CE 464 Ground Improvement
Middle East Technical University, Ankara,Turkey
Department of Civil Engineering
Prof. Dr. K. Önder Çetin
ASSIGNMENT 4 Stone Columns
1) Three different stone column construction procedures are to be followed as part of a
ground improvement application beneath a highway embankment.
•
The first procedure involves pushing a 10 m long, 36 cm diameter close-ended
pipe into the ground followed by expanding it to 50 cm with further ramming
action.
•
The second procedure involves auger-boring a 10 m long, 80 cm diameter
hole and expanding it to 90 cm with further ramming action.
•
The last procedure involves auger-boring a 10 m long, 80 cm diameter hole
and expanding it to 100 cm with further ramming action.
If the foundation soil is classified as silty, clayey sand with effective shear strength
parameters, c'=10 kPa and ϕ'=320 , and shear modulus G= 25 MPa, γ=18 kN/m3 .
a) estimate the radial stress, σ r,r , state immediately around the stone columns by using
Baguelin et al. (1978) cavity expansion concepts.
Hint: You may assume that the first construction procedure is equivalent to expanding
a cavity of 10 cm diameter to 50 cm.
b) plot radial stress, σ r,r , vs. ∆r, and σ r,r , vs. ∆r/r0 plots and comment on the effects of
construction procedures on the stress state around stone columns.
2) Estimate the ultimate vertical load capacity of a single 50 cm diameter stone column
installed in a soil profile presented in Figure 1, assuming that the loading is applied in
a rapid (undrained) manner.
Assignment 4 : Stone Columns
CE 464 Ground Improvement
Middle East Technical University, Ankara,Turkey
Department of Civil Engineering
Prof. Dr. K. Önder Çetin
6m
H’
Dolgu γsat=17.5
3
H=1.5 m
Kil cu=75 kPa P=15 γsat=18 kN/m
D=0.5m
Yumuşak Kil cu=25 kPa
3
1.5 m 2.4m
PI= 40 γsat=17.5 kN/m
Çok Yumuşak Kil
cu=15 kPa
cu=40 kPa PI= 25 γsat=19 kN/m
Kaya
Zemin
ötelenmesi
Assignment 4 : Stone Columns
3
PI= 40 γsat=17.5 kN/m
Deniz Çökeli
3
CE 464 Ground Improvement
Middle East Technical University, Ankara,Turkey
Department of Civil Engineering
Prof. Dr. K. Önder Çetin
3) If the stone column introduced in Question 2, is to be installed beneath a highway
embankment, which applies a uniform vertical stress of q= 75 kPa, estimate the
ultimate vertical load capacity of the stone column.
4) A 10 m thick clay layer overlies a 2 m layer of sand, below which a rigid rock layer is
located, as shown in the figure given below. Water table is measured to be at the
ground surface. As part of a rapid rail project, a 5 m high and a very wide
embankment (γ=20 kN/m3 ) needs to be constructed. Estimate the 50 cm diameter
stone column square pattern spacing to reduce consolidation-induced settlements by
50 %.
Fill
0.0
5 m γ=20 kN/m3
0.5 m
Sand
UD-1
Cc=0.25 e0=0.90
Silty clay
γ=19 kN/m3
3cv= ch =0.90 m2/month
UD-2
-10.0
Sand
-12.0
Assignment 4 : Stone Columns
Cc=0.20 e0=0.85
5m
5m