2.7 Evaluation of site investigations

2.7.1 Evaluation of the preliminary investigations

(1)P The evaluation of the ground conditions in the preliminary investigation phase for positioning of the structure and the preliminary design shall make use of all relevant information from the desk study and the investigations performed at the site, related to the actual project.

(2) Geological maps and descriptions of the site, penetration test results, in situ test results, classification of soil and rock samples, laboratory test results and groundwater measurements should be used to identify and describe the soil layers, the rock mass and the groundwater conditions of the total area involved in the project.

(3) The evaluation should be summarized in the report, presenting the factual investigation data according to paragraph 2.6 (6)P.

(4) A preliminary derivation of ground parameter values for a preliminary design can be made for identified layers and can, for example, be expressed in terms of density, water content, penetration resistance, strength and deformation properties and pore pressures.

2.7.2 Evaluation of investigations for design and construction

(1)P The evaluation of the ground conditions in a design and construction phase shall make use of all relevant information from the actual and earlier phases to describe the situation in relation to the actual project.

(2)P The influence from or on surrounding structures, services or civil engineering works shall be considered in the evaluation so that all necessary data are obtained.

(3) When deriving the boundary between different soil layers, soil and rock and the groundwater level a rectilinear interpolation between the investigation points may normally be sufficiently accurate, unless there is substantial heterogeneity.

(4) Evaluation of the unit weight may be based on density measurements on undisturbed soil samples or core samples in rock. In cases where only disturbed samples have been obtained the unit weight may be estimated from in situ density tests or from compiled local experiences especially considering the degree of saturation, the content of coarse material and the natural scatter in density.

(5) The unit weight may also be estimated from local classification charts on the basis of results from CPT or dilatometer tests. In rock, and soils within a casing the density may be estimated from calibrated geophysical loggings as an alternative.

(6)P When deriving ground parameter values for design purposes from site investigations the type of ground, the type of construction, the total and local experiences from similar design cases as well as the scatter of the test results shall be considered.

(7) When deriving ground parameter values, the profile of the ground should be schematised into a representative sequence of layers of soil and rock on the basis of a geotechnical identification and classification and fieldtests. Within the distiguised layers the strenght and deformation properties should not vary considerably.

(8) For the assesment of the strenght and deformation properties of the distinguished layers in the schematised profile of the soil or rock, the following should be taken into consideration:

  • direct measurement of the properties from field vane tests, plate load tests or pile load tests;
  • laboratory measurements of certain parameters at certain stress conditions, e.g. triaxial tests, direct shear tests or oedometer tests;
  • transformation of measured data to soil properties by using compiled correlations with different parameters, e.g. angle of shearing resistance, modulus of elasticity, relative density from e.g. cone penetration tests, dynamic probing tests, SPT-tests, dilatometer tests or pressuremeter tests. Since correlations of this kind normally are limited to only one investigation method and one type of experiment it is not recommended to use them for cross correlations e.g. to transform N60 to qc and then to N' or Em;
  • direct use of measured parameter values in a design method based on compiled experiences, e.g. calculating the bearing capacity and settlements from pressuremeter tests, cone penetration tests or standard penetration tests.

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