Adaptation and Correction of Dynamic Penetration Rod Length
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摘要: 西部地区河床深厚覆盖层勘探取样及工程特性是水电工程地质勘察中常遇技术难题，动力触探(dynamic penetration test，DPT)因操作简单、适用土类多而成为西部地区河床覆盖层原位测试首选方法.现行规范仅给出了20 m杆长范围的修正方法，但对超此范围重型、超重型动力触探杆长适用性及修正问题，长期以来业内则颇多争议却少有研究.鉴于此，利用现场试验与数值模拟相结合，通过对动力触探试验杆上各测点应变现场实测并得到各测点应力分布，再利用LS-DYNA软件进行反演分析并确定相关计算参数，而后进行杆长25 m、40 m、60 m、80 m、120 m的数值模拟计算得到了杆长适用范围及修正系数.试验研究方法及成果可供类似问题研究与深厚覆盖层地区工程勘察借鉴或参考.Abstract: In the geotechnical investigation of hydropower projects in western China, exploratory sampling and engineering property research are challenging on account of the thick overburden on the riverbed. The dynamic penetration test(DPT) has become the preferred method of in-situ tests for the river overburden layers in western China due to its simple operation and applicability for different soil types. The current standard only provides a correction method for the rod length within 20 m. For the problems of adaptation and correction of heavy and extra-heavy dynamic penetration rod length, there is always much controversy but rare research for a long time. To address this issue, a study is conducted, involving the following procedures. Firstly, combined with the field test and numerical simulation, the stress value of each monitoring point is obtained by monitoring the rod of field DPT. Then, LS-DYNA software is used for inverse analysis and relevant parameters are determinined. Lastly, different rod lengths of DPT, such as 25 m, 40 m, 60 m, 80 m and 120 m, are simulated, and the adaptation and correction of rod length are obtained. The research method and results can be used for reference in similar problems and other geotechnical investigation practices in areas with deep river overburden layers.
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图 4 杆长25.87 m动力触探试验过程沿杆应力分布情况
a.第18次锤击时各测点应力-时间曲线；b.第18次锤击时应力包络线；c.第30次锤击时各测点应力-时间曲线；d.第30次锤击时应力包络线
Fig. 4. The stress distribution along the rod of DPT, with the rod length of 25.87 m
图 5 杆长40.92 m动力触探试验过程沿杆应力分布情况
a.第21次锤击时各测点应力-时间曲线；b.第21次锤击时应力包络线；c.第41次锤击时各测点应力-时间曲线；d.第41次锤击时应力包络线
Fig. 5. The stress distribution along the rod of DPT, with the rod length of 40.92 m
图 6 杆长46.85 m动力触探试验过程沿杆应力分布情况
a.第20次锤击时各测点应力-时间曲线；b.第20次锤击时应力包络线；c.第40次锤击时各测点应力-时间曲线；d.第40次锤击时应力包络线
Fig. 6. The stress distribution along the rod of DPT, with the rod length of 46.85 m
图 9 杆长25.87 m、40.92 m和46.85 m数值模拟结果
a, c, e分别代表杆长25.87 m、40.92 m和46.85 m的各测点应力与时间关系曲线；b, d, f分别代表杆长25.87 m、40.92 m和46.85 m应力包络线
Fig. 9. The numerical simulation results of DPT with the rod length of 25.87 m, 40.92 m and 46.85 m
图 10 杆底端应力与土体弹性模量的关系
Fig. 10. The relation between stress at the bottom of rod and elastic modulus of soil
图 11 杆径50 mm、落锤质量120 kg时各工况应力包络线(考虑阻尼系数)
Fig. 11. The stress envelope of each condition when the rod diameter is 50 mm and the mass of drop hammer is 120 kg
图 12 杆径50 mm、落锤质量120 kg时各工况应力包络线(未考虑阻尼系数)
Fig. 12. The stress envelope of each condition when the rod diameter is 50 mm and the mass of drop hammer is 120 kg
表 1 动力触探现场试验应力沿杆长变化规律
Table 1. The rules of stress among the rod length in the field DPT
杆长(m) 杆顶应力(MPa) 杆底应力(MPa) 衰减比例(%) 沿杆长应力变化规律公式 25.87 160 95 40.63 y=0.143 4x2-0.203 6x-181.330 0 40.92 140 70 50.00 y=0.048 5x2-1.025 8x-137.000 0 46.85 140 68 51.43 y=0.021 8x2+0.337 0x-138.540 0 注：y为应力；x为杆长. 
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表 2 数值试验模型尺寸
Table 2. The model size of numerical simulation
材料(kg) 外径(cm) 内径(cm) 高度(cm) 落锤63.5 26.0 0.0 15.0 落锤120.0 28.0 0.0 24.8 土 150.0 0.0 1 000.0
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表 3 主要计算参数
Table 3. The main calculation parameters
材料 密度(g/cm3) 弹性模量(Pa) 泊松比 落锤 7.85 2.10×1011 0.269 探杆 7.85 2.16×1011 0.269 土 1.80 6.00×106 0.300
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表 4 探杆底端计算参数
Table 4. The parameters of rod at the bottom
序号 弹性模量(Pa) 杆长(m)/杆径(mm) 1 3.00×106 40/50 2 6.00×106 40/50 3 10.00×106 40/50 4 20.00×106 40/50 5 30.00×106 40/50
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表 5 数值计算工况
Table 5. The calculation conditions of numerical simulation
工况序号 重锤(63.5 kg) 超重锤(120.0 kg) 杆径42 mm (a) 杆径50 mm (b) 杆径50 mm (c) 工况1 25 25 25 工况2 40 40 40 工况3 60 60 60 工况4 80 80 80 工况5 120 120 120
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表 6 动力触探数值模拟应力沿杆长变化规律
Table 6. The rules of stress among the rod length in the numerical simulation of DPT
杆长(m)/杆径(mm) 考虑阻尼系数 未考虑阻尼系数 杆顶应力(MPa) 杆底应力(MPa) 衰减比例(%) 杆顶应力(MPa) 杆底应力(MPa) 衰减比例(%) 25/50 201 93 53.9 210 190 9.5 40/50 201 64 68.4 210 185 11.9 60/50 198 36 81.7 210 183 12.9 80/50 201 19 90.0 209 180 14.3 120/50 201 5 97.3 210 178 15.2 注：换算得到的杆底应力为多位小数，这里只作说明，故取整数；两个方案第1个监测点选取不同，考虑阻尼系数时，第1个监测点距离杆顶0.7 m，不考虑阻尼系数时，第1个监测点距离杆顶0.6 m.
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表 7 重型动力触探锤击数杆长修正系数
Table 7. The modified coefficients of rod length of heavy dynamic penetration
杆长(m) 杆底冲击力(kN) 有效能(N·m) 杆长修正系数 水工公式列出的杆长修正系数 有效能公式列出的杆长修正系数 2 90.954 421.231 1.00 1.00 1.00 4 78.137 411.204 0.97 0.97 - 6 70.640 383.320 0.91 0.92 0.94 9 63.143 358.046 0.85 0.86 0.84 12 57.824 345.409 0.82 0.81 0.79 15 53.698 332.772 0.79 0.77 0.74 18 50.327 324.348 0.77 0.73 0.71 21 47.477 311.711 0.74 0.70 0.68 24 45.008 299.074 0.71 0.67 0.65 27 42.830 290.649 0.69 0.65 0.63 30 40.882 278.012 0.66 0.62 0.61 33 39.120 269.588 0.64 0.60 - 36 37.511 261.163 0.62 0.58 0.57 39 36.031 252.739 0.60 0.57 - 42 34.660 240.102 0.57 0.55 0.55 45 33.385 231.677 0.55 0.54 - 48 32.191 223.252 0.53 0.53 - 51 31.071 219.040 0.52 0.52 0.52 66 26.303 181.129 0.43 - 0.48 69 25.481 176.917 0.42 - - 72 24.694 168.492 0.40 - - 注：杆长修正系数利用式(2) 计算得出；水工公式、有效能公式列出的杆长修正系数见林宗元(2005)；-表示未列出.
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表 8 超重型动力触探锤击数杆长修正系数
Table 8. The modified coefficients of rod length of extra heavy dynamic penetration
杆长(m) 杆底冲击力(kN) 有效能(N·m) 杆长修正系数 水工公式列出的杆长修正系数 有效能公式列出的杆长修正系数 2 136.777 1 124.803 1.00 1.00 1.00 4 117.584 1 079.811 0.96 0.97 - 6 106.356 1 057.315 0.94 0.92 0.94 9 95.129 1 023.571 0.91 0.86 0.84 12 87.163 978.579 0.87 0.81 0.79 15 80.984 944.835 0.84 0.77 0.74 18 75.936 899.842 0.80 0.73 0.71 21 71.667 877.346 0.78 0.70 0.68 24 67.970 821.106 0.73 0.67 0.65 27 64.708 798.610 0.71 0.65 0.63 30 61.791 776.114 0.69 0.62 0.61 33 59.152 753.618 0.67 0.60 - 36 56.742 719.874 0.64 0.58 0.57 39 54.526 697.378 0.62 0.57 - 42 52.474 674.882 0.60 0.55 0.55 45 50.564 652.386 0.58 0.54 - 48 48.776 629.890 0.56 0.53 - 51 47.098 607.394 0.54 0.52 0.52 66 39.958 584.898 0.52 - 0.48 69 38.728 562.402 0.50 - - 72 37.549 551.153 0.49 - - 78 35.333 517.409 0.46 - - 81 34.288 506.161 0.45 - 0.45 84 33.281 483.665 0.43 - - 87 32.309 472.417 0.42 - - 90 31.370 461.169 0.41 - - 93 30.462 449.921 0.40 - - 96 29.583 427.425 0.38 - 0.44 99 28.731 416.177 0.37 - - 102 27.905 404.929 0.36 - 0.43 105 27.102 393.681 0.35 - - 108 26.320 382.433 0.34 - - 111 25.556 371.185 0.33 - - 114 24.808 359.937 0.32 - - 注：杆长修正系数利用式(2) 计算得出；水工公式、有效能公式列出的杆长修正系数见林宗元(2005)；-表示未列出.
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