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Wednesday, January 23, 2019

Grouting Technique


Grouting, What is Grouting ,Grout
Grouting Technique
Grouting, what is grouting,Grout
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  during controlled withdrawal and rotation of the drill string from                                                    the hole.               
                                                 

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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