Section 2 Planning of ground investigations

2.1 Objectives

2.1.1 General

(1)P Geotechnical investigations shall be planned in such a way as to ensure that relevant geotechnical information and data are available at the various stages of the project, Geotechnical information shall be adequate to manage identified and anticipated project risks. For intermediate and final building stages, information and data shall be provided to cover risks of accidents, delays and damage.

(2) The aims of a geotechnical investigation are to establish the soil, rock and groundwater conditions, to determine the properties of the soil and rock, and to gather additional relevant knowledge about the site.

(3)P Careful collection, recording and interpretation of geotechnical information shall be made. This information shall include ground conditions, geology, geomorphology, seismicity and hydrology, as relevant. Indications of the variability of the ground shall be taken into account.

(4) Ground conditions which may influence the choice of geotechnical category should be determined as early as possible in the investigation.

NOTE As a result of the geotechnical investigations, it may be necessary to change the geotechnical category of the project (see 1.1.2 (4)).

(5) Geotechnical investigations should consist of ground investigations, and other investigations for the site, such as:

  • the appraisal of existing constructions, e.g. buildings, bridges, tunnels, embankments and slopes:
  • the history of development on and around the site.

(6) Before designing the investigation programme, the available information and documents should be evaluated in a desk study.

(7) Examples of information and documents that can be used are:

  • topographical maps;
  • old city maps describing the previous use of the site;
  • geological maps and descriptions;
  • engineering geological maps;
  • hydrogeological maps and descriptions;
  • geotechnical maps;
  • aerial photos and previous photo interpretations;
  • aero-geophysical investigations;
  • previous investigations at the site and in the surroundings;
  • previous experiences from the area;
  • local climatic conditions.

(8) Ground investigations should consist of field investigations, laboratory testing, additional desk studies and controlling and monitoring, where appropriate.

(9)P Before the investigation programme has been drawn up the site shall be visually examined and the findings recorded and cross-checked against the information gathered by desk studies.

(10) The ground investigation programme should be reviewed as the results become available so that the initial assumptions can be cheeked. In particular:

  • the number of investigation points should be extended if it is deemed necessary to obtain an accurate insight into the complexity and the variability of the ground at the site;
  • the parameters obtained should be checked to see that they fit into a consistent behavioural pattern for soil or rock. If necessary additional testing should be specified:
  • any limitations in the data, revealed according to EN 1997-1:2004, 3.4.3 (1) should be considered.

(11) Special attention should be paid to sites that have been previously used, where disturbance of the natural ground conditions may have taken place.

(12)P An appropriate quality assurance system shall be in place in the laboratory, in the field and in the engineering office, and quality control shall be exercised competently in all phases of the investigations and their evaluation.

2.1.2 Ground

(1)P Ground investigations shall provide a description of ground conditions relevant to the proposed works and establish a basis for the assessment of the geotechnical parameters relevant for all construction stages.

(2) The information obtained should enable assessment of the following aspects, if possible:

  • the suitability of the site with respect to the proposed construction and the level of acceptable risks;
  • the deformation of the ground caused by the structure or resulting from construction works, its spatial distribution and behaviour over time;
  • the safety with respect to limit states (e.g. subsidence, ground heave, uplift, slippage of soil and rock masses, buckling of piles, etc.);
  • the loads transmitted to the structure from the ground (e.g. lateral pressures on piles) and the extent to which they depend on its design and construction;
  • the foundation methods (e.g. ground improvement, whether it's possible to excavate, driveability of piles, drainage);
  • the sequence of foundation works;
  • the effects of the structure and its use on the surroundings;
  • any additional structural measures required (e.g. support of excavation, anchorage, sleeving of bored piles, removal of obstructions);
  • the effects of construction work onthe surroundings;
  • the type and extent of ground contamination on, and in the vicinity of, the site;
  • the effectiveness of measures taken to contain or remedy contamination.

2.1.3 Construction materials

(1)P Geotechnical investigations of soil and rock for use as construction materials shall provide a description of the materials to be used and shall establish their relevant parameters.

(2) The information obtained should enable an assessment of the following aspects:

  • the suitability for the intended use;
  • the extent of deposits;
  • whether it is possible to extract and process the materials, and whether and how unsuitable material can be separated and disposed of;
  • the prospective methods to improve soil and rock:
  • the workability of soil and rock during construction and possible changes in their properties during transport, placement and further treatment;
  • the effects of construction traffic and heavy loads on the ground;
  • the prospective methods of dewatering and/or excavation, effects of precipitation, resistance to weathering, and susceptibility to shrinkage, swelling and disintegration.

2.1.4 Groundwater

(1)P Groundwater investigations shall provide all relevant information on groundwater needed for geotechnical design and construction.

(2) Groundwater investigations should provide, when appropriate, information on:

  • the depth, thickness, extent and permeability of water-bearing strata in the ground, and joint systems in the rock;
  • the elevation of the groundwater surface or piezometric surface of aquifers and their variation over time and actual groundwater levels including possible extreme levels and their periods of recurrence;
  • the pore water pressure distribution;
  • the chemical composition and temperature of groundwater.

(3) The information obtained should be sufficient to assess the following aspects, where relevant:

  • the scope for and nature of groundwater-lowering work;
  • possible harmful effects of the groundwater on excavations or on slopes (e.g. risk of hydraulic failure, excessive seepage pressure or erosion);
  • any measures necessary to protect the structure (e.g. waterproofing, drainage and measures against aggressive water);
  • the effects of groundwater lowering, desiccation, impounding etc. on the surroundings;
  • the capacity of the ground to absorb water injected during construction work;
  • whether it is possible to use local groundwater, given its chemical constitution, for construction purposes.

Eurocode 7: Geotechnical design — Part 2: Ground investigation and testing