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Software for Designing Foundations on Reinforced Soil by Columns
Mounir BOUASSIDA and Lassaad HAZZAR
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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.
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Reinforced Soils by columns
Stone columns Sand columns Deep Mixing Acceleration of consolidation Reduction of settlement Performances Increase of bearing capacity
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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.
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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)
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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
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soil & Columns characteristics
Diagram of operations Loading Foundation Design of the bearing capacity Settlement Prediction Optimized design soil & Columns characteristics Columns 1.0
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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.
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Characteristics … 54 m Tank 7 m Loose silty sand Marl stone
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Mounir BOUASSIDA Geotechnical Engineering Research Team 05/UR/11-06 B.P. 37- Le Belvédère Tunis 1002 Tunisia
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00023 Oil storage tank Zarzis Tunisia Reinforcement by stone columns
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120
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7 25 3600 0.33 17
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7 36000 0.33 18 42
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2.3
55
6
61
54
69
31
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1.2
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Project1
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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
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