Costes de los eslabones del canal moderno de distribución

There are conflicting requirements when preparing a foundation code. From a viewpoint of statutory control under the Buildings Ordinance, the CoPF should be simple, rigid and conservative to make the approval of foundation plans a simpler task. From a technical point of view, rigid procedures and conservative guidelines

will stifle the advancement of foundation technology. In particular, the duration needed for obtaining approval of new foundation techniques is often too long to be acceptable to the developers or contractors.

The slow development of jacked piling is a good example to illustrate this point. 900-ton pile jacking machines with servo-control, which were perhaps the heaviest and most advanced pile jacking machine in the world at that time, were used in Hong Kong in 2001 for installation of jacked H-piles. A larger, 1050-ton pile jacking machine, again possibly the world record at the time, was introduced to Hong Kong in 2011 for installing jacked H-piles for a private residential development in Tai Po. After some initial teething problems, the technology for installation of jacked piles is now fairly mature (Li & Lam 2011). Jacked H-piles have been used successfully for the foundations at 8 sites in Hong Kong (Li & Lam 2011). Trial jacked H-piles with very satisfactory performance have also been constructed recently in 2012 at a site in Yuen Long. Hong Kong had perhaps led the advancement of jacked H-piles in the past because jacked H-piles with such a design high capacity were seldom if ever installed in other countries. Unfortunately, jacked H-piles are still not regarded as a recognized conventional pile type in the checking process by BD. If the developer/designer/contractor wants to adopt jacked piling for private development projects, the additional time required to be spent before consent for working piles can be granted can easily be 5 months or longer. Few developers can tolerate such a delay in their development. This has a significant deferent effect on advancing the foundation technology. In Macao, the approval time for accepting a new foundation technology is much shorter. The technology of jacked piling developed in Hong Kong has been “exported” to Macao in recent years and quickly become more advanced there, with high-capacity jacked spun piles also used for supporting tall buildings (Yeung 2013).

Streamlining the approval process to reduce the additional time needed for obtaining consent for working piles will provide a greater incentive for developer/designer/contractor to use newer technologies. Some suggestions for streamlining the process are:

a. Local experiences gained from public works projects can also be considered in assessing the need for trial piles. If there are sufficient experiences gained for the new technology in Hong Kong from other government buildings or civil engineering projects, waiving the requirement for trial piles or granting of consent of working piles and trial piles at the same time may be considered.

b. Foundations completed using new technologies can be abandoned if they fail to achieve the expected performance. The consequence of allowing new foundation types to be installed is not great from a view point of public safety as long as the developer/designer/contractor are well aware of the risk and prepared to replace the unsatisfactory piles if necessary. If so, the granting of consent for trial pile installation and partial if not full consent for the working piles at the same time may be a viable way to encourage the use of new foundation technologies.

7 CONCLUSIONS

Some guidelines in the current CoPF have weakness which may not be defensible under the scrutiny of soil mechanics principles. Some suggestions for updating the foundation codes are given in the paper. It is hoped that the paper can encourage further discussions by fellow engineers in Hong Kong to make the revised foundation code a document that is simple, suitably conservative and sufficient flexible to encourage wider use of new foundation technology.

REFERENCES

Barkan, D.D. 1962. Dynamics of Bases and Foundations. McGraw-Hill Book Company. Buildings Dpeartment (BD) 2004. Code of Practice for Foundations.

Geotechnical Engineering Office (GEO) 1993. Geoguide 1 – Guide to Retaining Wall Design.

Geotechnical Engineering Office (GEO) 2006. GEO Publication no. 1/2006 - Foundation Design and Construction.

Holmes, D.G., Keung, C.P.Y. and Li, K.S. 1990. Heavy foundations in karstic limestone. Proc. Conference on Deep Foundation Practice, Singapore, 105-110.

Hope, S., Young, S. and Dauncey, P. 2000. Airport railway pile tests. Proc. HKIE Annual Seminar – Foundations, 145-155.

Hill, S.J., Littlechild, B.D., Plumbridge, G.D. and Lee, S.C. 2000. End bearing and socket design for foundations in Hong Kong. Proc. HKIE Annual Seminar – Foundations, 167-178.

Li, V. 2007. Use of plate load test for design of shallow foundations – a suggested alternative practice. Bridging Research & Practice – the VLA experience, Centre for Research & Professional Development, 191-199.

Li, V. and Lam, J. 2011. Development of jacked piling in Hong Kong. The 2nd VLA Seminar – New Developments in Jacked Piling, Centre for Research & Professional Development, 88-116.

Li, V. and Lam, J. 2006. Discussion on Observations on using the energy obtained from stress-wave measurements in the Hiley formula. HKIE Transactions, 13(2), June, 63-64.

Li, V. and Lam, J. 2007. New criteria for formulating final set table for high-capacity steel H-piles. Bridging Research & Practice – the VLA Experience. Centre for Research & Professional Development, 213-237. Li, V. and Lam, J. 2012. When can we stop using drop hammers for driven piles?. Bridging Research &

Practice – the VLA Experience: Volume 2, Centre for Research & Professional Development, 75-95. Li, K.S., Lam, J. and Lee, P.K.K. 2003a. Design and Construction of Driven and Jacked Piles - Chapter 1:

General Principles, Centre for Research & Professional Development, 1-22.

Li, K.S., Lam, J. and Lee, P.K.K. 2003b. Design and Construction of Driven and Jacked Piles - Chapter 2: Jacked Piles. Centre for Research & Professional Development, 23-50.

Li, Victor & Lau, C.K. 2012. Some new developments in foundation design and construction in Hong Kong. Proc. HKIE Joint Structural Division Seminar, 63-79.

Shiekh, S.A. and O’Neill, M.W. 1988. Structural behavior of 45-degree underreamed footings. Transportation Research Record, Vol.1119, 83-90.

Terzaghi, K. and Peck, R.B. 1968. Soil Mechanics in Engineering Practice, 2nd Edition, John Wiley & Sons. Whitman, R.W. and Richart, F.E. 1967. Design Procedures for Dynamically Loaded Foundations. Research

Report, The University of Michigan.

Yeung, A.T. 2013. Non-percussive installation methods for precast prestressed concrete spun piles. Proc. Conference on Foundations: State-of-the-Practice, 143-157.

1 INTRODUCTION

Pile foundations are often required to support tall buildings and heavy infrastructures necessary to accommodate the rapid economic and population growth of Hong Kong. The common types of piles being used in Hong Kong include large-diameter bored piles, barrettes, steel H-piles, prestressed spun high strength concrete pipe piles (PHC piles) and mini-piles. The construction of large-diameter bored piles, barrettes and mini-piles requires excavation, installation of a reinforcement cage and in-situ concreting or grouting. The construction process is thus quite involved. Prefabricated piles, such as steel H-piles and PHC piles, are typically installed by preboring or percussion. The construction of a prebored socketed steel H-pile requires preboring, insertion of a steel H-pile, grouting and removal of casing. PHC piles are seldom installed by preboring in Hong Kong. Again, the construction process is quite involved. Installation of these prefabricated piles by percussion is most economical if the geological conditions are favorable. However, the construction method inevitably induces vibration, noise and air pollution problems despite of the stringent environmental requirements promulgated by the Hong Kong SAR Government. The limits on pile driving hours promulgated by the noise permit system operated by the Environmental Protection Department may reduce the adverse noise impact to sensitive receivers. The use of hydraulic hammer may alleviate the air pollution problem. However, the vibration problem remains. From a geotechnical standpoint, the founding conditions of a driven pile are not fully revealed. Although every driven pile is accepted using the Hiley formula in Hong Kong, there is no guarantee on its engineering performance, in particular its load-carrying capacity and the load-settlement characteristics. In fact, the engineering performance of a driven pile has to be evaluated by a pile integrity test, a pile dynamic analysis and/or a full-scale pile load test. Because of cost and time implications, these tests cannot be applied to every pile in a project. The energy impacted on a pile by the pile integrity test is probably inadequate to penetrate the full length of the pile. Therefore, the test is probably inappropriate for the evaluation of the founding conditions of the pile. Typically, pile dynamic analyses are performed on approximately 10% of the piles installed and full-scale pile load tests are performed on 1% of the piles installed. Therefore, there is a significant possibility that defective piles are not identified. The technique of hydraulic jacking can rectify most of these environmental problems and quality control problems. In this paper, the background of jacked piles is given. The experience of installing PHC piles by hydraulic jacking in Macau is also presented.

Installation of Prestressed Spun High Strength Concrete Piles by