10.2 Failure by uplift

(1)P The stability of a structure or of a low permeability ground layer against uplift shall be checked by comparing the permanent stabilising actions (for example, weight and side friction) to the permanent and variable destabilising actions from water and, possibly, other sources. Examples of situations where uplift stability shall be checked are given in Figure 7.1 and Figure 10.1.

(2)P The design shall be checked against failure by uplift using inequality (2.8) of 2.4.7.4. In this inequality, the design value of the vertical component of the stabilising permanent actions (Gstb;d) is the sum of, for example, the weight, of the structure (or ground layer), any friction forces, (T), and any anchor forces, (P). The design value of the vertical component of the destabilising permanent and variable actions, (Vdst;d), is the sum of the water pressures applied under the structure (permanent and variable parts) and any other upwards forces.

(3) In simple cases, the check of equation (2.8) in terms of forces may be replaced by a check in terms of total stresses and pore-water pressures.

Uplift of a buried hollow structure

a) Uplift of a buried hollow structure

 

Uplift of a lightweight embankment during flood

b) Uplift of a lightweight embankment during flood

  • 1 (ground)-water table
  • 2 water tight surface
 
  • 1 (ground)-water table
  • 2 water tight surface
  • 3 light weight embankment material

 

Uplift of the bottom of an excavation

c) Uplift of the bottom of an excavation

 

Execution of a slab below water level

d) Execution of a slab below water level

  • 4 former ground surface
  • 5 sand
  • 6 clay
  • 7 gravel
       
  • 1 (ground)-water table
  • 2 water tight surface
  • 5 sand
  • 6 sand
  • 8 injected sand

 

Structure anchored to resist uplift

e) Structure anchored to resist uplift

  • 1 (ground)-water table
  • 5 sand
  • 9 anchorage
Figure 10.1 — Examples of situations where uplift might be critical

(4) The measures most commonly adopted to resist failure by uplift are:

  • increasing the weight of the structure;
  • decreasing the water pressure below the structure by drainage;
  • anchoring the structure in the underlying strata.

(5)P Where piles or anchorages are used to provide resistance against failure by uplift, the design shall be checked according to 7.6.3 or 8.5, respectively, using the partial factors given in 2.4.7.4.

Eurocode 7 Geotechnical design Part 1 : General rules