Research On The Bearing Behavior Of Super-long Drilled Pile

The super-long bored pile has become an indispensable style of foundation at the highway bridges,especially at the spanning great rivers and gulfs bridges.But researches of the engineering properties of super-long piles are not sufficient for the requests of application,and we have not a befitting theory to guide the designs and calculations of the super-long bored piles,at the same time the economy and security of the super-long bored piles are not ensured completely by the methods and parameters of the existing code.For the problems upwards,we have done much of pertinence work.By collecting data and investigating,we have comprehensively known the application and research status quo of super-long bored piles and we have done a great deal of researches including field test technology,load transfer mechanism,laboratory and field test,calculation and analysis of bearing capacity and so on,Our main innovative conclusions are as followings:●The displacement-stress curves of pile and soil gained from field load tests and indoor model tests have been simulated and analyzed,based on which the hyperbola function adapted to pile and soil are brought forward,and the new method is advanced to estimate the bearing capacity and displacement of the super-long bored piles.●On the basis of the statistic and analysis of vast data obtained form field load tests,for the first time we have elucidated the definition and the judgment method of super long pile by analyzing the relationship between the assembled stiffness and piles' length and the super long piles' property under load.Further more,the propositional standard values of pile shaft friction and its decision method are brought forward which will provide theoretical basis to optimize the design of super long piles,and will also support the technique basis to modify the Specifications for Design of Ground Base and Foundation of Highway Bridges and Culverts.●For the first time,we put forward the parameters such as the assembled stiffness,the shearing rigidity of pile and soil and compressive rigidity of pile-end soils and so on,and the harmonized stiffness method to calculate the bearing capacity of super-long bored pile has been put forward that would help the design and calculation of super-long bored pile according to the real instance much more.●We have invented the prestressed reaction force equipment used at large weight dead-load pile experiment with intellectual property(The patent code is ZL2005 2 0114928.9).This equipment can enhance the load weight greatly and reduce the expenditure by using the engineering piles caps and piers.●The load cell used in pile self-balanced load test(or O-cell pile testing method) we have designed(The patent code is ZL2005 2 0114929.3) can eliminate the distorted digital,elevate the testing precision,and this technique has solved the problem that the load- sedimentation curves don't accord with the practice,so that the precision of O-cell pile testing method has been enhanced greatly.●The technology of using ultrasonic to inspect holes quality has been used at tens of great bridges.We have analyzed many data obtained from the inspection.The more accurate expanded ratio of design dia.of the super-long bored piles has been gained.Our research achievements have been popularized and applied at many bridge constructing projects,in ten of which,static load testing for piles with large bearing capacity have been used,in fourteen of which,the ultrasonic quality testing of bored holes have been used,in four of which pile disfigurement handling technique have been used.In total,13 anchor-pile loading tests,8 O-cell pile tests,2630 ultrasonic quality tests of bored holes and disfigurement handling for 13 piles have been finished and the results show that good societal and economic benefit has been gained. The maximal load has reached 40000kN in our static load test wit anchor pile and counterforce beam,which is the maximum load in the world with this method.The generalization and application all-around of our achievements will save the expense of highway bridges construction,enhance the security of bridges and boost the level of pile test inspection design and disfigurement handling.