9 Supervision and monitoring

9.1 Supervision

9.1.1 In order to check that construction complies with the design and other contract documents, suitably qualified personnel, experienced in the technique, shall be in charge of supervising the execution work.

9.1.2 Where unforeseen conditions are encountered or new information about ground conditions become available, they shall be reported immediately to those responsible for the design.

9.1.3 The specific procedures for verification, control and acceptance shall be established before the commencement of the work.

9.1.4 The actual frequency and method of control should be stated.

9.1.5 Identification of prefabricated drains on site shall be carried out according to EN ISO 10320, or according to similar procedures in case of drains with specific characteristics.

9.2 Monitoring

9.2.1 The extent and procedures of monitoring shall be specified by the design.

9.2.2 The extent of the monitoring system should account for the type of loading (e.g. step-wise loading, vacuum, groundwater lowering), for the choice of drain type and for previous experience of results achieved under similar soil and loading conditions and with similar types of drains.

9.2.3 The construction process shall be controlled and information concerning the ground conditions and construction tolerances shall be monitored during execution.

9.2.4 The consolidation process shall be monitored by appropriate settlement observations. The final primary consolidation settlement can be estimated with good accuracy from the time-related settlement observations (see Annex A).

9.2.5 The consolidation process should also be verified by appropriate methods of pore pressure observations, especially in the case of stability problems or when the observational method of design is used.

9.2.6 Where relevant, lateral time-related movements along the outer boundaries of the loaded area shall be monitored. Appropriate methods shall be used to evaluate these movements, e.g. by inclinometers.

9.2.7 The frequency of settlement and pore pressure observations should be adjusted to make a realistic interpretation of the consolidation process possible.

9.2.8 Monitoring instruments should be installed early enough to have stable reference values before the start of the loading process.

9.2.9 When relevant, the strength increase of the ground should be confirmed by means of laboratory tests on sampled specimens and/or in-situ tests.

10 Records

10.1 Records during construction

Records shall be made of relevant aspects of drain installation, tests and observations as described in Clauses 8 and 9 and these shall be available at the site.

10.2 Records at the completion of the work

Records shall be made of the as-built works, including:

  • a) records as in 10.1;
  • b) information detailing the completed drain installation, including test results, and any changes from the design drawings and specifications;
  • c) details of materials and products used;
  • d) details of relevant geotechnical soil conditions.

11 Special requirements

11.1 General

11.1.1 Only those aspects of site safety and protection of the environment that are specific to vertical drainage are considered in this clause.

11.1.2 All relevant European Standards and national standards, specifications and statutory requirements regarding safety and environment during execution of the work shall be respected.

11.1.3 The drain installation shall not damage existing underground utilities.

11.2 Safety

11.2.1 The installation equipment shall comply with European and/or national safety rules regarding construction and stability. Documents regarding operation, maintenance and safety shall be present in the installation equipment. Workers shall be trained according to national safety regulations regarding cranes and tall plant.

11.2.2 The drain installation rig should be equipped with a roll bar to protect the cabin in the case of machine overturning, caused by local, insufficient bearing capacity of the working platform.

11.2.3 The working platform shall have sufficient bearing capacity to carry the load of the installation rig.

11.2.4 To confirm that the working platform has sufficient bearing capacity to carry the load of the installation rig, the total area should be tested with a fully loaded shovel or a dumper for determining weak spots in the working platform.

11.2.5 During the drain installation works, in case two or more installation rigs are working on the same working platform, they should be separated horizontally by a distance larger than the total height of the rigs.

11.2.6. In the case of drain installation close to existing power lines or underground utilities, attention should be paid to relevant safety regulations.

11.3 Environmental protection

11.3.1 Construction shall identify and take into account environmental restrictions such as noise, vibrations, water pollution and impact on adjacent structures.

11.3.2 If contaminated groundwater is squeezed out of the soil through the drains during the consolidation process, it shall be treated.

11.3.3 At certain locations, the installation of drains may create a connection between aquifers, which can be detrimental to the environment. This should be assessed and the design modified if necessary.

11.4 Impact on adjacent structures

Where sensitive structures or unstable slopes are present in the vicinity of the site or the possible sphere of influence of the works, their condition should be carefully observed and documented prior to and during the works.

EN 15237:2007 Execution of special geotechnical works — Vertical drainage