(1. School of Civil Engineering，Southwest Jiaotong University，Chengdu，Sichuan 610031，China；2. Key Laboratory of High Speed Railway Engineering，Ministry of Education，Southwest Jiaotong University，Chengdu，Sichuan 610031，China)
Abstract：An in-situ vertical compression load test of a helical steel pile was conducted in silty sand and sand in order to study the bearing characteristics of helical piles in sandy soils under vertical compression loads. The difference of the existing methods for determining the ultimate bearing capacity of the helical pile tested was discussed. A finite element model of the helical pile under a vertical load considering installing effects was established based on soil layer parameters obtained from field cone penetration tests，and comparison of the pile load-displacement curves between the calculation and measuring results was performed. Based on the numerical simulation，the distributions of the axial force and shaft friction force of the pile along the depth under different load levels were explored，and the magnitudes of the shaft and end resistances and their ratio were investigated. The results show that the ultimate bearing capacity calculated by lgP-s method is larger than those obtained by Livneh & E1 Naggar and modified Davisson approaches，which indicates the later two methods over-conservative and that the simulation P-s curve considering installation effects gives better agreement with field measurement than that without considering installation effects. Under vertical compressive loading，the shaft resistance of the pile and the end resistance of middle-upper plates of the pile take effect almost simultaneously，and with increasing the vertical load，the end resistance provided by lower plates comes into play and increases gradually up to a peak value about 71% of the ultimate load with a displacement of the pile head exceeding about 4% of the diameter of plates.
[1] CLEMENCE S P，LUTENEGGER A J. Industry survey of state of practice for helical piles and tiebacks[J]. DFI Journal-The Journal of the Deep Foundations Institute，2015，9(1)：21–41.
[2] WANG T，LIU J，TIAN Y，et al. Frost jacking characteristics of screw piles by model testing[J]. Cold Regions Science and Technology，2017，138：98–107.
[3] 王腾飞，刘建坤，邰博文，等. 螺旋桩冻拔特性的模型试验研究[J]. 岩土工程学报，2018，40(6)：1 084–1 092.(WANG Tengfei，LIU Jiankun，TAI Bowen，et al. Model tests on frost jacking behaviors of helical steel piles[J]. Chinese Journal of Geotechnical Engineering，2018，40(6)：1 084–1 092.(in Chinese))
[4] WANG T，LIU J，ZHAO H，et al. Experimental study on the anti-jacking-up performance of a screw pile for photovoltaic stents in a seasonal frozen region[J]. Journal of Zhejiang University：Science A，2016，17(7)：512–524.
[5] 王腾飞，刘建坤，刘晓强，等. 季节冻土区光伏支架螺旋桩基的冻胀数值分析研究[J]. 冰川冻土，2016，38(4)：1 167–1 174.(WANG Tengfei，LIU Jiankun，LIU Xiaoqiang，et al. Numerical simulation on anti-jacking-up performance of helical piles of photovoltaic stents in seasonal frozen region[J]. Journal of Glaciology and Geocryology，2016，38(4)：1 167–1 174.(in Chinese))
[6] 赵华刚. 季节性冻土区光伏支架螺旋桩抗冻拔试验研究[硕士学位论文][D]. 北京：北京交通大学，2016.(ZHAO Huagang. Experimental study on anti-frost heaving of thotovoltaic piles in seasonal frozen soil[M. S. Thesis][D]. Beijing：Beijing Jiaotong University，2016.(in Chinese))
[7] 田彦德. 螺旋钢桩冻胀融沉特性试验研究[硕士学位论文][D]. 北京：北京交通大学，2017.(TIAN Yande. Experimental study on frost heave and thaw settlement characteristics of screw steel piles[M. S. Thesis][D]. Beijing：Beijing Jiaotong University，2017.(in Chinese))
[8] 胡 伟，刘顺凯，张亚惠，等. 单叶片全尺寸螺旋锚桩竖向拉拔试验研究[J]. 土木建筑与环境工程，2017，39(5)：31–39.(HU Wei，LIU Shunkai，ZHANG Yahui，et al. Uplift loading test on full-scale single blade screw anchor pile[J]. Journal of Chongqing Jianzhu University，2017，39(5)：31–39.(in Chinese))
[9] 郝冬雪，陈 榕，符胜男. 砂土中螺旋锚上拔承载特性模型试验研究[J]. 岩土工程学报，2015，37(1)：126–132.(HAO Dongxue，CHEN Rong，FU Shengnan. Experimental study on uplift capacity of multi-helix anchors in sand[J]. Chinese Journal of Geotechnical Engineering，2015，37(1)：126–132.(in Chinese))
[10] DONG T，ZHENG Y. Limit analysis of vertical anti-pulling screw pile group under inclined loading on 3D elastic-plastic finite element strength reduction method[J]. Journal of Central South University，2014，21(3)：1 165–1 175.
[11] 董天文，梁 力，黄连壮，等. 螺旋桩基础抗拔试验研究[J]. 岩土力学，2009，30(1)：186–190.(DONG Tianwen，LIANG Li，HUANG Lianzhuang，et al. Pullout test of screw pile foundation[J]. Rock and Soil Mechanics，2009，30(1)：186–190.(in Chinese))
[12] LIVNEH B，EL NAGGAR M H. Axial testing and numerical modeling of square shaft helical piles under compressive and tensile loading[J]. Canadian Geotechnical Journal，2008，45(8)：1 142–1 155.
[13] PERKO H A. Helical piles：a practical guide to design and installation[M]. Hoboken：John Wiley and Sons，2009：205–207.
[14] ELSHERBINY Z H，EL NAGGAR M H. Axial compressive capacity of helical piles from field tests and numerical study[J]. Canadian Geotechnical Journal，2013，50(12)：1 191–1 203.
[15] ELKASABGY M，EL NAGGAR M H. Axial compressive response of large-capacity helical and driven steel piles in cohesive soil[J]. Canadian Geotechnical Journal，2015，52(2)：224–243.
[16] TSUHA C H C，AOKI N，RAULT G，et al. Evaluation of the efficiencies of helical anchor plates in sand by centrifuge model tests[J]. Canadian Geotechnical Journal，2012，49(9)：1 102–1 114.
[17] TSUHA C D H C，FILHO J M S M，SANTOS T D C. Helical piles in unsaturated structured soil：a case study[J]. Canadian Geotechnical Journal，2016，53(1)：103–117.
[18] PÉREZ Z A，SCHIAVON J A，TSUHA C D H C，et al. Numerical and experimental study on influence of installation effects on behaviour of helical anchors in very dense sand[J]. Canadian Geotechnical Journal，2018，55(8)：1 067–1 080.
[19] ROBERTSON P K. Soil behaviour type from the CPT：an update[C] // The 2nd International Symposium on Cone Penetration Testing. Huntington Beach，CA，USA：[s. n.]，2010：9–11.
[20] ROBERTSON P K，CABAL K L. Guide to cone penetration testing for geotechnical engineering[M]. 5th ed. Signal Hill，California，USA：Gregg Drilling and Testing，Inc.，2012：34–35.
[21] ROBERTSON P K，CAMPANELLA R G. Interpretation of cone penetration tests. part I：sand[J]. Canadian Geotechnical Journal，1983，20(4)：718–733.
[22] JAMIOLKOWSKI M，LADD C C，GERMAINE J T，et al. New developments in field and laboratory testing of soils[C]// Proceedings of the 11th International Conference on Soil Mechanics and Foundation Engineering. San Francisco：[s. n.]，1985：57–153.
[23] KULHAWY F H，MAYNE P W. Manual on estimating soil properties for foundation design[R]. Palo Alto，CA：Electric Power Research Institute，1990.
[24] FLEMING K，WELTMAN A，RANDOLPH M，et al. Piling engineering[M]. New York：Taylor and Francis，2009：95–98.
[25] ICC-ES Evaluation Committee. AC358 Acceptance Criteria for Helical Foundation Systems and Devices[S]. California：ICC Evaluation Service，2007.
[26] 沈保汉. 评价桩工作特性的新方法─P/Pu-S/Su曲线法[J]. 建筑技术开发，1994，(2)：11–21.(SHENG Baohan. A new method for evaluating the working characteristics of pile─P/Pu-S/Su curve method[J]. Construction Technology Development，1994，(2)：11–21.(in Chinese))
[27] SAKR M. Installation and performance characteristics of high capacity helical piles in cohesive soils[J]. DFI Journal-The Journal of the Deep Foundations Institute，2012，6(1)：41–57.
[28] KISHIDA H. Stress distribution by model piles in sand[J]. Soils and Foundations，1963，4(1)：1–23.
[29] ROBINSKY E I，MORRISON C F. Sand displacement and compaction around model friction piles[J]. Canadian Geotechnical Journal，1964，1(2)：81–93.
[30] YANG J. Influence zone for end bearing of piles in sand[J]. Journal of Geotechnical and Geoenvironmental Engineering，2006，132(9)：1 229–1 237.
[31] YU F，YANG J. Base capacity of open-ended steel pipe piles in sand[J]. Journal of Geotechnical and Geoenvironmental Engineering，2012，138(9)：1 116–1 128.
[32] AL-DEFAE A H，CAUCIS K，KNAPPETT J A. Aftershocks and the whole-life seismic performance of granular slopes[J]. Géotechnique，2013，63(14)：1 230–1 244.
[33] LAUDER K D，BROWN M J，BRANSBY M F，et al. The influence of incorporating a forecutter on the performance of offshore pipeline ploughs[J]. Applied Ocean Research，2013，39(1)：121–130.
[34] 李广信，张丙印，于玉贞. 土力学[M]. 北京：清华大学出版社，2013：207–208.(LI Guangxin，ZHANG Binyin，YU Yuzheng. Soil mechanics[M]. Beijing：Tsinghua University Press，2013：207–208.(in Chinese))
[35] 单 昶. 计算砂土残余强度的新方法[J]. 工程勘察，1987，(3)：6–9.(DAN Chang. A new method for calculating residual strength of sand[J]. Geotechnical Investigation and Surveying，1987，(3)：6–9.(in Chinese))
[36] BRINKGREVE R B J. Selection of soil models and parameters for geotechnical engineering application[C]// Proceedings of the Sessions of the Geo-Frontiers Congress. Austin，Texas：[s. n.]，2005：69–98.
[37] BOLTON M D. The strength and dilatancy of sands[J]. Geotechnique，1986，36(1)：65–78.
2019, Vol. 38 
