DHARMSOIL STABILISATION 709Grouting materials
The following have been used for grouting:
(i) Soil
(ii) Portland cement
(iii) Bitumen
(iv) Chemicals
Bitumen is not used as much as other materials for this purpose.
The properties of the grout must fit the soil or rock formation being injected. The dimen-
sions of the pores or fissures determine the size of grout particle so that these can penetrate.
The following are the guide lines recommended:D 85 (Grout) <1
15D 15 (Soil) ...(Eq. 17.1)D 85 (Grout) <1
3B (Fissure) ...(Eq. 17.2)
Rg = (D 85 Grout/D 15 Soil) > 15 ...(Eq. 17.3)
Rg : Groutability ratio.
(Johnson, 1958; Kennedy, 1958)
Viscosity and rate of hardening are important characteristics of the grout material. Low
viscosity and slow hardening permits penetration to thin fissures and small voids whereas
high viscosity and rapid hardening restrict flow to large voids.
The grout must not be unduly diluted or washed away by ground water. Insoluble or
rapid setting grouts are used in situations where there is ground water flow.
‘Mudjacking’ is a form of soil injection used to raise highway pavements, railway tracks
and even storage tanks. This technique consists of injecting a mixture of soil, Portland cement
and water to shallow depths at relatively low pressures.
Cement grouting has been used to stabilise rock formations, as also alluvial sands and
gravels.
A number of chemicals have been used for grouting; among them, sodium silicate in
water, known as ‘water glass’ is the most common. This solution contains both free sodium
hydroxide and colloidal silicic acid. The addition of certain salts such as calcium chloride, mag-
nesium chloride, ferric chloride and magnesium sulphate, or of certain acids such as hydro-
chloric acid and sulphuric acid, results in the formation of an insoluble silica gel.
On ageing, the gel shrinks and cracks. Hence, the effectiveness of silicate injection in
the presence of ground water remains doubtful.
The grouting plant includes the material handling system, mixers, pumps and delivery
hoses. The mixing of components is done by a proportioning valve or pump at the point of
injection. A perforated pipe is driven into soil to the level of grouting; if it is rock, grouting
holes are drilled.
The injection pattern depends on the purpose of grouting. Generally a grid pattern is
used. The spacing may be 6 to 15 m. Sufficient pressure is used to force the grout into voids and
fissures.