The document discusses the vibro stone column method for soil improvement, highlighting its benefits such as reduced settlement, improved bearing capacity, and shear strength. It reviews mathematical analyses, including Priebe's 1995 equation and design chart, for estimating settlements before and after treatment. The paper concludes that while the proposed estimation method is conservative for homogenous soils, further research is needed to validate its applicability in layered soil conditions.

1. Ground Improvement by
Vibro Stone Column
CE 596 Soil Improvement
Term paper – Fall 2006
Civil Engineering Department
New Mexico State University
Desh Raj Sonyok
Saheem Ahmed

2. Importance of Vibro Replacement
• Reduce settlement of soil
• Improve bearing capacity
• Improve shear strength of soil
• Liquefaction mitigation

3. Soils Suitable for the Vibro
Replacement

4. Construction Procedures of the
Vibro Replacement Method

5. Analysis on Vibro Replacement
Stone Column
• Few mathematical analysis available for
the vibro replacement stone column
• Priebe (1995) proposed an equation for
the improvement factor as a function of
area replacement ratio. He further
proposed a design chart for the
improvement factor which is much more
common in practice.

6. Preibe’s (1995) Equation
• Improvement factor
equation (Preibe,
'1995)
• Settlement after the
improvement
ù
A A
n A
= + - 1
1 . 5 c c
0 K A A
( ) úû
é
êë
-
-
4. . 1
A
ac c
ïý ü
ù
A A
c c
( ) ïþ
S p d
ïî
ïí ì
úû
é
1 5
êë
-
-
+ -
¥ =
1
4 1
.K . A A
D A
A
ac c
s
2 (45 2)
Kac = tan ° - fc

7. Priebe (1995) Design Chart

8. Analysis and Comparison
• Stone Column to Prevent Settlement in
Ireland

9. Measured Settlements

10. Soil Parameters and Settlement
Before After Befor
e
Afte
r
Depth (m) Soil type N
va
l
ue
E
(M
Pa
)
N
val
ue
E
(M
Pa
)
s (mm) s
(
mm)
Recorded s
(mm)
Estimated s
(mm) *
0.0-3.5 SP 10 10 18 18 31 18 40 - 70 167
3.5-6.0 SP 2 2 20 20 120 12
6.0-7.0 ML/C
L
4 4 6 6 17 11
7.0-8.5 GW 6 12 10 20 12 7
8.5-11.0 GW 30 60 30 60 5 5
11.0-14.0 CI 27 38 27 38 6 6
14.0-16.0 GW 35 70 35 70 3 3

11. Stone Column to Prevent
Settlement in South Africa

12. Settlement Measurements

13. Calculate Settlement
Structural load: 500 kPa – 700 kPa
Grid type: triangular
Average length: 8 m –14 m
Diameter: 740 mm
Zone Spacing (m) A (m2) A/AC Settlement (mm)
1 1.5 1.94 6.5 90

14. Settlement for the Vibro Stone
Column Equation– Proposed Method
a A
s
s A +
A
s c
=
0
a = D
e
s 1 +
e
s
=
n s
c
s

15. s = ss .as + sc .(1- as )
ù
é
1
+ -
s = .
( ) s m = s úû
êë
1 n 1a
c
s
c
ù
é + m Ds
log P 0 c
.
S C c
H
( ) ( ) [ ] úû
êë
- + -
=
0
s s 0
P
1 a 1 a e
e = m Ds
d b . .
v s s
D = m Ds
V b .V. .
s s
D = m Ds
H b .H. .
s s
Average stress over the
unit cell
Stress concentration on the
surrounding soil
Settlement equation of
the surrounding soil
If compressibility of the stone
column is bs,
Settlement of the stone
column

16. • The proposed equation gives an estimation of
the settlement of the surrounding soil and the
column alone. The final settlement of the site will
be definitely with in the limit proposed above.

17. Limitation of the equation
• The proposed equation is applicable to the
homogeneous soil with clay to be improved. The
equation to be modified for the layered soils
• This method assumes constant compressibility
index before and after treatment

18. Conclusions
• The primary purpose of this method is to improve the
settlement characteristics of the soft soil, increase load
bearing capacity, and shear strength
• Estimation of settlement for the design of vibro stone
column proposed by Priebe is found to be more
conservative
• A rational method of estimating settlement in a
homogenous soil is proposed based on the basic concept
of composite material and soil mechanics.
• Result of this preliminary work is yet to validate
numerically and in the field.
• Detailed research in future is necessary to check its
validity and applicability.

19. Thank You