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| Grouting Technique |
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| Grouting |
Summary
Grouting uses in geotechnical engineering range from infilling voids to compensating
for volume loss in tunnelling. The variety of available techniques (permeation,
hydrofracture, jetting and mixing) and grouts (cements, clays, chemicals, resins,
polymers etc) provide the means to solve many ground engineering problems.
The objective of this report is to provide guidance, primarily for the non-specialist, on
all aspects of grouting to help improve the understanding and proper use of grouting as a
technique for ground treatment.
The document has three main parts. Sections 1 to 4 defme the main techniques and
explain the principles of grouting. They cover groutability, classification and chemistry
of grouts, and plant and equipment.
Sections 5 to 10 provide more detailed information on the six main techniques and
purposes of grouting, ie permeation, rock grouting, hydrofracture, ground compaction,
jet grouting, compensation grouting. Each section describes, with relevant case histories,
the principles of the technique; its applications, the plant and equipment used; typical
injection-hole layouts etc, and monitoring and site operational requirements.
Section 11 outlines typical contractual relationships between the parties in a grouting
contract (client, engineer, specialist adviser, contractor, specialist grouting contractor)
and discusses their responsibilities. Guidance is provided on types of specification and
measurement. Section 12 draws together the lessons from the report in concise
conclusions and recommends improvements in future practice.
CIRIA has also published three complementary reports on grouting:
• PR60 Geotechnical grouting: a bibliography (1997)
• PR61 Glossary of terms and definitions used in grouting: proposed definitions and
preferred usage (1997)
• PR62 Fundamental basis of grout injection for grout treatment (1997)
Glossary
Batch Quantity of grout mixed at one time.
Bleeding The flow of mixing water within, or its emergence from,
newly placed grout caused by the settlement of the solid
materials within the mass.
Cementitious grout A grout containing cement and water as major ingredients.
Chemical grouts Any grouting material characterised as a pure solution
with no particles (other than impurities) in suspension.
Colloid A substance consisting of very small particles dispersed in
a liquid. Colloidal particles are generally considered to be
have sizes between 5 A and 5000 A.
Compaction grouting A grouting method similar to displacement grouting in
which low-slump paste is injected. Normally a soilcement
based grout is used with sufficient silt sizes to
provide plasticity together with sufficient sand sizes to
develop internal friction. The grout generally does not
enter soil pores but remains in a homogeneous mass that
gives controlled displacement to compact loose soils. for
lifting of structures, or both.
Compensation grouting Compensation grouting is the responsive use of
compaction or hydrofracture grouting as an intervention
between an existing structure and an engineering
operation (particularly tunnel excavation) in order to
counteract any movement of the ground that would
otherwise affect the existing structure.
Gel A system, colloidal or polymeric, in which originally
dispersed substances form a continuous cohesive network.
Some gels (such as bentonite) are reversible and can be
restored to their original dispersed condition by shearing.
Others (such as silicate grouts) set irreversibly.
Grout A material injected into a soil or rock formation that gels,
stiffens or sets with time and thereby changes the physical
characteristics of the formation.
Grout take The measured quantity of grout injected into a unit
volume of formation, or a unit length of grouthole, or a
complete hole (by volume or weight. Grout includes
water, and the volume of the hole may be included).
Hydraulic fracture A fracture in a formation initiated by the injection of
water or grout under a pressure in excess of the local
formation tensile strengths. The propagation of a
hydraulic fracture causes the formation to move away
from the water- or grout-filled fracture.
Jet grouting A grouting technique utilising a special drill bit assembly
with horizontal water and grout jets to liquefy and mix grout
with or to excavate and replace alluvial soils, thus producing hard
impervious columns in the formation. Jetting and grouting are carried out
Lugeon A unit of permeability measured by the flow of water into
ground from a borehole of 76 mm diameter under an
excess pressure of 10 bars expressed in litres of water per
metre of hole.
Mortar A highly viscous, particulate grout.
Observational approach A continuous, managed, integrated, process of design,
construction control, monitoring and review of the
grouting works which enables modifications to be
incorporated during the process of the grouting works.
Packer A device inserted into a drillhole that acts to prevent
return of the fluid to be injected around the injection pipe
and through which the injection pipe passes. Usually an
expandable device activated mechanically, hydraulically
or pneumatically.
Permeation grouting Replacing the water in voids between soil grains or
particles with a grout fluid at a low injection pressure
without displacement or fracture of the natural structure of
the ground.
Refusal When the rate of grout take is low, or zero, at a given
pressure.
Rock grouting A general term for filling discontinuities in rock.
Set The condition reached by a cement paste or grout when it
has lost plasticity to an arbitrary degree, usually measured
in terms of resistance to penetration or deformation; initial
set refers to first stiffening and final set refers to an
attainment of significant rigidity
Slump A measure of consistency of freshly mixed concrete or grout.
Stage grouting Sequential grouting of a hole in separate steps or stages by
using packers as opposed to grouting the entire length at
once. Holes may be grouted in ascending stages by using
packers or in descending stages downward from the top of
the hole.
Suspension A mixture of liquid and solid materials.
Syneresis The exudation of liquid (generally water) from a set gel
which is not stressed, due to the tightening of the grout
material structure.
Tube-a-manchette A grout pipe perforated with rings of small holes at
specified intervals which is sleeve grouted into a drillhole.
Each ring of perforations is enclosed by a short rubber
sleeve fitting tightly around the pipe so as to act as a oneway
valve when used with a double ended packer with a
perforated mid section that isolates a stage for injection of
grout.
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