2.4 Investigations for design and construction
(1)P When planning investigations for design and construction account shall be taken of 3.2.3 of ENV 1997-1. The investigations for design and construction shall provide the necessary information for the construction works, the ground and groundwater conditions. The investigations shall be established for the ground below and around the construction site as far as the behaviour of the ground may adversity affect the construction works.
(2)P In cases where the preliminary investigations have not clearly shown that the overall stability is satisfactory, complementary investigations shall be performed during the design investigation phase.
(3)P The design investigations for the overall stability shall have such a composition and amount of investigation points that necessary stability analyses may be made and stabilization measures may be designed.
(4)P The composition of the ground investigation programme and location of the investigation points shall consider the size of the area, the topography, the geology, the groundwater conditions, the type and design of the construction and the type and location of neighbouring structures.
(5) The investigated area should extend into the neighbouring area for a distance of at least 1,5 times the expected excavation depth or depth of the soil layer that can generate settlements in the neighbouring area.
(6) When applicable, investigations in the design phase should comprise penetration tests, borings and/or test pits for sampling, in situ tests and groundwater measurements.
(7) The number of investigation points should be extended if it is deemed necesarry to obtain an accurate insight in the complexity and the variability of the ground at the building site. Where ground conditions are relatively uniform, a wider spacing or less investigation points may be sufficient. In either case this choice should be justified.
(8)P For identification and classification of soils, at least one boring with sampling shall be available. Samples shall be obtained from every separate soil layer influencing the behaviour of the actual structure.
(9) In cases of inhomogeneous soil layers, organic soils or when high quality samples are required, samples should be taken at least every 1 m in one boring.
(10) The depth of investigations should be extended to all strata that will be affected by the project. For dams, weirs, excavations below groundwater level, and where dewatering work is involved, the depth of exploration should also be selected as a function of the hydrogeological conditions. Slopes and steps in the terrain should be explored to depths below any potential slip surface.
(11) The groundwater pressure should be measured to a depth of at least 3 m below anticipated foundation level both in high and low points of the area or equal to the expected height of the phreatic surface above the foundation level.
2.5 Control Investigations
(1)P In order to check that the ground conditions, the delivered construction materials and the construction works correspond to those presumed or ordered a number of checks and additional tests shall be made during construction and execution of the project, when relevant.
(2) The following general control measures may apply:
- inspection of excavations;
- complementary site investigations;
- check of ground profile and properties;
- measurements of groundwater level or pore pressure and their fluctuations;
- measurements of the behaviour of neighbouring constructions, services or civil engineering works;
- measurements of the behaviour of the actual construction.
(3)P The results of the control measures shall be compiled, reported and checked against the design requirements. Decisions shall be taken based on the checks.
2.6 Reporting of site investigations
(1)P The results of a geotechnical investigation shall be reported and evaluated according to 3.4 of ENV 1997-1.
(2)P All site investigations shall be reported in such a way that the results may be checked and re-evaluated.
(3)P For identification and quality assurance purposes all investigation records, logs, samples and presentations shall contain the following information:
- name of company executing the test;
- identification of the actual site or area;
- identification number of the job or commission;
- borehole number;
- type of test.
(4)P In addition the following information shall be given on the field and laboratory investigation records in combination with the information required for each specific investigation method as indicated in sections 3 to 14:
- date of investigation;
- ground level;
- method of boring and borehole diameter;
- type of test methods used with reference to actual standards;
- calibration data for the actual measuring equipment;
- any deviations from the requirements of this prestandard, other relevant standards or recommendations;
- the signature of the operator in charge, or the field manager.
(5)P The ground investigation report shall include data indicating the basis for the survey of the site.
(6)P The factual ground investigation results shall be compiled in a report, with plans, in such a way that the total amount of basic information can be used in the evaluation of the results. The location of all investigation points shall be clearly indicated.
(7)P The evaluation of geotechnical information according to 3.4.2 of ENV 1997-1 shall be based on all relevant basic information available at the actual phase of the investigation.
(8)P Proposals for complementary investigations shall aim at clarifying the ground conditions in all the areas involved for the actual project and surrounding structures which are influenced by the project.
(9) Such proposals should account for the variations in the soil layer sequence, the variations in groundwater level or pore pressure and variations in the ground properties obtained from the investigations performed.