6.3 Grouts

6.3.1 General Grouts are classified as:

  • suspensions: either particulate or colloidal suspensions;
  • solutions: either true or colloidal solutions;
  • mortars.
Grout classification
Figure 1 — Grout classification The following intrinsic properties shall be considered when choosing a grout:

  • rheology (viscosity, cohesion, etc.), setting time, stability;
  • particle size, if applicable;
  • strength and durability;
  • toxicity. The main parameters that define the properties of grouts before and after setting are listed below.

Table 1 — Parameters characterizing grout properties
  Solutions Suspensions Mortars
Before setting setting time, density, pH, surface tension, pot life, film time, gel time, viscosity, cohesion, thixotropy setting time, density, pH, grain size distribution, viscosity, cohesion, yield, thixotropy, stability, water retention capacity setting time, density, pH, grain size distribution, viscosity, workability, water retention capacity
After setting hardening after setting, final strength, pH, deformability, durability, shrinkage, expansion, shear strength, syneresis (silicate based solutions) hardening time, final strength, deformability, durability, shrinkage, expansion, density, shear strength hardening time, final strength, deformability, durability, shrinkage, expansion


6.3.2 Suspensions Suspensions are characterized by:

  • the grain size distribution of the solid particles;
  • their water/solid ratio;
  • the rate of sedimentation and bleeding;
  • their water retention capacity under pressure filtration;
  • their rheological properties and behaviour with time. The granulometric curve of microfine suspensions should be determined with a laser granulometer or equally precise instrument. The tendency of suspended solids to flocculate (particularly in microfine suspensions) shall be taken into account. The tendency of solids in suspension to settle in water due to gravity forces, and their tendency to bleed under pressure, shall be considered in relation with the nature and properties of the host medium. Colloidal clay suspensions should be prepared so that the clay particles are thoroughly deflocculated and hydrated before injecting.

6.3.3 Solutions Some types of silicate grout are not stable with time and their use should be carefully assessed. Organic silicate gels may lead to the proliferation of bacteria in the ground. The effect of syneresis on the properties of the treated ground and on the environment, particularly their long term effect, shall be evaluated prior to treatment. The effect of temperature differences on the grout behaviour during production and placement shall be taken into account. Special attention shall be paid to:

  • the toxicity of individual resin grout components;
  • the risk of dilution of the grout mixture in the groundwater leading to prolongation of the setting time or even inhibition of the chemical reaction;
  • the toxicity of any substance released into the groundwater if the chemical reaction is not fully achieved or modified by the host medium. Resins are usually applied under the circumstances given in Table 2.

Table 2 — Application of resin grouts
Resin type Ground type Use/Application
Acrylic granular soil
finely fissured rock
Reduction of permeability
Improvement of strength
Polyurethane large voids Foaming to block water inflow (aquareactive resins)
Stabilization or local void filling (two component resins)
Phenolic fine sand and sandy gravel Tightening and consolidation
Epoxy fissured rock Improvement of strength
Reduction of permeability


6.3.4 Mortars Mortars showing high internal friction are used for compaction grouting or for the filling of voids. Their rheological behaviour is usually determined by slump tests (workability, see Table A.1). Mortars flowing under their own weight are generally used for filling cavities, large cracks, open fissures and voids in granular soils. They shall be stable and their rheological behaviour (similar to suspensions) is usually characterized with suitably selected flow cones. When used for compaction grouting, the mortar should contain a minimum of 15 % of fines passing 0,1 mm.

6.4 Sampling and testing

6.4.1 The constituent materials of a grout mix as well as the mix itself shall regularly be sampled and tested to verify compliance with the design requirements.

6.4.2 Standardized testing methods (equipment, boundary conditions, analysis) shall be employed to allow comparison of the characteristics of the products provided by different suppliers.

6.4.3 In the laboratory, grout characteristics should be tested at an ambient temperature of 20 °C.

6.4.4 If the conditions on site differ substantially from the laboratory conditions (especially the temperature) tests shall be conducted under the in situ conditions. The temperature development during testing shall be monitored.

6.4.5 Table A.1 presents methods for testing the more important grout parameters.

EN 12715:2000 Execution of special geotechnical work – Grouting