keller ground improvement

8/6/2019 Keller Ground Improvement

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Deep Vibro Techniques

Brochure 10-02 E


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Deep vibro techniques

present exible solutions

or soil improvement.

They are mainly used

under oundations o

structures that are to beconstructed on soils o

low bearing capacity.

Keller developed the depth

vibrator (patented in 1934),

which was originally used

to compact granular soils

such as sand and gravel.

Today Keller improves avariety o granular and

cohesive soils employing

a wide range o depth

vibrator models and

techniques.

Content

Overview o

deep vibro techniques......... 3

Vibro Compaction............... 4

Vibro Replacement.............. 6

Structural Foundation

Elements ............................... 8

Special Applications........... 10

Quality Control .................. 11

Keller Branches.................. 12


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4

The Vibro Compaction process

in granular soils

Equipment and execution

The compaction o granular soils is most

economically attained with vibrators oscillating

at a comparatively low requency to achieve

optimum compaction o the soil particles.

The vibrator is typically suspended rom a

crane. The penetration o the vibrator and,

to a certain extent also the compaction

process, is aided by water fushing with

jets o variable pressure. The pressure

pipes and jets orm an integral part o the

vibrator string. The compaction is carried

out rom the bottom o penetration

upwards in predetermined pull out steps

and compaction intervals. The compactionresult is dependant on the eectiveness

o the vibrator and the soil conditions.

Geotechnical aspects

Under the infuence o the induced vibration,

the soil particles within the zone o infuence

are rearranged and compacted. The range o

this zone depends on the vibrator used, the

soil and the method employed. The volume re

duction o the compacted soil can reach values

in the order o 15 % depending on

the soil conditions and the intensity

o the compaction eort. 1 Penetration

At ull water pressure the oscillating vibratorpenetrates to the design depth and is surgedup and down as necessary to agitate thesand, remove nes and orm an annulargap around the vibrator. At ull depth thewater ow is reduced or stopped.

The oundation concept

The range o compaction or an individual

point is governed by several parameters.

Keller is able to draw upon a wealth o

experience to propose a suitable oundation

concept. The optimum arrangement o

the vibro compaction points is usually best

achieved by an on-site trial, where dierent

compaction grids and methods can be

tested and evaluated. Ater compaction, high

loads can be saely carried and can reach

oundation pressures o up to 1 MN/m2.

The layout o the compaction points can be

adjusted in such a manner that soil volumes

o any size are compacted.

The achieved degree o compaction can be

easily and economically veried using a range

o dierent tests.

Nose cone

Eccentricweight

Electricmotor

Flexiblecoupling

Water

or

air supply

Extensiontube

Compaction below

rat ootings

Compaction below

single ootings

beore ater

The process


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Natural or man made deposits o sand and gravel are requently not dense

enough or are too inhomogeneous to allow a proposed structure to be saely

and reliably ounded. With Kellers depth vibrators the soil density can be

increased and homogenized independently rom the groundwater table.

2 Compaction

The compaction is carried outin steps rom the maximumdepth o penetration upwards.It encompasses a cylindrical soilbody o up to 5 m diameter.The increase in density isindicated by an increased powerconsumption o the vibrator.

3 Backlling

Around the vibrator acrater develops whichis backlled with sand,which is either imported(A) or taken rom theexisting soil (B). For thispurpose a volume o upto 5 % o the treatedsoil volume is required.

4 Finishing

Ater completion o thecompaction, the surace isrelevelled and, i required,compacted with a suracevibratory roller.

Special applications

With depth vibrators, slender elements

such as dolphins, soil anchors or steel

proles can be sunk into sandy soils and

securely anchored.A urther eld o application is the

densication o embankment zones

and excavation bases to reduce their

permeability.

Vibrator in a compaction crater

As early as 1939 a

compaction depth o

35 m was reached on a

site in Berlin. Nowadays

maximum compaction

depths beyond 50 m

have been achieved.

Depth


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1491636

64

100

225

400

9001600

Vibro Replacement in granular soils with

high nes content and in cohesive soils


For the construction o Vibro Replacement

columns the bottom eed process is requently

employed, which eeds coarse granular material

to the tip o the vibrator with the aid o pres-

surized air. To optimize the perormance o this

process and to accommodate the specialized

equipment, Keller has developed the vibrocat

base unit which guides the vibrator on its

leader and allows the exertion o an additional

pull-down pressure during penetration and

compaction. The Vibro Replacement process

consists o alternating steps. During the retrac-

tion step, gravel runs rom the vibrator tip into

the annular space created and is then com-pacted and pressed into the surrounding soil

during the ollowing re-penetration step. In this

manner stone columns are created rom the

bottom up, which act as a composite with the

surrounding soil under load.


Insoar as any compaction can be achieved in

mixed or ne grained soils through horizontal

vibrations and soil displacement (which depends

mainly on their degree o saturation), this im-

provement should be evaluated in the same

manner as Vibro Compaction. The pure VibroReplacement process, however, does not as-

sume any compaction in the surrounding soil.

1 Preparation

The vibrocat positions thevibrator over the requiredlocation o the compactionpoint and stabilises itselusing hydraulic supports.A wheel loader lls theskip with aggregate.

2 Charging

The skip is lited and emptiesits contents into the airchamber. Once the air lockis closed, the material owtowards the vibrator tip isassisted by pressurized air.

The process

input parameters. For the oundation design,the improved ground is treated like normal

subsoil. The allowable bearing pressure that is

achieved ater the improvement is typically in

the range o 150 to 400 kPa.

The improvement relies on the higher stiness

and higher shear strength o the stone column.


While the compaction o the surrounding

soil can be easily veried by soundings, the

improvement eect o the Vibro Replacement

can only be checked by in situ load tests.

Keller has developed a reliable design method

which uses the geometry o the columns and

the riction angle o the column material as

Nozzle

Air chamberand lock

Extension tubeand stone

eeder pipe

(material

storage)

Electricalmotor

Stone eederpipe

Eccentricweight

Flexible

coupling

S = 45.0

S = 42.5

S = 40.0

S = 37.5

S = 35.0

B =

Design diagram or Vibro Replacement

Settlement evaluation or single ootings

Improvementfactor

Se

ttlementratios/s*

No.ofs

tonecolumns

Area ratio A / AS

Depth ratio t/d

* s = settlement o a theoretical innite load area


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Mixed grained and ne grained soils requently do not possess a sucient bearing

capacity. For a nes content in excess o 10 % to 15 % a sucient compaction

result without imported material cannot be expected. For these cases the Vibro

Replacement technique is a viable option. This technique is also suitable or the

treatment o coarse lls such as rubble, building debris and slag heaps.

3 Penetration

The vibrator displacesthe soil and is loweredto the design depth,aided by the compressedair and by the vibrocatspull-down.

4 Compaction

Ater reaching the maximumdepth the vibrator is pulled upslightly, causing the aggregateto ll the cavity created.During re-penetration theaggregate is compacted andpressed into the surroundingsoil.

5 Finishing

The stone column is builtup in alternating stepsup to the design level.During the nal levelling,the surace requires tobe re-compacted or ablinding layer is requiredas an alternative.

View o the cut o level

ater Vibro Replacement

The Vibro Replacement

technique was developed

in the late 1950s. Without

any special modifcations

o the bottom eed setup

the vibrocat can install

columns up to 20 m depth.

Benets o working with the

bottom eed vibrator:

Theaggregateisalwaysfeddirectly to the tip o the vibrator,creating a continuous column.

Onlyasinglepenetrationisrequired.

Thecollapseoftheholeisnotpossible due to the compressedair even in critical soils.

Theleaderensuresthe

verticality o the columns. Nowaterisrequired,eliminating

the necessity to dispose o anymud otherwise created.

Depth


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8

Structural Foundation Elements

Premixed Vibro Concrete Columns (PVCC)

Excavated premixed vibro concrete column

Installation o premixedvibro concrete columns


These oundation elements are built in the

same manner as described or the Vibro

Replacement process.

For premixed vibro concrete columns, a

special coarse grained concrete mix typically

ranging between strengths C8/10 to C25/30

is installed. It behaves identically to the stone

material, allowing the same compaction and

displacement eects in the surrounding soil.


The load bearing behaviour o the structural

oundation elements is largely identical to the

behaviour o piles.


For Premixed Vibro Concrete Columns Keller

has the approval o the German supervisory

board or construction.

The external load bearing mechanism that is

used or the design o the soil improvement

is very well supported by a large number o

load test results as per DIN 1054. Depending

on the soil conditions and the materials

used, working loads o up to 900 kN can be

routinely achieved. Vibro concrete columns

can be easily combined with the normal Vibro

Replacement method by eliminating the use o

concrete in the upper or lower section o the

column as required, thus creating a buer or

transition zone to the rigid concrete columns.

Vibrator

with stone

eeding tube

Pull down

Vibrocat

Installation o the column

Material

charging

Penetration Formation o the toe

weak strata

competent strata

Nozzle

Column toe


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This method is employed i the ne grained subsoil does not mobilize sucient

lateral support or stone columns or when high organic contents are ound

which decompose and cause soil shrinkage. Another eld o application is the

oundation o structures with high loads.

Vibro Concrete Columns (VCC)

Excavated Vibro Concrete Columns

Cross Section o

a Vibro Concrete

Column

Installation o VibroConcrete Columns

Equipment and Execution

Vibro Concrete Columns consist typically o

pumpable concrete, with C20/25 strength.

The toe o the column is enlarged by repeated

retraction and repenetration o the vibrator,

however the shat is built in a single pull due

to the high internal strength o the concrete.


During the installation o Vibro Concrete

Columns no particular eort is taken todensiy any specic soil layer. As with other

structural oundation elements, a high degree

o improvement can be achieved at the toe o

the column, thus attaining a particularly high

capacity and low deormations under load.


For Vibro Concrete Columns Keller also

has the approval o the German supervisory

board or construction.

Vibro Concrete Columns are generally

more slender compared to other structural

oundation elements. Typical shat diameters

range between 40 cm and 60 cm. The capacity

under working load reaches up to 1200 kN

depending on the ground conditions and on

the possibility to enlarge the toe.

PreparationPenetration and

toe ormation

Installation o

the shat

weak strata

competent strata

Pull down

Vibrocat

Vibrator with

concrete

eeder pipe

Concrete

Pump

Readymixed

concrete

Concrete nozzle

Column toe


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Special Applications

Multiple Vibrators and

Ofshore Compaction

Vibro Compaction o large areas both

onshore and oshore can be carried out

with multiple vibrator assemblies.

For Vibro Replacement oshore, such as or

quay walls and bridge pillars, a special gravel

pump is used to construct columns with the

bottom eed process.

Vibro Replacement

Top Feed Method

In suitable ground conditions the Vibro

Replacement process can be perormed

using crane hung vibrators similar to the

Vibro Compaction setup. In this case water

or air fushing is used. The fushing medium

assists rapid penetration into the ground and

stabilizes the annulus around the vibrator.

It also can be used to increase the column

diameter.

sandstone

rock

clay, silt

weak soil

dredged andreplaced by sand

Gravel pump


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Quality Control

For all vibro techniques, electronic measuring

devices can be employed to ensure and

record constant high quality o workmanship.

The measuring device

To control the process, monitor the quality

and or production records, the relevant

construction parameters or each compaction

probe can be measured, saved and printed

as proo o production and quantities.

The measurement device consists o

Thedisplayunitintheoperatorscabin,

TheCPUwithdatastorage, PCwithprinteratthesiteoce,

Dot-matrixprintermountedonthebaseunit or real time printout (optional).

The measurement results

During compaction a number o dierent site

and production parameters are automatically

recorded.

Values such as time, depth, penetration/

pullout speed, pull-down orce and current

can be graphically displayed and printed. I

required, the energy consumption can be

recorded.

Display unit and CPU o

the M5 measuring device

Load tests are a suitable

option to veriy the

improvement o the soil

Time

[sec]

Process: Vibration Process (3.0.0)Inventory : 93057 Site: 23473Section: 0 Point: 24 Re. No.: 5

Date: 5.0.08 Time: 05:0:47 Interval: 4 sekWeight: .5 kN/m

Legend:

Total Time: 34.33 min Max. depth: 0.00 m Rel. weight: 0.58 ton/m

Thrust

[bar]

Depth

[m]

Power

[A]

Penetration Rate

[m/min]

Event Time Depth Electrical Susp. Net Total Inclination InclinationEnergy Point Weight Weight Right/Left For/Back

No. Type Description hh:mm:ss [m] [kVAh] [cbm] [ton] [ton] [Deg] [Deg]

01 09 Point Start 05:10:47 0.1 0.00 0.00 2.98 2.98 -0.2 +0.3

02 10 Point End 05:45:08 0.1 21.03 0.00 2.79 5.77 -0.4 +0.2


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A company o Keller Group plc

Keller Group plcGround Engineering Contractors

www.keller.co.uk

Continental Europe

Keller Grundbau GmbH

Kaiserleistrasse 4463067 Ofenbach

Germanywww.kellergrundbau.de

Keller Fondations Spciales

2 rue Denis Papin - CS 69224 Duttlenheim

6729 Molsheim Cedex

France

www.keller-rance.com

Keller Grundbau Ges.mbH

Mariahiler Strasse 127a1150 Vienna

Austria

www.kellergrundbau.at

Keller Polska Sp. z o.o.

ul. Poznaska 17205-850 Oarw Mazowiecki

Poland

www.keller.com.pl

Middle East

Keller Turki Co. Ltd

P.O. Box 718

Dammam 31421

Saudi Arabia

www.kellergrundbau.com

Keller Grundbau GmbH

Dubai Branch

Unit 407 Grosvenor HouseCommercial Tower, Shaikh Zayed Road

P. O. Box 3 23

Dubai, UAE

www.kellergrundbau.com

Asia

Keller Foundations

(SE Asia) Pte Ltd

18 Boon Lay Way

#04-103 Tradehub 21Singapore 60 99 66

www.kellerareast.com

Keller (Malaysia) Sdn. Bhd.

B5-0, Block B, Plaza Dwitasik

Bandar Sri Permaisuri

56000 Kuala Lumpur

Malaysia


Keller Ground Engineering

India Pvt. Ltd.

29, Best Arcade Building

Plot-3, Sector-2, Dwarka

New Delhi 0075

India


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