4 Information needed for the execution of the work

4.1 General

4.1.1 Prior to the execution of the work, all necessary information shall be provided

4.1.2 The information should include:

  • a) any legal or statutory restrictions;
  • b) location of main grid lines or reference points for setting out;
  • c) condition of structures, roads and services adjacent to the work;
  • d) suitable quality management system, including supervision, monitoring and testing.

4.1.3 The information regarding the site conditions shall cover, where relevant:

  • a) geometry of the site including boundary conditions, topography, access, slopes and headroom restrictions;
  • b) existing underground structures, services, known contaminants and archaeological constraints;
  • c) environmental restrictions including noise, vibration, displacements, pollution and effects of seasonal variations in weather including frozen surface layers;
  • d) future or ongoing activities such as dewatering, tunnelling, deep excavations and raising of site levels.

4.1.4 Other information which will be required is described in Clauses 5, 6, 7 and 8.

4.2 Special features for ground treatment by deep vibration

The information required in relation to the practical aspects of the execution of ground treatment shall include:

  • specific project design objectives which the execution of the ground treatment is intended to fulfil;
  • water supply and slurry disposal requirements for the wet process of installing vibrated stone columns.

5 Geotechnical investigation

5.1 General

5.1.1 All site investigation shall be undertaken in accordance with EN 1997-1 and prEN 1997-2, and the design of the project.

5.1.2 The extent and depth of the site investigation shall be sufficient to determine the characteristic ground conditions and topography of the site and to identify and locate all ground formations, layers, other geological features and ground water levels affecting the execution of the works.

5.1.3 All information from site investigations shall be made available in accordance with the requirements of Clause 4.

5.1.4 Some fills may be heterogeneous and examination in trial pits may be required for a representative geotechnical description.

5.1.5 Obstructions, hard layers and cobbles and boulders within the ground which would influence or prevent the insertion of the vibrating tool should be identified.

5.1.6 The presence of ground conditions which will affect the performance of treatment shall be identified including:

  • hard layers;
  • soils sensitive to disturbance;
  • soils with potential for collapse settlement on wetting;
  • soils with liquefaction potential;
  • fills currently settling under self-weight.

5.1.7 Any contaminants and pollutants in the soil or the groundwater should be identified.

5.2 Specific aspects for deep vibratory compaction

5.2.1 Special consideration shall be given to the extent of the treatable granular soils and the location and extent of any layers which restrict or reduce the efficiency of the treatment process including clay, silt and organic layers and layers preventing drainage.

5.2.2 Where clay, silt or organic soils are present, some or all the properties mentioned in 5.3 may be needed.

5.2.3 The following geotechnical properties of the granular soil may be relevant to the design and execution of ground treatment by deep vibratory compaction:

  • particle size distribution and fines content;
  • in situ density index (relative density);
  • permeability;
  • crushability of particles;
  • inter-particle bonding caused by cementation, suction or cohesion.

5.3 Specific aspects for vibrated stone columns

5.3.1 Particular attention should be given to the determination of physical and geotechnical properties required for the design and execution of the ground treatment by vibrated stone columns, for example:

  • compressibility;
  • consistency limits;
  • undrained shear strength;
  • sensitivity.

5.3.2 Certain ground conditions need particular consideration, including:

  • location and extent of peat and organic soil;
  • presence of biodegradable fill including domestic waste.

6 Materials and products

6.1 General

Imported materials may be naturally occurring sands and gravels, crushed rock or recycled materials such as crushed brick or concrete. Quality control testing is described in 9.2.4.

6.2 Materials for deep vibratory compaction

6.2.1 Material may be added during deep vibratory compaction. This may be the natural granular material being compacted at the site or imported material.

6.2.2 Added materials shall be sufficiently hard and chemically inert so as to remain stable during the treatment process and subsequent working life in the anticipated soil and groundwater conditions.

6.3 Materials for vibrated stone columns

Material used to form stone columns shall be:

  • sufficiently hard and chemically inert so as to remain stable during column construction and subsequent working life in the anticipated soil and groundwater conditions;
  • graded appropriately for compaction to form a dense column fully interlocked with the surrounding ground and in compliance with other requirements such as drainage;
  • compatible with the plant used and flow freely within bottom-feed and through-feed delivery systems without arching which may block these systems.

Gradings typically used with the different processes are given in the following table.

Process Grading in mm
Dry top-feed process 40 to 75
Wet process 25 to 75
Dry bottom-feed process 8 to 50

EN 14731:2005 Execution of special geotechnical works - Ground treatment by deep vibration