4 Information required for the execution of the work
The following information is required for the production of the working drawings and the execution of the work:
- site topography;
- previous use of site;
- geotechnical information and data as specified in clause 5;
- information on the adjacent roads and structures, in particular the type of foundation and precautions necessary to ensure their stability;
- location, type and condition of services (gas, electricity, sewers,...);
- presence of obstructions in the ground (old masonry,...);
- presence of archeological remains;
- presence of polluted ground;
- working restrictions if any (vibrations, noise, headroom, working area,...);
- all necessary information for the production of the working drawings;
- any specific requirements for the diaphragm wall, in particular those pertaining to tolerances, quality of materials, watertightness, and type of joints;
- environmental requirements;
- when available, previous experience with diaphragm walls or underground works on or adjacent to the site.
For cut-off walls, permeability, strength and deformation properties of the wall material, together with testing methods, shall be specified.
Diaphragm walls cannot be expected to be completely watertight, since leakage can occur at joints, at recesses or through the wall material. Damp patches and droplets of water on the surface of the wall cannot be avoided under normal circumstances.
Continuity of reinforcement between the cages and across the joints is not normally required, but may be specified in exceptional circumstances.
5 Site investigation
Site investigations for the design and execution of diaphragm walls shall be made according to the general rules given in ENV 1997.
All information from the site investigation shall be made available in accordance with the requirements of clause 4.
5.2 Specific aspects
Particular attention shall be paid to the following aspects, which are relevant to the execution of diaphragm walls:
- piezometric levels of all water-tables and permeability of the soils;
- presence of coarse, highly permeable soils or cavities (natural or artificial) , which may cause sudden losses of supporting fluid and instability of the trench, and thus may require special measures;
- presence, strength and deformation characteristics of soft soils, such as very soft clay or peat, which may cause difficulties during excavation (deformation or instability);
- presence of boulders or obstructions which may cause difficulties during excavation and, when possible, an assessment of their size and frequency;
- presence, position, strength and hardness of rock or other hard materials which may cause difficulties during excavation and may require the use of special tools;
- detrimental chemistry of groundwater, soil and rock, and water temperatures if required (see ISO 9690);
- detrimental chemistry of waste materials (see ISO 9690);
- presence of pretreated soil, which may have an adverse effect during excavation.
The piezometric levels of the various water-tables existing on the site shall be monitored separately and over a sufficient period of time to estimate the highest piezometric levels which may occur during construction of the diaphragm wall. Particular attention shall be paid to artesian conditions.
The strength of the soils and rocks shall be determined by laboratory tests and/or in situ tests over the full depth of the diaphragm wall and to a certain depth below the base depending on the nature of the ground and the function of the wall.
The grain-size distribution of cohesionless soils shall be determined.
When diaphragm walls are required to reach or penetrate into rock, the level of the rock surface shall be determined in both the longitudinal and transverse directions along the length of the diaphragm wall. The properties of the rock, including the degree of weathering and the extent of fissuring, shall also be determined.