Study On The Probability Limiting State Design Method Of Bored Piles In Loess Of Xi'an Area

Now the systematical study on pile foundations in Xi'an area was poor and the related theories and experiences of piles design developed in coastal area of China were indiscriminately imitated. The permissible stress design method dominates the field and a total safety coefficient is defined to judge a pile's reliability, neither taking loess's special properties nor taking many uncertainty factors in pile design and construction into account. This lead to a low level in pile design and the result is that an expensive or an unsafety design is inevitable. So,the research on reliability of bored piles in loess of Xi'an area has important engineering meaning.The thesis adopts probability mathematics and physics principle to analyzes variability characteristics and regularity of load and bearing capacity of bored piles in loess of Xi'an area:using the calibration method to proceed to the reliability calculations for piles in current codes and getting the reliability index within its target;calculating and defining load partial coefficients of piles; calculating soil limiting resistance characteristic values around the pile's outer surface and at pile tip and engaging in variation research for them; proceeding statistical analysis for negative friction resistance; proceeding statistical analysis and variation research for the pile diameter of bored piles; developing study of loess property itself using its random application fields; and presenting the bearing capacity design formula using the partial coefficient to express based on reliability theory for bored piles on an axle-load, and attains the aim to make pile design technique reasonable economics while applying safety measures. The statement from the given engineering examples proved that pile design by the probability limiting state method meets bearing capacity equirements.