How to use Foxta with CPT data?

July 20, 2018 by Terrasol


This document aims to show and clarify how to use Foxta with Cone Penetration Testing data (CPT) for shallow and deep foundations.

How to use Foxta with CPT data?Shallow foundationsFondsupParameters tabSoil definition tabTasplaq and TasseldoDeep foundationsFondprofParameters tabLayers tabSkin frictionTip resistanceTaspie+Reaction lawsSkin reaction lawTip reaction lawLayers tabSoil/pile tabPiecoef+Lateral reaction lawParameters tabSoil/pile tabGroupie+Soils tab

Shallow foundations

Foxta is appropriate for the design of shallow foundations, including :

Remember:

 

Fondsup

Fondsup allows for the design of rectangular or circular isolated and spread footings based on CPT data.

Parameters tab

If CPT data are available, one has to define the design method as From penetrometer results.

In this case, we recommend to process by measurements.

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Soil definition tab

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1531744153972The import wizard allows for the import a lot of data from clipboard (button Import).

For example, one may define all values in an Excel spreadsheet, select the range of data and then copy to clipboard.

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Tasplaq and Tasseldo

 

Tasplaq model (Cuira & Simon 2006)

The Tasplaq and Tasseldo modules require the input of soil elastic modulus () values.

How to determine soil elastic modulus () from CPT data?

In case of an important level of shear strains (raft under localized load, shallow foundation, embankment or slope edge...), Eurocode 7 (NF P 94-261 J.2.2) suggest to use Robertson model:

In case of important volumetric strains () (embankment on soft soil...), Eurocode 7 (NF P 94-261 J.2.3) suggest to use Sanglerat model:

Soil type
(MPa)
Stiff clay (low plasticity)< 0.7
0.7 to 2
> 2
3 to 8
2 to 5
1 to 2.5
Silt (low plasticity)< 2
> 2
3 to 6
1 to 2
Soft clay
Soft silt
< 2
> 2
2 to 6
1 to 2
Organic silt< 1.22 to 8
Peat and organic clay< 0.750%<w<100% → 1.5<< 4
100%<w<200% →1<< 1.5
w>200% → 0.4 < < 1.0
Chalk2 to 3
> 3
2 to 4
1.5 to 3
Sand< 5
>10
2
1.5

 

 

Deep foundations

Here are a few examples of deep foundations which may be designed with Foxta:

Remember:

 

Fondprof

Fondprof is used to evaluate the bearing capacity of a single deep foundation.

Parameters tab

First of all, define the design method as From penetrometer results** in the Parameters tab.

After, you may chose to process by measurements or by layers. In the case of CPT data, it can be useful to process by measurements.

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Layers tab

We recommend to define one soil layer per value from CPT data.

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Skin friction

 

Tip resistance

The and values may be defined by the user.

 

Final penetrometric factor for bearing capacity calculation will be obtained from the following expression:

In case one wants to impose a value, one has to define :

Pile typeClay soilIntermediate soilSandy soils and GravelsChalkMarl and Marly limestoneFragmented or alterate rock
10.40.30.20.30.30.3
20.450.30.250.30.30.3
30.50.50.50.40.350.35
40.450.40.40.40.40.4
50.350.30.250.150.150.15
60.40.40.40.350.20.2
70.350.250.150.150.150.15
80.450.30.20.30.30.25

values for proposed by Eurocode 7 NF P 94-262 (Table G.4.2.1)

 

1531727792720a Wizard may be used to calculate automatically and values for each soil categorie.

Pile types are detailed on the user interface.

 

Taspie+

Taspie+ handles :

t-z model

 

Reaction laws

Skin reaction law

Skin reaction law

 

value corresponds to value obtained using FondProf.

In the case of CPT data, may be evaluated with the following expression:

 

Tip reaction law

Stiffness diagram for lateral skin and tip resistance

 

value is obtained from FondProf at the bottom level of deep foundations.

In the case of CPT data, may be evaluated by following expression:

 

Layers tab

We consider a model composed by 3 soil layers.

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Soil/pile tab

One has to define mobilisation law for the skin friction and the the tip resistance point by point.

We will consider 3 layers, each one associated to a value. For each layer, a skin reaction law and a tip reaction law must be defined.

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Skin reaction law for each soil layer

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Tip reaction law for last soil layer

 

How to determinate input values for skin reaction law?

How to determinate input values for tip reaction law?

Piecoef+

Piecoef+ provides fine calculations for single deep foundations under lateral loading.

p-y model

 

Lateral reaction law

The lateral reaction law has to be chosen depending on the nature of the loads applied onto the deep foundation.

How to determinate input values for lateral reaction law?

 

 

 

Lateral reaction law - 2 plateaux

Manual input law (2 plateaux)

 

 

Lateral reaction law - 3 plateaux.

Manual input law (3 plateaux)

Type of soilSandy soilsIntermediate soilsClay soilsChalk and Marl
 IR< 2,052,05 ≤ IR ≤ 2,6IR> 2,6-
β4,57,5124,5
β11310513
β2863,58

 

Parameters tab

Choose manual input with 2 plateaux or 3 plateaux depending on the nature of the loads applied on the deep foundation.

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Soil/pile tab

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Groupie+

Groupie+ handles 3D calculations for pile group topped with a rigid footing and loaded with a torsor (6 components: 3 forces and 3 moments) taking into account the stiffness of the foundation and of the soil.

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The same reaction laws than Taspie+ and Piecoef+ are implemented in Groupie+, so one may refer to previous sections to define all input parameters.

Soils tab

If CPT data are available, one should define the reaction curve with Point-by-point input.

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Soil reaction laws may be defined through the provided wizards (input parameters are described in previous sections) :

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For more information, please contact support@terrasol.com

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