APPLICATION OF SEABED CONE PENETRATION TEST IN CALCULATION OF BEARING CAPACITY OF PILE FOUNDATION OF OFFSHORE PLAT ̄FORM
-
摘要: 静力触探探测具有原位性、连续性、高效性以及高分辨率的优点,利用海洋静力触探探测成果计算海上平台桩基承载力具有非常大的应用空间。以胜利油田埕岛海域某平台为例,使用ROSON100型海洋静力触探仪对平台各桩腿开展原位探测,同步进行钻探取样及室内土工参数测试。分别利用静力触探和钻探取样测试成果计算了平台桩基承载力,对比讨论了3种桩基承载力计算方法之间的异同。结果表明:3种方法对应的桩侧摩阻力随埋深变化整体趋势基本一致;基于一定区域工程经验,钻探规范法和静探间接法得到的桩端阻力、单桩极限承载力基本吻合,而静探直接法得到的桩端阻力和单桩极限承载力相较前两者明显偏大;考虑以粉砂作为持力层的前提下3种桩基极限承载力计算方法表现出较好的兼容性。研究成果可为海洋工程桩基承载力计算提供新的借鉴,具有一定科学意义和应用价值。Abstract: Cone penetration detection has the advantages of in-situ, continuity, high efficiency and resolution. The use of marine cone penetration detection results to estimate the bearing capacity of offshore platform pile foundation has a great application potential. This paper takes the pile foundation of a platform in the Chengdao sea area of Shengli Oilfield as an example. The ROSON100 marine cone penetration device was used to conduct in-situ detection around the platform's legs. Simultaneous drilling sampling and indoor geotechnical parameters testing were implemented. The results of cone penetration detection and geotechnical tests were used to estimate the bearing capacity of platform pile foundation, respectively. The similarities and differences between three different calculation methods of bearing capacity of pile foundation were discussed. The results show that the overall trend of the pile side friction resistance obtained by these three methods is basically the same with the buried depth. Based on certain regional engineering experience, the pile tip resistance and single pile ultimate bearing capacity obtained by the drilling specification method and the CPT indirect method are basically consistent. The pile tip resistance and the ultimate bearing capacity of single pile obtained by the CPT direct method are obviously larger than the former two. The ultimate bearing capacity of pile foundation shows good compatibility for these three calculation methods under the premise of considering silty sand as the bearing layer. The findings can provide a new reference for the calculation of the bearing capacity of offshore engineering pile foundation.
-
表 1 ROSON 100静力触探仪主要技术指标
Table 1. Major technical indices of ROSON 100 CPT
项目 参数 最大触探深度/m 50(水深≤20m); 15(水深>20m) 锥尖阻力/MPa ≥50,最大误差0.25% 侧摩擦力/MPa 0~0.75,最大误差0.5% 分辨率/cm 2 孔隙水压力/MPa 0~5.0,最大误差0.5% 探头倾斜度 0°~15°,最大误差1.0° 表 2 各层土静力触探参数代表值
Table 2. Representative indices of CPT for every soil stratum
工程分类 分层深度/m 锥尖阻力/MPa 侧摩阻力/MPa 摩阻比/% 粉土 0.0~3.8 8.788 0.0564 0.64 软塑粉质黏土 3.8~9.2 0.600 0.0166 2.76 可塑粉质黏土 9.2~11.7 0.941 0.0404 4.29 粉砂 11.7~14.9 12.090 0.0654 0.54 粉质黏土 14.9~19.1 2.003 0.0681 3.40 粉土 19.1~20.76 13.954 0.1664 1.19 表 3 3#桩腿钻探规范法计算参数表
Table 3. Calculating parameters for drilling method(3# pile)
层号 土体类别 分层深度/m 有效重度/kN·m-3 黏性土不排水抗剪强度Cu /kPa 桩-土摩擦角δ /(°) 承载力系数Nq 1 粉土 0~4.0 10.1 — 20 12 2 软塑粉质黏土 4.0~8.7 8.4 15 — - 3 可塑粉质黏土 8.7~11.6 8.6 40 — - 4 粉砂 11.6~15.4 10.9 — 25 20 5 粉质黏土 15.4~19.2 10.4 60 — - 6 粉土 19.2~20.76 10.7 — 20 12 表 4 3#桩腿静探间接法计算参数表
Table 4. Calculating parameters for CPT indirect method(3#pile)
层号 土体类别 分层深度/m 有效重度/kN·m-3 黏性土不排水抗剪强度Cu /kPa 桩-土摩擦角δ /(°) 经验圆锥系数Nkt 承载力系数Nq 1 粉土 0~3.8 10.1 — 21 — 12 2 软塑粉质黏土 3.8~9.2 8.4 20 — 17 - 3 可塑粉质黏土 9.2~11.7 8.6 40 — 17 - 4 粉砂 11.7~14.9 10.9 — 23 — 20 5 粉质黏土 14.9~19.1 10.4 80 — 19 - 6 粉土 19.1~20.76 10.7 — 22 — 12 表 5 3#桩腿静探直接法计算参数表
Table 5. Calculating parameters for CPT direct method(3#pile)
编号 土体类别 插桩深度/m 桩端附近等价平均锥尖阻力qca /MPa 端承系数ξc 摩阻力系数ξf 1 粉土 1.9 1.204 0.50 60 2 3.8 0.806 0.55 60 3 软塑粉质黏土 6.5 0.783 0.50 90 4 9.2 1.070 0.50 90 5 可塑粉质黏土 10.4 1.350 0.50 90 6 11.7 3.043 0.45 40 7 粉砂 13.3 2.798 0.50 100 8 14.9 2.392 0.50 100 9 粉质黏土 17.0 3.215 0.45 40 10 19.1 5.134 0.45 40 11 粉土 19.93 — — 60 12 20.76 — — 60 -
An Y N, Yan X C, Yang K, et al. 2013. Some misconceptions in pile insertion analysis of offshore platforms in Shengli Chengdao Oilfield[J]. Journal of Waterway and Harbor, 34 (6): 537-541. http://www.onacademic.com/detail/journal_1000038061457410_0733.html Bustamante M, Gianeselli L. 1982. Pile bearing capacity predictions by means of static penetrometer CPT[C]//Proceedings of the 2nd European Symposium on Penetration Testing: 493-500. Cai G J, Liu S Y, Tong L Y, et al. 2009. Soil classification using CPTU data based upon cluster analysis theory[J]. Chinese Journal of Geotechnical Engineering, 31 (3): 416-424. http://www.cnki.com.cn/Article/CJFDTotal-YTGC200903025.htm Chu L P, Sun Y F, Song Y P, et al. 2017. Application of seabed cone penetration test in research on the seafloor geotechnical engineering characteristics in the Yellow River estuary[J]. Coastal Engineering, 36 (1): 22-33. http://en.cnki.com.cn/Article_en/CJFDTOTAL-HAGC201701003.htm Dennis N D, Olson R E. 1983. Axial capacity of steel pipe piles in clay[C]//Proceedings of Conference on Geotechnical Practice in Offshore Engineering. Austin, Texas: ASCE: 370-388. Geng G Q. 2016. Research on penetration mechanism of Piezocone Penetration Tset(CPTU) and its application on pile foundation engineering[D]. Nanjing: Southeast University. Guo S Z, Liu R. 2015. Application of cone penetration test in offshore engineering[J]. Chinese Journal of Geotechnical Engineering, 37 (S1): 207-211. http://en.cnki.com.cn/Article_en/CJFDTOTAL-YTGC2015S1040.htm Han M, Li G, Ye J C, et al. 2020. Discussion of CPT derived undrained shear strength of cohesive soil in Chengdao Oilfield[J]. Soil Engineering and Foundation, 34 (4): 520-524. Hu Y, Wang Y. 2020. Identification of subsurface soil stratification using cone penetration tests and Bayesian learning[J]. Journal of Engineering Geology, 28 (5): 966-972. Jia Z L, Yan S W, Yang A W, et al. 2016. Application of cone penetration test for the analysis of pile-run of long and large diameter piles in offshore geotechnical engineering[J]. Chinese Journal of Rock Mechanics and Engineering, 35 (S1): 3274-3282. http://en.cnki.com.cn/Article_en/CJFDTotal-YSLX2016S1077.htm Kuiter J D, Beringen F L. 1979. Pile foundations for large North Sea structures[J]. Marine Geotechnology, 3 (3): 267-314. doi: 10.1080/10641197909379805 Li D Z, Tong S X. 1982. Discussion on reasonable depth of pile tip penetration into bearing stratum[J]. Architecture Technology, (6): 28-31. Li S D, Sun Y M, Chen W C, et al. 2019. Analyses of gas production methods and offshore production tests of natural gas hydrates[J]. Journal of Engineering Geology, 27 (1): 55-68. http://en.cnki.com.cn/Article_en/CJFDTotal-GCDZ201901007.htm Liu S Y, Cai G J, Zou H F. 2013. Practical soil classification methods in China based on piezocone penetration tests[J]. Chinese Journal of Geotechnical Engineering, 35 (10): 1765-1776. http://www.cnki.com.cn/Article/CJFDTotal-YTGC201310002.htm Randolph M F, Dolwin J B. 1994. Design of driven piles in sand[J]. Gotechnique, 44 (3): 427-448. doi: 10.1680/geot.1994.44.3.427 Randolph M F. 2003. Science and empiricism in pile foundation design[J]. Gotechnique, 53 (10): 847-875. doi: 10.1680/geot.2003.53.10.847 The Professional Standards Compilation Group of People′s Republic of China. 2017. Technical specification for piezocone penetration testing(T/CCES 1-2017)[S]. Beijing: China Architecture and Building Press. The National Standards Compilation Group of People′s Republic of China. 2009. Specifications for offshore platform engineering geology investigation(GB/T 17503-2009)[S]. Beijing: China Architecture and Building Press. Zhu J F. 2011. Study on properties of soil considering disturbance[D]. Hangzhou: Zhejiang University. Zou H F. 2018. Research on spatial variability and uncertainties within pile capacity of soft soils based on CPTU[D]. Nanjing: Southeast University. 安永宁, 阎锡臣, 杨鲲, 等. 2013. 胜利埕岛油田海上作业平台插桩分析中的几点误区思考[J]. 水道港口, 34 (6): 537-541. doi: 10.3969/j.issn.1005-8443.2013.06.013 蔡国军, 刘松玉, 童立元, 等. 2009. 基于聚类分析理论的CPTU土分类方法研究[J]. 岩土工程学报, 31 (3): 416-424. doi: 10.3321/j.issn:1000-4548.2009.03.018 楚立鹏, 孙永福, 宋玉鹏, 等. 2017. 海床式静力触探在黄河口海底土工程特性研究中的应用[J]. 海岸工程, 36 (1): 22-33. https://www.cnki.com.cn/Article/CJFDTOTAL-HAGC201701003.htm 耿功巧. 2016. 孔压静力触探贯入机理及其桩基工程应用研究[D]. 南京: 东南大学. 郭绍曾, 刘润. 2015. 静力触探测试技术在海洋工程中的应用[J]. 岩土工程学报, 37 (S1): 207-211. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC2015S1040.htm 韩猛, 李国, 叶纪超, 等. 2020. 基于CPT确定埕岛油田黏性土不排水抗剪强度方法的探讨[J]. 土工基础, 34 (4): 520-524. https://www.cnki.com.cn/Article/CJFDTOTAL-TGJC202004030.htm 胡越, 王宇. 2020. 静力触探识别场地土层分布的贝叶斯学习方法研究[J]. 工程地质学报, 28 (5): 966-972. doi: 10.13544/j.cnki.jeg.2020-263 贾沼霖, 闫澍旺, 杨爱武, 等. 2016. 静力触探在大直径超长桩溜桩分析中的应用[J]. 岩石力学与工程学报, 35 (S1): 3274-3282. https://www.cnki.com.cn/Article/CJFDTOTAL-YSLX2016S1077.htm 李大展, 佟世祥. 1982. 关于桩尖贯入持力层合理深度问题的探讨[J]. 建筑技术, (6): 28-31. https://www.cnki.com.cn/Article/CJFDTOTAL-JZJI198206005.htm 李守定, 孙一鸣, 陈卫昌, 等. 2019. 天然气水合物开采方法及海域试采分析[J]. 工程地质学报, 27 (1): 55-68. doi: 10.13544/j.cnki.jeg.2019-065 刘松玉, 蔡国军, 邹海峰. 2013. 基于CPTU的中国实用土分类方法研究[J]. 岩土工程学报, 35 (10): 1765-1776. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201310002.htm 中华人民共和国国家标准编写组. 2009. 海上平台场址工程地质勘察规范(GB/T 17503-2009)[S]. 北京: 中国建筑工业出版社. 中华人民共和国行业标准编写组. 2017. 孔压静力触探测试技术规程(T/CCES 1-2017)[S]. 北京: 中国建筑工业出版社. 朱剑锋. 2011. 考虑扰动影响的土体性状研究[D]. 杭州: 浙江大学. 邹海峰. 2018. 基于CPTU的软弱土空间变异性特征与桩基承载力不确定性设计方法研究[D]. 南京: 东南大学. -