ground improvement by vibro stone columns
Post on 08-Jul-2015
375 Views
Preview:
DESCRIPTION
TRANSCRIPT
Ground Improvement by Vibro Stone Column
Desh Raj Sonyok
Saheem Ahmed
CE 596 Soil Improvement
Term paper – Fall 2006
Civil Engineering Department
New Mexico State University
Importance of Vibro Replacement
• Reduce settlement of soil
• Improve bearing capacity
• Improve shear strength of soil
• Liquefaction mitigation
Soils Suitable for the Vibro Replacement
Construction Procedures of the Vibro Replacement Method
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.
Preibe’s (1995) Equation
• Improvement factor equation (Preibe, '1995)
• Settlement after the improvement
( )
−
−−+= 11..4
5.10 AAK
AA
A
An
cac
cc
( )
−
−−+
=∞
114
51
AA.K.
AA
A
AD
dpS
cac
ccs
( )2452cac tanK φ−°=
Priebe (1995) Design Chart
Analysis and Comparison
• Stone Column to Prevent Settlement in Ireland
Measured Settlements
Soil Parameters and SettlementBefore After Befor
eAfte
r
Depth (m) Soil type N value
E (MPa)
N value
E (MPa)
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/CL
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
Stone Column to Prevent Settlement in South Africa
Settlement Measurements
Calculate Settlement
Structural load: 500 kPa – 700 kPaGrid type: triangularAverage length: 8 m –14 mDiameter: 740 mm
Zone Spacing (m) A (m2) A/AC Settlement (mm)
1 1.5 1.94 6.5 90
Settlement for the Vibro Stone Column Equation– Proposed Method
cs
ss AA
Aa
+=
0s e1
ea
+∆=
c
snσσ
=
( )scss a.a. −σ+σ=σ 1
( ) σµ=σ
−+
=σ .a1n1
1c
sc
( ) ( )[ ]
σ∆µ+−+−
=0
c0
0ss
c
P
.Plog
ea1a1
HCS
σ∆µ=∆
σ∆µ=∆
σ∆µ=ε
..H.bH
..V.bV
..bd
ss
ss
ssv
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
• 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.
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
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.
Thank You
top related