1. Deep Replacement Presented by: M. Taromi
Principles and Practices of Ground Improvement
Deep Replacement
Presented by:
M. Taromi
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
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2. CHAPTER 5: DEEP REPLACEMENT
Introduction
Ch. 5.2
Principles
Ch. 5.3
Design Considerations
Ch. 5.4
Design Parameters and Procedure
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page

3. Deep Replacement Method
5.1. Introduction
Deep Replacement Method
Increase bearing capacity
Increase density
Decrease of settlement
Provide lateral stability
Increase resistance to liquefaction
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page

4. Excavation of Geomaterials from Ground in Two Method:
5.1. Introduction
Excavation of Geomaterials from Ground in Two Method:
by injecting water into the ground, turning the geomaterial into slurry, and flushing it out from the hole.
by drilling a hole in the ground
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
Page

5. Displacement of Soils in the ground in four Method:
5.1. Introduction
Displacement of Soils in the ground in four Method:
by injecting water/air into ground.
Vibro – replacement
Vibro - displacement
by driving a steel casing into the ground
Sand compaction column
Encased granular column
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
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6. 5.1. Introduction Displacement of Soils in the ground in four Method:
by driving a reverse auger.
Controlled stiffnes column
by dropping a tamper to penetrate into ground.
Dynamic replacement
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
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Page

7. 5.2. Principles The Vibro Replacement Technique (Vibro Stone Columns)
The stabilization of soils by displacing the soil radially with the help of a depth vibrator, refilling the resulting space with granular material and compacting the same with the vibrator is referred to as Vibro Replacement and was developed by Keller in the 1950’s.
The resulting matrix of compacted soil and stone columns has improved load bearing and settlement characteristics.
Basic principle of the vibro replacement technique
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
Page

8. The Vibro Replacement Technique (Vibro Stone Columns)
5.2. Principles
The Vibro Replacement Technique (Vibro Stone Columns)
Principle
Reinforcement and Drainage
Applicable soils
Mixed deposits of clay, silt and sand, Soft and ultra soft
silts (slimes) Soft and ultra soft clays, Garbage fills
Effects
Increased shear strength, Increased stiffness, Reduced
liquefaction potential
Common applications
Airport, Storage tanks,, Bridge abutments and
Offshore bridge abutments and land / offshore applications
Maximum depth
10-15 m
Particle size distribution illustrating applicability
of Vibro-Compaction and Vibro-Replacement
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
Page

9. The Vibro Replacement Technique
5.2. Principles
The Vibro Replacement Technique
Schematic of wet top feed method
Schematic of dry bottom feed vibrocat method
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page

10. 5.2. Principles 3-50 The Vibro Replacement Technique Page 10 - 28
Mechanisms of load transfer for
(a) a rigid pile and (b) a stone column
ó – Stress
óf - Mat/Pile Cap Pressure
óp – Stress Induced to Piles
ó – Stress
óf - Mat/Pile Cap Pressure
óc – Stone Column Stress
ós – Soil Stress
Idealized stress distribution pattern for deep foundation systems (piles)
Idealized stress distribution pattern for stone column systems
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

11. The Vibro Replacement Technique
5.2. Principles
The Vibro Replacement Technique
Advantage
Installation is fast and easy
Higher strength and stiffness than sand compaction columns
Disadvantage
Installation of stone columns by bottom feeding does not generate spoil; however, that by top feeding generates spoil, which is not environmentally friendly.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

12. The Vibro – Concrete Columns
5.2. Principles
The Vibro – Concrete Columns
Vibro Concrete Columns (VCCs) are an innovative piling technique developed to provide enhanced load bearing capacity at shallow depths through use of enlarged bases.
They are often used where weak organic soils overlie granular deposits.
VCC columns are classified and designed as unreinforced piles.
For the construction of VCC columns pump able concrete is generally used the strength classification C20/25.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

13. The Vibro – Concrete Columns
5.2. Principles
The Vibro – Concrete Columns
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

14. The Vibro – Concrete Columns
5.2. Principles
The Vibro – Concrete Columns
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

15. The Vibro – Concrete Columns
5.2. Principles
The Vibro – Concrete Columns
Advantage
Higher strength and stiffness because of the use of concrete.
The installation process is quick
Disadvantage
They are more expensive than granular column.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

16. The Controlled Stiffness Columns
5.2. Principles
The Controlled Stiffness Columns
A specially designed auger, powered by equipment with large torque capacity and high static down thrust, displaces the soil laterally, with virtually no spoil or vibration.
During the auger extraction process, a column is developed by grouting under controlled limited pressure (less than 5 bars) through the stem of the displacement auger to achieve a predetermined stiffness ratio with the surrounding soil.
The result is a composite soil/cement ground improvement system.
Current practice is to install columns with diameter varying between 250 and 450 mm.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

17. The Controlled Stiffness Columns
5.2. Principles
The Controlled Stiffness Columns
Application
CMCs can be applied to various soil conditions.
The technology works well in loose sands, soft loams, organic soils (peat, aggradate mud, gyttjas) with a moisture content above 100% and anthropogenic soils (uncompacted fills, heaps).
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

18. The Controlled Stiffness Columns
5.2. Principles
The Controlled Stiffness Columns
Advantages
can have strength and modulus according to project needs. Their strengths and moduli are higher than those of granular columns.
They are installed fast with real-time monitoring and without any vibration and spoil.
There is no issue of hole collapse.
It has a low mobilization cost.
Disadvantages
However, they are more expensive than granular columns.
Installation may be difficult in soils with rocks and boulders.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

19. The Rammed Aggregate Columns
5.2. Principles
The Rammed Aggregate Columns
Basic Function
Aggregate Piers are a ground improvement method that uses compacted aggregate to create stiff pier elements.
Aggregate Piers help increase bearing capacity, shear
strength, rate of consolidation, and liquefaction resistance; and reduces settlement.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

20. The Rammed Aggregate Columns
5.2. Principles
The Rammed Aggregate Columns
600 to 900 mm diameter holes are drilled into the foundation soils. The holes normally reach depths of 2 to 9 m below grade.
This lifts of well-graded aggregate are rammed into the holes.
The subsequent compacted lifts are typically 25 cm deep.
A high-energy beveled tamper mounted on excavator equipment is used to compact the aggregate.
Design parameters include pier length, spacing, pier stiffness, and stress concentration ratio.
Pier spacing is from1.5 to 2.5 m center to center of the piers.
Load capacities range from 222 to 445 kN.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

21. The Rammed Aggregate Columns
5.2. Principles
The Rammed Aggregate Columns
Geologic Applicability
Soft organic clays, loose silt and sand, uncompact fill, stiff to very stiff clays, and medium dense to dense sands.
Elevated water tables and cohesion less soils complicate the installation.
Advantages
Rapid installation
Cost effective compared to other foundations options
Creates additional drainage
Allows for high level of compaction.
Efficient QC/QA procedures
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

22. The Rammed Aggregate Columns
5.2. Principles
The Rammed Aggregate Columns
Disadvantages
Limited treatment depth.
Lack of bending resistance.
Difficult to install in clean sands when the groundwater table is above the bottom of the pier.
Not applicable of wide heavy load applications.
Usually only effective to a depth of 2 to 9 m below foundation.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

23. The Dynamic Replacement
5.2. Principles
The Dynamic Replacement
The Dynamic Replacement technology consists in construction of large diameter aggregate columns in cohesive soil.
The columns are formed by a heavy pounder with a weight ranging from 15 up to 30 tons which is dropped from a height ranging from 10 up to 30 m.
Large diameter columns (ranging from 1.6 m up to 3.0 m) are driven to a depth ranging from 4.0 m up to 7.0 m.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

24. The Dynamic Replacement
5.2. Principles
The Dynamic Replacement
Geologic Applicability
The Dynamic Replacement columns can be constructed both in loose non-cohesive and firm soils, soft cohesive soils as well as in organic deposits.
Advantages
High bearing capacity
high shear strength and low deformation capacity of columns formed in weak soil.
Comprehensive improvement
Environmentally friendly
The Dynamic Replacement columns can be formed of recycled material (concrete rubble, coarse grain rubble, Gravel, etc.).
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

25. The Geosynthetic-encased granular columns
5.2. Principles
The Geosynthetic-encased granular columns
Encased granular column technology is used for very soft soils and organic soils with undrained shear strength as low as 5 kPa. The typical depth of the columns is 5–10 m.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

26. The Geosynthetic-encased granular columns
5.2. Principles
The Geosynthetic-encased granular columns
Advantages
Impart lateral confinement
Increase the load capacity & stiffness
Stresses are transferred to deeper strata.
Higher lengths of stone column are possible.
Higher degree of compaction can be achieved.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

27. The Geosynthetic-encased granular columns
5.2. Principles
The Geosynthetic-encased granular columns
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50

28. The Geosynthetic-encased granular columns
5.2. Principles
The Geosynthetic-encased granular columns
Geosynthetic-encased granular columns can be used in very soft soil with undrained shear strength lower than 15 kPa and as low as 5 kPa.
Geosynthetic encasement increases the stiffness of columns as compared with granular columns.
However, geosynthetic-encased columns are more expensive and slower to install as compared with granular columns without geosynthetic.
Islamic Azad University – Islamshahr Branch
Department of geotechnical Engineering
Page
3-50