Field Test And Bearing Capacity Analysis On Bored Manual Digging Pile Socket Into Rock

With the rapid development of social economy and continually increase of urban population,the manual digging filling pile socket into rock has been widely used due to high bearing capacity and less head displacement in large-scale projects such as bridges,docks and high building.However,the model test and numerical simulation are unable to take all the factors affecting rock-socket pile's bearing capacity into consideration owing to the complexity of the rock-pile system.Hence,it's imperative to conduct the large-scale and well recorded field test.On the other hand,the side friction of dry bored pile is adopted as the side friction of the manual digging pile based on the “Technical code for building pile foundation JGJ94-2008”,which also ignores the actual loading distribution of the rock-socket pile.Based on this,static load test and internal force test were conducted on nine manual digging piles socket into rock in Qingdao in order to further study the load characteristics and load transfer mechanism of manual digging rock-socketed piles.The main work and research results are as follows:(1)The Q-s curve was slow type and the head displacement of nine piles was less than 11 mm,with high resilience ratio ranged from 51% to 75%.The bearing capacity of the rock-socket pile is high,which can meet the design requirements.The ultimate bearing capacity of testing pile D1,F1,F2,F3 is more than 10800 kN,while the value of testing pile D2,C1,C2,E1,E2 was more than 12960 kN in accordance with Technical code for testing of building foundation pile.(2)The ratio of head load supported by pile side friction decreased along with the increasing head load,but the ratio was up to 86% at the ultimate head load,which shows the characteristics of end-frictional pile.The ratio of end resistance to head load was up to 7.6% even at very small head displacement(0.45 mm),which needs more attention in real projects and design.(3)The side friction was mobilized along with the pile,the peak value of the side friction can be found at the medium of the rock depth.The recommendation of side resistance from reconnaissance report was conservative and the measured value was 2.3 times of the recommendation;the end resistance increased as head load got increased,but the measured value was 0.44 times of the recommendation at the ultimate load.(4)The bearing capacity of manual digging pile socket into rock under this condition was refreshed based on the test results,and the design of the pile was optimized in order to save cost and simplify the construction process.(5)The differences between manual digging excavation and bored excavation were discussed.In view of the shortcomings of the existing technical code of piles,the load performance coefficients of pile-soil side resistance and total socket resistance were introduced to analysis the load transfer mechanism at each load level.