4 Needs for the construction of bored piles

4.1 Any information important for the execution for the works on site should:

  • a) be provided with the specifications of the works;
  • b) be available before commencement on site; and
  • c) include:
    • the geotechnical information (see clause 5);
    • the site conditions, (e.g. size, site boundaries, topography, slope, access, limitations);
    • existence, location and condition of adjacent structures, (e.g. buildings, roads, utilities or services), underground structures and foundations, archaeological remains, headroom restrictions (e.g. power lines);
    • underground contamination or hazards that can affect the execution method, the working safety or the discharge of excavation material from the site;
    • environmental restrictions (e.g. on noise, vibration or pollution) and any legal or statutory restrictions;
    • the design and specifications for the works;
    • all necessary or relevant information for the production of the working drawings and method statements (where required);
    • previous experience with bored piling or other foundations or underground works on or adjacent to the site;
    • concurrent activities which can affect the work (e.g. dewatering, tunnelling, deep excavation);
    • additional requirements for the supervision, monitoring or testing of the works;
    • functional requirements for water tightness at joints of bored pile walls;
    • the location of main grid lines for setting out.

4.2 Necessity, extent, procedure and responsibility for any survey of the conditions of structures, roads, services, etc. adjacent to the works area shall be established. The survey shall be carried out and be available prior to the commencement of the works.

4.3 Bored piling works shall conform with this European Standard provided the criteria and requirements set out in the following clauses have been observed. A suitable quality control system shall be established for supervision and monitoring.

4.4 Any additional or deviating requirements falling within the permissions given in this European Standard shall be established and agreed before the commencement of the works and the quality control system shall be suitably amended.

EXAMPLES: Such additional or deviating requirements can be:

  • reduced or increased geometrical construction deviations;
  • application of different or varying construction materials;
  • precast concrete elements;
  • special anchorage or doweling of piles to underlying rock;
  • special reinforcement as the use of steel tubes or sections or of steel fibres;
  • grouting of pile shafts or bases;
  • cutting-off of pile heads by mechanical equipment;
  • extensive manual excavation.

5 Site investigation

5.1 General

NOTE: ENV 1997-1, 3 and 7 and the relevant national documents are valid for the general requirements of site investigation (as long as respective European Standards are not available). The provisions of this clause contain additional requirements and recommendations.

5.1.1 The site investigation depth shall be sufficient to identify all ground formations and layers affecting the construction and to recognize the capacity and the deformation properties of the ground.

5.1.2 The extent of the site investigation shall be sufficient for the determination of the characteristic ground conditions of the site in accordance with the requirements of ENV 1997-1

5.1.3 When geotechnical categories as defined in ENV 1997-1 are applied for the foundation, categories 2 or 3 shall be used as appropriate.

5.1.4 If the maintenance of stability of a pile bore is likely to be difficult, a trial bore of relevant dimensions should be carried out.

5.1.5 Relevant experience of the execution of comparable foundation works under similar conditions and/or in the vicinity of the site should be taken into account when determining the extent of site investigation.

5.1.6 Reference to relevant experience is permitted if appropriate means of verification are taken (e.g. by penetration tests, pressuremeter or other tests).

5.1.7 The site investigation report shall be made available together with all relevant data known to affect the choice of method.

5.1.8 Bore holes shall be suitably backfilled to such levels that subsequent pile construction and performance will not be affected.

5.2 Specific requirements

5.2.1 Apart from the general geological description and the details as listed in ENV 1997-1 the site investigation report shall contain the following information:

  • a) the ground level at any point of investigation or testing relative to the recognised national datum or to a fixed reference bench mark;
  • b) presence and characteristics of loose or soft soils or ground that is likely to soften, loosen or become unstable during excavation;
  • c) presence of soil- or rock formations with a tendency to swelling;
  • d) presence of coarse soils, ground with an open structure (high permeability) or cavities which can cause sudden loss of a stabilizing fluid or a sudden drop of concrete during the placement;
  • e) presence of cobbles and boulders or other underground obstructions that can cause difficulties for the excavation or could require special methods or tools for their penetration or removal;
  • f) thickness of any potential bearing stratum;
  • g) presence, extent and thickness of any strata that can be sensitive to water infiltration or to stress caused by piling tools (e.g. impact, percussion or vibration);
  • h) piezometric levels of ground-water and its variation, including any artesian ground-water tables;
  • i) underground strata where high ground-water velocities exist;
  • j) aggressiveness of ground-water or ground that can affect the properties of a stabilizing fluid or of fresh or hardened concrete (see ENV 206);
  • k) level and inclination of any relevant underlying rock; I) thickness and extent of any existing weathered rock; m) type and quality of rock, especially:
    • 1) strength;
    • 2) state of degradation;
    • 3) cavities;
    • 4) open or filled joints;
    • 5) zones of weakness;
  • n) presence, extent, thickness and nature of contaminated soil or waste, that can influence the disposal of the excavated material;
  • o) mining beneath the site; and p) site stability problems.

5.2.2 The site investigation has to demonstrate that, where end bearing is to be relied on, any competent founding stratum is not immediately underlain by a soft stratum where there is a possibility of a punching failure.

6 Materials and products

6.1 General

6.1.1 All materials and products for incorporation into the bored pile shall be in accordance with the relevant European Standards (or, as applicable and as long as respective European Standards are not available, national standards) and with the specifications for the works.

6.1.2 The sources of supply of materials shall be documented and shall not be changed without prior notification.

6.1.3 Rejected materials are to be removed promptly from the site.

6.2 Materials for concrete and grout

6.2.1 Cement Cement for bored piles shall be of the following types as defined in ENV 197-1, 5.1:

  • portland cement СЕМ I;
  • portland slag cement СЕМ Il/A-S and Il/B-S;
  • portland silica cement СЕМ Il/A-D;
  • portland fly ash cement СЕМ Il/A-V and Il/B-V;
  • blast furnace cement СЕМ Ill/A, Ill/B and Ill/C. Other cement types may be used when specified and of proven performance in the specific conditions. Calcium aluminate cement shall not be used. The use of cement containing additions (type II) should be preferred because they have been shown to have beneficial effects on concrete, such as

  • improved workability,
  • reduced heat generation during setting and
  • improved durability.

6.2.2 Aggregates Aggregates shall comply with prEN 12620 and ENV 206, 4.2. The sources of supply of material, the grain size distribution of aggregates, and their mineralogical types shall be agreed prior to commencement of work. Rounded aggregates should be preferred when placing concrete by tremie. The maximum size of the aggregate shall not exceed 32 mm or 1/4of the clear distance of the longitudinal bars, whichever is the less. Frozen aggregate shall be heated so that no adhering ice or hoar frost enters the mix.

6.2.3 Water Mixing water shall comply with prEN 1008 and ENV 206, 4.3. Water may be chilled or may be replaced by up to 50 % of its mass by ice-chips for cooling of fresh concrete at high ambient temperatures.

6.2.4 Additions and admixtures Additions and admixtures shall comply with ENV 206 4.4 and 4.5 As long as respective specific European Standards are not available, the use of additions or admixtures shall be in accordance with the national standards and/or regulations in the place of use of the concrete. Additions and admixtures shall be used in accordance with the approval document and the manufacturer's instructions. To provide the properties of the concrete required for the placement process the following admixtures may be used

  • water reducing/plasticizing,
  • high range water reducing/super-plasticizing and
  • set retarding. The mix and the application of the concrete and the specific addition or admixture shall be compatible. Additions and admixtures may be used

  • to give a mix of high plasticity and
  • to avoid bleeding, honeycombing or segregation that might otherwise result from a high water content
  • to prolong the workability as required for the duration of the placement and
  • to cater for any interruptions in the placement process.

NOTE: Inappropriate application of additions and admixtures can result into damages. The proportions of admixtures or additions in the mix shall be notified before any concrete is mixed. Where piles are constructed in a cold climate and the ground surrounding the upper part of the pile is to be excavated after concreting, air entraining admixtures may be used in the concrete for the part of the pile to be exposed to frost action.

6.3 Concrete in situ

6.3.1 General The mix composition for concrete for bored piles shall be designed in accordance with ENV 206, unless specified otherwise in this European Standard. Unless otherwise specified, the design strength class of concrete used for bored piles shall range between С 20/25 and С 30/37 with mix proportions and consistency in accordance with tables 1 and 2. For primary piles of bored pile walls a lower strength class of concrete or mortar may be used (see figure 6). If required by the design and compatible with the ground conditions and the construction procedure, higher strength concrete may be used. Concrete for piles shall

  • have a high resistance against segregation,
  • be of high plasticity and good cohesiveness,
  • have good flowability,
  • have the ability to self-compact and
  • be sufficiently workable for the duration of the placement procedure, including the removal of any temporary casings.
Table 1: Mix proportions
Cement content:
— placement in dry conditions
— placement in submerged conditions
≥ 325 kg/m3
≥ 375 kg/m3
Water-cement ratio (W/C) <0,6
Fines content d < 0,125 mm (inclusive of cement)
— coarse aggregate d > 8 mm
— coarse aggregate d < 8 mm
≥ 400 kg/m3
≥ 450 kg/m3
Table 2: Consistency ranges for fresh concrete in different conditions
Flow diameter range mm Slump range mm Typical conditions of use
460 Ø 530 130 ≤ H ≤ 180 — concrete placed in dry conditions
530 Ø 600 H ≥ 160 — placed by pumping or - concrete placed in submerged conditions under water by tremie
570 Ø 630 H ≥ 180 — concrete placed by tremie in submerged conditions under a stabilizing fluid.
NOTE: The measured slump (H) or flow diameter (Ø) is to be rounded off to the nearest 10 mm. Where the mix proportions and consistency ranges as set out in tables 1 and 2 do not provide a high density mix, the cement content and the consistency range may be adjusted. Adequate protection against aggressiveness of subsoil and/or groundwater shall be provided, e.g. by mix design or permanent lining.


  • a) In particularly severe water or ground conditions sufficient protection might not be provided through mix design only.
  • b) Contaminated ground and water can be additional risks (e.g. retarding influence or changes in the pore-structure of the concrete by heavy metals). Reliable protection for the fresh concrete against rapid groundwater flow that might have a washing-out effect can be achieved by means of a permanent casing or lining.

6.3.2 Mixing The general requirements for the mixing and the accuracy's for batching of constituent materials shall be in accordance with ENV 206, 9. Ready-mixed or site-mixed concrete may be used for the works. Unless otherwise specified, three separate concrete batches shall be prepared for trial mixes. From each trial batch sampling of 6 cubes or cylinders shall be made, two each to be tested after 7 and 28 days respectively and 2 to be kept in reserve for any additional evidence until the results of the 28 day tests are known and the concrete has been accepted. The addition of water to the mixed concrete is prohibited unless where required to permit the correct mixing of additions and admixtures just before placement. The design water-cement ratio shall be maintained.

6.3.3 Sampling and testing Unless it can be shown that the use of the same concrete mix has previously and in similar applications conformed with the requirements, preliminary trial mixes shall be prepared for suitability testing before commencement of concreting, preferably under full scale production conditions. If this is not possible the trials shall be made in an accredited laboratory. The trials shall contain a sufficient number of samples and be representative of the aggregates and cement to be used in pile construction. All sampling and testing of fresh concrete shall be in accordance with ENV 206. In addition, the subsequent provisions apply. The minimum number of cylinder or cube specimens in a sample is four. Sampling of concrete on site for compressive strength testing shall be carried out as follows:

  • a) one sample for each of the first three piles on a site;
  • b) one sample for every subsequent five piles (15 piles if the individual concrete volume is 4 m3 or less);
  • c) two additional samples after interruptions of the works longer than 7 days;
  • d) one sample for every 75 m3 of concrete cast on the same day; and
  • e) at least one sample for every pile cast where concrete stresses require concrete classes C35/45 and above. Where the concrete is produced in a continuous and certified quality assurance system, deviating requirements for concrete sampling on site may be agreed. Additional sampling and testing can be required in special cases.


  • End bearing piles on rock;
  • single piles;
  • high bending stresses. The frequency of testing of

  • consistence,
  • concrete temperature and
  • workability time

shall be in accordance with table 10. A full record of all tests carried out on the concrete shall be kept. Results shall be noted in the concrete placement record.

6.4 Grout

6.4.1 Cement-bentonite grouts and any other grouts shall be prepared, maintained and controlled in accordance with the respective national standards, as long as respective European Standards are not available or, where these do not apply, with other agreed procedures.

6.4.2 Grout composition and the grouting technique and procedure shall be planned and carried out in a manner appropriate to the application (e.g. external grouting around precast elements, base or shaft grouting) and the ground condition.

6.4.3 When selecting the type of cement for grout placed in contact with the ground, account shall be taken of the known or possible presence of aggressive substances.

6.4.4 Water/cement ratios should be appropriate to actual ground conditions.

NOTE:The water/cement ratios may typically range from 0,40 to 0,55 or more, if judged necessary.

6.4.5 Admixtures may be used to create a pumpable grout mix with a low bleed rate.

6.5 Stabilizing fluids

6.5.1 General Stabilizing fluids or drilling mud's shall be a suspension. To differ are

  • bentonite suspensions,
  • polymer suspensions or
  • other suspensions. The fluids shall be prepared by suspending the respective particles in water, with or without the use of admixtures.

6.5.2 Bentonite suspensions Preparation, maintenance and control of bentonite suspensions shall be in accordance with EN 1538 unless stated otherwise in the subsequent subclauses of 6.5.2. Properties of bentonite suspensions, when fresh, ready for re-use and before concrete placement shall be in accordance with table 3.

Table 3: Characteristics for Bentonite suspensions
  Unit Suspension
fresh ready for re-use before concreting
Density g/cm3 < 1,10 < 1,15
Marsh value sec 32 to 50 32 to 60 32 to 50
Fluid loss cm3 < 30 <50
pH   7 to 11 7 to 12
Sand content % (mass) < 4
— : no provision. The testing procedures for the bentonite suspensions shall follow EN 1538. At the stage before concreting, a value of density up to 1,20 g/cm3 is permitted for special cases such as in salty water or heavy mud. At the stage before concreting, a value up to 6 % by mass for sand content is permitted for special cases such as friction or unreinforced piles. Where bentonite suspension is also used as a means of transport for the excavated material, higher densities are permitted during the excavation process for the ready for reuse case.

6.5.3 Polymers and other suspensions Other suspensions or drilling mud's, for instance containing

  • polymers,
  • polymers with bentonite as an admixture,
  • other clays

may be used as stabilizing fluids on the basis of experience of

  • previous cases in comparable or worse geotechnical conditions or
  • full-scale trial excavations on the site. The suspensions shall be prepared, maintained and controlled in accordance with the respective national standards or requirements, as long, as respective European Standards are not available or, where these do not apply, to the manufacturer's instructions.

6.6 Steel

6.6.1 Steel bars, steel wire mesh, steel tubes or sections used for the reinforcement of bored piles shall comply with ENV 10080, EN 10210-1 and EN 10025.

6.6.2 When selecting the type and grade of steel, attention shall be given to the assembly of reinforcement cages and to weldability requirements.

6.6.3 Where steel tubes or sections are used for the reinforcement of piles their design shall be in accordance with ENV 1994-1-1.

6.6.4 Where bored piles are constructed with stabilizing fluids, other metallic elements, such as access pipes for testing purpose, shall, without special precautions, not consist of galvanised steel or other because of the risk for:

  • a build-up of filtercake by electrostatic effects, or
  • electrochemical corrosion problems of the reinforcement.

EN 1536:1999 Execution of special geotechnical work – Bored piles