Dynamic compaction of Soils.pdf

8/17/2019 Dynamic compaction of Soils.pdf

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DEPARTMENT OF CIVIL ENGINEERING

SEMESTER-7

ADVANCED FOUNDATION ENGINEERING

REPORT ON: DYNAMIC COMPACTION

Prepared by:

Jaspreet Chawla (11BCL009),

Vatsal patel (11BCL031),

Harshang shah (11BCL041)

Submitted to:

Dr. Trudeep Dave

http://www.google.co.in/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=0CAgQjRw&url=http://en.wikipedia.org/wiki/Pandit_Deendayal_Petroleum_University&ei=XTNsVKeDM-LsmAWZwoGoBg&psig=AFQjCNEF4g2QzjGqF48gSlKK0Rxmkp_rGQ&ust=1416463582006044


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Contents

1 Deep and Shallow Compaction methods...................................................................................

2

Dynamic Compaction..................................................................................................................

2.1 Method.......................................................................................................................................

2.2 Dynamic Compaction Stages.......................................................................................................

2.3

Generation of Waves...................................................................................................................

2.4

Tolerance Limit of Structures......................................................................................................

2.5 Distance between Impact points.................................................................................................

2.6 Monitoring and Control...............................................................................................................

2.7 Types of Dynamic Compaction....................................................................................................

2.8 Cost Information........................................................................................................................

2.9 Applicability.................................................................................................................................

2.10 Evaluation of Improvement.......................................................................................

2.11 Equipment Limitation..................................................................................................

2.12 Impact Energy, E.........................................................................................................

2.13 Applications & Uses....................................................................................................

2.14 Advantages & Disadvantages.....................................................................................


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1. Deep & Shallow Compaction Methods.

Soil compaction is defined as the method of mechanically increasing the density of the soil.

Compaction is possible by using shallow compaction methods and deep compaction methods. Deep

compaction techniques are required when the in-situ soil extending to large scale does not meet the

requirements of performance criteria specified for the expected loading and the environmental

conditions. It can be used to stabilize in-situ depth up to 10-30 meters whereas shallow compaction

methods are used to compact the soil about half a meter to 30 centimetres.

Deep soil improvement is possible by restoring to

Ground improvement Technique

Ground Reinforcement Technique

Ground Treatment

Ground Improvement Technique is possible by following methods:

Dynamic Compaction

Vibro-Compaction

Compaction Grouting

Pre-Fabricated Vertical Drains

Blast Densification

2. Dynamic Compaction

Dynamic Compaction technique was originally invented and developed by Mr. Louis Menard and

Menard Soiltraitement, Menard’s French affiliate

Dynamic compaction is a cost effective technique that is used to increase the density of the soil

when certain subsurface constraints make other methods inappropriate. It is a method that is used

to increase the density of soil deposits. It efficiently increases the bearing capacity of the granular

soil, reduces the volume of land-fills and lowers the post-construction settlements. Dynamic

compaction is commonly used to treat old uncontrolled fills, waste material and native granular soils

to depth up to 50 feet.

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The process involves of dropping a heavy weight repeatedly on the ground at regularly spaced

intervals. The weight and the height determine the amount of compaction that would occur. The

weight that is used depends on the degree of compaction desired and is between 8 to 36 tons. The

height varies from 1m to 30m.

The impact of the free fall creates stress waves that help in the densification of the soil. These stress

waves can penetrate up to 10m. In cohesion less soils, these waves create liquefaction that is

followed by the compaction of the soil, and in cohesive soils, they create an increased amount of

pore water pressure that is followed by the compaction of the soil. Pore water pressure is the

pressure of water that is trapped within the particles of rocks and soils.

The degree of compaction depends on the weight of the hammer, the height from which the

hammer is dropped, and the spacing of the locations at which the hammer is dropped. The initial

weight dropping has the most impact, and penetrates up to a greater depth. The following drops, if

spaced closer to one another, compact the shallower layers and the process is completed by

compacting the soil at the surface.

Most soil types can be improved with dynamic compaction. Old fills and granular soils are most often

treated. The soils that are below the water table have to be treated carefully to permit emission of

the excess pore water pressure that is created when the weight is dropped onto the surface.

This technique uses the dynamic effect of high energy impacts, caused by dropping large

steel weight weighing 15 to 40 tonnes from a height of 10-30 metres.

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Fig.1


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The basic principle behind the technique consists in the transmission of high energy waves through

a compressible soil layer in order to improve at depth its geotechnical properties. Dynamic

Compaction is normally associated with an intensive programme of in situ-testing in order to verify

that the specified improvement has been achieved.

Dynamic Compaction is applicable to all types of granular soils. This technique is particularly

well adapted to non-organic, non-homogeneous fill, made ground, and reclamation areas with

variable characteristics, even where underground obstructions are present.

Dynamic Compaction is effective in both saturated and un-saturated soils. Typically this

technique should not be carried out within 15m of existing services and 30m from existing buildings.

2.1 Method

10-40 tons weights are propped in free or quasi-free fall, from a height of 10-30m. The spacing of

the impact points and the unit energy, phasing & rest periods, depend on the soil types and level of

improvement required. Specially designed 80-120 ton cranes are normally used.

Degree of densification achieved is a function of the energy input (weight and drop height) as well as

the saturation level, fines content and permeability of the material.

6-30 ton can densify the loose sand up to the depth of 3-12m. When using the Dynamic Compaction

the removal and the replacement of undesirable soil is not required. Dynamic Compaction applies

energy at the ground surface and compact relatively deep layer. The process is efficient, economical,

and can be used to improve wide range of soil type

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Fig.2


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High Energy Dynamic Compaction

For compaction of soils to more than 10-12m, High Energy Dynamic Compaction can be performed.

This technique employs High Energy of more than 600 t.m using drop weights of more than 30tons,

drop heights of more than 30m and cranes

weighing more than 120t.

High Energy Compaction uses specialist equipment including free fall drop weights requiring a

specially designed weight release system using hydraulic clamps to avoid cable damping and friction,

plus repeat cycle lifting hooks, shown above. Due to the greater treatment depths of High Energy

Dynamic Compaction the design of the work phases is particularly important, in order to obtain a

homogeneous compaction over the thickness of the soil mass.

2.2Dynamic Compaction Stages

When the compaction is to be carried out at a greater depth (>12m), then it is done in a systematic

manner in a rectangular or a triangular method. Then each phase can have a number of phases i.e.

primary, secondary and tertiary. Primary means first of all you just compact in a particular place.

Next, in between one you need to compact. Since the previous ones are already compact it is called

secondary pass.

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Fig.3


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The immediate effect is normally predominant and results in the immediate reduction in the

void ratio, measured by the settlement after impact. A slower phenomenon occurs in some

saturated soils caused by the increase in pore pressure and localised liquefaction. This

dissipates during the rest period and results.

2.3 Generation of waves.

Due to dropping of weight energy is transferred in the form of the Rayleigh (Surface) wave and

volumic wave (Shear & Compressive). Rayleigh wave is more significant in case of the energy

transfer.

Here the kinetic energy which is produced upon tamping is converted into the potential energy

which gets introduced into the soil system.

In case of saturated soil compressibility is due to the presence of micro bubbles. Gradual liquefaction

occurs due to the repeated impacts and hence saturated soil gets consolidated.

Surface wave is generated with the frequency of 3-12 Hz. Rayleigh wave contributes 67% of the total

vibration energy and hence major concern for the design engineers because of the nearby building

foundation.

The ground vibrations are quantified in terms of PPV (Peak Particle Velocity). The measurement is

necessary to determine any risk to the nearby structures. The frequency of Rayleigh decreases with

the increase in distance from the point of impact.

2.4Tolerance Limit of the Structures.

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Fig.4


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British Standard 7385: Part 2-1993 lays down the following safety limits for various structures

having different natural frequencies.

Building Type Frequency Particle Velocity

Reinforced of framed heavy industrial/commercial 4Hz & above 50mm/s

Unreinforced or light framed residential/commercial. 4-15 Hz 15-20mm/s

Unreinforced or light framed residential/commercial. 15-40Hz 20-50mm/s

2.5 Spacing between the Impact Points.

Spacing between the Impact points Depends on:

Depth of the Compressible Layer

Permeability of Soil

Location of Ground Water Level

Deeper layers are compacted at wider grid spacing, upper layers are compacted with closer grid

spacing.

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Fig.5


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2.6 Monitoring & Control

Monitoring and control is another important point in the dynamic compaction. What we do

here is that – you can see that this is the machine that can do that dynamic compaction. It

has a tamper with accelerometer and FM transmitter. This is one thing. Then, you have total

station to measure tamper position after impact. There is some surveying equipment, which

is sophisticated, which can measure the tamper position. You would be interested in the

depth and what is the impression it has caused and all that. Van with receiving and

processing unit – it is another

Then there is a van for receiving and processing unit, you have all that data acquisitioned

and all that. What it gives is that what is that is going

2.7 TYPES OF DYNAMIC COMPACTION:

1. Dynamic compaction

2. Dynamic consolidation

3 .Dynamic replacement

4. Rotational dynamic compaction

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Fig.6


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5. Rapid impact dynamic compaction

1. Dynamic compaction

It is the compaction of unsaturated or highly permeable saturated granular materials by heavy

tamping.

The response to tamping is immediate.

2. Dynamic consolidation

The improvement by heavy tamping of saturated cohesive materials in which the response to

tamping is largely time dependent.

Excess pore water pressures are generated as a result of tamping and dissipate over several hours or

days after tamping.

3 .Dynamic replacement

The formation by heavy tamping of large pillars of imported granular soil within the body of soft

saturated soil to be improved.

The original soil is highly compressed and consolidated between the pillars and the excess pore

pressure generated requires several hours to dissipate. The pillars are used both for soil

reinforcement and drainage.

4 .Rotational dynamic compaction

A new dynamic compaction technique which makes use of the free fall energy as well as rotational

energy of the tamper called Rotational Dynamic Compaction (RDC).

The technique increases depth of improvement in granular soils.

Comparative study showed that the cone penetration resistance was generally larger than

conventional dynamic compaction and the tamper penetration in rotational dynamic compaction

was twice as large as that of conventional dynamic compaction.

5. Rapid impact dynamic compaction

This technique is preferred when project is a large scale project. It is not suitable for a small scale

project

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2.8 Cost Estimation

The cost estimation of the Deep Dynamic Compaction (DDC) is typically captured in a contract bid

item which is measured by each drop of tamper or by the square yard. Included in this bid item are

associated incidental cost such as:

Layout of Grid Spacing

Monitoring of crater depth and Ground Displacement

Other costs associated with DDC which may be measured and paid for separately include:

Mobilization

Material for backfilling and levelling craters between passes and to restore the treated area

back to original elevation.

2.9 Applicability

It is applicable to wide variety of soils and the grouping is done on the basis of grain size. Zone 1

consists of pervious soil with plasticity index 0 like non-cohesive and large grain size. Zone 3 consists

of impervious materials with plasticity index more than 8.

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Fig.7


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Type of Deposit Applied energy Improvement

Zone 1 20-25 txm/m3 Excellent

Zone 2 25-35 txm/m3 Moderate-Good

Zone 3 Not applicable Not applicable

2.10 Evaluation of improvement.

The depth of the improvement is proportional to the energy per blow.

The improvement can be estimated through the SPT and CPT test.

Dmax=n(WH)^1/2

Where Dmax= max depth of improvement

n=Coefficient caters for soil and equipment variability

W=weight of tamper

H=height of tamper

Depth of Improvement depends on:

1. Soil Condition

2. Energy per drop

3. Contact pressure of tamper

4.

Grid spacing.

5. Number of passes.

6. Time lag between phases.

2.11 Equipment limitation

Crane Capacity

Height of drop

Mass of tamper

Tamper Size

2.12 Impact Energy

Weight of tamper times the height of drop.

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Main parameter in determining the depth of improvement.

Can be calculated from the equation

Dmax= n(WH)^1/2

(Free Falling of Weights)

2.13 Applications and Uses

Treatment for industrial warehouses, port and airport platforms, road and railways

embankments, heavy storage, tanks.

Airport runways, Buildings, Parking Lots, Roads & Road ways, Treatment Plants etc.

Well adapted to the treatment of non-organic heterogeneous fill or made ground

containing larges blocks that can create obstructions for inclusions and columns

solutions (Stone Columns, Rigid Inclusions…),

Well adapted to the improvement of very large flat platform because of very high

production rates (> 10,000 m²/month),

Well adapted and commonly used for liquefaction mitigation.

Well adapted for improvement of landfills.

In sanitary fills compaction is caused either by compression of voids or decaying of

thrash material overtime.DDC is effective in reducing the void ratio, and therefore

reducing the immediate and long term settlement.

For older fills where decomposition is complete, DDC has greatest effects by

increasing unit weight and reducing long-term ground subsidence.

2.14 Advantages & Disadvantages

Advantages of Dynamic Compaction are:

Suitability at wide range of soils.

Allow treating soil below water table.

It is a rapid Treatment.

Low in cost

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Disadvantages of Dynamic Compaction:

The process is expensive and relatively time consuming; due to the development of the pore

pressure in the fine grained soil its applicability is reduced.

This method is not valid for populated or fully developed areas because the shock waves

generated by this method may affect other underground utilities or the adjoining structures.

This can be avoided, while working in crowded or populated areas by using small weights,

which reduces the intensity of vibrations, produced; it can also be done by dropping the

weights from smaller heights. It is reported by experienced contractors that they the soil can

be treated as close as 3 m from underground services and can be treated 6 m from the

sound structures.

The treatments may be complicated when GWT is about 2 m below the ground level, for the

success of the treatment the level of whole site is to be raised up by the use of imported

materials.

It causes environmental pollution by making noise, gusts of air, vibrations and permanent

deformation of the soil.

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References:

http://www.menardusa.com/Landfill2000.Pdf

http://www.civilengineeringterms.com/soil-mechanics-2/ground-improvement-

methods-deep-compaction-method-of-dynamic-compaction/

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact

=8&ved=0CB4QFjAA&url=http%3A%2F%2Fnptel.ac.in%2Fcourses%2F105108075%2Fmo

dule2%2FLecture06.pdf&ei=nd52VNOXJ5eWuATjrYCYCQ&usg=AFQjCNFmsLsbRmGnjnD

mG-wFtVrfp6ntPA

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