1.6 Test results and derived values

(1) Test results and 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 EN 1997-1:2004.

NOTE 1 The process of geotechnical design consists of a few successive phases (see Figure 1.1), the first of which covers the site investigation and testing, whereas the next one is devoted to the determination of characteristic values, and the last phase covers the design verification calculations. Rules for the first phase are given in the present standard. The determination of characteristic values and the design of the structures are covered by EN 1997-1.

(2) Test results can be experimental curves or values of geotechnical parameters. In Annex A, a list of test results is given to serve as a reference to test standards⁷.

(3) Derived values of geotechnical parameters and/or coefficients, are obtained from test results by theory, correlation or empiricism.

NOTE 2 The examples of correlations used to determine derived values given in the annexes to Section 4 of this standard arc obtained from the literature. These correlations may correlate the value of a geotechnical parameter or coefficient with a test result, such as the q_c-value of a CPT. They may also connect a geotechnical parameter to a test result by means of theoretical considerations (for example, when deriving a value of the angle of shearing resistance φ' from pressuremeter lest results or from the index of plasticity).

NOTE 3 In certain cases, the derivation of geotechnical parameters by means of a correlation is not made before the determination of the characteristic value, but after the test results have been corrected or transformed into conservative estimates.

1.7 The link between EN 1997-1 and EN 1997-2

(1) Figure 1.2 presents the general architecture of the CEN standards related to geotechnical engineering problems and those directly linked to EN 1997. The design part is covered by EN 1997-1. The present standard gives rules for ground investigations and obtaining geotechnical parameters or coefficients values to be used for determining the characteristic values (as specified in EN 1997-1). It gives also informative examples of calculation methods for spread and deep foundations. The implementation of EN 1997 needs information based on other standards, in particular those related to ground investigations and to the execution of geotechnical works.

EN 1997-1

EN 1997-2

Test standards (CEN/TC 341)

Execution of geotechnical works (CEN/TC 288)

1.8 Symbols and units

(1) For the purpose of EN 1997-2 the following symbols apply.

NOTE The notation of the symbols used is based on ISO 3898:1997.

Latin letters

k

coefficient of permeability

Greek letters

α

correlation factor for E_oed and q_c, (see Equation (4.3))

σ_p

effective pre-consolidation pressure or effective vertical yield stress in situ

σ_v0

initial vertical total stress

σ_ν0

initial vertical effective stress

Abbreviations

CPT

electrical cone penetration test

CPTM

mechanical cone penetration test

(2) For geotechnical calculations, the following units or their multiples are recommended:

• force kN
• moment kNm
• mass density kg/m³
• weight density kN/m³
• stress, pressure, strength and stiffness kPa
• coefficient of permeability m/s
• coefficient of consolidation m²/s