Coast Construction of Large Diameter Open Steel Pipe Pile Driving Analysis and Bearing Properties Research
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摘要: 某电厂码头项目基础桩拟采用大直径开口钢管桩，为获取工程桩设计施工参数进行了工前试桩。试验过程中采用高应变动力测试和静载试验桩身内力测试等综合手段，对不同龄期钢管桩的受力及变形特性进行了综合测试分析。试桩研究得出如下成果：（1）通过统计端阻力占比判定试桩承载类型为摩擦桩；（2）通过观测桩管内外泥面差结合端阻–变形曲线特征判定试桩存在桩端蔽塞效应；（3）静载内力测试显示，随着荷载的不断增大，端阻发挥程度逐级快速增大，摩阻在0～12 m段出现软弱化区域，其余段整个加载过程表现为增强状态；（4）综合后3 m沉桩锤击数–承载力关系曲线和龄期–土体恢复系数关系曲线，得出钢管桩最终承载力的预判公式。Abstract: Large diameter open steel pipe pile is proposed to be used for the foundation pile of a power plant wharf project. In order to obtain the design and construction parameters of engineering pile, the pre-construction test pile was carried out. During the test, the stress and deformation characteristics of steel pipe piles at different ages are comprehensively tested and analyzed by means of high strain dynamic test, static load test pile internal force test and so on. The results of pile test research are as follows: (1) The bearing type of test pile is determined as friction pile by counting the proportion of end resistance; (2) By observing the difference of soil surface inside and outside the pile pipe and combining the characteristics of end resistance deformation curve, it is determined that the test pile has pile end clogging effect; (3) The static load internal force test shows that with the continuous increase of load, the exertion degree of end resistance increases rapidly step by step, the soft weakening area of friction resistance appears in the section of 0~12 m, and the whole loading process of other sections shows an enhanced state; (4) The prediction formula of the final bearing capacity of steel pipe pile is obtained by synthesizing the relationship curve between the number of blows and bearing capacity and the relationship curve between age and soil recovery coefficient of the upper 3 m pile.
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表 1 地层力学参数
序号 S1(BK10) S2(BK07) 土层编号 极限侧摩阻/kPa 土层编号 极限侧摩阻/kPa 1 ② 6.06 ② 6.06 2 ③ 17.2 ③ 13.79 3 ③1 9.91 ③2 11.11 4 ③ 24.31 ③ 21.97 5 ④ 33.52 ④ 32.4 6 ④1 37.07 ⑤ 50.27 7 ④ 36.45 ⑤3 54.29 8 ⑤ 47.67 ⑤ 55.56 9 ⑤3 45.86 ⑤3 74.06 10 ⑤ 51.29 11 ⑤1 55.82 12 ⑤3 70.7 
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表 4 桩周土体恢复情况统计
桩号 动力测试承载力/kN 最终土体恢复系数 初打 7 d复打 14 d复打 28 d复打 S1 5865.6 7298.4 7727.7 8012.4 1.366 S2 5770.8 7202.0 7685.2 7986.8 1.384
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表 5 钢管桩闭塞效应判定
序号 Qp/As Qp/Asg 曲线变形 判定结果 1 <qpk或>qpk >qpk或接近 平缓 桩端闭塞 2 <<qpk <<qpk 陡峭聚变 桩端开口 3 <qpk 介于二者之间 半闭塞 注：桩端阻力为Qp；整桩桩端面积为As；钢管桩桩壁面积为Asg；勘察资料极限端阻标准值为qpk。
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表 6 S1、S2闭塞效应判定结果
桩号 Qp/As Qp/Asg 判定结果 桩身内力测试结果判定 S1 460.9<2500 5879.0>2500 桩端闭塞 S2 427.8<2500 5456.7>2500 桩端闭塞 高应变动力测试结果判定 S1 467.4<2500 5961.8>2500 桩端闭塞 S2 413.2<2500 5270.0>2500 桩端闭塞
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