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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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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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32
3
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34
35
48
49
50
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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2 3 4 5 6 7 8 9 10 111
0,2
0,4
0,6
0,8
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0 4 8 12 16 20 24 28
1491636
64
100
225
400
9001600
Vibro Replacement in granular soils with
high nes content and in cohesive soils
Equipment and execution
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.
Geotechnical aspects
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.
The oundation concept
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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Structural Foundation Elements
Premixed Vibro Concrete Columns (PVCC)
Excavated premixed vibro concrete column
Installation o premixedvibro concrete columns
Equipment and execution
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.
Geotechnical aspects
The load bearing behaviour o the structural
oundation elements is largely identical to the
behaviour o piles.
The oundation concept
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.
Geotechnical aspects
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.
The oundation concept
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
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#04-103 Tradehub 21Singapore 60 99 66
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