Environmental Engineering Reference
In-Depth Information
and, for serviceability limit states, to check that the deformations do not exceed the limiting
criterion:
E d ≤ C d
(10.2)
where E d is the design value of the effect of the actions, which for ultimate limit states is the
design force or moment and for serviceability limit states is the calculated design deforma-
tion, R d is the design value of the resistance, and C d is the limiting value of the deformation,
that is, the relevant serviceability criterion.
The components of limit state design calculations, with examples of their constituents
shown in brackets, are
• Geometrical data (ground proile, structural geometry)
• Actions (weight of soil, rock, and water, earth and water pressures, dead and imposed
loads, ground movements due, for example, to mining and tunneling, temperature
effects)
• Geotechnical parameters (geotechnical investigations, ield and laboratory tests,
derived parameters)
• Veriication method (consideration of all relevant limit states, use of calculation meth-
ods, prescriptive measures and load tests, an observational method)
• Design complexity (ground conditions, nature of the structure, groundwater condi-
tions, influence of the environmental, regional seismicity)
These components are presented in the form of the Geotechnical Design Triangle shown
in Figure 10.1 , based on Orr (2012), similar to Burland's (1987) Soil Mechanics Triangle,
with geometrical data, the combination of actions and geotechnical parameters, and the
verification method at the apexes of the triangle, each connected to the design complexity at
the center of the triangle as this affects all aspects of a geotechnical design. The safety ele-
ments and safety features associated with each of these components in design calculations in
order to achieve the appropriate degrees of reliability are shown in italic type in Figure 10.1,
together with the linkages between them.
The components of geotechnical design calculations to Eurocode 7, their constituents, and
safety elements are also shown in Table 10.3 and explained in the following paragraphs. The
list in Table 10.3 of what constitute actions in Eurocode 7 is taken from §2.4.2(4) and shows
that earth pressures, movements caused by mining or other caving or tunneling activities,
movements due to creeping, or sliding or settling ground masses, downdrag and temperature
effects should all be considered as actions. Since earth pressures and downdrag are actions
that also involve the strength of the soil and since soil strength is frictional, so that the resis-
tance is a function of actions, care is needed when calculating E d and R d to ensure that the
actions and soil strengths or resistances are factored appropriately to achieve the appropriate
degrees of reliability. This is commented on in Section 10.4.2.5 on design effects of actions
and design resistances. Example 10.2 examines the effect of the interaction between actions
and soil resistance in the case of earth resistance to uplift on the side wall of a deep basement.
10.4.2.2 Design geometrical data
The geometrical data involved in geotechnical design calculations include the level and slope
of the ground surface, water levels, the levels of the interfaces between strata, excavation
levels, and the shape of the foundation or other structural elements. Deviations and uncer-
tainties in the geometrical data are usually small and therefore the characteristic values of
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