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GROUND WATER FREEZING By:- Humaira Athar Mahesh Sharma

Ground freezing

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Page 1: Ground freezing

GROUND WATER FREEZING

By:-Humaira AtharMahesh Sharma

Page 2: Ground freezing

CONTENTS:Introduction

Principle

Purpose

Process

Equipments

Characteristics

Advantages

Application

Case Studies

Steps in Ground Freezing

Conclusion

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“Nothing in the world is more flexible and yielding

than water. Yet when it attacks the firm and the

strong, none can withstand it, because they have

no way to change it. So the flexible overcome the

adamant, the yielding overcome the forceful.

Everyone knows this, but no one can do it.”

ROLE OF WATER

ROLE OF WATER

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DEWATERING

“The separation of water from the soil”

Construction below ground water level

Costly issue if overlooked

Common methods—

Sumps

Wells

Well points

Other techniques—

Ground freezing

Electro osmosis

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Fig 1.1 Steps of Dewatering

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GROUND FREEZING

Principle:—

To change the water in the soil into

solid wall of ice, which is completely

impermeable.

Water inflow can cause enormous problem in excavation and tunneling projects so the best way to stop water is to freeze it.

Frozen ground is twice as strong as concrete and it is essentially impermeable.

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Groundwater cutoff

Earth support

Temporary underpinning

Stabilization of Earth for tunnel excavation

Arrest landslides

Stabilize abundant mine shafts

PURPOSE

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GROUND FREEZING (CONTD.)

Process—

It is analogous to pumping ground water from wells.

Arrow of freeze pipes placed vertically in the soil and

heat

energy is removed through these pipes using chilled

brine.

Isotherms move out from freezepipes with time.

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GROUND FREEZING (CONTD.)

Fig 1.2 Freezing Process

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GROUND FREEZING (CONTD.)

Water in soil pores turns to ice at 32°F

In granular soil, ground water in pores freezes readily.

Further decrease in temperature increases strength

marginally.

In cohesive soil, below freezing temperature ,only

some portion of pore water freezes to stiffen the clay.

Further reduction in temperature enables it to gain more

strength.

A temperature of +20°F may be sufficient in sand,

whereas

-20°F may be required in soft clay.

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GROUND FREEZING (CONTD.)Formation of frozen Earth barrier is governed by

thermal and hydraulic properties of each stratum.

Typically, rock and coarse-grained soils freeze

faster than clays and silts.

Fig 1.3 Formation of frozen earth barrier in different soils

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Referring to the figure, the frozen earth first forms in

the shape of vertical cylinders surroundings the freeze

pipes.

As cylinders gradually enlarge they intersect, forming a

continuous wall. Once the design thickness is achieved

freeze plant is operated at a reduced rate.

GROUND FREEZING (CONTD.)

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GROUND FREEZING (CONTD.)

Fig 1.4 Steps of freezing

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FREEZING EQUIPMENTS Most common method is by circulating brine (Calcium

Chloride).

Chilled brine is pumped to the bottom of the freeze pipe and

flows up drawing heat from the soil.

Fig.1.5 Portable twin 60 ton brine refrigeration unit

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FREEZING EQUIPMENTS (CONTD.)

The other method is using liquid nitrogen (LN2).

Cost per unit of heat extracted is much higher.

Occasionally competitive for small, short term projects.

Fig. 1.6 Typical LN2 system for ground freezing

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CHARACTERISTICS OF GROUND FREEZING

Not limited by soil types irrespective of complex

geologic and hydrological conditions.

Strength of freezing soil can be controlled.

Equipments can be recycled and reused.

No frost heaving and freezing-thawing settlements for

gravel soil whereas for fine grained soil settlements are

predictable.

Can be used in congested areas.

Method is relatively fast.

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ADVANTAGES

Lesser risk to surrounding structures particularly in built-up areas.

No shuttering is required.

Environment friendly process.

Unlimited depth can be frozen from the surface.

Can be removed easily and completely.

Allows frozen soil barriers can be easily monitored.

Can be used either for temporary containment or as long term

barrier.

It freezes loose ,wet sand to prevent liquefaction during an

earthquake.

It bonds soil and waste together to prevent dangerous mixing during

removal

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APPLICATIONS1) Circular excavation supported by freeze wall:

Freezing can perform dual function of water cutoff

and earth support, eliminating sheeting and

bracing.

Penetration of freeze does not vary readily with

permeability, so more effective as a cutoff than

grout.

Fig 1.7 Circular excavation

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2) Excavation supported by gravity wall of frozen earth:

A combination of vertical and inclined freeze pipes is

typical, to achieve the shape illustrated.

APPLICATIONS (CONTD.)

Fig:- 1.8

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APPLICATIONS (CONTD.)3) Shaft sinking :

When it is applied to inclined shaft construction, the inclined

shaft freezing drilling method can be adopted as shown in Fig.

Fig 1.9 Shaft sinking

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APPLICATIONS (CONTD.)

4) Tunnels and subways:

Mainly applied with side channel and shield entrance.

Two construction plans—

Top-down vertical layout Horizontal layout

Overlaying soil is not too Thick overlaying soil

thick

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CASE STUDY: IGround Freezing for Tunnel Support

No. 7 Line Subway Extension, New York City

Project consist of two 6.1m dia. Tunnels connecting the

Javitz Center with the Times Square subway station.

Two tunnels boring machine (TBMs) were designed for

bedrock conditions.

The first construction was in a bedrock depression that

contain unconsolidated, water bearing soil.

To prevent excessive inflow of water into the TBMs the soil

was artificially frozen.

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Fig :1.9 Freeze pipe layout in 3D

CASE STUDY I: (CONTD.)

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CASE STUDY: IIAquarius Project – Artificial Ground Freezing in

Timmins, Ontario

Water table was high and the site

was rich in gold concentration.

To extract gold, while preventing

inflows of groundwater to the mine

excavation, a frozen earth barrier

was constructed around the

perimeter of the Aquarius open pit

gold mine.

The frozen barrier is the most

environmentally compatible

technique.

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CONCLUSION

The viability and versatility of ground freezing

for construction purposes is thus demonstrated

through this presentation including few case

studies along with mentioning of some of its

many applications. In addition, given that the

current interest in ground freezing is becoming

increasingly focused on environmental

remediation.

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REFERENCES

Winter Quarter 2007 .Professor Kamran M. NematiCM 420 TEMPORARY STRUCTURES Lesson 7: Construction Dewatering and Ground Freezing .

Arz, P.;Semprich, S. (1993) Modern Methods of Tunnel Support in NATM Tunnelling. Proc. Symp.Taipei Rapid transit Systems, Taipei, Taiwan, Vol. C, 677-686.

Borkenstein; Jordan; Schäfers (1991) Construction of a shallow tunnel under protection of a frozen soil structure, Fahrlach Tunnel at Mannheim. Proc. 6th Int. Symp. on Ground Freezing, Beijing, China.

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