Keller Foundations are renowned for providing innovative and cost effective solutions to ground engineering and foundation problems. Keller has unrivalled coverage in the United Kingdom where its services are used in infrastructure, building and civil engineering projects.
Dunfermline 15 Pitreavie Court, Pitreavie Business Park Queensferry Road, Dunfermline, KY11 8UU T: 01383 749531 E: william.scott@keller.co.uk
Not only does Keller Foundations offer a wide range of geotechnical solutions, but is backed by extensive experience gained by technology transfer from operations in Europe, North America and Australia.
Ground Improvement Piling Piled Retaining Walls Enlarged Head Piles Innovations
Whether your site has a foundation, stability or ground water problem, Keller has the solution. www.keller-foundations.co.uk
Belfast 44-46 Elmwood Avenue Belfast, BT9 6AZ T: 02890 668827 E: gordon.nimmons@keller.co.uk Coventry Oxford Road, Ryton on Dunsmore, Coventry, CV8 3EG T: 02476 511266 E: derek.taylor@keller-ge.co.uk Design & Layout: Kragedesign.co.uk
London Capital House, 25 Chapel Street, London, NW1 5DH T: 020 7616 7599 E: derek.taylor@keller-ge.co.uk
www.keller-foundations.co.uk www.keller-foundations.co.uk www.keller-geotechnique.co.uk www.phigroup.co.uk www.colcrete-eurodrill.com www.getec-uk.com www.intermesh.co.uk
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Ground Improvement Solutions 3
Ground Improvement Solutions
Vibro Stone Columns
Introduction Ground Improvement Solutions Keller Ground Engineering’s ground improvement systems are designed to reduce the costs of developing problem ground and brown field sites. Their ground improvement techniques are designed to both densify and strengthen weak or poorly compacted soils. Thus saving on construction time and cost by removing the need to by-pass problem soil with piles or deep foundations.
Piling Solutions Keller Foundations provides a comprehensive range of piling systems suited to a wide range of soils and a wide range of building and civil engineering applications. Highly efficient and cost effective, Keller piling systems are also designed to be environmentally friendly by reducing the amount of spoil generated to a minimum.
Index Ground Improvement 3-9
Vibro Stone Columns, Vibro compaction, Dynamic Compaction
Piling 10-15
Displacement Systems: Driven Cast in Situ, Vibro Concrete Columns Replacement Piles: Continuous Flight Auger
Piled Retaining Walls 16-17
Contiguous Piled Walls, Secant Piled Walls, Hard/Soft Walls
Enlarged Head Piles 18
Learn more about the benefits of this innovation
Innovations 19
Environmental Stone Columns, Vibrex, Rigid Inclusions, Liquid Soil
Construction methods Keller’s Vibro Replacement method of constructing stone columns through fill material and weak soils, to improve their load bearing and settlement characteristics, provides an economic and technically sound solution to a wide range of geotechnical and foundation problems.
To construct the stone columns, the vibrator is allowed to penetrate to the design depth and the resulting cavity is filled with hard inert stone, free of clay and silt fines. The required interaction between the stone columns and the surrounding soils, is developed by the stone infill being introduced and compacted in stages, each charge of stone being thoroughly compacted. The stone columns and the confining soils form an integrated foundation support system having low compressibility
and improved load bearing capacity. In cohesive soils, relatively rapid consolidation is achieved through excess pore water pressures being readily dissipated by the stone columns. The stone column layout can be arranged to suit varying combinations of load, soil type and required settlement performance. In general, column spacings are in the range of 1.2 to 2.3 metres beneath main load bearing foundations, and up to 3.0 metres beneath floor slabs.
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Ground Improvement Solutions 5
Ground Improvement Solutions
There are two principal methods for constructing Vibro Replacement stone columns:
Technical application
The conventional Top Feed process
In granular and mixed materials the stone columns densify the surrounding soil. Whereas, in cohesive soils, the stone columns, often stronger than the surrounding soil, act initially as reinforcement with excess pore water being dissipated through the stone column to achieve a rapid consolidation. The confining action of the ground surrounding the stone columns
This is where the hole formed by a purpose built base machine with a vibrator mounted on the mast or crane suspended vibrator remains open and the stone infill is added and compacted by the vibrator in stages, assisted by compressed air. 1. Vibrator penetrates weak soils under action of vibrations and ‘compressed air’ jetting medium and forms a hole to design, usually a competent bearing stratum. 2. After being held at depth for a short time, the vibrator is withdrawn and a charge of stone is placed into the hole.
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2
3
3. The vibrator is reintroduced into the hole, the stone is compacted, forced out and tightly interlocked with the surrounding ground. 4. by adding successive charges of stone and compacting each one, a column of
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very compact stone is built up to ground level. The reinforcing and compacting action of the stone columns serves to significantly improve the load bearing and settlement characteristics of the ground.
The Bottom Feed process This is a ‘dry’ process used to treat unstable soils and/or soils with a high ground water level. 1. With the vibrocat stabilised on hydraulic outriggers, the leaders are elevated to the vertical and the vibrator located on the ground at the stone column position. The skip is charged with stone. 2. The skip travels up the leaders and automatically discharges stone into the reception chamber at the top of the vibrator. 3. The vibrator penetrates the weak soils to the design depth under the action of the vibrations, compressed air and pull-down winch facility.
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2
3
4. At the required depth, stone is released and compacted by small upward and downward movements of the vibrator, the pull-down being employed on the downward compacting action.
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5. W ith stone being added to the system as necessary at any stage of the construction procedure, a stone column of very high integrity, tightly interlocked with the surrounding soil, is built up to ground level.
determines the settlement performance. The bearing pressure offered in weak soil is determined therefore by the settlement requirements of the performance specification. Vibro column spacing and treatment dept is a function of soil type, load and performance criteria. Column spacing generally ranges from 1.2 metres to a maximum of 3 metres and
Soil Types
fully dimensioned stone column layout drawings are produced as part of the treatment design process. A guide to achievable bearing pressures for differing soil types along with a guide to anticipated settlement performance are shown in the table.
Bearing Pressure (kN/m2)
Settlement Range (mm)
Mixed cohesive & granular made ground
100 - 165
5 - 15
Granular made ground - ash, brick, rubble
100 - 250
5 - 25
Natural sands & gravels
200 - 500
5 - 25
Soft alluvial clays
50 - 100
25 - 75
Ground Improvement Solutions 7
Ground Improvement Solutions
Vibro Compaction Construction sequence
Stage 1
Stage 2
Stage 3
At full water pressure, the vibrator penetrates to design dept and is surged up and down as necessary to agitate sand, remove fines and form an annular gap around the vibrator.
Once at depth, the water pressure is reduced and with the vibrator remaining in the ground, sand infill is added from ground level and compacted a the base of the vibrator.
When the required compaction resistance is achieved, the vibrator is raised and more sand infill added and compacted as before. This procedure is repeated until compaction point is built up to ground level.
The Vibro Compaction Process This process is used in fully saturated and very weak soils. Water jetting removes soft materials, stabilises the hole and allows the stone backfill to reach the bottom of the vibrator. This is then compacted and interlocked with the surrounding soil. Vibro Compaction Construction method. This is a compaction process for purely granular soils. It relies on the fact that particles of noncohesive soil can be re-arranged into a denser condition under the influence of
vibrations from specially designed poker vibrators. The action of the vibrator, usually accompanied by water jetting, reduces the inter-granular forces between the soil particles allowing them to move into a more compact configuration. This process is used in fully saturated and very weak soils. Water jetting removes soft materials, stabilises the hole and allows the stone backfill to reach the bottom of the vibrator. This is then compacted and interlocked with the surrounding soil.
After a certain compaction time, the particles are arranged in such a way that the optimum density has been achieved. Keller’s Vibro Compaction process ensures permanent densification above and below the water table. Tidal variations and natural changes in ground water level do not adversely affect the stability of the densified granular soil. Vibro Compaction has been used to achieve in-situ densification of loose sands to depths in excess of 30 metres.
Silt
Sand
Gravel
100 Passing by weight (%)
6
80 Vibro Replacement
60 Vibro Compaction
40 20
0.002 0.006
0.02
0.06
0.2
0.6
Particle size (mm)
2.0
6.0
20
60 100
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Ground Improvement Solutions
Dynamic Deep Compaction
The treatment pattern, energy level, number of passes and phasing of passes must be designed to take into account the soil conditions, type of development and required bearing capacity and settlement characteristics. It is essential to have a thorough understanding of the soils prior to treatment, and to maintain very close geo-technical control during all phases of the work. Typically, insitu testing by borehole or static cone penetrometer, allied with measurement of print volume and site surface settlement is performed during the dynamic deep compaction contract.
Compaction after first pass Compaction after second pass
Dynamic deep compaction (DDC) is an important ground improvement technique, capable of compacting a wide variety of weak soils. The improvement results in increased bearing capacity and reduced settlement. In this way soil conditions on many marginal sites can be improved to the point where shallow foundations can be used without recourse to deep excavation or piling.
Whilst the principle of dynamic deep compaction is of considerable antiquity, it is only in the past 15 years that the technique has been seriously applied on a large scale to the solving of problems by ground improvement. Keller have been actively engaged in successfully applying the system internationally during this period, and are able to offer DDC alongside their other geo-technical techniques to provide a complete ground engineering service.
With DDC, the ground is subjected to repeated surface tamping using a heavy steel and concrete weight. Typically the tamper weighs between 5 and 20 tonnes, dropping in free fall from heights of up to 25 metres. The tamper is dropped a set number of times on a grid pattern over the site to form a pass. Two to five passes on a site, dependent on soil type and condition, can be required. The imprints formed at each drop position are infilled with granular material after each pass.
10 Piling Solutions
Piling Solutions 11
Driven Cast in Situ Piling
First the robust drive tube is fitted with a flat heavy steel shoe and driven to either a length or set in to the bearing stratum. In highly contaminated areas or when driving in to rock a pointed shoe can be used.
Head of Head of Head of Head of concrete concrete concrete concrete
When the required depth has been reached, full length reinforcement designed for axial, shear or uplift loads is placed inside the casing which is then filled with high slump concrete. The casing is then vibrated on extraction whilst maintaining a positive head of concrete.
Nominal Normal diameter working load
Max length
340mm
up to 600 kN
21.5m
380mm
up to 800 kN
25.0m
430mm
up to 1000 kN
25.0m
480mm
up to 1300 kN
25.0m
530mm
up to 1500 kN* 21.0m
650mm
up to 1800 kN* 21.0m * subject to soil
Keller Displacement Piling systems are in growing demand, particularly on contaminated sites where the cost of spoil removal is becoming increasingly expensive. Driven Cast Insitu Highly efficient, the Keller Driven Cast Insitu Pile is designed to make maximum use of the available skin friction and end bearing potential of the surrounding soil. It is capable of achieving high working loads in a variety of weak subsoil conditions, regardless of water table.
Robust, the construction method used is ideally suited to piling ‘brownfield sites’ where obstructions can frequently create programme and cost control problems. The Keller Driven Pile system can frequently drive through obstructions that would create problems for other piling techniques. Environmentally Friendly Apart from the key benefit of not producing spoil, the cast insitu construction process also provides a tight bond to the surrounding soil and limits the potential of vertical migration of soil contaminates.
Soil Types The Keller Driven Pile is ideally suited to granular soils above or below the water table but it also develops high working loads in weak rocks such as marl and chalk. In addition, the pile can be used effectively in silty or sandy clays. The driving resistance and the soil profile are correlated to control the length of each pile to ensure that the design requirements are achieved. Driven Pile Sizes and Capacities Keller Driven Piles are constructed in a range of sizes.
Steel ShoeSteel Shoe Steel Shoe Steel Shoe
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Piling Solutions 13
Vibro Concrete Columns The Keller Vibro Concrete Column (VCC) system provides a quiet, economical, mess free piling solution for sites underlain by weak alluvial or organic deposits such as peat and soft clays.
to be developed at much shallower depths than alternative piling systems and thus generally provide a far more economical solution. Rapid Installation
Extremely quiet with low vibration, the Keller VCC piling system is an environmentally acceptable alternative to driven precast or cast insitu systems. Vibro Concrete Columns are constructed with enlarged bases and designed to develop the full potential of the founding strata. Highly Efficient VCCs are ideal for weak alluvial soils such as peats and soft clays overlying competent founding stratum such as sands and gravels, soft rocks etc. Working loads up to 750kN can be achieved in appropriate soils. The “bulb end� and frictional components of the VCCs enable high safe working loads
Programme benefits can be gained from the highly efficient VCC construction process which can produce over 1,000 metres of concrete column per rig week. Mess Free The VCC system is a quiet low vibrationdisplacement process with none of the mess and high cost of spoil removal associated with continuous flight auger and bored piling systems. Cut offs With the VCC system it is possible to reduce pile heads to cut off level prior to placing reinforcement, thus providing considerable savings in trimming costs and time.
Construction Sequence 1. The purpose built Keller Vibrocat rig is stabilised by hydraulic outriggers and the guide leaders positioned for verticality/ tremmie system is connected to a powerful mobile concrete pump. 2. B efore penetrating, system is charged with concrete. The poker then penetrates the soil until the required resistance of depth has been achieved. 3. T he founding layer, if granular, is further compacted by the vibrator. Concrete is pumped out from the base of the tremmie at positive pressure. After
raising the poker by up to 1 metre, it re-enters the concrete shaft displacing it into a bulb until a set resistance has been achieved. 4. O nce the bulb end is formed, the poker is withdrawn at a controlled rate from the soil whilst concrete continues to be pumped out at positive pressure. 5. O nce completed the columns can be trimmed and reinforcement placed as required. To form an enlarged head the poker is reintroduced into the top of the finished column, whilst maintaining a concrete flow.
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Piling Solutions 15
Continuous Flight Auger Keller’s Augercast Continuous Flight Auger (CFA) piling system provides a quiet low vibration form of piling that is ideal in built-up areas. Keller’s CFA rigs can construct piles in most soils including sands, gravels, silts, clays, chalk and weak bedrock, in high water tables without the need for temporary support systems. Instrumentation Constant monitoring is essential to the success of the CFA system. Keller’s sophisticated in-cab instrumentation allows the monitoring of the movement and position of the auger digging head as well as the rate of flow, amount and pressure of concrete delivered during formation of the pile shaft. Reinforcement The reinforcement cage has to withstand the rigours of placement through the recently pumped high slump concrete. Typically, Keller Augercast Bored Piles are reinforced with a rigid six metre long cage as a minimum. However, there is the ability to install much longer cages as and when required by the design or specification. A specially developed vibrator unit assists with the placing and accurate location of the reinforcement cages. Concrete cover is afforded to the reinforcement by the effective use of Keller’s 75mm plastic ‘sledge’ spacers clipped onto the main bars. Enlarged Head CFA Piles When CFA piles are required to support floor slabs or loads from embankments etc. the connection would traditionally be made through a pile cap or network of ground beams. With the Keller CFA system however, the piles can be installed with insitu, enlarged heads of predetermined diameter (typically around 900mm). This innovative approach can save considerably on slab reinforcement and the cost/time involved in trimming pile heads.
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Piling Solutions 17
Earth Retention Contiguous Bored Pile Walls Bored Pile Walls provide a cost effective method of forming insitu soil retention structures. Keller has wide experience in the design and construction of all forms of piled wall. Dependent upon stiffness and/or water tightness required, Keller offer either hard/ hard or hard/soft Secant Piled Walls and also Contiguous Bored Pile Walls. The latter can also be supplied with ‘between pile’ grout seals to economically provide a high level of ground water control. Bored Pile Walls Using Keller’s state-of-the-art design analysis methods, Secant and Contiguous Bored Pile Retaining Walls can be constructed to form deep basements or retaining structures. Piles are either interlocking or installed leaving a nominal 150mm to 300mm gap between them. Bored Pile Retaining Walls can be constructed in a variety of soils or soft rocks using Keller Rotary Auger Bored Piles, Tripod Piles or Keller Continuous Flight Auger Piling systems.
Keller Piled Walls can be constructed either as free standing cantilevers, propped or anchored walls. Keller also offers fully removable high capacity ground anchors for temporary wall support as a means of speeding up construction programmes for follow on trades. Design of Retaining Walls All Keller Retaining Walls are designed in-house by highly experienced design engineers. Stability and wall displacements can be investigated using a range of design software, which includes finite element programs for use on the larger or more complex projects. The Keller design department is available at all times to provide advice and assistance to clients. Minimising Deflection Where deflection has to be kept to an absolute minimum, Keller can incorporate its compensation grouting system behind most walls to control and correct any movement.
Secant Bored Pile Walls Keller can install hard/soft Secant Bored Pile Walls with piles up to 0.9 metres in diameter.
Contiguous Bored Pile Wall
Wing jet grouting to seal Bored Pile Wall
The walls provide excellent performance in terms of stiffness and ground water control and are ideal for where basements have to be formed in areas of high water table. Keller have full design and construct capability with state of the art rotary piling rigs enabling construction of the deepest of city centre basements in all soil types possible. Secant walls can be combined with Jet Grouting for either underpinning adjacent foundations or sealing the base slab.
Secant hard/soft Bored Pile Wall
Secant hard/stiff Bored Pile Wall
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Piling Solutions 19
Enlarged Head Piles
Innovations Keller Foundations have an impressive record of introducing new systems to the foundations market. This is helped by technology transfer from around the globe where other regions or group companies are particularly experienced in a technique. Using Recycled material Some 50% and rising of Keller vibro projects are now undertaken with a certificated recycled material forming the stone columns and on this housing site (below right) the recycled material was a by product of a waste incinerator i.e. the hard inert materials such as brick and china left as the waste is burnt. These materials can attain a high friction value necessary for maximum integrity of stone columns and of course behave in the ground in exactly the way natural aggregates do. So, if a project has recycling targets to achieve we can try to find an approved material for use in the stone columns. This could be better for the BREEAM rating of the project and may reduce costs.
Keller’s enlarged head piling system provides a very economical approach to the construction of piled floor slabs, rafts and embankments. Piles formed with enlarged heads can be constructed and concreted in situ as an integral part of Keller’s Continuous Flight Auger, VCC and Driven Cast In situ Piling Systems. Enlarged head piles are conical in shape and generally finished at piling platform level. The piles are conventionally reinforce with steel wither protruding from the head or crimped off to provide a clear surface. To meet particular loading requirements, the pile heads can also be supplied with lateral reinforcement.
Reduced punching Shear The enlarged head acts as an integral pile cap and serves to reduce punching shear to give direct contract support to the slab or to provide a uniform bearing pressure via a granular load transfer platform.
Ground Bearing Slab
Subgrade
DPC/Gas Membrane (as required)
Geogrid Reinforced Granular Mattress
Non-suspended slab using a load transfer system
Environmental Stone Columns (ESC) In the long term, developments such as retail parks and supermarkets are covered with hard standing and this surfacing and the buildings are effectively a barrier to downward percolation of surface water. However, it is during the construction period that stone columns could provide a small risk to an aquifer below with flash storms or similar. Keller can mitigate this risk by installing ESC’s. ESC’s have a minimum one metre thick lean mix concrete plug at their base installed with a modified bottom feed vibro rig. This technique prevents contact of the stone column with any permeable stratum which could be an aquifer but allows the benefits of vibro to be taken advantage of. Vibrex Piling was first used by Keller in Poland and brings the benefits of displacement piling without the noise and vibration. The system uses a top vibrator to vibrate a tube in place and thereafter construct a pile in the same way as a Driven Cast In Situ Pile.
Rigid Inclusions (Inclusion Rigide) is a system which has been offered by Keller France for many years and utilises a concrete column or pile which is topped off by a minimum 3m long stone column. On top of this improved zone conventional floor slabs or pad foundations can be placed. This enables sites with deep deposits of very soft clays and organic bands, normally unsuitable for conventional ground improvement, to be developed utilising the advantages of ground bearing slabs. Several high profile sites for international clients have been undertaken with this system in mainland Europe.
Liquid Soil is technology that Keller Foundations will be sharing around Europe where the pressure to avoid spoil removal is less. This system was developed to treat piling spoil enabling it to be re used either as drainage excavation infill or as the soft piles in secant walls. By carefully mixing the patented chemical we can create a material ranging in strength from 0.5N/mm2 to 10N/mm2 according to the end use. If you feel your project could benefit from any of these systems then contact us on techinfo@keller.co.uk