20 no.7, 2004년, pp.159 - 169

정삼성 (School of Civil & Environmental Engrg., Yonsei Univ.) , 김재홍 (Dept. of Civil Engrg, Univ. of Colorado) , 박성완 (Dept. of Civil & Environmental Engrg., Dankook Univ.)

초록
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얕은사면 파괴는 지표로 침투하는 강우에 의해 주로 발생한다. 이는 지표수의 침투시 모관흡수력의 감소에 의한 포화깊이 증가에 의해 발생한다. 본 연구에서는 국내의 전형적인 화강풍화토를 대상으로 강우시 사면에서의 습윤영향을 분석하였다. 이를 위하여 filter paper와 tensiometer 실험을 수행하여 함수특성곡선을 산정하였으며, 그에 따른 함수특성곡선의 방정식을 추정하였으며, 기존에 사용되고 있는 Green & Ampt의 포화 깊이 추정식과 수치해석결과를 비교 분석하였다. 본 연구 결과, Green & Ampt모델에 의한 이론 해는 포화깊이를 과소 추정하였으며, 포화깊이가 증가함에 따라 사면안전율은 감소하는 것으로 나타났다. 특히 포화깊이가 약 1.2m이상부터 사면안전율은 현저하게 감소하는 것으로 나타났다.

Abstract ▼ AI-Helper

Surface failures of slopes in weathered soil are caused by infiltration due to prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in suction induced by the infiltrating water. This paper reports trends of rainfall-induced wetting band depth in two types of weathered soils that are commonly found in Korea. Both theoretical and numerical analyses are presented based on the soil-water characteristic curve (SWCC) obtained using filter paper as well as tensiometer tests. It is found that the magnitude of wetting front suction plays a key role in the stability of slopes in weathered soils. Theoretical analysis based on modified Green and Ampt model tends to underestimate the wetting band depth for typical Korean weathered soils. It was also deduced that for Korean weathered soils, the factor of safety drops rapidly once the wetting band depth of 1.2 m is reached.

주제어

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문제 정의

Although such an increase in factor of safety is small, it can make a difference between stability and feilure for slopes with factors of safety only slightly greater than unity. It should also be noted that the present study was focused on investigating the effect of infiltration of rainfall. Other effects such as evaporation and run-off were not considered.
A study of rainfall-induced instability in infinite slopes of typical Korean weathered soils (classified as SW and SM according to USCS) was undertaken using Pradel and Raad's (1993) modification of theoretical equations for the Green and Ampt (1911) model. The objective of this study was to establish the applicability of these theoretical equations to Korean weathered soils. The wetting band depth calculated using theoretical equations was compared with those obtained from finite element transient seepage and slope stability analyses.
(1994) have noted that these theoretical equations generally tend to overestimate the factor of safety of such slopes, resulting in slope failures and extensive damage. This paper aims to evaluate the potential shortcomings of these theoretical equations in predicting the rainfall- induced stability of slopes located in weathered soils. Several seepage analyses using a two-dimensional finite element seepage program are conducted to establish the wetting band depth and the wetting front suction for a wider range of initial conditions.

가설 설정

Eq. (2) shows an increase in 瓦 with W whereas numerical analysis shows a decrease in with 0. The two trend lines appear to cross each other at a W value close to 80 cm. The overall discrepancy between 瓦 values obtained from Eq.
The results for both SW and SM soils are shown in Fig. 5. The initial matric suction value at the tensiometer level depended mainly on the initial w value. For the SW weathered soil, it was not possible to maintain an initial matric suction of more than 8 kPa.

제안 방법

Several seepage analyses using a two-dimensional finite element seepage program are conducted to establish the wetting band depth and the wetting front suction for a wider range of initial conditions. For these analyses, the input parameters for soil governing the groundwater flow are derived from soil water characteristic curves (SWCC) obtained using filter paper and tensiometer tests. The results of this parametric study are compared with theoretical results.
In order to assess the effect of wetting band depth and the magnitude of wetting front suction on the stability of slopes in weathered soils, two sets of analyses were conducted using the limit equilibrium based program SLOPEAV (Geo-Slope, 1998). For both sets, two infinite slopes - inclined at 27° and 45° with respect to horizontal -were considered.
The total duration of rainfall is 100 hours. It was divided into 11 time stages - 0.1, 0.5, 1, 2, 3, 5, 10, 24, 48, 72 and 96 hours - and wetting front depth was obtained for each of these 11 time stages. For simplicity, the intensity of rainfall was kept constant for the entire duration of rainfall.

이론/모형

A study of rainfall-induced instability in infinite slopes of typical Korean weathered soils (classified as SW and SM according to USCS) was undertaken using Pradel and Raad's (1993) modification of theoretical equations for the Green and Ampt (1911) model. The objective of this study was to establish the applicability of these theoretical equations to Korean weathered soils.
Filter paper test as specified in ASTM D5298-94 (ASTM, 2000) was used for establishing the SWCC for the two weathered soils. Two types of filter papers - Schleicher and Schuell No.

성능/효과

The values of constants a, m and n for the fitted SWCC are given in Table 1. It was found that tests done using Whatman No. 42 filter paper showed repeatability and gave SWCC that were consistent with SWCC for sandy soils. Leong et al.

참고문헌 (23)

ASTM (2000), Annual Book of ASTM Standards: Measurement of Soil Potential (Suction) Using Filter Paper. Vol.04.08, D5298-94, pp.154-159
Chow, V. T., Maidment, D. R. and Mays, L. W. (1988), Applied Hydrology, McGraw-Hill, New York
Fourie, A. B., Rowe, D. and Blight, G. E. (1999), 'The effect of infiltration on the stability of the slopes of a dry ash dump', Ge otechnique, Vol.49, No.1, pp.1-13
Fredlund, D. G. and Xing, A. (1994), 'Equations for the soil-water characteristic curve', Canadian Geotechnical Journal, Vol.31, pp.521-532

상세보기
Fredlund, D. G. and Rahardjo, H. (1993), Soil Mechanics for Unsaturated Soils, John Wiley and Sons
Geo-Slope (1998), User's manual for SEEP/W and SLOPE/W: Version 4, Geo-Slope International Ltd, Canada.
Green, W. H. and Ampt, G. A. (1911), 'Studies on soil physics. 1: The flow of air and water through soils', J. Agric. Sci., Vol.4, No.1, pp.1-24

상세보기
Holtz, R.D. and Kovacs, W.D. (1981), An Introduction to Geotechnical Engineering, Prentice-Hall Inc, USA
Kim, S. I., Park, C. H., Lee, S. R. and Jeong, S. S. (1994), Report of the Stability Analysis of Natural Slope of Yongseong Industrial Complex in Yeocheon, Lucky-Development Company, Korea
Lee, S. G. and de Freitas. M. H. (1989), 'A revision of the description and classification of weathered granite and its appli-cation to granites in Korea', J. of Engrg. Geol., Vol.22, No.1, pp.31-48

상세보기
Leong, E. C. and Rahardjo, H. (1997), 'Review of Soil-Water Characteristic Curve Equations', Journal of Geotechnical and Geoenvironmental Engineering, Vol.123, No.12, pp.1106-1117

상세보기
Leong, E.C., He, L. and Rahardjo, H. (2002), 'Factors affecting the filter paper method for total and matric suction measurements', Geotechnical Testing Journal, Vol.25, No.3, pp.1-12
Lumb, P. B. (1962), 'Effects of rain storms on slope stability', Symp. on Hong Kong Soils, Hong Kong, pp.73-87
Lumb, P. B. (1975), 'Slope failures in Hong Kong', Q. J. Engng Geol, Vol.8, pp.31-65

상세보기
Maidment, David R. (1993), Handbook of hydrology. David R. Maidment, McGraw-Hill, pp.5.32-5.51
Moore, R. E. (1939), 'Water conduction from shallow water tables', Hilgardia, Vol.12, No.6, pp.383-426

상세보기
Ng, C. W. W. and Shi, Q. (1998), 'A numerical investigation of the stability of unsaturated soil slopes subjected to transient seepage', Computers and Geotechnics, Vol.22, No.1, pp.1-28

상세보기
Pradel D. and Raad G. (1993), 'Effect of Permeability on Surficial Stability of Homogeneous Slopes', Journal of Geotechnical Engineering, Vol.119, No.2, pp.315-332

상세보기
Rahardjo, H., Lim, T. T., Chang, M. F., and Fredlund, D. G. (1995), 'Shear-strength characteristics of a residual soil', Canadian Geotechnical Journal, Vol.32, pp.60-77

상세보기
Rawls, W. J., Brakensiek, D. L. and Soni, B. (1983), 'Agricultural Management Effects on Soil Water Processes: Part I . Soil Water Retention and Green-Ampt Parameters. Trans', American Society of Agricultural Engineers, Vol.26, No,6, pp.1747-1752

상세보기
Skagg, R .W. and Khaleel, R. (1982), 'Hydrologic Modeling of Small Watersheds, Monograph 5', Infiltration. In C.T. Haan, ed. American Society of Agricultural Engineers, St. Joseph, Mich., pp.4-166
Van Genuchten, M. T. (1980), 'A closed-form equation for predicting the hydraulic conductivity of unsaturated soils', J. Soil Sci. Soc. Am., Vol.44, pp.892-898

상세보기
Vanapalli, S. K., Fredlund, K. G., Pufahl, D. E. and Clifton, A. W. (1996), 'Model for prediction of shear strength with respect to matric suction', Canadian Geotechnical Journal, Vol.33, pp. 379-392

상세보기

표제어: PCR

동의어: Packet Collision Rate

용어 설명 출처 목록 (6)

용어 설명: PCR은 세균 특이성이 있는 primer를 이용하여 적은 수의 세균이 있을지라도 쉽게 검출할 수 있는 유용한 방법이며, 이를 이용하여 구강 내 치면세균막이나 타액에서 직접 세균을 검출할 수 있게 되었다[8].

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