Ground Treatment with Using Grouting - Ground Improvement - Lecture Slides, Slides of Geology

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GROUND IMPROVEMENT

GROUND TREATMENT

USING GROUTING

Grouting technology has become a common groundimprovement method used frequently for underground andfoundation constructions. The process of grouting consistsof filling pores or cavities in soil or rock with a liquid formmaterial to decrease the permeability and improve theshear strength by increasing the cohesion when it is set.Cement base grout mixes are commonly used for gravelylayers or fissure rock treatment. But the suspension grainsize may be too big to penetrate sand or silty-sand layers.In this case, chemical or organic grout mixes are alsoused. In recent years, the availability of ultrafine groutmixes has extended the performance of hydraulic basegrout for soil treatment.

•^

The grout mix can be generally classified into four types:

• •^

(1) mortar and pastes such as cement to fill in holes oropen cracks;

-^

(2) suspensions such as ultra-fine cement to seal andstrengthen sand and joints;

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(3) solutions such as water glass (silicate) and

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(4) emulsions such as chemical grout.

The operational limits of different grout mix are

dependent on the type of soils and the grain sizedistribution of the soil.

•^

The design for grouting and/or alternatives needs

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(a) preliminary design or project planning and feasibilitystudies; adequate investigation to be carried out at thefeasibility stage includes the characterization of groundand ground water and identifications of fractured rock,weathered rock, granular soils (alluvium, sand, & siltsetc.), natural cavities (karsts), or galleries (mineworkings, tunnels, storage galleries etc.).

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(b) detailed design or special studies.

Investigation methods

• Drilling and direct inspection to accurately locate and determine local

conditions;

• Taking coring samples for laboratory tests;• Drilling with drilling data recording to locate fissured zones, voids and

the interface between structure and surrounding ground;

• Borehole logging with BHTV Scanner examination (optical/seismic);• Non-destructive geophysical investigations (seismic resistivity);• Water testing (constant head or falling head tests conducted in

borehole;

• Underground flow & temperature measurements;• Pumping test to assessment of initial hydraulic conditions.

•^

Akbulut and Saglamer (2002) proposed a new N valueas:

-^

where w/c is the water cement ratio of the grout; FC isthe total soil mass passing through 0.6 mm; P is thegrouting pressure; D

r^

is the relative density of the soil; k

1

and k

2

are two constants. K

1

= 0.5 and k

2

= 0.01 1/kPa

are suggested. Soil is considered groutable when N > 28and not groutable when N < 28.

10(

)

1

2

90(

)

soil grout

r

D

w

c^

P

N

k^

k

D

FC

D

Categories of Grouting

a. Penetration groutingb. Displacement groutingc. Compaction groutingd. Grouting of Voidse. Jet grouting

Typical applications of Grouting

Classification of Grout Materials

When

injected

into

very

dense

soils

or

bedrock,

compaction grout remains somewhat confined, sincethe

surrounding

material

is

quite

dense.

However,

when

injected

into

under-consolidated

or

poorly-

compacted soils, grout is able to "push" these materialsaside.When grouting treatment is applied on a grid pattern,the result is improved compaction of displaced soils,and greater uniformity of the treated soil mass.

As a

secondary

benefit,

the

resulting

grout

columns

add

strength

in

the

vertical

axis,

as

typical

grout

compressive strengths exceed those of the surroundingsoils.

Compaction grouting applications include densificationof foundation soils, raising and relieving of structuresand

foundation

elements,

mitigation

of

liquefaction

potential, augmentation of pile capacity and pile repair,and densification of utility trench backfill soils.

Although

densification

of

foundation

soils

subject

to

long-term

settlement

remains

to

be

the

principal

application,

ground

improvement

methods

incorporating

compaction

grouting

methods

have

become

increasingly

accepted

by

the

engineering

community as a means of mitigating liquefiable soilsinfluencing existing facilities.

Inherent in the grouting

process is the capacity to work in areas of limitedaccess

and

existing

improvements

to

treat

discrete

zones within the soil profile.

Permeation Grouting

The image shows a sample of permeation grouted sandfrom

a^

project

that

required

steep-walled

footing

excavations in running sands.

The proposed excavation

area was permeation grouted with a microfine cementslurry

prior

to

cutting

footing

trenches,

resulting

in

a

significant

reduction

in

project

cost.

Unconfined

compressive

strength

tests

performed

confirmed

the

improvement

Particulate grouts are typically water-based slurries ofcement, fly ash, lime or other finely ground solids thatundergo

a^

hardening

process

with

time.

These

materials may be used to fill pores and joints in soil androck, provided the grout particles are small enough tobe carried through the pore or joint openings.

A good

rule of thumb is that the effective particle diameter inthe grout suspension should be less than the dimensionof the pore or joint aperture divided by 5.

Slurry grout mixes used for permeation grouting

are designed primarily to promote passage of the groutparticles into the porous medium.

The grain size of the

slurry is matched to the pore aperture and steps aretaken

to

assure

the

grout

particles

are

properly

dispersed in the grout.