Analysis And Application Of Load Test Results Of High Strengh Composite Foundation

In recent years, composite foundation especially high strength compositefoundation with rigid-flexible piles was successfully applied in subsoil treatment ofhigh-rise even ultra-high-rise buildings, which has been proved by practice that it canmeet the carrying and deformation requirements, and has achieved good economicbenefits and social benefits.Firstly, the current theories and applications at home and abroad of compositefoundation especially high strength composite foundation with rigid-flexible piles aresummarized in this paper, and research methods and characteristics of the compositefoundation are introduced. But generally, theoretical research is lagging engineeringpractice; the lack of field test data accumulation in high-rise and ultra-high-risebuildings limited the application of high strength composite foundation withrigid-flexible piles in some degress.Secondly, the high strength composite foundation engineering of Hengda RoyalPeninsula high-rise residential buildings is taken as the basis, focusing on the anlysis ofloading test results, the following major work is done:1) Through the analysis and appraisal of the two feasible foundation plans of theprogram, rotary drilling pile high strength composite foundation is taken as the subsoiltreatment plan;2) The loading test results on natural foundation are analyzed; depending ondifferent engineering test indicators, the bearing capacity of natural foundation isanlysized by multi-method, and the calculation results show that the bearing capacitydetermined by in-situ standard penetration test and static loading test are close whilechange a lot determined by the soil test parameters;3) The loading test results on single pile composite foundation improved byflexible piles and rigid piles are analyzed; the calculation results determined by staticloading test and the formula remcommanded in specifications are compared, and theresults indicate that in the area reinforced by mixing piles, the bearing capacity ofcomposite foundation determined by the formula remcommanded in specifications is23percent smaller than the static loading test result which ensures that the design bearing capacity of composite foundation is a safety reserve. In the area reinforced by mixingpiles and chemical churning piles, security reserves will be greater for shaft strength inchemical churning pile is larger than in mixing pile. The single pile compositefoundation improved by rigid piles is not added to its limit load, which causes a bigdifference between design value and the bearing capacity determined by the value ofrelative deformation; therefore, the detection method of composite foundation improvedby rigid piles is supposed to be comsummated;4) In this loading test, the load transfer law is tested in the stress-strain testing offlexible and rigid single pile and pressure cells test in soil between piles, whose resultshave important reference, especially for rigid pile, which is designed as end-bearing pileand pile length is not long, but the soil between piles is pre-reinforced, which formedrigid-flexible high strengh composite foundation. The lateral resistance of rigid pilessoon gets to play and resistance is large, making load in the top of rigid pile overcameby side resistance, and thus end resistance can’t get effectively play, but this isimportant to control the deformation of the overall composite foundation.5) Comparative research on theoretical and measured sedimentation value is done,and the settlement observations show that high strength composite foundation can meetthe deformation requirements in ultra-high-rise buildings very well, which is proved tobe a very typical success case in the complex foundation conditions.In this loading test, vibrating wire strain gauge and pressure box are also buried indifferent depths of piles and inter-pile soil to study the working mechanism ofrigid-flexible pile high strength composite foundation, the results is not ideal owing tothe influence of all sorts of reasons, but some trend conclusions can still be drawed. Thereasons for the unsatisfactory test are simply explained in this paper, and hope it canprovide references for similar testing researches.