Embed Size (px)
DESCRIPTION
Deep vibro technique.(Keller brochure, 2006)
Citation preview
Brochure 10 -02E
Deep Vibro Techniques
Content
3 Overview ofdeep vibro techniques
4 Vibro Compaction
6 Vibro Replacement
8 Structural FoundationElements
10 Special Applications
11 Quality Control
12 Keller Branches
Deep vibro techniquespresent flexible solutionsfor soil improvement.They are mainly usedunder foundations ofstructures that are to beconstructed on soils oflow bearing capacity.
Keller developed the depthvibrator (patented in 1934),which was originally usedto compact granular soilssuch as sand and gravel.
Today Keller improves avariety of granular andcohesive soils employinga wide range of depthvibrator models andtechniques.
100
80
60
40
20
0
100
80
60
40
20
00,60,002 0,006 0,02 0,06 6,0 20 600,2 2,0
3
Clay Silt Sand Gravel Cobbles
Grain size [mm]
Vibro Replacement
Vibro Compaction
Transition zone
Siev
e pa
ssin
g [%
by
wei
ght]
Overview of deep vibro techniques
Limits of application for deep vibro techniques
The subsoilUsually the soil conditions are described in asoil investigation report. If the properties ofthe existing soil cannot fulfil the requirementsset by the proposed loading conditions, deepvibro techniques offer an economical solutionfor the ground improvement. They can becarried out to almost any depth.
The depth vibratorThe cylindrical depth vibrator is typically be-tween 3 m and 5 m long and weighs approxi-mately 2 tons. The core element of the vibratoris an electrically driven eccentric weight whichinduces the horizontal oscillation of the vibra-tor. The vibrator string is assembled with thevibrator and extension tubes to suit the im-provement depth and suspended from a craneor mounted on a custom built basemachine (i.e. the Keller vibrocat).
The techniquesThe depth vibrator is used for 3 distinct tech-niques which differ both in their soil improve-ment and in their load transfer mechanism.The foundation design is therefore frequentlydeveloped in close cooperation between boththe consultant’s geotechnical and structuralengineers and Keller.
The Vibro Compaction technique compactsgranular soils with negligible fines content byrearrangement of the soil particles into adenser state.The Vibro Replacement technique builds loadbearing columns made from gravel or crushedstones in cohesive soils and granular soils withhigh fines content.
The third technique creates structuralfoundation elements in the ground whichwill allow comparatively high loads to besafely carried by soils where no adequatelateral support for Vibro Replacementcolumns can be mobilized.
The executionFor all techniques the vibro process startswith the penetration of the oscillating depthvibrator into the ground to the requiredimprovement depth. Subsequently, thevibrator is then removed as required by theemployed technique to either compact thesoil from the bottom up, to build a stonecolumn or to construct a structuralfoundation element.
The benefitsThe deep vibro techniques present a veryversatile ground improvement method thatcan be adjusted to a wide variety of groundconditions and foundation requirements. Itsexecution is comparatively fast even if largevolumes of soil are to be improved andsubsequent structural works can follow veryquickly. The soil improvement enables thecontractor to utilise standard shallowfootings which, in turn, leads to additionalsavings.
Another advantage is the environmentalfriendliness of the deep vibro techniques,as natural and in situ materials are used.In addition, only a comparatively smallquantity of soil is removed in the process.
The principle ofthe vibro process
4
h
The Vibro Compaction processin granular soils
The foundation conceptThe range of compaction for an individualpoint is governed by several parameters.Keller is able to draw upon a wealth ofexperience to propose a suitable foundationconcept. The optimum arrangement of thevibro compaction points is usually bestachieved by an on-site trial, where differentcompaction grids and methods can be testedand evaluated. After compaction, high loadscan be safely carried and can reach foun-dation pressures of up to 1MN/m2.
The layout of the compactions points can beadjusted in such a manner that soil volumesof any size are compacted.
The achieved degree of compaction can beeasily and economically verified using a rangeof different tests.
NoseCone
EccentricWeight
Electricmotor
Flexiblecoupling
Water
or
air supply
Extensiontube
Compaction belowraft footings
Compaction belowsingle footings
Density of the soil
before after
1 Penetration
At full water pressure the oscillat-ing vibrator penetrates to thedesign depth and is surged up anddown as necessary to agitate thesand, remove fines and form anannular gap around the vibrator.When at full depth the water flowis reduced or stopped.Th
e pr
oces
s
Equipment and executionThe compaction of granular soils is mosteconomically attained with vibrators oscillat-ing at a comparatively low frequency toachieve optimum compaction of the soilparticles. The vibrator is typically suspendedfrom a crane. The penetration of the vibratorand, to a certain extent also the compactionprocess, is aided by water flushing with jetsof variable pressure. The pressure pipes andjets form an integral part of the vibratorstring.The compaction is carried out from thebottom of penetration upwards in predeter-mined pull out steps and compaction inter-vals. The compaction result is dependant onthe effectiveness of the vibrator and the soilconditions.
Geotechnical aspectsUnder the influence of the induced vibration,the soil particles within the zone of influenceare rearranged and compacted. The range ofthis zone depends on the vibrator used, thesoil and the method employed. The volumereduction of the compacted soil can reachvalues in the order of 10% depending onthe soil conditions and the intensity of thecompaction effort.
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
...
-31
-32
-33
-34
-35
......
-48
-49
-50
A
B B
5
Special applicationsWith depth vibrators, slender elementssuch as dolphins, soil anchors or steelprofiles can be sunk into sandy soils andsecurely anchored.
A further field of application is thedensification of wall zones and excava-tion bases to reduce their permeability.Vibrator in a compaction crater
As early as 1939 acompaction depth of35 m was reached ona site in Berlin. Nowadaysmaximum compactiondepths beyond 50 mhave been achieved.
Depth
Natural or man made deposits of sand and gravel are frequently not denseenough or are too inhomogeneous to allow a proposed structure to be safelyand reliably founded. With Keller’s depth vibrators the soil density can beincreased and homogenized independently from the groundwater table.
2 Compaction
The compaction is carried out insteps from the maximum depthof penetration upwards.It encompasses a cylindrical soilbody of up to 5m diameter. Theincrease in density is indicated byan increased power consumptionof the vibrator.
3 Backfilling
Around the vibrator a craterdevelops which is backfilled withsand, which is either imported(A) or taken from the existingsoil (B). For this purpose avolume of up to 10% of thetreated soil volume is required.
4 Finishing
After completion of thecompaction, the surface isrelevelled and, if required,compacted with a surfacevibratory roller.
0
0,2
0,4
0,6
0,8
1
4 8 12 16 20 24 28
149163664100225400
9001600
2 3 4 5 6 7 8 9 10 111
2
3
4
5
6
7
6
Vibro Replacement in granular soils withhigh fines content and in cohesive soils
Equipment and executionFor the construction of Vibro Replacementcolumns the bottom feed process is frequentlyemployed, which feeds coarse granular materialto the tip of the vibrator with the aid of pres-surized air. To optimize the performance of thisprocess and to accommodate the specializedequipment, Keller has developed the vibrocatbase unit which guides the vibrator on itsleader and allows the exertion of an additionalpull-down pressure during penetration andcompaction. The Vibro Replacement processconsists of alternating steps. During the retrac-tion step, gravel runs from the vibrator tip intothe annular space created and is then com-pacted and pressed into the surrounding soilduring the following re-penetration step. In thismanner stone columns are created from thebottom up, which act as a composite with thesurrounding soil under load.
Geotechnical aspectsInsofar as any compaction can be achieved inmixed or fine grained soils through horizontalvibrations and soil displacement (which de-pends mainly on their degree of saturation),this improvement should be evaluated in thesame manner as for Vibro Compaction.The pure Vibro Replacement process, however,does not assume any compaction in thesurrounding soil. The improvement relies onthe higher stiffness and higher shear strengthof the stone column.
Nozzle
Air chamberand lock
Extensiontube and
stone feederpipe (material
storage)
Electricalmotor
Stonefeeder pipe
EccentricWeight
The foundation conceptWhile the compaction of the surrounding soilcan be easily verified by soundings, the im-provement effect of the Vibro Replacementcan only be checked by in situ load tests.Keller has developed a reliable design methodwhich uses the geometry of the columns andthe friction angle of the column material asinput parameters.For the foundation design, the improvedground is treated like normal subsoil.
Area ratio A / AS
Impr
ovem
ent
fact
or
Design diagram for Vibro Replacement
µB = 1/3
ϕS = ˚45.0
ϕS = ˚42.5
ϕS = ˚40.0
ϕS = ˚37.5
ϕS = ˚35.0
Sett
lem
ent
ratio
s/s
*∞
= settlement of a theoretical infinite load area* s∞
No.
of s
tone
col
umns
Depth ratio t/d
Settlement evaluation for single footings
The allowable bearing pressure that is achievedafter the improvement is typically in the rangeof 150 to 400 kPa.
Flexiblecoupling
1 Preparation
The vibrocat positionsthe vibrator over therequired location of thecompaction point andstabilises itself usinghydraulic supports.A wheel loader fills theskip with aggregate.
2 Charging
The skip is lifted andempties its contentsinto the air chamber.Once the air lock isclosed, the materialflow towards thevibrator tip is assistedby pressurized air.Th
e pr
oces
s
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
...
-14
-15
-16
-17
-18
...
-19
-20
7
Benefits of working with thebottom feed vibrator:
• The aggregate is always fed directlyto the tip of the vibrator, creating acontinuous column.
• Only a single penetration is required.• The collapse of the hole is not
possible even in critical soils.• The leader ensures the verticality
of the columns.• No water is required, eliminating the
necessity to dispose of any mudotherwise created.View of the cut off level after Vibro Replacement
The Vibro Replacementtechnique was developedin the late 1950s.Without any specialmodifications the bottomfeed setup the vibrocatcan install columns upto 20 m depth.
Depth
Mixed grained and fine grained soils frequently do not possess a sufficientbearing capacity. For fines content in excess of 10% to 15% a sufficientcompaction result without imported material cannot be expected. For thesecases the Vibro Replacement technique is a viable option. This technique isalso suitable for the treatment of coarse fills such as rubble, building debrisand slag heaps.
3 Penetration
The vibrator displaces thesoil and is lowered to thedesigned depth, aided bythe compressed air and bythe vibrocat’s pull-down.
4 Compaction
After reaching the maximumdepth the vibrator is pulled upslightly, causing the aggregateto fill the cavity so created.During re-penetration theaggregate is compacted andpressed into the surroundingsoil.
5 Finishing
The stone column is built upin alternating steps up to thedesigned level. During the finallevelling, the surface requires tobe re-compacted or a blindinglayer is required as analternative.
8
Grouted Stone Columns (VSS) andPremixed Grouted Stone Columns (FSS)
Excavated grouted stone column
Installation of groutedstone columns within-situ grouting usingcement slurr y
Replacement method by eliminating the useof grout in the upper or lower section of thecolumn as required, thus creating a buffer forthe rigid grouted columns. These columns arecalled Partially Grouted Stone Columns.
Equipment and executionThese foundation elements are built in thesame manner as described for the VibroReplacement process.For the grouted stone columns (VSS), thegravel is fed into the ground and during thesame process mixed in-situ with cementgrout. This creates a solid column once thegrout has set.For premixed grouted stone columns, aspecial coarse grained concrete mix typicallyranging between strengths C15 and C20 isinstalled. It behaves identically to the stonematerial, allowing the same compaction anddisplacement effects in the surrounding soil.
Geotechnical aspectsThe load bearing behaviour of the structuralfoundation elements is largely identical to thebehaviour of piles.
The foundation conceptFor Grouted Stone Columns and PremixedGrouted Stone Columns Keller has theapproval of the German supervisory boardfor construction.
The external load bearing mechanism that isused for the design of the soil improvementis very well supported by a large number ofload test results as per DIN 1054. Dependingon the soil conditions and the materials used,working loads of up to 600 kN can be rou-tinely achieved. Grouted stone columns canbe easily combined with the normal Vibro
Installation of the grouted stone column
Pull down
Vibrator with stone feeding tube and separate grout pipe
weak strata
Penetration Formation of the toe
Cement grout from mixer
Material charging
Nozzle
Gravel toecompetent strata
Vibrocat
Structural Foundation Elements
9
These methods are employed if the fine grained subsoil does not mobilizesufficient lateral support for the columns or when high organic contents arefound which decompose and cause soil shrinkage. Another field of applicationis the founding of structures with high loads.
Equipment and ExecutionVibro Concrete Columns consist typically ofpumpable concrete, grade C25. The toe ofthe column is enlarged by repeated retractionand repenetration of the vibrator, howeverthe shaft is built in a single pull due to thehigh internal strength of the concrete.
Geotechnical aspectsDuring the installation of Vibro ConcreteColumns no particular effort is taken todensify any specific soil layer. As with otherstructural foundation elements, a high degreeof improvement can be achieved at the toe ofthe column, thus attaining a particularly highcapacity and low deformations under load.
The foundation conceptFor Vibro Concrete Columns Keller also hasthe approval of the German supervisoryboard for construction.
Vibro Concrete Columns are generally moreslender compared to other structural founda-tion elements. Typical shaft diameters rangebetween 40 cm and 60 cm. The capacity underworking load reaches up to 800 kN depend-ing on the ground conditions and on thepossibility to enlarge the toe.
Vibro Concrete Columns (BRS)
Excavated Vibro Concrete Columns
Cross Section of aVibro Concrete Column
Installation ofVibro Concrete Columns
Installation ofthe shaft
Vibrocat
Vibrator with concrete feeder pipe
weak strata
competent strata
Preparation Penetration andtoe formation
Concrete nozzle
Toe
Concrete Pump
Readymixed concrete
Pull down
10
Special Applications
Multiple Vibrators andOffshore CompactionVibro Compaction of large areas bothonshore and offshore can be carried outwith multiple vibrator assemblies.
Vibro Replacement –Top Feed MethodIn suitable ground conditions the VibroReplacement process can be performedusing crane hung vibrators similar to theVibro Compaction setup. In this case wateror air flushing is used. The flushing mediumassists rapid penetration into the ground andstabilizes the annular around the vibrator.It also can be used to increase the columndiameter by flushing.
For Vibro Replacement offshore, such as forquay walls and bridge pillars, a gravel blanketcan be placed which is then installed into theground. Bottom feedsystems are alsoavailable.
clay, silt
sandstone
dredged and replaced by sand
aggregate
mud
sand
0
500
1000
1500
2000
1
2
-40
-20
0 20 400 5 10 15 0 200
400
0 50 100
150
11
Quality Control
For all vibro techniques, electronic measuringdevices can be employed to ensure andrecord constant high quality workmanship.
The measuring deviceTo control the process, monitor the qualityand for production records, the relevantconstruction parameters for each compactionprobe can be measured, saved and printed asproof of production and quantities.
The measurement device consists of
• The display unit in the operator's cabin,
• The CPU with data storage,
• PC with printer at the site office,
• Dot-matrix printer mounted on the baseunit for real time printout (optional).
Display unit and CPUof the M4 measuringdevice
Load tests are asuitable option toverify the improve-ment of the soil
The measurement resultsDuring compaction a number of different siteand production parameters are automaticallyrecorded. Values such as time, depth, penetra-tion/pullout speed, pull-down force and cur-rent can be graphically displayed and printed.If required, the energy consumption can berecorded.
Time
[sec]
Process: Vibration Process (3.0.0)Inventory: 9130517 Site: 1234173Lot: 0 Point: 241 Ref. No.: 15Date: 15.09.04 Time: 05:10:47 Interval: 4 sekWeight: 1.5 kN/m³Legend:
Dep.: Consultingand Development
Total Time: 34.33 min Max. depth: 10.00 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 +0.302 10 Point End 05:45:08 0.1 21.03 0.00 2.79 5.77 -0.4 +0.2
A company of Keller Group plc
Keller Grundbau GmbHInternational Geotechnical Contractorswww.KellerGrundbau.com · www.Keller-Asia.com
GermanyHead Office and Overseas DivisionP.O. Box 10 06 6463006 OffenbachTel. +49 69 8051-0 · Fax +49 69 8051-270E-mail: [email protected]
BahrainKeller Grundbau GmbHFlat 205, Bldg. 63 · P.O. Box 5452Manama 332Tel. +973 17741677 · Fax +973 17741688E-mail: [email protected]
U.A.E.Keller Grundbau GmbHOffice 208, 2nd Floor · Moh’d Al Makhawi BuildingUmm Hureir Road · P.O. Box 11 13 23DubaiTel. +971 4 3355283 · Fax +971 4 3355278E-mail: [email protected]
Saudi ArabiaKeller Turki Co. Ltd.P.O. Box 718Dammam 31421Tel. +966 3 8333997 · Fax +966 3 8335325E-mail: [email protected]
EgyptGENCO · Geotechnical Engineering Contractor Ltd.462, Horreya Avenue, RoushdyAlexandriaTel. +20 3 5458443 · Fax +20 3 5427372E-mail: [email protected]
MalaysiaKeller (M) Sdn. Bhd.No. 35, Kg PakarBatu 5, Jalan Sungei Besi57100 Kuala LumpurTel. +60 3 79802894 · Fax +60 3 79800349E-mail: [email protected]
SingaporeKeller Foundations (S E Asia) Pte Ltd.25 International Buisiness Park#04-01 German CentreSingapore 609916Tel. +65 65 629012 · Fax +65 65 629014E-mail: [email protected]
IndiaKeller Ground Engineering India Pvt. Ltd.2 Cenotaph Court, No. 28 Cenotaph RoadTeynampet, Chennai 600018Tel. +91 44 24334582 · Fax +91 44 24334584E-mail: [email protected]
Hong KongKeller Grundbau GmbHNo. 272, San Hing TsuenLam Tei, Tuen MunNew Territories, Hong KongTel. +852 24659711 · Fax +852 24831814E-mail: [email protected]
Korea (Rep.)Keller-Tuksu Ltd.1688-1, Seochong-DongSeoul 137-882Tel. +82 2 34817901 · Fax +82 2 34817905E-mail: [email protected]
