Managing risk and achieving reliable geotechnical designs using Eurocode 7 - Risk and Reliability in Geotechnical Engineering - page 398

Table 10.3 Components of geotechnical designs, their constituents, and related safety elements
Component

Constituents Safety elements

Geometrical
data

•Levels and slope of ground surface
•Water levels
•Levels of interfaces between strata
•Excavation levels
•Dimensions of geotechnical structure

•Nominal values
•Geometrical allowance, for example,
change to a geometrical parameter
such as the overdig allowance in
front of a retaining wall

•Characteristic values
•Nominal values

Actions •Weight of soil, rock, and water

•Earth and water pressures
•Stresses in the ground
•Seepage forces
•Dead and imposed loads
•Surcharges
•Mooring forces
•Removal of load or excavation of ground
•Trafic loads
•Movements causing by mining or caving or
other tunneling activities
•Swelling and shrinkage caused by vegetation,
climate, and moisture changes
•Movements due to creeping or sliding or
settling of ground masses
•Movements and accelerations caused by
earthquakes, explosions, vibrations, and
dynamic loads
•Temperature effects, including frost action
•Ice loading
•Imposed pre-stress in ground anchors or struts
•Downdrag

Geotechnical
parameters

•Geotechnical investigations
•Field and laboratory tests
•Derived parameters

•Characteristic values
•Correlation factors, ξ

Verification
method

•Consideration of all relevant limit states
•Use of calculation methods
•Prescriptive measures
•Load and model tests
•An observational method

•Combination factors, ψ
•Representative values
•Partial factors, γ
•Allowable deformations

Design
complexity

•Ground conditions
•Groundwater conditions
•Inluence of the environment
•Regional seismicity
•Nature of the structure
•Impact on neighboring structures

•Risk assessment
•Geotechnical Categories
•Comparable experience

where Δa is the change to the nominal geometrical parameter to provide the required safety
margin and achieve the appropriate degrees of reliability. An example of a situation where
deviation in a geometrical parameter is significant is in the design of an embedded retaining
wall whose stability depends on the passive pressure of the soil in front of the wall. In this
situation, Eurocode 7 specifies that the design ground surface in front of the wall should be
obtained by lowering the characteristic ground surface by an amount Δa.

10.4.2.3 Design actions
Since Eurocode 7 is one of the harmonized sets of Eurocodes, the values of the partial factors
for actions and the requirements for combining actions are given in EN 1990. The design