Development and application of a small-scale vertical cyclic loading system for model tests of pile foundations
LIU Ying1,2,XU Panlong1,HUANG Maosong3,GAN Qing4,MA Shaokun1,2,YANG Kai1
(1. College of Civil Engineering and Architecture,Guangxi University,Nanning,Guangxi 530004,China;2. Key Laboratory of Disaster Prevention and Structural Safety,Guangxi University,Nanning,Guangxi 530004,China;3. Department of Geotechnical Engineering,Tongji University,Shanghai 200092,China;4. Guangxi Hualan Design and Consulting Group,
Nanning,Guangxi 530011,China)
Abstract:A small-scale vertical cyclic loading system for model tests of pile foundations,consisting of a loading system,a pressure chamber,a lifting device,model piles and a data acquisition system,is introduced. The model pile top is vertically loaded through a rotating roller screw driven by a coupler which is controlled by a servo motor,and soils samples are exerted with the confining pressure by hydraulic loading in order to simulate the in suit stress and consolidation of soil layers at different depths. The small-scale vertical cyclic loading system can be applied to carry out model tests of different pile foundations under vertical cycle loading in saturated soft soil,general clay,silty soil,sandy soil and other homogeneous or heterogeneous soils. Model tests of single pile under vertical cyclic loading are carried out and numerical simulation is performed for verification. Results show that the dynamic load amplitude and the consolidation pressure have great influence on the bearing capacity of the pile foundation. When the dynamic load amplitude is small,the bearing capacity of the pile foundation hardly weakens. When the consolidation pressure of the foundation soil increases,the bearing capacity of the pile foundation will be significantly enhanced,and the weakening will slow down. With increasing the cycle number and the amplitude,the axial force of the pile top gradually weakens to the residual value. During the cyclic loading,the degradation of the soil around the pile leads to a negative friction resistance of the pile foundation,and the bearing capacity of the pile foundation is weakened significantly. The test results are in good agreement with those obtained by the numerical simulation. Preliminary application proves that the test system can make up for the deficiency of low confining pressure in conventional 1 g small scale model test and that the nonlinear relationship between the load and the displacement of the pile top and that the cyclic degradation of the bearing capacity can be well reflected. This test system can output accurate load waveform,has high sensitivity and good stability in measurement and can be used to study the vertical cyclic loading characteristics of pile foundations under multiple working conditions.
刘 莹1,2,徐盼龙1,黄茂松3,甘 庆4,马少坤1,2,杨 凯1 . 小型桩基竖向循环加载模型试验系统研制与应用[J]. 岩石力学与工程学报, 2020, 39(2): 374-383.
LIU Ying1,2,XU Panlong1,HUANG Maosong3,GAN Qing4,MA Shaokun1,2,YANG Kai1. Development and application of a small-scale vertical cyclic loading system for model tests of pile foundations. , 2020, 39(2): 374-383.
刘 莹,黄茂松,李 帅. 海上风电桩基础竖向承载力循环弱化简化分析[J]. 岩土力学,2013,34(9):2 655-2 660.(LIU Ying,HUANG Maosong,LI Shuai. Simplified analysis of cyclic degradation of axial bearing capacity for offshore wind turbine pile foundations[J]. Rock and Soil Mechanics,2013,34(9):2 655-2 660.(in Chinese))
[3]
杜子博,钱建固,黄茂松. 考虑主应力轴旋转效应的交通荷载下饱和软黏土变形特性试验研究[J]. 岩石力学与工程学报,2016,35(5):1 031-1 040.(DU Zibo,QIAN Jiangu,HUANG Maosong. Experimental study on deformation behavior of saturated soft clay under traffic loading considering effect of principal stress rotation[J]. Chinese Journal of Rock Mechanics and Engineering,2016,35(5):1 031-1 040.(in Chinese))
[6]
LOMBARDI D,BHATTACHARYA S,MUIR WOOD D. Dynamic soil-structure interaction of monopile supported wind turbines in cohesive soil[J]. Soil Dynamics and Earthquake Engineering,2013,49:165-180.
[8]
章 敏,王星华,杨光程,等. 循环荷载作用下单桩动力模型试验与桩土界面特性研究[J]. 岩土力学,2013,34(4):1 037-1 044. (ZHANG Min,WANG Xinghua,YANG Guangcheng,et al. Study of dynamic model testing of single pile and behaviors of pile-soil interface under cyclic load[J]. Rock and Soil Mechanics,2013,34(4):1 037-1 044.(in Chinese))
[10]
HE B,WANG L,HONG Y. Field testing of one-way and two-way cyclic lateral responses of single and jet-grouting reinforced piles in soft clay[J]. Acta Geotechnica,2017,12(5):1 021-1 034.
[13]
LIU B,ZHANG D,XI P. Mechanical behaviors of SD and CFA piles using BOTDA-based fiber optic sensor system:A comparative field test study[J]. Measurement,2017,104:253-262.
[16]
王富强,荣 冰,张 嘎,等. 水平循环荷载下风电机桩基础离心模型试验研究[J]. 岩土力学,2011,32(7):1 926-1 930.(WANG Fuqiang,RONG Bing,ZHANG Ga,et al. Centrifugal model test of pile foundation for wind power unit under cyclic lateral loading[J]. Rock and Soil Mechanics,2011,32(7):1 926-1 930.(in Chinese))
[18]
杨龙才,郭庆海,周顺华,等. 高速铁路桥桩在轴向循环荷载长期作用下的承载和变形特性试验研究[J]. 岩石力学与工程学报,2005,24(13):2 362-2 368.(YANG Longcai,GUO Qinghai,ZHOU Shunhua,et al. Dynamic behaviors of pile foundation of high-speed railway bridge under long-term cyclic loading in soft soil[J]. Chinese Journal of Rock Mechanics and Engineering,2005,24(13):2 362-2 368. (in Chinese))
[4]
JEONG Y H,KIM J H,PARK H J,et al. Cyclic behavior of unit bucket for tripod foundation system supporting offshore wind turbine via model tests[J]. Wind Energy,2019,22(2):257-268.
[14]
FUTAI M M,DONG J,HAIGH S K,et al. Dynamic response of monopiles in sand using centrifuge modelling[J]. Soil Dynamics and Earthquake Engineering,2018,115:90-103.
[1]
范书立,陈健云,张俊清. 波浪荷载作用下斜向抗拔桩的承载特性分析[J]. 岩土力学,2012,33(1):301-306.(FAN Shuli,CHEN Jianyun,ZHANG Junqing. Research on bearing capacity of inclined uplift pile under wave cyclic loading[J]. Rock and Soil Mechanics,2012,33(1):301-306.(in Chinese))
[11]
朱 斌,杨永垚,余振刚,等. 海洋高桩基础水平单调及循环加载现场试验[J]. 岩土工程学报,2012,34(6):1 028-1 037.(ZHU Bin,YANG Yongyao,YU Zhengang,et al. Field tests on lateral monotonic and cyclic loadings of offshore elevated piles[J]. Chinese Journal of Geotechnical Engineering,2012,34(6):1 028-1 037. (in Chinese))
[5]
任 宇. 长期竖向循环荷载作用下桩的变形特性试验及理论研究[博士学位论文][D]. 杭州:浙江大学,2013.(REN Yu. Model test and theoretical study single piles to long-term on deformation behavior of cyclic axial loading[Ph. D. Thesis][D]. Hangzhou:Zhejiang University,2013.(in Chinese))
[9]
JARDINE R J,STANDING J R. Field axial cyclic loading experiments on piles driven in sand[J]. Soils and Foundations,2012,52(4):723-736.
[7]
陈仁朋,任 宇,陈云敏. 刚性单桩竖向循环加载模型试验研究[J]. 岩土工程学报,2011,33(12):1 926-1 933.(CHEN Renpeng,REN Yu,CHEN Yunmin. Experimental investigation on a single stiff pile subjected to long-term axial cyclic loading[J]. Chinese Journal of Geotechnical Engineering,2011,33(12):1 926-1 933.(in Chinese))
[12]
钱建固,王其伟. 循环动载下软黏土路基变形响应的离心试验模拟[J]. 岩土工程学报,2017,39(增2):99-102.(QIAN Jiangu,WANG Qiwei. Centrifuge tests on behaviors of soft clay subgrade under cyclic loading[J]. Chinese Journal of Geotechnical Engineering,2017,39(Supp.2):99-102.(in Chinese))
[15]
DIMITRA Z,SUSAN G,O'LOUGHLIN C D. Vertical cyclic loading response of a shallow skirted foundation in soft normally consolidated clay[J]. Canadian Geotechnical Journal,2019,56(4):473-483.
[17]
黄茂松,刘 莹. 基于非线性运动硬化模型的饱和黏土桩基础竖向循环弱化数值分析[J]. 岩土工程学报,2014,36(12):2 170-2 178. (HUANG Maosong,LIU Ying. Numerical analysis of axial cyclic degradation of a single pile in saturated soft soil based on nonlinear kinematic hardening constitutive model[J]. Chinese Journal of Geotechnical Engineering,2014,36(12):2 170-2 178.(in Chinese))