9 Supervision of execution and monitoring (p. III)

Table 7 — Controls for plastic concrete cut-off walls
Construction phase or item Control Comments
Setting-out – Position of wall – From lay-out drawings and fixed setting out points
– Position and level of guide-walls – Shall be checked before they are concreted and again after removal of the formwork
– Position of panels and joints – The position of the joints shall be marked on the guide-walls
Water – Suitability for use – Usually not required for potable water
Bentonite – Source of supply – Delivery document shall be checked for each load
Fresh bentonite suspension – Fluid loss, filter cake, pH – Shall be checked at the start of work, and as required thereafter
– Density, Marsh value – At least once per shift
– Gel strength – To be carried out when deemed to be necessary
Plastic concrete – Composition, consistency and compressive strength
– Deformation modulus
Suitability tests as specified, similar to those for concrete given in ENV 206
Excavation – Position of tool, overlapping (in the case of no stop ends) – Visual observation
– Verticality and twist of excavation – Shall be checked for each panel during and at the end of excavation a
– Ground profile  
– Depth of excavation  
– Bentonite suspension level – Visual observation
Bentonite suspension to be placed in the excavation – Fluid loss, filter cake, pH, density, Marsh value – Shall be carried out at least once per panel or shift. See Table 1 ("fresh" or "ready for re-use" characteristics) b
– Gel strength – To be carried out when deemed to be necessary
Cleaning – Depth of excavation – To be checked after cleaning at a minimum of three locations per panel or at specified spacing
Bentonite suspension before concreting – Density, Marsh value, sand content – Shall be carried out for each panel. See Table 1 ("Before concreting" characteristics) c
– Gel strength – To be carried out when deemed to be necessary
Placing stop ends (if any) – Alignment of stop end elements and composition – To be checked before insertion
– Verticality, position and depth – The stop end should be against the end of excavation
Concreting – Length of the concreting pipes, length and position of each individual element – To be checked for each panel
– Plastic concrete delivery certificate – To be checked for each load. Applies only to ready-mix plastic concrete
– Plastic concrete appearance – To be checked by visual observation
– Plastic concrete consistency – To be checked at the beginning of each panel and when required (according to ENV 206)
– Plastic concrete strength – One sample shall be taken at least every 100 m3 of concrete from one single sourced
– Method of starting concreting – To be made for each panel according to 8.8. The first load through each concreting pipe shall be placed in its entirety, without interruption
– Depth of concrete in relation to the volume of concrete poured – To be checked after each concrete load or set of loads. The top of the concrete at each concreting pipe shall be kept at a uniform level. A corresponding graph should be established for panels of depth greater than 20 m, or when the consumption of concrete is significantly different from the theoretical volume
– Concrete level before shortening the concreting pipe(s), number and length of pipe elements being removed, immersion of pipes – To be checked each time pipes are removed
– Time between mixing and the start of pouring – To be checked for each load
– Duration of concreting – To be recorded for each panel
– Plastic concrete temperature – May be appropriate in the case of extreme weather conditions (see ENV 206)
– Final plastic concrete level – To be checked for each panel
Extracting stop ends (if any) – Application of the extraction procedure established on the first panels of each type – Applies to all panels (see 8.6)
Trimming (when required) – Level of cut-off and quality of concrete at cut-off level – Quality of concrete to be checked for each panel by visual observation
a Verticality and twist of the excavation shall be controlled in order to remain within the required tolerances. The monitoring frequency shall be increased for cases presenting high risk, such as where boulders or obstructions are present in the ground, or where concrete from the adjacent panel is encountered. These controls shall normally be by visual observation or simple measurements (e.g. position of grab cables). Special measures (e.g. inclinometers) to determine the excavated profile may be necessary in some cases, e.g. in deep panels.
b The control of the characteristics of the bentonite suspension should be more frequent in special cases such as in the presence of organic content in soils, or chemically active groundwater, or when the joint between panels is formed by cutting into the hardened plastic concrete of the previously cast adjacent panel.
c The samples for determining the characteristics of the bentonite suspension before concreting shall be taken near the bottom of the panel. They can be taken either from the desanding circuit or by a sampling device, whichever is more convenient and appropriate to the technique used for excavation and mud replacement.
d Where the concrete is produced under a continuous and nationally certified quality assurance system, different requirements for concrete sampling on site may be agreed. The minimum number of cylinder or cube specimens in a sample is four.

10 Site records

The site records consist of two sections, the first section giving the general references and general information pertaining to the concrete and supporting fluid. The second section gives detailed information on the execution of the wall.

The forms shown in annex B are examples of the general information and detailed information sheets for the various types of diaphragm walls.

11 Special requirements

Diaphragm walls shall be executed in compliance with the national standards, specifications and statutory requirements, pertaining to:

  • health and safety of personnel;
  • security of the site;
  • safety of the work procedures;
  • operational safety of construction equipment and tools;
  • nuisance and/or environmental damage.

On site, particular attention shall be paid to:

  • all processes requiring men to work alongside heavy equipment and heavy tools;
  • the danger of open trenches;
  • manual work procedures and inspections performed inside excavations.

Nuisance and/or environmental damage can be caused by:

  • noise;
  • ground vibration;
  • ground pollution;
  • surface water pollution;
  • groundwater pollution;
  • air pollution.

EN 1538:2000 Execution of special geotechnical works — Diaphragm walls