Uplift and hydraulic failure
Two sums of actions compared against each other, not one number against a resistance — EN 1997-1 §2.4.7.4 and §2.4.7.5.
The whole structure floats. Compares the vertical destabilising actions against the stabilising permanent weight plus any additional uplift resistance. Expression (2.8).
γG;dst = 1.00 · γG;stb = 0.90 · γQ;dst = 1.50 Tab. A.15
Water uplift and anything else pushing the structure up.
Permanent vertical weight only. The code provides no variable stabilising action — a load that may be absent cannot be relied on to hold the structure down.
Wall friction, piles in tension, anchorages — already divided by the factors of Table A.16 (1.25 on tan phi', 1.40 on undrained cohesion, pile tension and anchorage). §2.4.7.4(2) allows it to be treated as a stabilising permanent action instead.
▸ Fill in the data on the left and press Calculate
Tool information
What this page computes
The two ultimate limit states in EN 1997-1 that are compared against no material resistance at all:
- UPL — §2.4.7.4, expression (2.8): loss of equilibrium by water uplift;
- HYD — §2.4.7.5, expressions (2.9a) and (2.9b): hydraulic failure of the ground under upward seepage.
Why they are not in EN 1990
Because they are not there. §6.4.1(1) of EN 1990 lists exactly four ultimate limit states — EQU, STR, GEO and FAT — and A1.3.1(7) says plainly that failure caused by hydraulic effects and uplift is verified in accordance with EN 1997.
There is no "Table A1.2(D)". The factors come from Annex A of EN 1997-1: Table A.15 for UPL, Table A.17 for HYD.
Why it looks different from the other combinations
The other combinations produce one number, \(E_d\), then compared against a resistance. Here two sums of actions are compared — destabilising against stabilising — each with its own factor.
The practical consequence: the same self-weight lands on one side or the other depending on whether it helps, and the factor changes with the side. That is not a notational subtlety; it is the difference between 1.00 and 0.90 on the same kilogram of concrete.
The difference between the two sets
| γ_G;dst | γ_G;stb | γ_Q;dst | |
|---|---|---|---|
| UPL — Table A.15 | 1.00 | 0.90 | 1.50 |
| HYD — Table A.17 | 1.35 | 0.90 | 1.50 |
The stabilising side is identical. The destabilising side is not: the same permanent action is charged 35% more for hydraulic failure than for uplift.
This is not an inconsistency in the code. They are two different mechanisms: in UPL the whole body floats, like a boat; in HYD the soil between the walls lifts, and there the uncertainty about the flow regime is far greater.
What cannot go on the stabilising side
No variable action. Tables A.15 and A.17 give a factor for temporary actions only on the destabilising side — there is no γ_Q;stb at all.
The reason is obvious once stated: a load that may be absent cannot be relied on to hold the structure down. That is why the page offers no “permanent” checkbox on the stabilising side — it is not an omission. The service, which can be called from outside the page, ignores such an entry and flags it rather than accepting it silently.
The two HYD expressions are not equivalent
The code gives two checks for the same limit state:
\(u_{dst;d} \le \sigma_{stb;d} \qquad (2.9a)\) \(S_{dst;d} \le G'_{stb;d} \qquad (2.9b)\)
The first works in total pressures — pore water pressure at the base of the column against the total vertical stress. The second works with the seepage force against the weight of the same column in the submerged state.
This is not a matter of convention: for the same soil column they can leave different margins. Run both.
R_d — additional uplift resistance
For UPL, §2.4.7.4(1) allows an additional resistance \(R_d\) on the stabilising side: wall friction, piles in tension, anchorages.
Note where the reduction applies. Table A.16 gives its own factors — 1.25 on \(\tan\varphi'\) and on effective cohesion, 1.40 on undrained cohesion, on pile tension and on anchorage. The page's field expects the value already reduced; it is not divided again here.
§2.4.7.4(2) leaves one more door open: uplift resistances may instead be treated as a stabilising permanent action \(G_{stb;d}\) — that is, with 0.90 rather than the factors of A.16. The two routes do not give the same answer.
What it does not cover
- The calculation of \(R_d\) itself — friction, pile tension, anchorage. Here it is entered as a number.
- The seepage analysis producing \(u_{dst}\) and \(S_{dst}\): flow net, gradient, permeability.
- EQU, STR and GEO — those are on the EN 1990 combinations page.
- Design approaches 1, 2 and 3 of §2.4.7.3.4, which concern STR/GEO, not UPL/HYD.
The texts of §2.4.7.4, §2.4.7.5 and Tables A.15–A.17 are transcribed from EN 1997-1:2004, pages 31–32 and 124–125.
Related calculations
- Combinations of actions — EQU, STR, GEO, plus prestress and the fire situation.
- Winkler pressures — bearing pressures, for the stabilising weight.
- Propped diaphragm wall — the excavation geometry from which the HYD column follows.