The Research On The Vertical Load-bearing Characteristics Of Rock-socketed Pile Group Foundation In The Highway Bridges

With the development and upgrading of the modern expressway, rock-socketed pilegroup foundation has a larger and larger proportion in some areas of highway bridgefoundation, the load-bearing and deformation characteristics of rock-socketed pile groupfoundation is the key of the engineering design and construction. As its large carrying capacity,expensive institution test and the difficulty to conduct the destructive test, the reaserch onlong rock-socketed pile foundation was scarce, only few people have discussed its theory,there is still no systematic research, complete test data and measured data are not enough,which restraint people to understand its bearing behavior. For this reason, the paper combinedwith geological terrain features and engineering practice of a highway in guangxi province,using theoretical analysis and numercial simulation methods, made a research on the bearingcapacity of long pile group foundation and its working mechanism. The main results are asfollows:(1) Given the unchanged other conditions, the bearing capacity of rock-socketed pileincreased with the increase of rock-socketed depth increasing, but not infinitely increasing.when the embedded depth was greater than3D, continuing to increase the depth ofrock-socketed pile to the ultimate bearing capacity of pile foundation began to decrease, itwas known the rock-socketed depth should not be greater than three times of the pilediameter.(2) Given the unchanged other conditions, long pile group effect coefficient increasedwith the pile distanse increasing, generally when the pile distanse was greader than3.5timesthe pile diameter, the soil stress in pile bottom rarely overlapped with each other, pile groupeffect coefficient was approximately equal to1. At this moment, the work properties of eachpile of pile group foundation were the same with a single pile, so the pile group effectcoefficient could be not taken into consideration.(3) Given the unchanged number of pile, with the increase of pile diameter, the netdistance between piles had reduced, the contact area of pile and pile lateral soil became larger,the affect among piles also got enhancing, The stress of the pile bottom section would haveoverlap when the pile distanse was less than2.5times the pile diameter, its pile group effectcoefficient was less than1. thereby when calculated the bearing capacity of the longrock-socketed pile foundation and the pile distanse was less than2.5times the pile diameter,the pile group effect coefficient should be taken into consideration.(4) Given the unchanged other conditions, adding pile lengh could make the bearing capacity of pile foundation increasing, but the more pile length, the less pile group effectcoefficient, when pile length reached to a certain value, stress overlying was obvious.Therefore, the pile group effect coefficient should be taken into account when calculated thebearing capacity of the long rock-socketed pile foundation.The paper results provide a theoretical basis for the bearing capacity of rock-socketedpile group foundation, which has a certain guiding significanse and engineering use value forthe application of pile group foundation of in highway bridge.