Calculation formula of vertical displacement caused by side friction of pile in homogeneous foundation soils
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摘要: 根据半无限体内受集中力作用的Mindlin位移解,通过线积分完整地推导出均质地基中桩侧摩阻均匀分布、桩侧摩阻随深度呈线性增加分布以及桩侧摩阻随深度呈任意形态分布情况下引起的地基竖向位移计算公式,通过有限元计算程序和具体工程算例验证了所推导公式的正确性和可行性。文中所推导公式对于纯摩擦单桩沉降的估算、桩土体受荷前期弹性变形阶段的计算、弹塑性变形及有限元计算的对比验算,均具有重要的作用。西安部分地区地层主要由压缩性中等偏低的黄土和古土壤组成,土质较均匀,运用本文计算方法可以取得较为可靠的计算结果,具有实际应用价值。Abstract: According to Mindlin’s displacement solution regarding a semi-infinite mass subjected to a point load, the calculation formulas for vertical displacement caused by skin friction in piles under uniformly distributed loads have been derived thoroughly. This includes scenarios with linearly increasing distribution loads along the length of the pile and arbitrary distribution loads within uniform foundations. Through concrete project examples, it is confirmed that these formulas are both accurate and practical. The formula presented plays a crucial role in calculating the settlement of pure friction single piles, the elastic deformation in the early stage of pile and soil under load, and the comparison of elastic-plastic deformation and finite element calculation. The strata in some areas of Xi’an are mainly composed of medium and low compressible loess and paleosol, and the soil quality is relatively uniform. The results obtained by this calculation method are reliable and have practical application value.
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图 1 h深度处集中荷载P引起的任意点M的竖向位移[11]
表 1 模型1桩中心点下各点竖向位移
距桩顶
深度/mS1/
mmS1′/
mm差异率/
%S2/
mmS2′/
mm差异率/
%0 34.0 33.6 1.2 19.4 19.2 1.0 2 35.0 34.6 1.1 20.9 20.7 1.0 4 33.8 33.4 1.2 22.8 22.6 0.9 6 32.8 32.5 0.9 25.0 24.7 1.2 8 31.8 31.5 0.9 27.3 27.1 0.7 10 30.9 30.6 1.0 29.6 29.4 0.7 15 27.8 27.5 1.0 33.7 33.3 1.2 20 19.4 19.1 1.5 25.3 25.0 1.2 22 14.6 14.3 2.1 17.7 17.5 1.1 26 10.3 10.0 3.0 11.6 11.2 3.4 30 8.3 7.9 3.6 9.0 8.6 4.4 35 6.8 6.3 7.4 7.2 6.7 6.9 40 5.8 5.2 10.3 6.0 5.4 10.0 50 4.5 3.6 20.0 4.6 3.7 19.6 注:S1,S2分别为代入式(3)、式(8)计算位移;S1′,S2′分别为桩侧均布荷载、递增荷载作用下有限元计算位移。 表 2 模型2桩中心点下各点竖向位移
距桩顶
深度/mS3/
mmS3′/
mm差异率/
%S4/
mmS4′/
mm差异率/
%0 29.8 29.2 2.0 12.8 12.6 1.6 2 31.0 30.5 1.6 14.4 14.1 2.1 4 30.4 29.9 1.6 16.2 15.8 2.5 6 30.0 29.4 2.0 18.1 17.7 2.2 10 29.2 28.7 1.7 22.2 21.8 1.8 15 28.2 27.7 1.8 27.4 26.9 1.9 20 27.0 26.5 1.9 32.1 31.5 2.0 25 25.0 24.4 2.4 35.0 34.3 2.0 30 16.7 16.2 3.0 24.3 23.6 2.9 32 11.1 11.0 0.9 14.3 13.7 4.2 34 9.1 8.8 3.3 11.1 10.5 5.4 36 8.0 7.5 6.3 9.3 8.7 6.5 40 6.6 5.9 9.1 7.4 6.6 10.8 45 5.5 4.7 14.5 6.0 5.1 16.3 50 4.7 3.8 19.1 5.1 4.1 19.6 备注:S3,S4分别为代入式(3)、式(8)计算位移;S3′,S4′分别为桩侧均布荷载、递增荷载作用下有限元计算位移。 表 3 西安地区典型钻孔灌注桩试桩工程算例
编号 工 程名称 成孔工艺 桩顶
荷载/kN平均侧
摩阻/kPa桩径/m 桩长/m 计算桩底
竖向位移/mm计算桩身
压缩量/mm计算总
沉降量/mm实测试桩平均
沉降量/mm1 华山机械厂 锅锥成孔 4400 77.0 0.70 26.0 2.63 4.95 7.58 6.52 2 景天佳苑住宅楼 锅锥成孔 3690 63.1 0.60 31.0 1.96 6.74 8.70 4.14 3 西勘商住楼 锅锥成孔 5900 81.3 0.70 33.0 2.89 8.43 11.32 9.77 4 旺座时代A区1#、2#楼 锅锥成孔 8250 107.2 0.70 35.0 3.85 10.42 14.27 12.46 5 豪盛时代C区 锅锥成孔 8200 113.0 0.70 33.0 4.02 10.65 14.67 13.25 6 长安区土地综合
开发公司1#、2#楼锅锥成孔 5000 82.9 0.60 32.0 2.58 8.32 10.90 10.94 7 西关正街商住楼B座 锅锥成孔 8400 97.9 0.70 39.0 3.59 12.90 16.49 16.83 8 世家星城三期93#楼 锅锥成孔 5000 75.9 0.60 35.0 2.40 9.38 11.78 8.38 9 乾唐雁月1#楼 锅锥成孔 7000 88.4 0.70 36.0 3.19 9.92 13.11 12.60 10 融发·沁园西区20#、
21#住宅楼锅锥成孔 2300 49.0 0.60 25.0 1.46 3.28 4.74 3.60 11 陕西省公务员培训楼 锅锥成孔 5000 83.0 0.60 32.0 2.58 8.57 11.15 8.37 12 金源都市公寓 锅锥成孔 3520 62.0 0.60 30.0 1.92 5.84 7.76 6.94 13 广丰大厦 锅锥成孔 11000 125.0 0.80 35.0 5.02 11.61 16.63 16.04 14 西安市卫生学校高层住宅楼 锅锥成孔 7200 93.5 0.70 35.0 3.36 9.63 12.99 13.11 15 元丰怡家住宅小区9#、11#楼 锅锥成孔 6000 106.0 0.60 30.0 3.27 9.95 13.22 12.34 16 长丰园Ⅱ区2#高层住宅楼 旋挖成孔 6600 113.0 0.60 31.0 3.50 11.31 14.81 13.82 17 西安现代花城A、B座 旋挖成孔 7200 93.5 0.70 36.0 3.29 10.86 14.15 14.04 18 西安小寨住宅小区1#住宅楼 旋挖成孔 6800 81.4 0.70 38.0 2.97 10.17 13.14 10.86 19 旺座曲江四期H座 旋挖成孔 7600 106.1 0.60 38.0 3.40 14.59 17.99 20.12 20 旺座曲江四期N座 旋挖成孔 8400 109.8 0.60 40.6 3.56 17.23 20.79 21.19 注:按式(3)计算时,土的弹性模量统一取80 MPa,土的泊松比取0.38,桩的弹性模量根据砼的强度等级C30~C55取值30~36 GPa。 -
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