Research On Time-and-space Mechanical Parameters Of Cast-in-place Pile

The change of aperture diameter for cast-in-place pile have something to do with many factors, such as soil quality, specification of the drill, construction technology, time of pore forming, etc. In this paper, much emphasis will be placed on the following problems, such as quality control of pore forming, mainly in contraction technology, the rales of aperture diameter for filling pile on time and space and what influences on the pile quality and bearing capacity of pile caused by the rules.In this paper, statistic soil mechanics will be used for the accounting, comparison and induction of data for more than 3000 holes on the construction site of some residential quarter in Pudong, Shanghai, in combination with the results of static load test, to summarize the above rales and factors and get the formular of aperture diameter along with time, examplified with some cases for its instruction in the design of pile foundation and construction quality control.The following results can be achieved from the reseach:1.on the space: there is a critical depth from 10m to 15m. The measured values of all kinds of pore diameters are more than the designed values of 61-182mm. Above the critical depth and the mean value and coefficient of variation are relatively greater. Beyond the critical depth, the measured values of all kinds of pore diameters are more than the designed values of 27-42mm and the mean value and coefficient of variation becomes constant gradually. As for all kinds of pore diameters, the difference values (AD) between the measured values and the designed values are basically same, of basically same features.2.On the time: the testing pores and formed pores will be small after 24h. The range of variation of 90% of the pores is within 10 mm. The less the pore diameter is, the more evident the trend of shrinkage is. The absolute values of changes in pore diameter are commonly within the period from Oh to 6h after the pores are formed. The formula of exponential function can be arrived through drawing the proportional curve of alternation of pore diameter along with time factor.3.On the bearing: normal-circulation pore-forming process is more helpful to the increase of frictional resistance around the pile than reverse-circulation pore-forming process. Double-girdle drill is more helpful to the formation of sawshaped pore wall. The duration of exposure pile pore has a great importance on the normal play of the bearing capacity of pile. Too long time of pore forming will lead to the loss of the resiting forces on the sides and the ends of piles.