Unformatted text preview: Review #3 1. For the drilled shaft shown on the figure, determine the allowable load for a FS = 4.
D = 5 ft
20 ft 15 ft Clay
Cu = 1000 lb/ft2 Clay
Cu = 1800 lb/ft2 Pile Group
2. Consider a square 24” wide concrete pile with length of 60 ft and an allowable load of 220 tons. This pile will be used to support the load in a 12‐pile group, with three rows of 4 piles at 3B center‐
center spacing. What is the allowable capacity of the pile group if the individual allowable capacity is 258 kips? Check all 3 of the methods.
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– Soil: clay
cu = 1 tsf
= 0
m = 110 pcf Pile Group
3. For the pile group below, determine which pile will have the maximum and minimum load. 1 5 2 3 6 4 7 Q = 300 k
Mx = 50 k‐ft
My = 100 k‐ft
8 Summary of Slope Stability Methods (or when to use what) Summary of Slope Stability Methods (or when to use what) What to do if FS < 1.5 (or required minimum FS)
• Improve Slope Stability
– Soil weight is generally the prime driving force, especially if wet but not submerged
– Reduce driving forces: cut slope, reduce seepage, remove live loads and structures
– Add resisting force: berms, piles, walls
– Change borrow pit to improve properties of fill (can't do much about cuts) • Methods to improve slope stability (from McCarthy, 1998): 4. For the infinite slope shown, determine FS against sliding along the soil‐rock interface. If there is seepage through the soil and the GWT coincides with the ground surface, what would be FS if γsat = 118 lb/ft3 and H = 3.66? 5. A cut is made in a soil having γ = 105 lb/ft3, c’=600 lb/ft2 and ϕ’=15. The side of the cut slope will make 45° with the horizontal. What should be the depth of the cut slope that will have FS = 3? 6. A cut is to be made in a soft clay with an angle of 75°
with the horizontal. Given cu = 650 lb/ft2 and γ = 110 lb/ft3, determine the maximum depth up to which the excavation can be carried out. Find the radius of the critical circle. 7. Determine the minimum FS of a slope with the following parameters: H = 10.5m, i = 25°, c’= 10.5 kN/m2, ϕ’= 25°, γ = 18.5 kN/m3, ru = 0.35. 8. A reservoir will be submitted to sudden drawdown. The slope is 2:1 and the height is 60m. The embankment properties are γ = 20 kN/m3, c’= 30 kN/m2 and ϕ = 20. Is it safe to to a complete drawdown? If not, what level of drawdown is safe? ...
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 Fall '08
 Staff
 pile group, Slope Stability Methods

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