Study On The Uncertainties Of Geotechnical Parameters And Its Application

Uncertainty of geotechnical parameters restricts the development of reliability analysis of geotechnical engineering. Compared with safety factor used in traditional determination design method, reliability index can reflect the safety degree of the structure more reasonably. The reliability analysis method based on probability theory has been wildly applied in structure design maturely since the unified standard for reliability design of building structures announced, while it is far from being maturely used in geotechnical engineering design. One important reason for that is the calculated reliability index of geotechnical structure is often too small to be accepted. Much research work on reliability analysis of geotechnical engineering has been done, and many scholars believe that this problem is mainly cause by neglecting the autocorrelation properties of the geotechnical materials. The variance of the geotechnical parameters calculated by traditional statistic method is usually too large for reliability analysis. In order to solve that problem, the random field theory is proposed to analyse the autocorrelation properties of the geotechnical materials. After using the reduction function of variance obtained from the random field theory to reduce the variance of the geotechnical parameters, a proper reliability index can be calculated in the reliability analysis of geotechnical structure.Based on a large amount of geotechnical investigation data in Ningbo rail transit project, the characteristics of correlation and spatial variation in geotechnical material parameters were identified according to grey correlation theory, probability theory and random field theory, and the adequate representative value of the correlation distance was obtained from those calculations. Then a numerical example on retaining wall reliability analysis was given to illustrate the rationality of the random field theory.