Quality assurance and reliability of pile foundations (PI: Prof. WH Tang, Co-I: Prof. Zhang LM; MPhil student: Mr. Eric Wong, Post-Doc fellow: Dr Dianqing Li )

Reliability of pile foundations is an important issue in Hong Kong following several quality problems in the past two years.  Two 31-story residential buildings have been demolished due to serious defects in the pile foundations. Apart from societal impact, the direct costs for constructing, retrofitting, and demolishing the buildings with problematic foundations are very high. To ensure the safety of foundations and to avoid the use of excessively conservative designs, many quality assurance measures are employed during and after pile construction, such as site inspection, pile integrity tests, coring, and load tests. However, criteria for planning the quality assurance measures and the impact of these measures on the reliability of pile foundations have not been seriously investigated.  Also, the influences of defects in piles on the capacity and reliability of the foundation are still not well understood.

The objectives of the proposed research are to evaluate the reliability of bored pile foundations considering the impacts of quality assurance measures and defects in piles potentially found by those measures, and to develop methods for maximising the value of information from those measures.  Field investigations on pile defects will be reviewed; laboratory tests and numerical analyses will be carried out to study the effects of geotechnical defects on the pile capacity. Systematic analysis of the influence of quality assurance measures will be conducted in terms of the Bayesian reliability frame- work.  The results from the project will provide a basis for evaluating the impact of quality assurance on the reliability of piles and a sound understanding of the influence of defects in piles on foundation reliability. Guidelines for selecting a proper quality assurance program to safeguard the safety and property of society will also be compiled.  The method may be further extended to obtain a basis for comparing the relative effectiveness of alternative remediation measures to rectify the defects.