Okiryu
Civil/Environmental
- Sep 13, 2013
- 1,094
Hi, I am doing a preliminary slope stability analysis and would like to hear your opinions.
The slope is 1:2 (V:H), about 10 meters in height and covered by vegetation. Visual inspection indicates that the slope is stable. Water table at 10 below the top of the slope. Soils are sandy silts (ML) however they have about 23% of clays. Sands are about 41%, the remaining are silts. Moisture contents are about 27% with Atterberg limits from NP to LL=43 and PL=30. Degree of saturation is 73%~86%. I did some unconfined compression tests (qu=130~160 kPa) and some UU triaxial tests (c=38~55 kPa and phi=12~28 degrees).
My question is about how do you consider the shear strength for this analysis:
#1. c-phi soil
#2. Total stress/short term analysis (Su= "X" , phi = zero)
#3. Effective stress/long term analysis (Su= zero , phi = "Y"). For this case, perhaps the fully softened strength may be appropriate but based on the actual conditions of the slope, I doubt that wetting-drying process can affect the slope as it is properly covered with vegetation.
Anyways, I am inclined to use #1 above because of the proportions between sand, silts and clays. I was also looking at shear strengths using #2 and # 3, but the factors of safety resulted in less than 1. That is one more reason to use #1.
Talking with one of my seniors, he also suggested to use #1.
What do you think?
The slope is 1:2 (V:H), about 10 meters in height and covered by vegetation. Visual inspection indicates that the slope is stable. Water table at 10 below the top of the slope. Soils are sandy silts (ML) however they have about 23% of clays. Sands are about 41%, the remaining are silts. Moisture contents are about 27% with Atterberg limits from NP to LL=43 and PL=30. Degree of saturation is 73%~86%. I did some unconfined compression tests (qu=130~160 kPa) and some UU triaxial tests (c=38~55 kPa and phi=12~28 degrees).
My question is about how do you consider the shear strength for this analysis:
#1. c-phi soil
#2. Total stress/short term analysis (Su= "X" , phi = zero)
#3. Effective stress/long term analysis (Su= zero , phi = "Y"). For this case, perhaps the fully softened strength may be appropriate but based on the actual conditions of the slope, I doubt that wetting-drying process can affect the slope as it is properly covered with vegetation.
Anyways, I am inclined to use #1 above because of the proportions between sand, silts and clays. I was also looking at shear strengths using #2 and # 3, but the factors of safety resulted in less than 1. That is one more reason to use #1.
Talking with one of my seniors, he also suggested to use #1.
What do you think?