1.4 Definitions

1.4.1 Defenitions common to all Eurocodes

(1)P The terms used in common for all Eurocodes are defined in ENV 1991-1.

1.4.2 Definitions used in Eurocode 7

(1)P For terms which are specific to Eurocode 7 reference is made to 1.5.2 of ENV 1997-1.

1.4.3 Definitions used in ENV 1997-3

(1) In sections 3 to 14 specific definitions relating to that section are given.

(2) For the purpose of this prestandard the following terms apply: derived value: value of a geotechnical parameter obtained by theory, correlation or empiricism from test results. Derived values form the basis for the selection of characteristic values of ground properties to be used for the design of geotechnical structures, in accordance with 2.4.3 of ENV 1997-1. Concept of derived values

(1) The concept of 'derived values' is elaborated as a way to link test results to geotechnical parameters. From the test results the values for geotechnical parameters for the use in analytical methods and coefficients for the use in semi-empirical or direct methods may be arrived at through:

— results of field tests -----> through correlations -----> to geotechnical parameter values
  -----> to coefficients in direct methods
— results of lab. tests -----> to geotechnical parameter values
  -----> through correlations
           with other tests ----->
to geotechnical parameter values

These values of the geotechnical parameters and/or coefficients, arrived at through, for example correlations, are called 'derived values'.

(2) ENV 1997-3 provides a set of examples of derived values for geotechnical parameters. From this the characteristic and the design values according to the requirements of ENV 1997-1 have to be established.

(3) The concept of 'derived values' is as follows: assume a homogeneous zone of ground governing the behaviour of a geotechnical structure. Assume that two types of field tests are carried out (see Fig. 1.1): five Cone Penetration Tests (CPT) and five pressuremeter tests (gives PLM), and assume five laboratory tests to establish the undrained shear strength. From the five (over the depth of the layer averaged) CPT values and PLM-values from pressuremeter tests, the following sets of derived values are established through certain correlations with the undrained shear strength:

Concept of derived values
Figure 1.1 Concept of derived values

(4) From these three sets of derived values for the undrained shear strength of a homogeneous soil mass, the characteristic value to be used in the design has to be assessed. Correlations

(1) The examples in the annexes, to subclauses #.7 of this prestandard, are based on various correlations obtained from the literature. These correlations may correlate a geotechnical parameter derived value either with a measured value, for example the qc-value of a CPT, or with a corrected value, for example the qt-value of a CPTU being the qc-value corrected for the measured excess pore pressure.

(2) Apart from this, the correlation may connect a geotechnical parameter derived value either with the mean value of the measured/corrected value or a conservative estimate of the measured/corrected value (see Fig 1.2).

Types of correlation
Figure 1.2 Types of correlation

(3) Each subclause #.7 of the tests covered by ENV 1997-3 gives examples on how to derive values of geotechnical parameters or coefficients in direct methods. In the examples in the annexes, the subclauses #.7 of ENV 1997-3 refer to, either 'mean' or 'conservative' correlations are used.

Sometimes the correlation can even be meant as a correlation of a geotechnical parameter and the characteristic value of the measured/corrected value. Normally the type of correlation is unknown. Also the theory used to determine a soil parameter value may differ between references and are not always presented in the references. In evaluating the examples in the annexes this should be kept in mind. If the type of correlation is known, this is indicated in the annexes. excess pore pressure: the pore water pressure over and above the equilibrium pore pressure at the end of the consolidation

1.5 Symbols and units

1.5.1 Symbols common to all Eurocodes

(1)P The symbols used in common for all Eurocodes are defined in ENV 1991-1 "Basis of design".

1.5.2 Symbols and units used in Eurocode 7

(1)P The symbols commonly used in ENV 1997-3 are defined in each section. Other symbols are defined where they are used locally in the text.

(2)P The units recommended for geotechnical calculations are defined in 1.6 of ENV 1997-1.

(3) The symbols follow the rules given in ISO 3898.

1.6 The link between ENV1997-1 and ENV 1997-3

(1) The flow chart shown below demonstrates the link between design and field and laboratory tests. Design is covered by ENV 1997-1; the parameter values part is covered by ENV 1997-2 and ENV 1997-3.

Flowchart geotechnical design
Figure 1.3 Flowchart geotechnical design

Eurocode 7 Geotechnical design — Part 3: Design assisted by fieldtesting