Comparative Analysis On Economics And Load-bearing Characteristics Between Variable Cross-section Pipe Pile And Constant Section Pipe Pile

Precast concrete pipe piles are widely used in pile foundationengineering, since it have the characteristics of simple making, shortconstruction period, substantial economic benefits, easily adaptable toengineering geological conditions and others. In the paper, based on theNational Natural Science Foundation of China "Study on single pilebearing capability and connection key technology of steps sectionconcrete precast pipe pile", by large indoor model test, numericalsimulation, and economic analysis, and combined with practicalengineering to research working behavior and economic of ladder-typetapered Piles. The main contents and results of the paper are as follows:Based on indoor large scale model experiments, the differences oftwo kinds of closed mouth pipe piles were studied in the load-settlement,pile stress, skin resistance and pile-tip resistance. Results show thatbearing capacity of segmentally variable section pipe piles is bigger thanconstant section pipe piles if the average diameter of pipe piles are equal,and the bearing vertical capacity, unit volume bearing vertical capacityand availability of material of pipe pile will increase with theimprovement of average diameter and variable section ratio ofsegmentally variable section pipe pile; To variable section pipe pile, axialforce suffered a sudden drop on position of variable section and axialforce of small diameter pipe piles decrease quickly than constant sectionpipe piles. When settlement of pile-top are the same, Resistance on pile-end of variable section pipe piles are bigger than constant section pipepiles, Resistance and ratio of resistance on pile-end to bearing capacity ofvariable section pipe piles would increase to a large extent withimprovement of average diameter of variable section pipe pile. Actionpoint of max skin resistance of variable section pipe piles are closer topile top than constant section pipe piles and max skin resistance willincrease with decline of ratio of segmentally variable section pipe pile. Ifpile-top settlements of pipe piles are equal, force of skin resistance ofvariable section pipe piles are bigger than constant section pipe piles withthe same average diameter in different dregree, conducive to exert pile lateral friction.Using FLAC3Dsoftware to establish pile-soil models of two kinds ofpipe piles under vertical loads, and study the ultimate bearing capacity ofsingle pile, pile soil stress and displacement fields. The results showedthat with the pile-top exerted small loads, the soil under pile show upliftphenomenon, the difference of settlement is inconspicuous. When thepile-top exerted large loads, the pile-top settlements of ladder-typecross-section pipe piles are significantly less than the constant section pilepile’s.According to the basic principles of technical and economic analysis,using carrying capacity per unit volume, carrying capacity per unit cost,economic input and other indicators to comparative study the economicof two kinds of pipe piles through quantitative analysis, data analysis andengineering project example. The results showed that with the same ofaverage diameter of pipe piles, the carrying capacity per unit volume ofladder-type variable cross-sectional pipe pile are higher than constantsection pipr pile’s, but the carrying capacity per unit cost of ladder-typevariable cross-sectional pipe pile are lower, and with the increase ofdiameter and length, the amount of concrete between variablecross-section pipe pile and constant section pipe pile are more and moreapproximative, the increase degree of ultimate bearing capacity per unitand carrying capacity per unit volume of ladder-type variablecross-sectional pipe pile are more obvious than constant section piprpile’s, and the decrease degree of carrying capacity per unit cost of ladder-type variable cross-sectional pipe pile are more obvious than constantsection pipr pile’s. Carrying capacity and settlement to meet therequirements, compared with constant section pipe piles, the ladder-typevariable cross-section pipe piles can better reduce the project cost andshorten the construction time.