132 Ground improvement by deep vibratory methods
justifiable. It is therefore proposed to utilize the method after Barksdale and
Bachus (1983), assuming planar failure surfaces within the column group.
The failure load q ult is calculated as follows, utilizing the notations of
Figure 4.18:
q
c
ult
avg
= ⋅
+ ⋅
⋅
σ
δ
δ
3
2
2
tan
t an
(4.22)
where:
σ 3 is the average horizontal soil pressure in kPa
δ
is the inclination of failure plane of the composite soil
c avg is the average cohesion in kPa
σ 3
Cavity expansion
approximation
Plan views
σ 3
σ 3
σ 3
σ 3
σ 3
δ
q ult
B
B
B
δ
B · tan δ
Failure
surface
Square group
q ult
Infinitely long group
(b)
(a)
Figure 4.18 Bearing capacity of vibro stone column groups (a) below square footings and
(b) long strip footings. (Based on Barksdale and Bachus, Design and Construction
of Stone Columns. FHWA/RD-83/026, US Department of Transportation, Georgia
Institute of Technology, Atlanta, GA,1983.)
justifiable. It is therefore proposed to utilize the method after Barksdale and
Bachus (1983), assuming planar failure surfaces within the column group.
The failure load q ult is calculated as follows, utilizing the notations of
Figure 4.18:
q
c
ult
avg
= ⋅
+ ⋅
⋅
σ
δ
δ
3
2
2
tan
t an
(4.22)
where:
σ 3 is the average horizontal soil pressure in kPa
δ
is the inclination of failure plane of the composite soil
c avg is the average cohesion in kPa
σ 3
Cavity expansion
approximation
Plan views
σ 3
σ 3
σ 3
σ 3
σ 3
δ
q ult
B
B
B
δ
B · tan δ
Failure
surface
Square group
q ult
Infinitely long group
(b)
(a)
Figure 4.18 Bearing capacity of vibro stone column groups (a) below square footings and
(b) long strip footings. (Based on Barksdale and Bachus, Design and Construction
of Stone Columns. FHWA/RD-83/026, US Department of Transportation, Georgia
Institute of Technology, Atlanta, GA,1983.)