8 Execution

8.1 General

8.1.1 Grouting works shall be staffed with qualified personnel. All key personnel shall have prior grouting experience.

8.1.2 The equipment required to perform a grouting operation includes:

  • drilling and driving equipment;
  • mixing and proportioning equipment;
  • pumping equipment;
  • injection piping;
  • packers;
  • monitoring and testing equipment.

8.1.3 The equipment used for grout processing shall safely withstand the anticipated maximum grouting pressures.

8.1.4 Competent personnel shall maintain the grouting equipment for the duration of the works.

8.2 Drilling

8.2.1 The following drilling methods may be employed:

  • rotational drilling;
  • percussion drilling using either an external or down-the-hole hammer;
  • cased percussion drilling;
  • grab-, chisel- and bailer borings;
  • driving of lances;
  • vibrating of casing or drill pipes.

In unstable ground full borehole penetration may require:

  • the use of drilling muds, grouts or foams;
  • temporary casing;
  • direct insertion of sleeve pipes;
  • progressive stabilization as the borehole advances.

If artesian conditions are expected counter-pressure drilling may be required.

8.2.2 Flushing media and drilling techniques shall be chosen so as not to impede the success of any subsequent grouting operation (particularly regarding changes in permeability at the point of injection).

8.2.3 Local adjustments to the angles, orientation, and spacing of grout holes should be made as necessary. New holes should replace holes that are prematurely plugged and holes that show unacceptable borehole deviation.

8.2.4 In open holes, if grouting does not follow immediately after cleaning, the hole collar should be protected to avoid borehole contamination.

8.2.5 After drilling, open boreholes in rock shall be flushed in order to remove detritus and loose material, and to open cracks and fissures. This treatment shall not be applied in the case that the rock might be adversely affected by the flushing medium.

8.3 Grout preparation

8.3.1 Storage

Stored grout components shall be protected from the weather (especially temperature and humidity).

8.3.2 Batching and mixing Contamination of the grout and its constituents shall be avoided during storage, handling and delivery. The storage containers (tanks) for ready-mixed grout shall ensure that the rheological or other properties of the grout are not unduly altered during storage. Containment vessels for chemical grouts shall consist of materials that do not react with the chemicals used. For grouts containing bentonite, the bentonite should be hydrated before introducing the binders. The proportioning of grout components shall be carried out with calibrated measuring devices in accordance with tolerances specified for the works. Mixers shall be selected to ensure the homogeneity of the mix. In order to allow uninterrupted delivery of particulate grouts, an intermediate holding tank should be located between the mixing tanks and the pump(s). The mix in the holding tank should be agitated to prevent separation and/or premature setting. Grouts with a fast setting time should be mixed as close as possible to the point of injection.

8.3.3 Pumping and delivery The grout pumps and injection systems shall be chosen in accordance with the intended injection technique. The following should be considered when selecting injection pumps:

  • an adjustable rate of grout delivery;
  • outputs which permit sufficient volume of grout to be injected or pressure to be achieved within a given period of time;
  • regulation of the injection velocity;
  • low-wear pumps (e.g. plunger pumps) for abrasive grouts;
  • ease of cleaning and maintenance;
  • valve diameters which are able to accommodate the viscosity of the injected material. The injection pressure should be measured as close to the point of placement as is practicable. The injection systems shall dampen pressures surges to minimize the risk of unintended and undetected initiation of hydraulic fractures. If the grout preparation plant is remote from the point of injection, an intermediate relay station should be considered. Grout delivery lines (pipes) shall resist the maximum anticipated pump pressure with an adequate factor of safety. Their diameter shall permit flow rates high enough to avoid separation of the mixed grout components (suspensions). If using sleeve pipes, the interior of the injection tube should be washed at the end of each injection phase. Suspensions shall be agitated until injection of the grout in order to prevent sedimentation. Solutions which tend to separate shall be agitated until injection. At low injection rates, a return flow system should be used to avoid sedimentation.

EN 12715:2000 Execution of special geotechnical work – Grouting