3. “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.”
4. ―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
6. 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.
7. Groundwater cutoff
Earth support
Temporary underpinning
Stabilization of Earth for tunnel excavation
Arrest landslides
Stabilize abundant mine shafts
8. 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.
10. 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.
11. 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
12. 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.
14. 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
15. 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
16. 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.
17. 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
18. 1) 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
19. 2) Excavation supported by gravity wall of frozen earth:
A combination of vertical and inclined freeze pipes is typical, to
achieve the shape illustrated.
Fig:- 1.8
20. 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
21. 4) Tunnels and subways:
Mainly applied with side channel and shield entrance.
Two construction plans—
Top-down vertical layout
Overlaying soil is not too
thick
Horizontal layout
Thick overlaying soil
22. Ground 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.
24. Aquarius 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.
25. 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.
26. 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.
Notas del editor
The most common freezing method is by circulating brine (a strong saline solution – as of calcium chloride). Chilled brine is pumped down a drop tube to the bottom of the freeze pipe and flows up the pipe, drawing heat from the soil.
The liquid nitrogen (LN2) process has been applied successfully to ground freezing. The cost per unit of heat extracted is much higher than with circulated brine. Nevertheless for small, short term projects, particularly in emergencies, the method can occasionally be competitive.
The advantages of this system would seem to be that as you are not removing water from the sub-soil and you are reducing the vibration associated with traditional piling there is a lesser risk to surrounding structures particularly in built up areas, the ground when frozen is impermeable which is of benefit in a tidal zone and stable therefore requiring no shuttering, the process is also said to be environmentally friendly.
