7.4 Grout

7.4.1 Type and composition

7.4.1.1 The type and composition of the grout shall be selected according to the ground conditions and specifications of the works.

7.4.1.2 The national standards shall be consulted for restrictions in the use of specific types of grouts.

7.4.2 General considerations

7.4.2.1 In order to achieve the performance specifications for grouting works the design shall consider:

• the purpose of the treatment;
• grout placement, timing and sequencing;
• environmental conditions;
• rheological properties of the grout and their change with time, such as the water content of the solid constituents of a grout mix;
• setting and hardening time of the grout;
• the compatibility of the grout with the components of the delivery system and the ground;
• physical properties after setting;
• the effects of syneresis on the mechanical stability of the injected ground (for silicate based grouts).

7.4.2.2 The following environmental conditions shall be considered for the design:

• the size of openings to be filled by the grout and the size of the solid (hydrated) grout constituents, particularly the sizes of the pore necks (smallest access area) rather than the porosity;
• the permeability of the medium to be injected and the penetrability of the grout;
• the chemistry of the groundwater, mix water, and the ground;
• ground and grout temperature;
• the risk and effect of grout drying out upon exposure;
• the environmental impact during mixing, processing and the placement of the grout;
• the pollution potential of the grout.

7.4.2.3 If permeation grouting is to be undertaken, the dimensions of interconnected voids in the soil (effective porosity) or interconnected fissures in rock, should be known before designing the grout. This is particularly relevant for suspensions, where the filter criteria (relating particle size to void opening) and the stability of the mix under in situ gradients should be investigated. The cohesion of the mix should further be related to the desired reach of the treatment, and the viscosity of the grout to the permissible working pressures.

7.4.2.4 The determination of the setting time depends on:

• the volume of grout to be prepared and injected;
• the ground permeability;
• the interconnected porosity of the ground;
• the rate of groundwater flow;
• the time of injection for one pass;
• the anticipated placement time of a prepared batch of grout.

7.4.3 Parameters and criteria

7.4.3.1 The execution design shall state the range and median values of the following grout parameters for given environmental conditions:

• density, viscosity, yield or cohesion;
• shear and compressive strength;
• particle size of cement or binder;
• water retention capacity;
• for silicate gels the relative percentage of the reagent and silicate (neutralization rate);
• sedimentation rate.

7.4.3.2 Table A.1 presents the measuring conditions for the main parameters of each class of grout.

7.4.3.3 The design should further specify criteria for the selection of a specific mix if different mixes have been suggested, and the permitted maximum and minimum grout temperatures during processing and placement.

7.4.3.4 In soils, a groutability ratio, such as the D₁₀/d₉₀ or D₁₅/d₈₅ criterion, can be used to assess the penetrability of particulate grouts (see glossary, annex B). In rock, the maximum particle size to fissure width is considered (a ratio of three is commonly used).

7.4.3.5 Limit criteria for changing the mix design should be decided upon at the outset of the works for the case that:

• grout takes are significantly in excess of those anticipated in the design;
• no grout acceptance can be achieved with the design mix;
• undesirable ground movement occurs.

7.4.4 Applicability

7.4.4.1 The types of grout applicable for different types of ground are shown in Table 3.

7.4.4.2 Sleeve grouts for sealing the sleeve pipe shall be designed to prevent migration along the annulus, and to facilitate fracturing between the sleeve and the ground.