Members of the Keller team from around the world will be presenting technical papers at this conference.

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Traction pile calculation – cone effect

Pile calculation is particularly complex when it’s necessary to consider traction resistance. The French Standard for pile design NF P 94 262 describes two methods that we will analyze and compare to define their relevance and limits of application. These two methods will also be compared to a numerical calculation to determine whether the mechanisms highlighted by numerical modelling are consistent with the two analytical approaches.

Léo Quirin
Design Office Manager
Keller Fondations Spéciales

Multiphase deep vibro solution for biodiesel plant expansion in Singapore

A state-of-the-art biodiesel plant in Singapore proposed its expansion plans in 2018 comprising various structures such as steel storage tanks , pipe racks, and ancillary structures. The foundations of storage tanks are to be designed to satisfy a stringent differential settlement criteria of 13mm over 10m of circumference prescribed by API standard 650, while other structures are to satisfy a criteria of 30mm over 10m span. The soil profile consists of a top layer of firm to stiff silty clay, followed by loose to medium dense sand. The sand layer is underlain by firm marine clay followed by stiff-very stiff clay. Underneath the firm clay layer are residual soils of Jurong formation with SPT N more than 50. An innovative 3-phase deep vibro techniques scheme is adopted to treat the 3 main types of soil in the cross section: Phase 1 Vibro stone columns to treat bottom firm clay; Phase 2 Vibro compaction of over-lying loose-medium dense reclaimed sand; Phase 3 Vibro stone columns to treat firm to stiff silty clay near the surface. Hundreds of Cone Penetration Tests (CPTs) are carried out to capture soil variation and design the treatment depths precisely catering to the varying soil conditions. In this paper, the deep vibro techniques solution would be described with predicted settlements compared with actual monitored settlements during hydrostatic test. With deep vibro techniques, estimated carbon savings is about 75% compared to a driven piling solution, the details of which are presented.

Selvaganesh Selvaraju
Deputy Design Manager
Co-Authors: ZhiWei He & Kam Weng Leong
Keller Foundations (S E Asia) Pte Ltd

Design of ground improvement in the upcoming EN 1997-3, Clause 10

The current EN 1997-1 has only a very short and rather unspecific clause 5.5 about the design of ground improvement (GI) covering only half a page. This does not represent the current geotechnical reality where plenty of ground improvement technologies have a vast range of applications. Ground improvement reaches from dynamic compaction and vibro compaction over improvement of the ground with granular columns or rigid inclusions up to bulk solidifications with soil mixing, grouting and jet grouting or even ground freezing. Therefore the future EN 1997-3 will contain two whole chapters (clauses 11 and 12) dealing with the design of GI. Work on this started with Evolution Group 14 (EG14) as part of CEN TC 250 SC7 and its report from 2015 and has evolved since then through a number of iterations and discussions between the project team drafting the code and the task group advising and supporting this work. The result of this efforts, that will be made available in the near future, is a comprehensive design approach to GI based on a system of design models (2 classes x 2 families = 4 models) to cover all possible technologies for GI for ultimate and serviceability verifications and 3 design models for groundwater control. This will provide sufficient guidance for existing technologies as well as the necessary flexibility to accommodate new methods of GI. The authors of this paper as convenor and members of the relevant working group and task group will explain this new approach and the set of rules coming with it, both for ultimate limit state as well as for serviceability limit state design.

Paul Pandrea & Cecilia Bohn
Keller Holding GmbH, Offenbach, Germany
Cyrille Plomteux
Menard SAS, Orsay, France
Norbert Vogt
Technical University of Munich, Germany

Measurement of pore water pressure in saturated sand during deep vibro compaction

The role of different mechanisms responsible for the rearrangement of soil particles during deep vibro compaction (vibroflotation) is an extensively discussed subject. Nevertheless, the literature remains inconclusive on this topic. In different scientific papers, a temporary decrease of shear strength due to excess pore pressure (soil liquefaction) or a specific grain acceleration (soil fluidization) are pointed out as crucial reasons for the compaction effect. Large-scale experimental field tests were realized on a construction site to understand the subsoil processes during deep vibro compaction better. Special tests were designed and carried out to disclose the role of the mechanisms leading to the compaction effect. In these experiments, pore water pressure measurements were executed during the vibrocompaction process using a CPTu cone positioned close to the compaction device. The tests were realized in homogenous reclaimed sand fill, under fully saturated conditions. This paper focuses on the experiments wherein pore water pressure measurements were conducted. The testing concept and the test procedure are presented. Furthermore, the registered pore water pressure is compared to the vibrocompaction process parameters. Based on the test results, the mechanisms linked to the compaction effect are pointed out.

Peter Nagy 
Design Engineer
Keller Grundbau Ges.m.b.H.

In situ chemical oxidation/reduction using the jet grouting technique (HaloCrete®)

In 2018, after more than 8 years of development, Keller conducted the first remediation work according to the new HaloCrete® remediation technique. HaloCrete® extends the field of application of jet grouting to enable in situ treatment of sites contaminated with chlorinated hydrocarbons. Due to the high-pressure jet, the remedial slurry is mixed homogeneously with the contaminated soil, below as well as above the groundwater table. As the source of pollution can be treated in situ, no additional measures like excavations or long-term groundwater treatments are required. 
In 2012, after some preliminary tests, the first extensive research work started with a series of lab experiments examining basic behaviour of contaminant, binder and reductant as well as the leaching behaviour of the simulated columns. Because of the promising results, large-scale field test using typical jet grouting equipment were executed. In addition to the challenging test setup, e.g. the management of a constant ground water flow, the development of verification procedures suitable for on-site usage was one of the most important tasks. Consequently, the main research process was completed applying the new technique to a former laundry in Austria, heavily contaminated with chlorinated hydrocarbons. HaloCrete® was part of a combined solution of soil decontamination and retaining structure. In addition to the preparatory works required for Halocrete®, also logistic and legal challenges due to working on a narrow site with potential harmful materials will be described in the paper. Other key aspect discussed are the possibilities and limitations of extensive quality control to verify a successful remediation.

Authors: Peter Freitag1, Alexander Zöhrer1, Thomas Reichenauer2
1)    Keller Grundbau GmbH, Guglgasse 15, 1110 Vienna, Austria
2)    Austrian Institute of Technology, Center for Health & Bioresources, Konrad-Lorenz-Strasse 24, 3430 Tulln, Austria.

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