method to improve capacity of soil by freezing the pore water

1. Ground Freezing
Presented by:
Rahul Verma
31702217
Presented to:
Prof. Anupam Mittal
Dept. Of Civil Engineering

2. * Introduction.
* Purpose of ground freezing.
* Principle of ground freezing.
* Process of ground freezing.
* How ground freezing works.
* Applications
* Advantages
* Reference's

3. INTRODUCTION
➢ Ground freezing is a process of making water-bearing strata temporarily
impermeable and to increase their compressive and shear strength by
transforming joint water into ice.
➢ Frozen ground is nearly twice as strong as concrete and is essentially
impermeable.

4. PURPOSE OF GROUND
FREEZING
➢Groundwater cut off
➢Earth support
➢Temporary underpinning
➢Stabilization of Earth for tunnel excavation
➢Control contamination

5. ➢ When wet soil freezes, the water present in soil pores changes from
liquid to solid that turns the soil into a hard mass resembling concrete.
➢ Basic principle of ground freezing is to circulate a cold medium through
a suitable pipe system, which cools the strata and thus converts the in-
situ pore water to ice.
➢ Ice is so formed bonds adjacent soil particles together and forms an
impermeable structure with increased strength.
PRINCIPLE OF GROUND
FREEZING
➢ The strength achieved depends on freeze temperature, moisture content
and the nature of the soil

6. PROCESS OF GROUND
FREEZING
➢ A row of freeze pipes placed vertically in the soil and heat energy is
removed through these pipes using chilled brine.
➢ Isotherms move out from freeze pipes with time.

7. ➢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.
➢ The -10°F to -20°F brine circulates down along the outside pipe and up
through an inside pipe thus freezing the soil around the pipes.
➢A temperature of +20°F is sufficient in sand, whereas - 20°F is required
in soft clays.

8. ➢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.
Fig. showing process of ground freezing

9. There are two methods used of ground freezing.
1 Indirect method
2 direct method
In above methods we use liquid nitrogen, calcium chloride as a cooling
agents
HOW GROUND FREEZING
WORKS

10. *This type of freezing method is commonly used for the
stabilization of tunnel headings.
* In this method, a secondary coolant is circulated through
tubes which are driven into the ground.

11. Fig. Showing Schematic Diagram of indirect process

12. 1. Direct, by circulation of the primary refrigerant fluid
through the ground tubes
This type of direct ground freezing method is same as that of
indirect method, but difference is only Ammonia is used in this
method as a cooling agent.
The ammonia is compressed and passed into the tubes driven
into the ground. This ammonia freezes the tubes which in turn
freezes the surrounding ground.
Time required for this process is same as that of indirect
process.

13. 2. Direct, by injection of a coolant into the ground, such as liquid
nitrogen
*This method doesn’t require any refrigeration plant.
*Ammonia is brought to the site under moderate pressure and stored
at site in insulated tanks. Tubes are driven into the ground with the
provision of return pipes to exhaust to atmosphere.

14. Fig. Showing schematic diagram of soil freezing with nitrogen

15. APPLICATIONS
1. Circular Excavation Supported By Freeze Wall:
➢ Freezing can perform dual function of water cut-off and earth
support, eliminating sheeting and bracing.
➢ Penetration of freeze does not vary readily with permeability, so
more effective as a cut-off than grout.

16. 2. Ground Freezing used for Contamination control :

17. Advantages of Ground Freezing
Temporary underpinning of adjacent structure and support during
permanent underpinning
 Lesser risk to surrounding structures particularly in built-up areas
 No shuttering is required.
 Can be used in congested areas
 Can be removed easily and completely
 It freezes loose ,wet sand to prevent liquefaction during an earthquake
 Can be used in any type of soils
 It bonds soil and waste together to prevent dangerous mixing during
removal

18. REFERENCES
➢ Winter Quarter 2007 .Professor Kamran M. Nemati CM 420
TEMPORARY STRUCTURES Lesson 7: Ground Freezing .
➢ Arz, P. Semprich, S. (1993) Modern Methods of Tunnel Support in
NATM Tunnelling. Pro., Taipei, Taiwan, Vol. C, 677-686.
 Paul C. Schmall1 and Bernd Braun,Moretrench, 100 Stickle Avenue,
Rockaway, NJ 07866; Ground Freezing – A Viable and Versatile Construction
Technique,Vol. B,556-998

19. THANK YOU