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FLEXIBLE TANK FOUNDATION ON ELASTIC SATURATED SOIL

FLEXIBLE TANK FOUNDATION ON ELASTIC SATURATED SOIL

In this case a flexible tank on elastic saturated soil is tested. The test includes the

verification of the settlement of the centre of the tank for the condition of homogeneous,

isotropic soil of finite depth in PLAXIS.

Used version:

• PLAXIS 2D - Version 2011

• PLAXIS 3D - Version 2012

Input: In this case a flexible tank on elastic saturated soil is tested. The test includes

the verification of the settlement of the tank for the condition of homogeneous, isotropic

soil of finite depth. The tank will impose a pressure difference in the soil of

∆q = 263.3 kN/m2. The soil properties are:

E ' = 95.8 MN/m2ν  = 0.499

The dimensions of the tank used in the test calculation in PLAXIS 2D are shown in Figure

1. An axisymmetric model is used. Geometry lines to be used for local refinement are

introduced at the corners of the foundation and 4 m below it.

4 m

23.35 m

116.75 m

116.75 m

Figure 1 Model geometry and dimensions (PLAXIS 2D)

The dimensions of the tank used in the test calculation in PLAXIS 3D are shown in Figure

2.

Meshing: The Coarse option is selected for the Global coarseness . The horizontal

geometry under the foundation is refined with a factor of 0.2.

Calculations: In the Initial phase zero initial stresses are generated by using the K0

procedure with Σ - Mweight equal to zero. The footing is activated in a separate phase

(Phase 1). The calculation type is Plastic analysis  and a Tolerated error  of 0.001 is

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VALIDATION & VERIFICATION

116.75 m

125 m

125 m

125 m

125 m

φ46.70 m

Figure 2 Model geometry and dimensions (PLAXIS 3D)

defined.

Output: The vertical settlement of the surface at the centre of the tank are 74.21 mm

and 75.02 mm for PLAXIS 2D and PLAXIS 3D respectively. The vertical displacements

shadings are shown in the Figures 3 and 4.

Figure 3 Vertical displacements (PLAXIS 2D)

Verification: The settlement at the centre of the tank is given by Lancellota (2008):

u y  =∆qRI p 

E 

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FLEXIBLE TANK FOUNDATION ON ELASTIC SATURATED SOIL

Figure 4 Vertical displacements (PLAXIS 3D)

Where I p  is the influence coefficient, which can be determined with Figure 5.

Figure 5 Influence coefficients for settlement under uniform load over circular area (Terzaghi (1948))

The settlement at the centre of the tank is therefore:

u y  =263.3 · 23.35 · 1.15

95.8 · 1000= 0.07380 m = 73.80 mm

This is in good correspondence with the numerical value from PLAXIS.

REFERENCES

[1] Lancellota, R. (2008). Geotechnical engineering. Balkema.

[2] Terzaghi, K. (1948). Theoretical soil mechanics.

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VALIDATION & VERIFICATION

4 Validation & Verification | PLAXIS 2012