Managing risk and achieving reliable geotechnical designs using Eurocode 7 - Risk and Reliability in Geotechnical Engineering - page 395

10.4 VerIFICatIon oF DeSIgnS to euroCoDe 7

10.4.1 limit state design method
The limit state design method has been adopted in EN 1990, and hence in Eurocode 7, to
ensure that the basic requirement stated in Section 10.3.1 regarding geotechnical structures
having the appropriate degrees of reliability is fulfilled. The design requirement to be ful-
filled when using the limit state method is that, for each geotechnical design situation, no
relevant limit state is exceeded. Eurocode 7 states that limit states should be verified by one
or a combination of the following methods:

• Use of calculations
• Adoption of prescriptive measures
• Experimental models and load tests
• An observational method

In most cases, geotechnical designs are verified by the use of calculations and, hence,
Eurocode 7 and this chapter focus on that method. However, if one or a combination of
the other methods is used, then the resulting design should still aim to have the appro-
priate degrees of reliability as achieved when using calculations. When using calcula-
tions, the reliability of the design is verified by checking that the occurrence of either
an ultimate limit state (failure involving collapse or risk to life) or a serviceability limit
state (excessive deformations or vibrations) will not occur for all relevant design situa-
tions when using design values of the input parameters (design geometrical data, design
actions, and design material parameters or resistances). Design values are obtained by
applying partial factors, combination factors, and correlation factors to characteristic,
representative, or nominal parameter values, as appropriate. As explained in Section
10.5.1, the values of these factors can be determined either on the basis of calibration
with previous experience or on the basis of statistical evaluation to achieve the required
degrees of reliability.
When using one of the other methods on its own, the reliability of the design is verified by
monitoring the performance of the structure or a component, and checking that the occur-
rence of either an ultimate or a serviceability limit state is sufficiently unlikely for the design
conditions. The other methods, such as load tests or the observational method, are often
used in combination with calculations to justify the choice of reduced partial factor values
and, hence, more economical designs that still have the appropriate degrees of reliability.
An example of the use of load tests to achieve a more economical design is given in Section
10.5.2. This example is the use of the reduced partial resistance factors for the design of
piles in the UK National Annex to Eurocode 7, shown in Table 10.10 , when the serviceabil-
ity limit state is explicitly checked.

10.4.2 Verification by use of calculations
10.4.2.1 Design equations and their components
The equations to be satisfied when designing by the use of calculations are, for ultimate limit
states, to check that equilibrium is not violated; that is:

E d ≤ R d (10.1)