curtain grouting

8/17/2019 Curtain Grouting

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B.Tech Seminar on

CURTAIN GROUTING

For the subject of

Advanced Foundation Engineering

By

Devendra Singh Shekhawat (11BCL061)

Ayush Misra (11BCL073)

Ritika Kashyap (11BCL089)

Submitted to

Dr. Trudeep N Dave

Dept of Civil Engineering

School of Technology

Pandit Deendayal Petroleum University

Gandhinagar Gujarat


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GROUT

Grout is a construction material used to embed rebar's in masonry walls, connect sections of

pre-cast concrete, fill voids, and seal joints (like those between tiles). Grout is generally a

mixture of water, cement, sand, often colour tint, and sometimes fine gravel (if it is being

used to fill the cores of concrete blocks). It is applied as a thick emulsion and hardens over

time, much like its close relative mortar. Unlike other structural pastes such as plaster or jointcompound, grout, when mixed and applied correctly, creates a waterproof seal.

TYPES OF GROUTING

a. Penetration grouting

b. Displacement grouting

c. Compaction grouting

d. Jet grouting

e. Curtain grouting

a. Penetration grouting

Process of filling joints or fractures in rock or pore spaces in soil with a grout without

disturbing the formation. It refers to the replacement of water in voids between soil, particles

with a grout fluid at low injection pressure so as to prevent fracturing.

Fig.1 Penetration grouting


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b. Displacement grouting:

It is the injection of grout into a formation in such a manner as to move into the formation, it

may be controlled, as in compaction grouting or uncontrolled. As in high pressure soil or rock

grouting which leads to splitting of the ground, also called hydro fracture.

Fig.2 Displacement grouting

c. Compaction grouting:

It is a very stiff (say 25-mm slump) mortar is injected into loose soils, forming grout bulbs

which displace. and densify the surrounding ground, without penetrating the soil, pores.

d. Jet grouting:

It is a technique where high –speed water jets emanating from a drill bit cut into alluvial

soils: as the drill but is withdrawn grout is pumped through horizontal nozzles and mixes with

or displaces the soil. The original foundation material is thus replaced with a stranger and/or

more impermeable grout-soil mixture. Jet grouting may be used to form cut off walls, form adeep foundation.


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Fig 3. Jet grouting

e. Curtain Grouting

A Grout curtain is a barrier that protects the foundation of a dam from seepage and can be

made during initial construction or during repair. Additionally, they can be used to strengthen

foundations and contain spills.

Fig 4. Grout curtain


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CURTAIN GROUTING

A Grout curtain is a barrier that protects the foundation of a dam from seepage and can be

made during initial construction or during repair. Additionally, they can be used to strengthen

foundations and contain spills.A grout curtain usually consists of a row of vertically drilled holes filled with

pressurized grout, a process commonly known as pressure grouting. The holes are drilled in

intervals and in such a way that they cross each other, creating a curtain.

In earth / rock fill dams, curtain grouting is usually completed before a dam is constructed

and involves filling a narrow excavated trench in the foundation with concrete. The exception

to the timing of the grouting operation is grouting after construction for a grouting cap at the

upstream heel of a dam.

Curtain grouting of the foundations of concrete dams is most effective after completion of the

dam, at a time when the full load is being applied to the foundation. Under such

circumstances higher pressures may be used in grouting so as to assure maximum travel ofgrout in all directions along flow paths intersected by grout holes.

In gravity and gravity arch dams of moderate to large size it is common practice to construct

a gallery inside the dam for drilling curtain grout holes and drainage holes. Foundations of

small gravity and thin arch dams are efficiently grouted from grout caps along the contact of

the upstream face of the dam with rock.

Where there are no geological controls the depths of curtain pattern grout holes are

determined by a formula. A frequently used formula is: the vertical depth of grout holes shall

be a third of the dam height at the location of the hole plus (15 - 20m).

Fig. 5


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CURTAIN GROUTING I DAM


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Quantitatively Engineered Grout Curtains

Grouting designs must be site specific to address the specific project goals. The performance

criterion from the quantitative design identifies the maximum permissible residual

permeability and minimum width of the grouted zone. Prerequisite information required to

perform quantitative design of a grout curtain include:

• Thorough geologic investigations identifying structure, stratigraphy, weathering, and

hydraulic conductivity of the foundation rock.

• Establishment of project performance requirements in terms of seepage quantities and

seepage pressures. Design requirements should consider dam safety, cost, and political

acceptability or public perception as they relate to residual seepage.

• Seepage analyses to determine the need for grouting, the horizontal and vertical limits of

the cut-off, the width of the curtain, and the location of the curtain.

• Where relevant, the value of the lost water should be compared to the cost of more

intensive grouting in a cost benefit analysis.

• Specifications written to require best practice for field execution of every element of the

work.

Quantitative design of grouting requires that the curtain be treated in seepage analyses as an

engineered element. The specific geometry of the curtain in terms of depth and width must be

included in the model and the achievable hydraulic conductivity of the curtain must also be

assumed.

GROUT MIX DESIGN

The vast majority of grout curtains in prior to 1990 utilized neat cement grouts with little

consideration of the grout properties other than the water cement ratio. Today, grout mix

designs are tailored to the application and desired results. Most rock grouting is performed

with high mobility grouts (HMG). Fundamental properties of HMG to be considered when

developing a mix design include the grain size of the particulate constituents, viscosity,

cohesion, sedimentation or bleed potential, segregation, resistance to pressure filtration,

particle agglomeration minimization during injection, resistance to washout, matrix porosity,

and durability. The desired grout is one that will penetrate the fractures a sufficient distance

to provide overlap of grouted zones, but will have sufficient cohesion to not travel too far

while having a viscosity that permits the grout to be injected in a reasonable amount of time.

During injection the grout will have a constant or nearly constant rheology and once in place

the grout will not bleed or washout prior to hardening. Once hardened, the grout will be

resistant to leaching and provide permanent seepage control.


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DESIGN CONSIDERATION

1. Geological Considerations

The data already obtained from the exploration of the foundation should be analysed to assessthe characteristics of foundation rocks and the location and orientation of faults.. seams,

cavities, joints and bedding planes and discontinuities. The permeability values of foundation

strata at various depths should be used for the design since the stages and spacing of the holes

for grouting should be based on this data.

2. Drilling of Grout Holes

Percussion drills can be used for drilling the grout holes, provided the foundation rock is of a

type that will produce granular cuttings, rather than slimes. In case of rocks having

weaknesses such as faults and seams it is recommended that at least one hole should be bored

with suitable boring machines which are capable of recovery of rock cores and which will

facilitate inspection of bore hole walls. Diamond core drilling permits the examination of

cores and the location of seams by means of a TV borehole camera.

3. Inclination of Grout Holes

The holes may be either vertical or inclined. The orientation, plan and inclination of grout

holes depends upon the type of joints and other discontinuities in the foundation rock. The

most common practice is to drill holes inclined towards upstream at 5 to 10 degrees with the

vertical.

4. Spacing of Grout Holes

Single line grout curtains are generally used. The usual practice is to try a widely spaced

system of primary boles at a spacing of 6 m to 8 m, followed by secondary and tertiary holes

at a progressively smaller spacing till the desired results are obtained. However, hole spacing

less than one meter should be avoided.

5. Depth of the Grout Curtain

The depth of the grout curtain depends upon the type and conditions of the rock mass with

respect to its permeability. The following empirical criteria may be used as a guide which is

based on going practice:


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where

D = 2/3 H + 8

D == Depth of the grout curtain in m, and

H = Height of reservoir water in m.

6. Grout Procedure

i. Curtain grouting is normally done from the foundation cum drainage gallery after

masonry/ concrete is laid up to half of the design height or 20 m from the bottom of the

gallery, whichever is earlier. However in special cases an additional grout curtain can also be

provided at the heel of the dam.

ii. Drainage holes should be drilled in the foundation gallery. Drainage holes should,

however, not be drilled in the foundation gallery till curtain grouting is completed within 30

m from the location of the drainage holes.

Patterns of Holes for Curtain Grouting

a. Single Line Grout Curtains

Single line. grout curtains are effective only in rocks having a fairly regular network of

discontinuities with reasonably uniform size of openings. In such cases a curtain of adequate

width can be achieved by grouting a single line of holes.

In single line curtains it is customary to drill a widely spaced system of primary holes,subsequently followed by secondary and tertiary holes at a progressively smaller spacing.

The initial spacing usually varies between 6 m to 12m but the choice of spacing should be

based on the geological conditions and on experience.

Spacing's below one metre are rarely necessary and the requirement of a spacing closer than

one. metre may often indicate an unsuitable orientation and inclination of holes.

b. Multiple Line Grout Curtain

In rocks with a wide range of sizes or openings. cavities and discontinuities which areirregularly distributed, a single line curtain may not be effective. The larger openings may

absorb excessive volumes of grout if high pressures and thin grouts are used.

In such cases it may be advantageous to use a multiple line curtain consisting of' outer lines

which are drilled and grouted initially with thicker grouts.

The final spacing of Inner and outer rows may be different in a multiple line pattern, the

spacing in each row being governed by the nature of rock discontinuity, intended to be treated


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by the particular row. In any case in the central row the split spacing method should be

followed until the desired degree of impermeabilization is achieved.

APPLICABILITY

Grout curtains may be used up-gradient of the contaminated area, to prevent clean water from

migrating through waste, or down-gradient, to limit migration of contaminants. Grout

curtains are generally used at shallow depths (30 to 40 ft maximum depth). High-pressure

jetting appears to be a cost effective means to place physical barriers in unstable soils, near

foundations, and around underground obstructions.

LIMITATIONS

• An underground injection permit may be required.

• Keeping nozzles clear, maintaining air flow, and effectively creating a wall without

defects have been problematic in certain environments and operating conditions. For

instance, if very coarse-grained materials are encountered, defects in the curtain may

occur. Therefore, the site must be well characterized to minimize unexpected geologic

conditions. Additionally, if the jets are turned on and off, they may become clogged.

• The orientation of the jets must be precise to ensure the curtain is continuous. At one

demonstration, magnetic anomalies created problems with the orientation of the

directional tool.


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REFERENCES

• Grout curtains

(http://www.cpeo.org/techtree/ttdescript/grocur.htm)

• CONCRETE WALLS AND GROUT CURTAINS IN THE TWENTY-FIRST

CENTURY: THE CONCEPT OF COMPOSITE CUT-OFFS FOR SEEPAGE

CONTROL by Dr. Donald A. Bruce1,Trent L. Dreese, Douglas M. Heenan

(http://www.geosystemsbruce.com/v20/biblio/241%20Concrete%20Walls%20and%20

Grout%20Curtains%20in%20the%2021st%20Century.pdf )

• IS 11293 ( Part 2 ) : 1993; Indian Standard GUIDELINES FOR THE DESIGN

OF GROUT CURTAINS.

• IS 6066 : 1994; Indian Standard PRESSURE GROUTING OF ROCK

FOUNDATIONS IN RIVER VALLEY PROJECTS- RECOMMENDATIONS

curtain grouting

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