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APPLICATION OF SEABED CONE PENETRATION TEST IN CALCULATION OF BEARING CAPACITY OF PILE FOUNDATION OF OFFSHORE PLAT￣FORM
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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.
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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° 
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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
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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
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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
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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
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