Recommended Values for Shear Force Transfer Coefficients according to EN 1993-5
Type of U-pile unit | Number of structural support levels (see Note 1) | Reduction factors βB and βD referred to in 5.2.2(2); 5.2.2(9); 5.2.3(2); 6.4(3) (see notes 2,3,4 and 5) | |||||
Hihgly unfavourable conditions (see Note 6) | Unfavourable conditions (see Note7) | Favourable conditions (see Note8) | |||||
βB | βD | βB | βD | βB | βD | ||
Singles or unscripted doubles | 0 | 0,40 | 0,30 | 0,50 | 0,35 | 0,60 | 0,40 |
1 | 0,55 | 0,35 | 0,60 | 0,40 | 0,70 | 0,45 | |
>1 | 0,65 | 0,45 | 0,70 | 0,50 | 0,80 | 0,55 | |
Crimped or welded doubles | 0 | 0,70 | 0,60 | 0,75 | 0,65 | 0,80 | 0,70 |
1 | 0,80 | 0,70 | 0,85 | 0,75 | 0,90 | 0,80 | |
>1 | 0,90 | 0,80 | 0,95 | 0,85 | 1,00 | 0,90 | |
NOTE 1
Any restraint device which leads to the shear force changing from positive to negative or vice versa may be considered as a structural support. The toe of the piles should not be considered as a restraint. The benefit of the restraint should only be taken into account for design situations following installation of the restraint. Restraints may be regarded as structural supports only when designed as such in accordance with relevant standards.
NOTE 2
If interlocks are not treated with sealants or lubricants, the coefficients may be increased by +0.05 (to a maximum value of 1.0).
NOTE 3
The interlocks of single or uncrimped U-piles should be connected after installation by a structural weld (minimum 6 mm fillet) near the top. The minimum length of this weld should be 100 mm for walls with retained heights up to 2.5 m; for greater retained heights, an additional 100 mm of weld should be provided for every additional 1 m of retained height, up to a maximum of 500 mm (applies to retained heights above 6.5 m). Provision of this weld permits the β₀ coefficients to be increased by +0.1, +0.15 or 0.2 respectively for highly unfavourable, unfavourable and favourable conditions (to a maximum value of 1.0), and the βR coefficients likewise by +0.1, 0.2 or 0.25 (to a maximum value of 1.0).
NOTE 4
The enhancement of β values by additional methods may be considered by the designer subject to demonstration, by calculation, testing or by other means, that the appropriate degree of shear force transmission will take place to justify higher coefficients than those values obtained from this table and notes.
NOTE 5
The βR and β₀ coefficients for the entire U-pile should be selected according to the most unfavourable conditions that apply.
NOTE 6
Highly unfavourable conditions are:
retaining substantial depths of free water;
significant presence of very low strength fine soil or very loose coarse soil (as defined in BS EN ISO 14688-1) below formation;
artificial loosening by pre-augering in fine soil below final excavation level (unless it can be demonstrated by testing or other means, that the pre-augered soil offers friction equivalent to or better than that of a low strength fine soil or loose coarse soil, in which case better conditions may be assumed);
artificial loosening of fine soil by water jetting at a rate exceeding 240 L/min (see Annex D.2 of BS EN 12063:1999);
artificial loosening of coarse soil by water jetting at a rate exceeding 480 litres per minute (see Annex D.2 of BS EN 12063:1999).
NOTE 7
Unfavourable conditions are:
significant presence of low strength fine soil or loose coarse soil (as defined in BS EN ISO 14688-1) below formation;
artificial loosening by pre-augering in coarse soil below final excavation level (unless it can be demonstrated by testing or other means, that the pre-augered soil offers friction equivalent to or better than that of a medium dense soil, in which case better conditions may be assumed);
artificial loosening of fine soil by water jetting at a rate between 60 L/min and 240 L/min (see Annex D.2 of BS EN 12063:1999) or where coarse soil has been artificially loosened at a rate between 240 L/min and 480 L/min.
NOTE 8
Favourable conditions may be assumed if none of the highly unfavourable or unfavourable conditions apply.