An Analytical Study on the Slope Safety Factor Considering Various Conditions

다양한 조건을 고려한 사면안전율에 관한 해석적 연구

Abstract

This paper demonstrates safety factor for effective planning at initial stage by utilizing results on changes of safety factor according to various conditions of slop and examines impacts of factors that affect slope safety factors as well. Firstly, it describes shear strength which satisfies minimum allowable safety factor: 1.20 depending on height and slope. As the height increases by 5.0 m, the safety factors decrease by 0.04 while it tends to consistently reduce by approximately 20%, 30% and 40% after height goes to 10.0 m. As slope reduces by about 0.3, the safety factors increases by 0.4, which shows the rate of safety factors on slope grows by about 10%, 20% and 30% on lowering slope. When cohesion goes up by 10.0 kPa the safety factors increases by around 40% respectably while the angle of internal friction grows by $5^{\circ}$, it increases by about 8%. The rate of safety factors is identified as $Fs=3.86H^{-0.59}$, Fs = 0.43 s, Fs = 0.04 c, $Fs=0.02{\phi}$ depending on height, slope and shear strength. The safety factor with rainfall infiltration tends to increase by 18% compared to the condition of saturated surface on earth.

본 연구는 다양한 조건에 대한 사면 안정성 검토에 따른 안전율 변화 결과를 활용하여 초기 설계단계에서부터 참고하여 효율적인 설계가 될 수 있는 안전율을 제시하였으며, 사면안전율에 영향을 주는 인자들에 대한 영향성을 검토하였다. 우선 사면 높이 및 사면 기울기에 따라 최소 허용안전율 1.20을 만족하는 지반 전단강도를 제시하였다. 사면높이가 5.0m씩 증가함에 따라 안전율은 0.04씩 감소하는 것으로 나타났고, 사면높이에 따른 안전율은 사면높이 10.0m에 비해 높이가 높아질수록 약 20%, 30%, 40%씩 일정하게 감소하는 경향을 나타내었다. 사면 기울기가 약 0.3씩 완만해질수록 안전율은 0.4 정도씩 증가하는 것으로 나타났고, 사면기울기 증가에 대한 안전율 증가비는 기울기가 완만해질수록 약 10%, 20%, 30% 증가하는 것으로 나타났다. 점착력이 10.0kPa씩 증가할수록 안전율은 약 40%씩 증가하는 것으로 나타났고, 내부마찰각은 $5^{\circ}$씩 증가할수록 약 8%씩 증가하는 것으로 나타났다. 또한 사면 높이, 사면 기울기, 전단강도에 따른 안전율 변화비는 각 영향인자에 따라 $Fs=3.86H^{-0.59}$, Fs = 0.43 s, Fs = 0.04 c, $Fs=0.02{\phi}$ 의 증가비 관계를 나타내었다. 강우침투 시는 지표면 포화 시의 안전율보다 약 18% 정도 크게 나타났다.

Fig. 1. Forces for one slice

Fig. 2. Change of average safety factor with regard to height

Fig. 3. Normalized safety factor on height 10.0m

Fig. 4. Decreasing ratio of safety factor with regard to height

Fig. 5. Change of average safety factor with regard to slope

Fig. 6. Normalized safety factor on slope 1:1.2

Fig. 7. Increasing ratio of safety factor with regard to slope

Fig. 8. Normalized safety factor on cohesion 10kPa

Fig. 9. Normalized safety factor on angle of internal friction 20°

Fig. 10. Change of average safety factor with regard to cohesion

Fig. 11. Increasing ratio of safety factor with regard to cohesion

Fig. 12. Change of average safety factor with regard to angle of internal friction

Fig. 13. Increasing ratio of safety factor with regard to angle of internal friction

Fig. 14. Ground water level by rainfall infiltration (height=25.0m, slope=1:2.0)

Fig. 15. Safety factor with regard to ground water level

Fig. 16. Safety factor on height 10m

Fig. 17. Safety factor on slope 1:1.2

Fig. 18. Safety factor on cohesion 10kPa

Fig. 19. Safety factor on angle of internal friction 20°

Table 1. Minimum shear strength with regard to height and slope

Table 2. Decreasing ratio of safety factor on height 10.0m

Table 3. Increasing ratio of safety factor on slope 1:1.2

Table 4. Increasing ratio of safety factor on cohesion 10.0kPa

Table 5. Increasing ratio of safety factor on angle of internal friction 20°