With over 140 years of ground engineering experience Keller's contribution in the Gulf has been significant since the 1970s, as they find themselves constantly carrying out value engineering to benefit their clients with a cost effective package. Construction World learns more ...
About the Company
Keller Group plc, headquartered in London and listed on the London Stock Exchange since 1994, is the world's largest specialist ground engineering contractor. From its origin in 1860 to the present day, Keller has been built on two things above all - engineering excellence and a commitment to continual innovation.
Keller's business is the solution of soil and foundation problems for the construction industry. From its principle operating centers in Europe, North America and Australia, Keller is well established in over 30 countries around the world. The establishment in the Gulf has been since early 1970s and all offices in the GCC countries report to Keller Grundbau GmbH (overseas division) based in Offenbach, Germany. With over 30 years of experience in this region gives Keller that competitive edge of being reliable, backed with an extensive reference list of projects of every dimension.
Keller's unique combination of resources and experience backed by size and financial strength enables the Keller Group to undertake the full range of ground engineering solutions worldwide.
Keller's services are used across the entire construction spectrum from industrial, commercial and housing projects to infrastructure construction for dams, tunnels, transportation and water treatment plants. Keller also meets the specialized geotechnical requirements relating to the renovation of existing buildings and the increasingly important environmental contracting market.
The Keller group turnover in 2004 reached a record high of 881.9 million Euros.
Keller's prime operating fields in the Gulf
Keller has a record of innovative developments across a wide spectrum of geotechnical engineering techniques. Detailed below are Keller's operations in the Gulf in the field of geotechnical engineering.
Keller's prime contribution to the ground engineering industry has been the development of the 'depth vibrator' the state of the art technology that is used in the direct densification and reinforcement process of soils at depths that cannot be improved by any conventional means. Currently the most modern of the Keller vibrators fixed on custom built rigs called the "Vibrocat" can be inspected for faults by our specialists in Germany while the rig is being operated in another country - all you need is a mobile phone and modem.
Ground improvement by VIBRO Techniques
Ground improvement techniques are used to prepare the ground for new construction projects and to reduce the risk of liquefaction in areas of seismic activity.
Keller, with its Vibro techniques offers for soil improvement works a complete design and build package and has won several prestigious jobs by offering economical soil improvement schemes. Amongst its very prestigious clients who have benefited from Keller's value engineered product are Nakheel on the Palm and IBN BATUTTA Mall, DUBAL with its various POTLINE projects, AL-FUTTAIM with its City Centres in Dubai and AJMAN, the GHURAIRS with their 50m high Grain Silos and Flat Storage facilities and DEWA for power JEBEL ALI Power Plants G, K1 and K2.
The vibro-technique offers an excellent alternative to piling and has been found to be 20 to 30% more economical in most cases where it finds its application. For building foundations, Vibro-technique has been applied up to 14-storeyed structure; the famous Regency Intercontinental hotel in Manama, Bahrain.
The prime advantages of the vibro-techniques include:
only naturally occurring material used that only improves in strengthen with time
offers seismic stability by reducing soil liquefaction risk
enhances soil bearing capacity and slope stability
requires short mobilization and
execution periods
allows foundation construction to start almost immediately
allows flexibility incase of design changes
can treat almost the entire range of soil types
can reach down to 50m if required for granular soil densification only
can reach down to 20m with vibro-replacement (stone columns)
The 'depth vibrator'
This state of the art tool is cylindrical in shape and is typically between 3m and 5m long and weighs approximately 2 tons. The core element of the vibrators is the electrically driven eccentric weight, which induces horizontal oscillation of the vibrator. Depending on the depth to which ground improvement is to be carried out, the vibrator string is assembled using hollow extension tubes. The complete vibrator assembly is then suspended from a crane or mounted on custom built base machine (i.e. the Keller vibrocat).
The Techniques
The depth vibrator can be used for three distinct techniques, which differ both in their soil improvement and in their load transfer mechanism. The foundation design is therefore frequently developed in close cooperation between both the consultant's geotechnical and structural engineers and Keller.
The Vibro Compaction technique compacts the granular soils with negligible fines content by rearrangement of the soil particles into a denser state. The effective ground densification achieved at depth is evident by the overall ground subsidence which can be up to 10% of the treated depth. This technique has been applied successfully for onshore and offshore works.
The Vibro Replacement technique builds load-bearing columns made from gravel or crushed stones in cohesive soils and granular soils with high fines content. The depth vibrator penetrates the ground to the designed depth by water jetting and while the fines are being washed out, the coarse aggregate is filled in to replace them, resulting in a composite column of stones and existing soil in the ground. Stone columns also have been installed largely on onshore but also for offshore works.
The this technique creates structural foundation elements in the ground, which allow comparatively high loads to be safely carried by soils where no adequate lateral support for Vibro Replacement columns can be mobilized. Structural foundation elements can be developed in the following ways:
a. Grouted stone columns (VSS)
b. Premixed Grouted stone columns (FSS
c. Vibro Concrete Columns (BRS)
Grouted stone columns are developed by simply introducing cement grout while a stone column is being constructed.
Premixed grouted columns are constructed by feeding coarse-grained concrete mix of strength 15 to 20Mpa instead of just stones as in the construction of stone columns. The custom built vibrocat is used in this process so that the premix is discharged at the tip of the vibrator and the column is built from bottom to top.
Vibro concrete column is constructed by pumping flowing concrete of 25Mpa strength through the tremie attached to the vibrator. The toe if the vibrator is enlarged by repeated retraction and penetration of the vibrator.
In the Gulf, Keller has executed to date more than 1000 Vibro-replacement and compaction projects dealing with loads as light as 50kPa to 400kPa. Keller currently seeks an opportunity to introduce the VSS, FSS and BRS techniques that are mere extensions of the vibro-process and can provide cost effective alternatives to conventional bored piling techniques.
Specialty grouting
Keller has various options available for application of grouting techniques, which are usually required for specialized jobs. Specialty grouting strengthens target areas in the ground and controls ground water flow through rocks and soils be reducing their permeability.
Piling
Piling involves the installation of structural elements to transfer foundation loads through weak soils to stronger underlying ground. The most popular piling system adopted in this region is cast-in-situ bored piles. Although major projects using cast-in-situ driven piles have been executed in Saudi Arabia but very rarely.
Mini Piles
Mini piles of diameter ranging from 150 mm to 300 mm. can be a very effective solution for locations where conventional piling system cannot be adopted. The company has adopted mini piles in cases where building floors had to be increased and additional loads were to be imposed on existing foundations.
Deep Soil Mixing
This is another ground improvement technology available with Keller more suited for very soft cohesive soils. In this process cement or lime is used in wet or dry state depending on the design and mixed into the soft soil with a special tool. There are some projects in UAE where its application is being reviewed but it is yet to prove its viability in comparison to the vibro-techniques. It is interesting to not that wet deep soil mixing is offered extensively by keller in Poland to build foundations for buildings and highway bridge piers.
Keller's win-win formula in the Middle East
Ground Engineering is in great demand in a region like the Middle East, where 60 to 70% of the habitation is on coastal plains. The aggressive ground conditions and climatic characteristics throughout the region are very exacting on foundation contractors and Keller with its existence in the region for more than 30 years has acquired vital understanding of the existing soil conditions and the environment to be in a strong position to propose appropriate solutions to complex soil problems.
Keller's success story is attributed to:
Its' long serving employees with global experience and local knowledge
Decentralized regional structure bringing them closer to Clients
Acknowledged industry experts in ground behavior
Knowledge & access to a wide range of processes to produce cost-effective solutions.
Keller is well accepted in this industry as a company with global experience and strong local knowledge and presence.
Construction World 2005
