Application Of Random Field Theory In Foundation Reliability Analysis On Port And Ocean Engineering

The reliability analysis is an advanced design method to estimate the failure riskin structural engineering. However, there is still a long way to go for the attempt ofdrawing the reliability theory into geotechnical engineering because the variances ofthe properties obtained by using the conventional statistical method are too large,resulting in unacceptable failure probabilities for earth structures (such as slope,retaining structure et al.). The gap between the estimated failure probability andengineers’ experience suggests that the reliability theory may not be able to be appliedin the geotechnical engineering.The random field theory, which can obtain the real variance by considering thespatial correlation of soil, can ensure the failure probability within the reasonablerange, which is the key to analyze reliability of geotechnical structrues. As toquantities of uniform data needed for establishment of random field model is hard toobtain and also costly, therefore slow progress has been made in this research area athome and abroad.With the ecnomic development of economy in the costal areas, more and moreseaport wharfs and economic development areas have been established in the areasformed by land reclaimation activities. Due to concentrated development andengineering investigation of these areas, a lot of physical mechanical indexes of soilmake the construction of random field of soil a reality, which lays a foundation for theapplication of reliability theory in design of geotechnical structures. In this paper,reliability of clay slope and foundation in recent land reclaimation in Tianjin BinhaiNew Area was studied through theoretical research, field investigation and statisticalanalysis. Systematical analysis on properties of random field is made, and itsapplication on port and ocean foundations are discussed. Main results and innovationsof this paper are as follows:(1) With the purpose of establishing spacial random field of physical property ofsoil formed by land reclaimation activities in Tianjin Binhai New Area, drillings andcone penetration tests were employed to get data describing physical properties ofsamples.(2) Random field theory was employed in statistical analysis of soil indexes, and the method which can consider both cross correlation and self correlation wasdeveloped, which can ensure the result more resonable.(3) Improvement was made on the no correlation method for calculating variancereduction function indicates, which not only makes the calculation more convinient,but also is a breakthrough of theory.(4) Soil indexes of support project were analyzed accoording to the random fieldtheory. Correlation distances, no correlation distances and variance reductionfunctions of the support project were obtained through the proposed statisticalmethod.(5) Change rule of the variance reduction function was obtained from the analysisresult of different soils, and variance reduction function corresponding to any value ofω/b can be obtained through linear interpolation.(6) For the most common stability problems of slope and bearing capacity offoundation in port engineering, limite state equations were established, and failureprobabilities of many projects were calculated through the variance reduction methodput forward in this paper. Compare results with safty factors and those directlycalculated by reliability theory, it can be found that failure probabilities after reductionare more reasonable.(7) In the standard of port foundation, the shearing strength index of consolidatedundrained test is employed to estimate the reliability of foudations, which representsthe reliability of foundation after consolidation. As to estimation of the reliability offoundation in construction, the shearing strength index of unconsolidated-undrainedtest should be used. This paper made some helpful discussion about this problem.(8) Study on reliability of foundation in ocean engineering is not popular atpresent. Take reliability of submarine pipeline under thermal stress as an example,establishing limite state equaitons of low-order buckling of ideal pipeline, calculatingfailure probability of the design pipeline using the reduction method put forward inthis paper, comparing the result with safty factor and that directly calculated byreliability theory, and it can be found that, the failure probability after reduction ismore reasonable. The same method can be applied to calculation of reliability offoundation with similar ocean structures.