Shaking table tests on negative friction of piles in soft soils under strong earthquake motion
-
摘要: 为研究强震作用下软土场地中桩基负摩阻力的产生机理及分布特性，设计开展了软土静力学试验、动三轴震陷试验和软土场地–单桩体系振动台试验，验证了震陷软土场地对桩基的负摩阻力作用，得到了软土的震陷特性、不同输入地震动下桩土体系地震动响应和桩负摩阻力分布发展规律，讨论了强震作用下负摩阻力的产生及发展过程。结果表明：①软土震陷的产生存在一定的屈服动应力，可利用动三轴试验来初步判断震陷引发负摩阻力的启动震级；②水平向地震动下负摩阻力主要产生在桩身的上部，竖向地震动下全桩均会产生负摩阻力；③震陷引发的桩基负摩阻力具有突发性，且微小的桩土相对位移量即可产生显著的负摩阻力，这种瞬时加载可能会对结构造成破坏；④利用桩侧土体和接触面的抗剪强度可初步估算软土场地中桩基可能受到的负摩阻力值。试验成果可为软土场地桩基负摩阻力的判别与计算提供参考，对软土场地抗震设防具有一定的理论和工程实用价值。Abstract: The negative friction of piles caused by seismic settlement of soft soils will produce the downward loads on pile foundation and cause serious damage to the foundation and structures. In order to study the formation mechanism and distribution characteristics of negative friction of pile foundation in soft soils under strong earthquake motion, the static tests and dynamic triaxial tests on soft soils and the shaking table tests on single pile in soft soil field are carried out. The negative friction on piles caused by seismic settlement of soft soils is proved. The seismic subsidence characteristics of soft soils, the dynamic response of pile-soil system under different input ground motion and the distribution development law of negative friction resistance of piles are obtained. The generation and development of negative friction under strong earthquakes are discussed. The results indicate that: (1) There is a certain yield dynamic stress in the formation of seismic subsidence in soft soils. The dynamic triaxial tests can be used to preliminarily judge the initial magnitude of negative friction induced by seismic subsidence. (2) Under the horizontal ground motion, the negative friction resistance is mainly generated at the upper part of the piles, while under the vertical ground motion, the negative friction resistance is generated at the whole pile. The development law of negative friction resistance is different in these two cases. (3) The negative friction resistance of the pile foundation caused by seismic subsidence of soft soils is sudden. At the initial stage of ground motion loading, the small relative displacement of the piles and soils can produce significant negative friction resistance, so attention should be paid to the damage effect of such instantaneous loads on the foundation and superstructure. (4) The potential negative friction resistance of pile foundation in soft soils can be estimated preliminarily by using the shear strength of pile-side soil and contact surface. The above results may provide reference for the discrimination and calculation of negative friction resistance of pile foundation in soft soil sites, and have certain theoretical and engineering practical value for seismic fortitude of soft soil sites.
-
Keywords:
- strong earthquake motion /
- soft soil /
- pile /
- negative friction /
- shaking table test
-
-
![]()
图 1 墨西哥城10层建筑物震害情况（Mendoza，1988）
Figure 1. Damage of a ten-story building in Mexico City (Mendoza, 1988)
![]()
图 2 重塑土剪应力与剪切位移关系
Figure 2. Relationship between shear stress and shear displacement of remolded soft soil
![]()
图 3 动剪切模量比和阻尼比随剪应变关系变化关系
Figure 3. Relationship among dynamic shear modulus ratio, damping ratio and shear strain
![]()
图 4 不同动应力下试样残余应变与振次关系
Figure 4. Relationship between residual strain and vibration times under different dynamic stresses
![]()
图 9 峰值加速度放大系数随深度的变化
Figure 9. Variation of peak acceleration amplification factor with depth
![]()
图 10 土体孔压和表层沉降时程
Figure 10. Time histories of pore pressure of soil and surface settlement
![]()
图 11 不同地震动输入下桩身测点应变时程
Figure 11. Time histories of strain of pile at various measuring points under different ground motions
![]()
图 13 水平向加载下桩身负摩阻力分布
Figure 13. Distribution of negative friction of pile under horizontal loads
![]()
图 14 竖向加载下桩身负摩阻力分布
Figure 14. Distribution of negative friction of pile under vertical loading
表 1 重塑软土基本物理指标
Table 1 Physical properties of remolded soft soil
名称 含水率/% 填土密度/(t·m-1) 孔隙比/% 塑限/% 液限/% 塑性指数 重塑软土 33 1.79 1.04 17.2 42.2 25 
下载: 导出CSV
表 2 模型主要相似参数
Table 2 Similarity ratios of test model
物理量 相似关系 桩相似比 土体相似比 长度 SL 1∶25 1∶25 位移 Sr 1∶25 1∶25 密度 Sρ 1∶2 1∶1 弹性模量 SE 1∶10 1∶1 加速度 Sa 1.0 1.0 时间 ST 0.09 0.04 应力 Sσ 1∶10 1∶1 频率 Sω 11.2 25
下载: 导出CSV
-
[1] LIU Hui-xian. Tangshan Earthquake Damage[M]. Beijing: Seismological Press, 1986. (in Chinese) [2] 江席苗. 汶川地震地基基础震害调查研究[D]. 上海: 同济大学, 2009. JIANG Xi-miao. Investigation and Research on Earthquake Damage of Wenchuan Earthquake Foundation[D]. Shanghai: Tongji University, 2009. (in Chinese)
[3] MENDOZA M J, AUVINET G. The mexico earthquake of september 19, 1985—behavior of building foundations in Mexico city[J]. Earthquake Spectra, 1988, 4(4): 835–853. doi: 10.1193/1.1585505
[4] MEYMAND P J. Shaking Table Scale Model Tests of Nonlinear Soil-Pile-Superstructure Interaction in Soft Clay[D]. Berkeley: University of California, 1998.
[5] 黄雨, 舒翔, 叶为民, 唐益群. 桩基础抗震研究的现状[J]. 工业建筑, 2002, 32(7): 50–53. doi: 10.3321/j.issn:1000-8993.2002.07.017 HUANG Yu, SHU Xiang, YE Wei-min, TANG Yi-qun. Recent studies on seismic resistance of pile foundation[J]. Industrial Construction, 2002, 32(7): 50–53. (in Chinese) doi: 10.3321/j.issn:1000-8993.2002.07.017
[6] SEED H B, CHAN C K. Clay Strength under Earthquake Loading Condition[J]. Journal of the Soil Mechanics and Foundations Division, 1996, 92: 53–78.
[7] POULOS H G, MATTES N S. The analysis of down drag in end-bearing piles[C]//Proc 7th ICOSMFE, 1969, Mexico.
[8] CHOW Y K, CHIN J T, LEE S L. Negative skin friction on pile groups[J]. International Journal for Numerical & Analytical Methods in Geomechanics, 1990, 14(2): 75–91.
[9] SHIBATA T, SEKIGUCHI H, YUKITOMO H. Model test and analysis of negative skin friction acting on piles[J]. Soil and Foundations, 1982, 22(2): 29–39. doi: 10.3208/sandf1972.22.2_29
[10] 陆明生. 桩基表面负摩擦力的试验研究及经验公式[J]. 水运工程, 1997(5): 54–58. https://www.cnki.com.cn/Article/CJFDTOTAL-SYGC705.013.htm LU Ming-sheng. Model tests and experience formula for negative skin friction of a single pile[J]. Chinese Journal of Port & Water Engineering, 1997(5): 54–58. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-SYGC705.013.htm
[11] LEUNG C F, LIAO B K, CHOW Y K, et al. Behavior of pile subject to negative skin friction and axial load[J]. Soils and Foundations, 2004, 44(6): 17–26. doi: 10.3208/sandf.44.6_17
[12] 童建国, 朱瑞燕. 固结软土中单桩负摩擦离心机模型试验研究[J]. 电力勘测设计, 2006(1): 12–15. https://www.cnki.com.cn/Article/CJFDTOTAL-DLKC200601003.htm TONG Jian-guo, ZHU Rui-yan. The study on single pile negative friction centrifuge model in consolidated soft soil[J]. Electric Power Survey and Design, 2006(1): 12–15. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-DLKC200601003.htm
[13] 王兰民, 孙军杰, 黄雪峰, 等. 黄土场地震陷时桩基负摩阻力的现场试验研究[J]. 岩土工程学报, 2008, 30(3): 38–45. http://manu31.magtech.com.cn/Jwk_ytgcxb/CN/abstract/abstract12780.shtml WANG Lang-min, SUN Jun-jie, HUANG Xue-feng, et al. Field tests on negative skin friction along piles along piles caused by seismic settlement of loess[J]. Chinese Journal of Geotechnical Engineering, 2008, 30(3): 38–45. (in Chinese) http://manu31.magtech.com.cn/Jwk_ytgcxb/CN/abstract/abstract12780.shtml
[14] 孔纲强, 杨庆, 郑鹏一, 等. 考虑时间效应的群桩负摩阻力模型试验研究[J]. 岩土工程学报, 2009, 31(12): 1913–1919. http://manu31.magtech.com.cn/Jwk_ytgcxb/CN/abstract/abstract8408.shtml KONG Gang-qiang, YANG Qing, ZHENG Peng-yi, et al. Model tests on negative skin friction for pile groups considering time effect[J]. Chinese Journal of Geotechnical Engineering, 2009, 31(12): 1913–1919. (in Chinese) http://manu31.magtech.com.cn/Jwk_ytgcxb/CN/abstract/abstract8408.shtml
[15] 许成顺, 豆鹏飞, 高畄成, 等. 地震动持时压缩比对可液化地基地震反应影响的振动台试验[J]. 岩土力学, 2019, 40(1): 147–155. https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201901012.htm XU Cheng-shun, DOU Peng-fei, GAO Liu-cheng, et al. Shaking table test on effects of ground motion duration compression ratio on seismic response of liquefied foundation[J]. Rock and Soil Mechanics, 2019, 40(1): 147–155. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201901012.htm
[16] 田兆阳, 李平, 郑志华, 等. 软土动力特性动三轴试验研究[J]. 地震工程学报, 2017, 39(1): 95–99. https://www.cnki.com.cn/Article/CJFDTOTAL-ZBDZ201701014.htm TIAN Zhao-yang, LI Ping, ZHENG Zhi-hua, et al. Dynamic triaxial tests on dynamic characteristics of soft soil[J]. China Earthquake Engineering Journal, 2017, 39(1): 95–99. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-ZBDZ201701014.htm
[17] 李平, 田兆阳, 肖瑞杰, 等. 基于三轴试验的软土震陷简化计算方法研究[J]. 震灾防御技术, 2017, 12(1): 145–156. https://www.cnki.com.cn/Article/CJFDTOTAL-ZZFY201701016.htm LI Ping, TIAN Zhao-yang, XIAO Rui-jie, et al. Study of simplified calculation method for seismic settlement of soft soil based on triaxial test[J]. Technology for Earthquake Disaster Prevention, 2017, 12(1): 145–156. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-ZZFY201701016.htm
[18] 吴跃东. 软土震陷计算方法及影响研究[D]. 南京: 河海大学, 2008. WU Yue-dong. Calculation of Soft Soil Seismic Settlement and Impact Studies[D]. Nanjing: Hohai University, 2008. (in Chinese)
[19] 律文田, 冷伍明, 王永和. 软土地区桥台桩基负摩阻力试验研究[J]. 岩土工程学报, 2005, 27(6): 45–55. http://manu31.magtech.com.cn/Jwk_ytgcxb/CN/abstract/abstract11694.shtml LÜ Wen-tian, LENG Wu-ming, WANG Yong-he. In-situ tests on negative friction resistance of abutment piles in soft soil[J]. Chinese Journal of Geotechnical Engineering, 2005, 27(6): 45–55. (in Chinese) http://manu31.magtech.com.cn/Jwk_ytgcxb/CN/abstract/abstract11694.shtml
[20] 夏力农, 王星华, 蒋春平. 桩顶荷载对桩基负摩阻力特性的影响[J]. 防灾减灾工程学报, 2005(4): 11–14. https://www.cnki.com.cn/Article/CJFDTOTAL-DZXK200504001.htm XIA Li-nong, WANG Xing-hua, JIANG Chun-ping. Influence of working load on negative skin friction characters of pile[J]. Journal of Disaster Prevention and Mitigation Engineering, 2005(4): 11–14. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-DZXK200504001.htm
[21] 程学磊, 崔春义, 孙宗光. 饱和软土自由场地地震反应特性振动台试验[J]. 地震工程学报, 2019, 41(1): 108–116. https://www.cnki.com.cn/Article/CJFDTOTAL-ZBDZ201901015.htm CHENG Xue-lei, CUI Chun-yi, SUN Zong-guang. Shaking table tests on the seismic response characteristics of characteristics of a free field in saturated soft soil[J]. China Earthquake Engineering Journal, 2019, 41(1): 108–116. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-ZBDZ201901015.htm
[22] 孔纲强. 群桩负摩阻力特性研究[D]. 大连: 大连理工大学, 2009. KONG Gang-qiang. Study on Negative Friction Resistance Characteristics of Pile Group[D]. Dalian: Dalian University of Technology, 2009. (in Chinese)
计量
- 文章访问数:
- HTML全文浏览量: 0
- PDF下载量:
