3.3.10 Geotechnical parameters from field tests

3.3.10.1 Cone penetration test

(1)P In assessing values of the cone resistance, the sleeve friction and, possibly, the pore-water pressure during penetration, the following aspects shall be taken into account:

  • the detailed design of the cone and friction sleeve. This may affect the results significantly and allowance must therefore be made for the type of cone used;
  • the results can only be interpreted with confidence when the succession of soil layers is established; in many situations borings will therefore be needed in conjunction with the penetration tests;
  • the effects of ground-water and overburden;
  • in heterogeneous soils in which widely fluctuating results are recorded, the penetration values shall be selected for the zone of soil relevant to the construction;
  • established correlations with other test results, such as density measurements and other forms of penetration testing.

3.3.10.2 Standard penetration and dynamic probing test

(1)P In assessing blow counts, the following features shall be considered:

  • type of test;
  • detailed description of the test procedure;
  • ground-water conditions;
  • the influence of the overburden pressure;
  • the nature of the ground, particularly if cobbles or coarse gravel are encountered.

3.3.10.3 Vane test

(1)P The following shall be considered when assessing the test results:

  • details of the test procedure;
  • whether standardised vane equipment has been used;
  • whether measurements have been made at several depths to provide a profile of strength in the succession of soil layers;
  • skin friction along the rod.

(2) Vane tests may be used for the assessment of undrained shear strength, cu, of cohesive soil.

NOTE The vane test is a simple and cheap way of checking the trafficability of soft ground for heavy equipment and vehicles.

(3)P To obtain derived values of cu, the measured values shall be corrected by a factor depending on the liquid limit, plasticity index and effective vertical stress, and based on local experience.

3.3.10.4 Weight sounding test

(1)P In assessing weight sounding test results, the following features shall be taken into account:

  • detailed description of the test procedure;
  • ground-water conditions;
  • influence of overburden pressure;
  • nature of the ground, particularly if cobbles or coarse gravel are encountered.

(2) Weight sounding tests may be used for the assessment of soil layer boundaries and the density of non-cohesive soils.

3.3.10.5 Pressuremeter test

(1)P In assessing the values of the limit pressure and the pressuremeter modulus, the following features shall be taken into account:

  • the type of equipment;
  • the procedure used to install the pressuremeter in the ground.

(2) Test curves, which exhibit more than a moderate degree of disturbance should not be used. Where the limit pressure is not reached during the test, a moderate and conservative extrapolation of the curve may be used to estimate it. For tests in which only the initial part of the pressuremeter curve is determined, general correlations or, preferably, local correlations from the same site may be used conservatively to estimate the limit pressure from the pressuremeter modulus.

3.3.10.6 Dilatometer test

(1)P In assessing dilatometer values the installation procedure shall be taken into account.

(2)P The succession of soil layers and especially some basic parameters such as granularity and degree of saturation shall be determined prior to the test.

(3) If strength parameters are to be evaluated, the penetration resistance should be taken into account.

(4) The dilatometer values should be used as an index for determining derived values of the stiffness moduli of the soil succession.

3.3.10.7 Compactibility tests

(1)P In assessing the compactibility of a fill material, the following features shall be taken into account:

  • type of soil or rock;
  • grain size distribution;
  • grain shape;
  • the heterogeneity of the material;
  • the degree of saturation or water content;
  • type of plant to be used.

(2) When using field measurements (e.g. soundings, dynamic compaction tests, plate load tests, settlement records) to control site compaction, the results of field compaction trials (see 5.3.3 (4)) should be related to standard laboratory compaction test values in order to obtain a direct measure of the compactibility of a soil or a rock fill.

Eurocode 7 Geotechnical design Part 1 : General rules