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Quality assurance and testing

Topic One

Daniel Goossens, moderator of Topic One.

Introduction

The subject of this session is of growing interest to the construction industry, because quality has become very important in a very competitive market.

At the DFI 94 conference in Bruges most of the papers touched only briefly on the question of quality assurance. At the DFI 96 conference in Mumbai we saw the introduction of papers which paid more attention to quality assurance in deep foundations. DFI 98 in Vienna will touch off a discussion about real quality assurance, which will take into account the total geotechnical situation and even the total construction.

Pile testing

Several papers deal with the continued evolution of pile testing. Results of static and dynamic load testing on steel pipe piles and precast or cast in situ concrete piles are discussed, as well as the parameters which influence them. Alternative testing (load cells on or near the bottom of the pile), or testing on alternative pile types (auger piles with cement grouting) may provoke an interesting discussion.

Bored cast in situ concrete piles

Testing and instrumentation of bored piles will be discussed. The piles can be socketed in rock, post-grouted or with an expanded base.

Quality assurance in general

Selected papers deal with monitoring procedures and laboratory tests, but also with general items such as QA strategy and critical aspects of construction design and execution, causes of construction damages, customer confidence and QA for the whole project.

New developments

New techniques, for example the vibro concrete column technique and the slurry sludge detector, will be highlighted.

Topic Two

Codes and standards

Flor de Cock, moderator of Topic Two.

Over the last decade, tremendous efforts have been made in the elaboration of European Codes, some covering design, others execution of work in the geotechnical field. Within the framework of Technical Committee CEN/TC250, the EU Commission aims to bring about the harmonisation of codes in construction. This will be followed up by the development of codes of execution for geotechnical work (Technical Committee CEN/TC288) which begun in 1991 at the urging of the EFFC.

The situation today is both hopeful and challenging: Various codes or parts of them are ready for adoption, for example those covering diaphragm walls, bored piles and sheet piles, whereas in other areas (for example, design and execution of soil improvement techniques) they require further development.

The debate on the content and procedures for structural Eurocodes, in particular Eurocode 7, is still going on. Various national commissions are also still trying to draw up their own national application document and find a way to adjust, adapt or implement national rules within the EC7-framework.

One of the most important questions remaining, which people have been scared to raise so far, concerns the way future research work and new technologies will be implemented in updates of the Eurocodes.

Papers submitted for discussion within this section of the DFI Conference cover most geotechnical work within the Eurocode. They cover the code as it exists at present and new ways of implementing it plus the results of new research. Under the heading TC250/Design, papers cover the design of steel sheet piling, the Polish piling code and dynamic pile testing. Sheet pile walls and bored piles will be discussed under TC288/Execution. New research covers work in steel piles in chalk, a lateral-loaded pile model and surcharge loading on piles in clay.

The rather limited number of contributions and presentations in this section is likely to be counterbalanced by forceful discussion on the sense or nonsense of codes and standards in general, and the harmonisation of interstate codes, such as the Eurocodes, in particular.

Provocative statements, such as 'Codes are only needed by the uneducated', or 'Codes put the brakes on renovation', may be highlighted during the session debates. Not all outstanding problems are likely to be resolved during the DFI event.

Nevertheless, one has to take maximum advantage of events such as the DFI conference, which offers geotechnical experts from both sides of industry, as well as scientists, the opportunity to express and exchange opinions on such important matters as codes and standards. Be there, and raise your voice.

Topic Three

Environmental issues

Professor Pedro Seco e Pinto, moderator of Topic Three.

Introduction

High population growth coupled with limited land and energy resources draw our attention to the need to avoid environmental deterioration. With these problems as a backdrop, the UNCED Conference on Official Develoment Assistance in Rio de Janeiro in June 1992, and the Kyoto conference last year, have created a forum to discuss ideas and courses of action for the 21st century.

Underpinning all action is the need to integrate knowledge gained from various disciplines such as natural sciences, the humanities and the social sciences.

An emerging topic of particular relevance to this audience is environmental geotechnics, which covers a range of subjects from air pollution to water, soil and underground water pollution. These subjects interact with the established geotechnics branches such as soil mechanics, rock mechanics and engineering geology.

The International Society for Soil Mechanics & Geotechnical Engineering is a co-sponsor of the DFI conference. Its technical committee TC5 on environmental geotechnics has played an important role in preparing a comprehensive report covering the following topics: (i) monitoring systems; (ii) contaminant migration test methods, modelling and monitoring; (iii) waste stability; (iv) controlled landfills; (v) contaminated land reclamation; (vi) assessment of geo-environmental hazards from dredging materials; (vii) assessment of geo-environmental hazards from non-traditional geotechnical construction materials; (viii) long term behaviour of containment systems including risk assessment; (ix) dynamic behaviour of stored wastes and lining system of landfills; and (x) landfill behaviour under extreme loading- assessment of possible scenarios.

The final edition of the TC5 report will be discussed during the 3rd International Congress on Environmental Geotechnics to be held in Lisbon 7-11 September 1998.

At Vienna, conference papers in the environmental geotechnics session cover three themes: energy piles for heating buildings; prediction and control of vibrations; and waste mechanics.

Energy piles for heating buildings

The use of geothermal energy from the ground for environmental and economical reasons has become more popular.

The piles contain plastic pipes and the energy derived from the ground is compressed by a heat pump, thus generating heat which is transmitted through the heating circuit of the building.

This system provides two main benefits: savings of up to two thirds of conventional heating costs, and environmental protection by providing clean and self-renewable energy.

For the economical operation of energy foundations, a normal ground temperature of at least 10C is required, and there is no limitation on the depth of piles or diaphragm walls. Pile parameters, such as diameter, depth, thermal properties and spacing, play an important role in the heat absorption process.

To analyse the effects of temperature changes, the piles are fitted with pressure cells, fissuremeters and thermo-elements.

The shaft resistance of energy piles is not affected by the heat absorption process, but the surface of the pile shaft should not be exposed to a temperature below freezing point. Fine grained soils with a high content of active clay mineral are especially critical.

The optimum spacing of piles in a pile group depends on the available thermal storage capacity of the surrounding soil, and on the pile parameters (diameter, depth and thermal properties).

Predictions of vibrations

The use of sheet piles and concrete piles is becoming more popular in urban areas but can cause damage to buildings and inconvenience the public. For this reason, prediction and measurement of vibrations is becoming increasingly popular.

Damage from piling vibrations is related to the tension wave and depends on the extension values. Relationships to describe vibrations have been proposed by Duval et al (1953), Ambraseys and Hendron (1968), and Medvedev (1968).

Waste mechanics

The engineering of waste mechanics covers the assessment of the static and dynamic stability of waste structures, the evaluation of deformation and settlement of waste structures, and the behaviour of embedded structures in landfills.

To investigate waste landfill, the following techniques have been used: aerial photography, boreholes, SASW, sampling, standard penetration tests (SPT) and cone penetration tests (CPT).

For municipal solid waste, the following parameters are commonly defined: unit weight, water content, permeability, shear strength and settlement behaviour.

For the determination of shear strength by laboratory tests representative grain size distribution samples are needed. The shear parameters of municipal solid waste are determined from large triaxial or direct shear tests. The definition of failure is difficult as the waste hardens with deformation. Consequently for the definition of shear parameters, the deformation criterion is used.

For improvement of waste disposed in landfills, preloading, sand compaction piles, dynamic compaction and pressure injection stabilisation can be used.

The efficiency of dynamic compaction can be assessed using vibration measurements, standard penetration tests, cone penetration tests, dynamic cone penetration tests, plate loading tests or borehole pressuremeter tests.

References

Duval, W.S. (1953) 'Strain Waves Shapes in Rock near Explosions'. Geophysics, vol. 18, no 2.

Medvedev, S.V. (1968) 'Evaluation of Seismic Safety during Blasting Operations in Mines'. Bulletin of the Earthquake Research Institute, Vol. 46, pp. 687-696.

Moura Esteves, J. (1993) 'Controlo de Vibracoes Provocadas por Explosoes na Industria da Construcao LNEC.

NP-2074 (83) 'Valores Limites de Velocidade de Vibracao de pico (mm/s)'.

Seco e Pinto, PS, and Rodrigues, LF. (1989) 'Pile integrity tests for Boinas Bridge' (in Portuguese). 3rd National Geotechnical Congress, Oporto.

Specifications DIN 4150 (1986) 'German specifications relating to vibrations'.

Topic Five

Case Histories

Christopher Thompson, moderator of Topic Five.

At least 26 papers have been submitted as case histories for the proceedings of the conference. It is intended that 15 of these will be presented by their authors. The papers have been arranged into categories of: Research and Development; Design and Construction, Pile Load Tests (PLT); and Design and Construction - Other.

Some very interesting and innovative research case histories are described. These include data on: extendable blade piles; hollow tapered piles; and the use of microwave energy to strengthen soils.

Helpful information is provided in other research type papers on: the correlation of Standard Penetration Tests with the bearing capacity of sands; the use of 3-D Finite Element Analysis for the seismic design of pile foundations; and comparisons of Statnamic and Static Load Tests.

There are numerous papers which describe the use of PLTs in design and construction. Some of these include the use of PLTs to obtain parameters for the design of bored caissons in a variable sequence of volcanic rocks; correlation with CAPWAP analyses which were then used to determine the adhesion values of consolidated alluvium;

lateral pile capacities in stiff glacial tills; and the increased pile capacities from values that would be estimated from unconsolidated, undrained triaxial tests in a glacial lake deposit.

Other papers presenting innovative approaches to design and construction deal with: small diameter rock-socketed threaded pipe piles to underpin a concrete tunnel; a combination of top down substructure construction and a piled raft foundation in an urban area; use of a bored pile cofferdam to resolve problems caused by the collapse of subway station tunnels; and complicated deep excavation techniques to limit movements in a confined urban area.

Another paper of interest documents the history of the construction approaches and the difficulties encountered over a 100 year period developing an urban site with difficult Glacial Outwash deposits.

The papers are helpful to all involved in the design and construction of deep foundations and excavations. They present innovative approaches to difficult founding conditions that can be applied in other situations.

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