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De Beer Method

This method determines the unit pile base resistance. It is based on the so-called "scale effect" for CPT-cone and pile base.

The method is described by the following steps which are performed in the standard 0,2 m interval along the pile length.

1) The calculation of the angle of internal friction φ according to the formula (1)

where:

qc

-

cone tip resistance

σeff

-

effective stress

φ

-

angle of internal friction

2) The calculation of the βc and βp angles according to the formulas (2) and (3).

Note: Both angles βc a βp can be maximally 90°.

where:

h

-

measurement depth

dc

-

diameter of the CPT-cone

D

-

pile base diameter

δ

-

pile base shape coefficient

For the circular and square piles:

For the rectangular piles:

where:

B

-

shorter side of the pile base

L

-

longer side of the pile base

3) Calculation of homogeneous values qp(1) according to the formula (4).

4) Calculation of downward values qp, j+1 according to the formula (5).

where:

a

-

measurement interval

hcrit

-

critical depth

γ

-

unit weight of soil

qp(1), crit

-

homogeneous value in the critical depth hcrit

The critical depth hcrit depends on the pile base diameter D and angle of internal friction φ:

For piles D < 0,4 m

- hcrit = 0,2 m

For piles 0,4 m ≤ D ≤ 0,6 m

- hcrit = 0,2 m for φ < 32,5°

- hcrit = 0,2 m and 0,4 m for φ ≥ 32,5°

For piles D ≥ 0,6 m

- hcrit = 0,2 m for φ < 32,5°

- hcrit = 0,2 m and 0,4 m for 32,5° ≤ φ < 37,5°

- hcrit = 0,2 m and 0,4 m a 0,6 m for φ ≥ 37,5°

Note: The final downward value is minimum for all relevant critical depths.

Note: The downward value must be smaller or equal to the homogeneous value.

5) Calculation of upward values qp, q+1 according to the formula (6).

Note: The upward value must be smaller or equal to the downward value.

6) Calculation of blended (mixed) qr,b values as an average from n upward values qp, q+1. The unit pile base resistance is the blended value in the pile base level.

Note: The blended value must be smaller or equal to the homogeneous value.

Literature: Prof. Dr. ir E. DE BEER: METHODES DE DEDUCTION DE LA CAPACITE PORTANTE D´UN PIEU A PARTIR DES RESULTATS DES ESSAIS DE PENETRATION (MEMOIRES - VERHANDELINGEN), online: https://www.bggg-gbms.be/l/library/download/urn:uuid:05c758bb-bf51-4eb7-9dc0-5a03b293f7e0/overige+publicaties.pdf?format=save_to_disk&ext=.pdf

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