1. Software for Designing Foundations on Reinforced Soil by Columns
Mounir BOUASSIDA and Lassaad HAZZAR

2. Design of foundations on reinforced soil by columns
optimization of the improvement area ratio (Total cross section of columns by the area of foundation) that ensuring overall stability of project: verifications of bearing capacity and settlement.

3. Reinforced Soils by columns
Stone columns
Sand columns
Deep Mixing
Acceleration of consolidation
Reduction of settlement
Performances
Increase of
bearing capacity

4. Prediction of bearing capacity
The design methods of ultimate bearing capacity
The design methods of ultimate bearing capacity
French recommendations NFP (2004).
Broms’s method (1982).
Method of Terashi & Tanaka (1981).
Limit analysis approach ( ).
It is noticed that all methods, quoted above, do not take into account the improvement of ambient soil characteristics due to columns installation.

5. Estimation of settlement
The majority of methods for settlement prediction consider the linear elastic behaviour both for intial soil (to reinforce) and column material.
The settlement prediction s in linear elasticity is determined as a function of the apparent modulus of reinforced ground , which generally expressed as (Bouassida et al, 2003)
The design methods of settlement
Variational approach
Balaam & Booker (1981)
Chow’s method (1996)
French recommendations NFP (2004)
The evolution of settlement versus time, of columnar reinforced soil is predicted with the poroelastic approach (Guetif and Bouassida, 2005)

6. Software “Columns” New methodology Bounding the substitution factor
Design including bearing capacity, settlement, and (or) consolidation verifications.
Or,
Design by taking account, first, of the bearing capacity verification, and, second, the settlement verification as suggested by (Bouassida, 2007).
New methodology
Bounding the substitution factor
hmin Minimum required reinforcement complying with bearing capacity
hmax Maximum reinforcement depending on the allowable settlement

7. soil & Columns characteristics
Diagram of operations
Loading
Foundation
Design of the
bearing capacity
Settlement
Prediction
Optimized
design
soil & Columns characteristics
Columns 1.0

8. Oil storage tank at Zarzis (Tunisia), 54 m of diameter
Case Histories
Oil storage tank at Zarzis (Tunisia), 54 m of diameter
The reservoir was built on reclaimed area as embankment (Solétanche, 1990). The carrying load of the tank is approximated quasi-uniform stress of 120 kPa, which largely exceeds the allowable bearing capacity of the initial soil. In order to increase the bearing capacity and to reduce the settlement of tank at allowable values, a reinforcement by stone columns was decided to make sure the stability of tank guaranted.

9. Characteristics …
54 m
Tank
7 m
Loose silty sand
Marl stone

13. Mounir
BOUASSIDA
Geotechnical Engineering Research Team 05/UR/11-06
B.P. 37- Le Belvédère
Tunis
1002
Tunisia

19. 00023
Oil storage tank
Zarzis Tunisia
Reinforcement by stone columns

27. 120

31. 7 25
3600
0.33 17

35. 7
36000
0.33 18 42

42. 2.3

55. 6

61. 54

69. 31

78. 1.2

130. Project1

133. Conclusions
New methodology for designing foundation on reinforced soil by columns: incorporated in a software « Columns »
Rational design allows to optimize the substitution factor (improvement area ratio), that conditions the cost of the reinforcement
Currently «Columns » is in a state of marketing

134.
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