Managing risk and achieving reliable geotechnical designs using Eurocode 7 - Risk and Reliability in Geotechnical Engineering - page 392

where an action is defined in EN 1990 as a set of forces (loads) or an imposed deformation
or acceleration. As the above clause states, it is the basic requirement of the Eurocodes to
design structures that have appropriate degrees of reliability. Reliability is defined in EN
1990 §1.5.2.17 as “ the ability of a structure or structural member to fulfill the specified
requirements, including the design working life, for which it has been designed.” Calgaro
(2011), referring to the Eurocodes, notes that structural reliability covers four aspects:
safety, serviceability, durability, and robustness. Also, as pointed out in Guidance Paper
L—Application and use of the Eurocodes (EC, 2003), the word safety is encompassed in
the Eurocodes in the word reliability.
10.3.2 Measures to achieve reliable designs
While reliability is usually expressed in probabilistic terms, it is noted in §2.2(5) of EN 1990
that achieving the appropriate degrees of reliability of a structure does not only involve
using the limit state method, which is described in Section 10.4.1, but also involves adopting
a combination of the following measures relating to the different aspects of the whole design
and execution process:
a. Good quality investigations of the ground conditions and environmental influences
b. Preventative and protective measures
c. Measures relating to quality management
d. Measures aimed to reduce errors in design and execution, including gross human errors
e. Measures to provide adequate robustness
f. Efficient execution
g. Adequate inspection and maintenance
Further details of these measures are provided in the following paragraphs:
a. Good quality investigations : The importance of carrying out suitably extensive and
good quality geotechnical investigations for ensuring the reliability of geotechnical
designs is noted in §2.4.1(2) which states that “ Knowledge of the ground conditions
depends on the extent and quality of the geotechnical investigations. Such knowl-
edge and the control of workmanship are usually more significant to fulfilling the
fundamental requirements than is precision in the calculation models and partial fac-
tors. ” Some guidance on the spacing and depth of investigation points is provided in
§2.4.1.3(1)P of Part 2 of Eurocode 7.
b. Preventative and protective measures: Some measures provided to prevent the occur-
rence of a limit state or protect a structure from environmental influences when design-
ing to Eurocode 7 are not determined using calculations and partial factors. Such
measures include, for example, the provision of drains behind a retaining structure to
prevent the development of pore water pressures behind the retaining structure caus-
ing failure or excessive movement, and the use of a protective sheath or the provision
of sacrificial steel to protect the steel tendons in a ground anchor against corrosion.
c. Measures relating to quality management : Eurocode 7 provides a number of orga-
nizational measures and controls at the design, execution, use, and maintenance
stages of a project. For example, Eurocode 7 includes lists of many items to be taken
into account, to receive attention or be considered in the geotechnical design pro-
cess. These checklists are an important quality management feature of Eurocode 7
to achieve the required reliability of geotechnical designs apart from by means of
numerical calculations. Another important measure related to quality management