6 BARRIERS IN APPLICATIONS OF NEW
TECHNOLOGIES TO PRACTICES
A number of new technologies and new design meth- ods have been developed in Japan, as have been mentioned so far. However, it seems that there are dif- ficulties or barriers in applying the new developments
Figure 64. Ongoing analysis of penetration of an open-
ended pipe pile into the ground from the ground surface.
Japan Railway code and code for Port and Harbour facilities. In addition, there are several local pile design codes. Even if a pile is constructed in a site, bearing capacity of the pile estimated using the above codes are different. This situation often confuses pile designers and pile engineers. In the authors' opinion, the safety factor could be varied according to type of superstructure, but the design codes to estimate the bearing capacity should be unified.
The current pile design codes sometimes refuse the use of new developments in practice. For example, in the Japan Road Association code, it is specified that all external loads on the foundation must be sup- ported by piles alone. Therefore, use of piled rafts for foundations of bridges is not possible at present, although most actual bridge abutments are piled rafts
Figure 63. Mobilised coefficient of friction along the inner
pile shaft.
to practices, because of a number of reasons,
including:
i) too many codes or specifications
ii) codes or specifications are not flexible to accom-
modate new developments
iii) excessive persistence of governmental officers and
foundation designers on codes or specifications
iv) current system of approval or authorisation of
bearing capacity of new pile type
v) foundation and superstructure are designed sep-
arately
vi) lack of education of foundation engineering to
students.
There are four main pile design codes in Japan:
Japan Road Association code for bridge foundations, Architectural Institute code for building foundations,
170
from a view point of their bearing mechanisms.
Safety factor used for piles is typically three in the design codes. If a load test is performed in a con- struction site, safety factor of 2.7 can be applied to the piles in the site. However, number of load tests is not considered to reduce the value of safety factor more rationally. If the number of load tests in a site is taken into account in pile design properly, rapid pile load testing will play an important role in pile design and guarantee the safety of the constructed foundation.
In the first author's experience, government offi- cers and pile designers tend to persistent excessively to the design codes, even if a load test is carried out. If the bearing capacity of the pile is less than the value from the design codes, most government officers and pile designers have no idea to respond it. Sometimes they doubt of the reliability of the test or tend to neg- lect the test results. Allowance of the number of load tests in the design may improve such situation. And, education of new design concepts to government offi- cers and pile designers would be needed.
As mentioned earlier, if new pile construction
method is approved or authorised, pile load test is not needed for the constructed piles. This system should be improved, because it is widely recognised that bearing capacity of piles in a site is variable largely. Pile load tests on a few piles may be useful to confirm the performance of the constructed piles, even if they have been authorised.
Foundation and superstructure are designed sep- arately in usual. Designer for superstructure designs the superstructure assuming that not settlement of foundation occurs. Much more communication between structural designer and geotechnical designer is of a benefit for rational design. And a design tool for design of whole structure including superstructure and foundation structure will be useful.
In most text books of soil mechanics used in uni- versities in Japan, description and discussion about pile foundation seems to be insufficient. Methods to estimated deformation of pile foundations and pile dynamics are scarcely mentioned. Education of deformation analysis of pile foundations to students would be desired to accommodate new design frame- works where estimation of deformation of the foun-
dation structure is one of important design issues.
7 CONCLUDING REMARKS
Trend of research and practice of pile foundations and new developments of pile technologies in Japan were reviewed. And, discussion was made to utilise new technologies in practice more effectively.
The authors would like to express their appreci- ation to JASPP, COPITA, Civil Engineering Research Institute for Cold Region, Japan Pile Corporation, System Keisoku Corporation, Marubeni Construction Material Lease Corporation, JibanShikenjo Corpora-
tion for their supports in summarising this paper.
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Kusakabe, O. & Matsum
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