铁路作为国民经济的关键组成部分，对于国家交通运输系统的运行和发展至关重要。桩网结构路基通过竖向桩基增强体和水平向加筋垫层增强体的双向增强，从而提高路基的稳定性和耐久性。本文采用室内模型试验和数值计算相结合的方法，研究锥形帽桩-土工格栅桩网结构路基的承载特性，主要研究内容与结论如下：

（1）开展等截面桩、方形帽桩和锥形帽桩三种单桩竖向承载力室内模型对比试验，主要分析桩顶荷载-沉降曲线、桩身轴力分布曲线、桩身侧摩阻力曲线和荷载分担比。试验结果表明：相较于等截面桩和方形帽桩，锥形帽桩的极限承载力分别提高了40.0%和16.7%；锥形桩帽的锥角有效减少了桩侧负摩阻力，因锥形桩头具有的倾斜状态而使桩顶处的侧摩阻力发挥更充分；当桩顶荷载为3.0 kN时，锥形帽桩的桩侧摩阻力占比约较等截面桩与方形帽桩分别提高了128.3%和59.4%，表现为摩擦桩承载特点。

（2）建立锥形帽桩-土工格栅桩网结构路基室内缩尺模型，分析桩身轴力、桩侧摩阻力、桩土应力比及土工格栅垫层应力分布的变化规律。研究结果表明：桩体承载力主要由桩侧摩阻力承担，锥角的存在能够有效减少负摩阻力对桩的影响，提高桩体的承载能力；荷载在路基中是沿中心向路肩两侧传递，路基中心处桩土应力比峰值平均值比加载中心边缘桩大62.0%，整体平均值大66.8%；路基纵向桩土应力比大于横向；土工格栅有效调节了路基中差异沉降，使得荷载在路堤内部进行重新分配。

（3）建立锥形帽桩-土工格栅桩网结构路基数值计算模型，进一步验证该结构承载特性的有效性和合理性。通过控制单一变量方法分析了锥角、长径比和土工格栅抗拉强度对桩网结构路基承载特性的影响。结果表明：在一定范围内，增大锥角、增加长径比和提高土工格栅抗拉强度可以有效减小路基土体沉降量，提升其承载能力。提高土工格栅抗拉强度对路基土体沉降控制效果最佳。数值计算取值范围内，锥角取11.3°对沉降控制最佳；土工格栅抗拉强度取80 kN/m对沉降控制效果最好；考虑材料利用率，长径比取25时对沉降控制效率最高。

As a key component of the national economy, railways are essential for the operation and development of the country's transportation system. The pile-network structure subgrade is strengthened by the two-way reinforcement of the vertical pile foundation reinforcement and the horizontal reinforced cushion reinforcement, so as to improve the stability and durability of the subgrade. In this paper, the bearing characteristics of the subgrade of conical cap pile-geogrid pile network structure are studied by using the combination of indoor model test and numerical calculation, and the main research contents and conclusions are as follows:

(1) The comparative tests of the vertical bearing capacity of three types of single piles, such as equal cross-section piles, square cap piles and conical cap piles, were carried out, and the load-settlement curves of the pile top, the axial force distribution curve of the pile, the friction resistance curve of the pile side and the load sharing ratio were analyzed. The test results show that compared with the equal-section pile and the square cap pile, the ultimate bearing capacity of the conical cap pile is increased by 40.0% and 16.7%, respectively. The cone angle of the tapered pile cap effectively reduces the negative friction resistance on the pile side, and the lateral friction resistance at the top of the pile is more fully exerted due to the inclined state of the tapered pile head. When the pile top load is 3.0 kN, the proportion of pile side friction of conical cap pile is about 128.3% and 59.4% higher than that of equal-section pile and square cap pile, respectively, which shows the bearing characteristics of friction pile.

(2) The indoor scale model of the subgrade of the conical cap pile-geogrid pile network structure was established, and the variation law of the axial force of the pile, the friction resistance of the pile side, the stress ratio of the pile and the stress distribution of the geogrid cushion were analyzed. The results show that the bearing capacity of the pile is mainly borne by the frictional resistance of the pile side, and the existence of the cone angle can effectively reduce the influence of the negative friction resistance on the pile and improve the bearing capacity of the pile. The load is transferred along the center to both sides of the shoulder in the subgrade, and the average value of the pile-soil stress at the center of the subgrade is 62.0% larger than that of the edge pile at the center of loading, and the overall average value is 66.8% larger. The longitudinal pile-soil stress ratio of subgrade is greater than that of transverse. The geogrid effectively regulates the differential settlement in the subgrade, so that the load is redistributed within the embankment.

(3) A numerical calculation model of the subgrade of the conical cap pile-geogrid pile network structure was established to further verify the effectiveness and rationality of the bearing characteristics of the structure. The effects of cone angle, aspect ratio and tensile strength of geogrid on the bearing characteristics of pile network structure were analyzed by controlling the single variable method. The results show that within a certain range, increasing the cone angle, increasing the aspect ratio and improving the tensile strength of the geogrid can effectively reduce the settlement of the subgrade soil and improve its bearing capacity. Improving the tensile strength of geogrid has the best effect on the control of subgrade soil settlement. Within the range of numerical calculation, the cone angle of 11.3° is the best for settlement control. The tensile strength of geogrid is 80 kN/m, which has the best effect on settlement control. Considering the material utilization rate, the settlement control efficiency is the highest when the aspect ratio is 25.

[1] 樊曦. 开年看铁路：三大亮点书写发展新篇章[J]. 现代企业, 2024, (03): 6.

[2] 黄奇帆. 伟大复兴的关键阶段——学习《中华人民共和国国民经济和社会发展第十四个五年规划和2035年远景目标纲要》的认识和体会[J]. 人民论坛, 2021, (15): 6-10.

[3] Laird D A, Brown R C, Amonette J E, et al. Review of the pyrolysis platform for coproducing bio‐oil and biochar[J]. Biofuels, bioproducts and biorefining, 2009, 3(5): 547-62.

[4] 2020年我国交通运输行业发展统计公报发布[J]. 隧道建设(中英文), 2021, 41(06): 963.

[5] 刘钢, 罗强, 张良, 等. 基于累积变形演化状态控制的高速铁路基床结构设计计算方法[J]. 中国科学:技术科学, 2014, 44: 744-54

[6] 胡一峰, 李怒放. 高速铁路无砟轨道路基设计原理[M]. 中国铁道出版社, 2010.

[7] Lal R. Soil carbon sequestration in China through agricultural intensification, and restoration of degraded and desertified ecosystems[J]. Land degradation & development, 2002, 13(6): 469-78.

[8] 孙广超, 刘汉龙, 孔纲强, 等. 振动波型对X形桩桩–筏复合地基动力响应影响的模型试验研究[J]. 岩土工程学报, 2016, 38: 1021-9

[9] Peng Y, Liu J-Y, Ding X-M, et al. Performance of X-section concrete pile group in coral sand under vertical loading[J]. China Ocean Engineering, 2020, 34(5): 621-30.

[10] Ren L W, Guo W D, Yang Q W. Analysis on bearing performance of Y-shaped piles under compressive and tensile loading[J]. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 2020, 173(1): 58-69.

[11] 李飞, 杨俊杰, 宋琦, 等. 多层砂土地基扩底桩单桩抗压模型试验及颗粒流模拟研究[J]. 中国海洋大学学报(自然科学版), 2020, 50: 116-25

[12] 王奎华, 童魏烽, 肖偲, 等. 楔形桩的动力响应与试验研究[J]. 湖南大学学报(自然科学版), 2019, 46: 94-102

[13] 陈浩华, 李镜培, 李林, 等. 楔形桩极限承载力提高机理研究[J]. 哈尔滨工业大学学报, 2017, 49: 110-6

[14] 邓友生, 李龙, 刘俊聪, 等. 波纹塑料套管煤矸石CFG桩复合路基承载试验[J]. 中国公路学报, 2023, 36: 48-57

[15] Zhang C, Zhao M, Zhou S, et al. A theoretical solution for pile-supported embankment with a conical pile-head[J]. Applied Sciences, 2019, 9(13): 2658.

[16] 邓友生, 宋虔, 张克钦, 等. 锥形帽单桩竖向承载力模型试验研究[J]. 武汉科技大学学报, 2023, 46: 472-7

[17] Ismael N F. Behavior of step tapered bored piles in sand under static lateral loading[J]. Journal of geotechnical and geoenvironmental engineering, 2010, 136(5): 669-76.

[18] 王景梅, 蒋浩然. 大直径阶梯型变截面桩水平承载特性试验研究与理论分析[J]. 公路, 2020, 65(03): 141-7.

[19] 许德祥. 超大直径阶梯型变截面桩的荷载传递模型与沉降计算方法[D]. 福州: 福州大学, 2018.

[20] Ismael N F. Axial load tests on bored piles and pile groups in cemented sands[J]. Journal of geotechnical and geoenvironmental engineering, 2001, 127(9): 766-73.

[21] 杨庆光, 田捷, 刘杰. 阶梯型变截面管桩沉桩阻力计算方法与模型试验研究[J]. 工业建筑, 2015, 45: 104-10

[22] 方焘, 张胤红, 王宁, 等. 一阶变截面桩与等截面桩对比试验研究[J]. 华东交通大学学报, 2019, 36: 94-9

[23] 刘新荣, 方焘, 耿大新, 等. 大直径变径桩横向承载特性模型试验[J]. 中国公路学报, 2013, 26: 80-6+190

[24] 易耀林, 郗文, 刘松玉, 等. 变截面搅拌桩加固路堤下成层软弱地基数值模拟[J]. 岩土工程学报, 2013, 35: 433-8

[25] Xiong L, Chen H. A numerical study and simulation of vertical bearing performance of step-tapered pile under vertical and horizontal loads[J]. Indian Geotechnical Journal, 2020, 50: 383-409.

[26] Kodikara J, Kong K H, Haque A. Numerical evaluation of side resistance of tapered piles in mudstone[J]. Geotechnique, 2006, 56(7): 505-10.

[27] Vali R, Mehrinejad Khotbehsara E, Saberian M, et al. A three-dimensional numerical comparison of bearing capacity and settlement of tapered and under-reamed piles[J]. International Journal of Geotechnical Engineering, 2019, 13(3): 236-48.

[28] Kong G, Zhou L, Peng H, et al. Reduction rate of dragload and downdrag of piles by taper angles[J]. Transactions of Tianjin University, 2016, 22(5): 434-40.

[29] Wang J, Zhou D, Zhang Y, et al. Vertical impedance of a tapered pile in inhomogeneous saturated soil described by fractional viscoelastic model[J]. Applied Mathematical Modelling, 2019, 75: 88-100.

[30] Ghazavi M. Response of tapered piles to axial harmonic loading[J]. Canadian geotechnical journal, 2008, 45(11): 1622-8.

[31] Shafaghat A, Khabbaz H. Recent advances and past discoveries on tapered pile foundations: A review[J]. Geomechanics and Geoengineering, 2022, 17(2): 455-84.

[32] 李镜培, 陈浩华, 李林, 等. 楔形单桩与群桩非线性荷载-沉降曲线计算方法[J]. 哈尔滨工业大学学报, 2017, 49: 102-9

[33] 曹兆虎, 孔纲强, 周航, 等. 基于透明土的静压楔形桩沉桩效应模型试验研究[J]. 岩土力学, 2015, 36: 1363-7+74

[34] El Naggar M H, Wei J Q. Axial capacity of tapered piles established from model tests[J]. Canadian Geotechnical Journal, 1999, 36(6): 1185-94.

[35] El Naggar M H, Wei J Q. Uplift behaviour of tapered piles established from model tests[J]. Canadian Geotechnical Journal, 2000, 37(1): 56-74.

[36] Fellenius B H, Altaee A. Experimental study of axial behaviour of tapered piles: Discussion[J]. Canadian Geotechnical Journal, 1999, 36(6): 1202.

[37] El Naggar M H, Wei J Q. Response of tapered piles subjected to lateral loading[J]. Canadian Geotechnical Journal, 1999, 36(1): 52-71.

[38] El Naggar M H, Sakr M. Cyclic response of axially loaded tapered piles[J]. International Journal of Physical Modelling in Geotechnics, 2002, 2(4): 01-12.

[39] 刘杰, 王忠海. 楔形桩承载力试验研究[J]. 天津大学学报, 2002: 257-60

[40] 刘杰, 何杰, 闵长青. 楔形桩与圆柱形桩复合地基承载性状对比研究[J]. 岩土力学, 2010, 31: 2202-6

[41] Paik K, Lee J, Kim D. Axial response and bearing capacity of tapered piles in sandy soil[J]. Geotechnical Testing Journal, 2011, 34(2): 122-30.

[42] 杨贵, 孔纲强, 曹兆虎, 等. 楔形桩和等截面桩沉桩施工过程数值模拟对比分析[J]. 铁道科学与工程学报, 2016, 13: 40-5

[43] Hataf N, Shafaghat A. Optimizing the bearing capacity of tapered piles in realistic scale using 3D finite element method[J]. Geotechnical and Geological Engineering, 2015, 33: 1465-73.

[44] Hataf N, Shafaghat A. Numerical comparison of bearing capacity of tapered pile groups using 3D FEM[J]. Geomech Eng, 2015, 9(5): 547-67.

[45] Nasrollahzadeh E, Hataf N. Experimental and numerical study on the bearing capacity of single and groups of tapered and cylindrical piles in sand[J]. International Journal of Geotechnical Engineering, 2022, 16(4): 426-37.

[46] 赵明华, 徐泽宇, 张承富. 带锥形桩帽复合地基桩土应力比计算及其数值模拟[J]. 湖南大学学报(自然科学版), 2020, 47(03): 1-10.

[47] Dias D, Grippon J. Numerical modelling of a pile-supported embankment using variable inertia piles[J]. Structural Engineering and Mechanics, 2017, 61(2): 245-53.

[48] Kempfert H G. Berechnung von geokunststoffbewehrten Tragschichten uber Pfahlelementen[J]. Bautechnik, 1997, 74(12): 818-25.

[49] Hewlett W, Randolph M. Analysis of piled embankments; proceedings of the International journal of rock mechanics and mining sciences and geomechanics abstracts, F, 1988 [C]. Elsevier Science.

[50] 陈云敏, 贾宁, 陈仁朋. 桩承式路堤土拱效应分析[J]. 中国公路学报, 2004: 4-9

[51] Van Eekelen S J, Bezuijen A, Lodder H, et al. Model experiments on piled embankments. Part I[J]. Geotextiles and Geomembranes, 2012, 32: 69-81.

[52] Van Eekelen S J, Bezuijen A, Lodder H, et al. Model experiments on piled embankments. Part II[J]. Geotextiles and Geomembranes, 2012, 32: 82-94.

[53] Carlsson B. Reinforced soil, principles for calculation[J]. Terratema AB, Linköping, 1987, 525.

[54] Card G, Carter G. Case history of a piled embankment in London's Docklands[J]. Geological Society, London, Engineering Geology Special Publications, 1995, 10(1): 79-84.

[55] Jenner C, Austin R, Buckland D. Embankment support over piles using geogrids; proceedings of the Proceedings of 6th International Conference on Geosynthetics, F, 1998 [C]. Industrial Fabrics Association International.

[56] Russell D, Pierpoint N. An assessment of design methods for piled embankments[J]. Ground Engineering, 1997, 30(10).

[57] 刘吉福. 路堤下复合地基桩、土应力比分析[J]. 岩石力学与工程学报, 2003: 674-7

[58] Kuo S-S, Desai K, Rivera L. Design method for municipal solid waste landfill liner system subjected to sinkhole cavity under landfill site[J]. Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management, 2005, 9(4): 281-91.

[59] Sloan J, Filz G, Collin J. A generalized formulation of the adapted Terzaghi method of arching in column-supported embankments [M]. Geo-Frontiers 2011: Advances in Geotechnical Engineering. 2011: 798-805.

[60] Naughton P, Kempton G. Comparison of analytical and numerical analysis design methods for piled embankments [M]. Contemporary Issues in Foundation Engineering. 2005: 1-10.

[61] 郑俊杰, 张军, 马强, 等. 双向增强体复合地基桩土应力比三维分析[J]. 华中科技大学学报(自然科学版), 2010, 38: 83-6

[62] 蔡燕燕, 江文放, 俞缙, 等. 考虑筋材旋转抛物面变形的桩承式路堤桩土应力比[J]. 岩土工程学报, 2013, 35: 963-7

[63] 上官士青, 杨敏, 陈飞, 等. 基于最小势能原理的加筋垫层与路堤桩土相互作用研究[J]. 岩土工程学报, 2015, 37: 1264-70

[64] Kraft Jr L M, Ray R P, Kagawa T. Theoretical t-z curves[J]. Journal of the Geotechnical Engineering Division, 1981, 107(11): 1543-61.

[65] Richard R M, Abbott B J. Versatile elastic-plastic stress-strain formula[J]. Journal of the Engineering Mechanics Division, 1975, 101(4): 511-5.

[66] Kuwabara F, Poulos H. Downdrag forces in group of piles[J]. Journal of geotechnical engineering, 1989, 115(6): 806-18.

[67] Chow Y K, Chin J T, Lee S L. Negative skin friction on pile groups[J]. International Journal for Numerical and Analytical Methods in Geomechanics, 1990, 14(2): 75-91.

[68] Chow Y, Lim C, Karunaratne G. Numerical modelling of negative skin friction on pile groups[J]. Computers and Geotechnics, 1996, 18(3): 201-24.

[69] Poorooshasb H, Alamgir M, Miura N. Negative skin friction on rigid and deformable piles[J]. Computers and Geotechnics, 1996, 18(2): 109-26.

[70] Lee C, Bolton M, Al-Tabbaa A. Numerical modelling of group effects on the distribution of dragloads in pile foundations[J]. Geotechnique, 2002, 52(5): 325-35.

[71] 王建华, 高绍武, 陆建飞. 表面堆载作用下群桩负摩擦研究[J]. 计算力学学报, 2003: 169-74

[72] Reddy E S, Chapman D, Sastry V. Direct shear interface test for shaft capacity of piles in sand[J]. Geotechnical Testing Journal, 2000, 23(2): 199-205.

[73] Gómez J E, Filz G M, Ebeling R M, et al. Sand-to-concrete interface response to complex load paths in a large displacement shear box[J]. Geotechnical Testing Journal, 2008, 31(4): 358-69.

[74] Alamgir M, Miura N, Poorooshasb H, et al. Deformation analysis of soft ground reinforced by columnar inclusions[J]. Computers and Geotechnics, 1996, 18(4): 267-90.

[75] 曹新文, 卿三惠, 周立新. 桩网复合地基土工格栅加筋效应的试验研究[J]. 岩石力学与工程学报, 2006, (S1): 3162-7.

[76] 芮瑞, 万亿, 陈成, 等. 加筋对桩承式路堤变形模式与土拱效应影响试验[J]. 中国公路学报, 2020, 33: 41-50

[77] Chen R, Wang Y, Ye X, et al. Tensile force of geogrids embedded in pile-supported reinforced embankment: A full-scale experimental study[J]. Geotextiles and Geomembranes, 2016, 44(2): 157-69.

[78] 陈庚, 陈永辉, 徐锴, 等. 桩承式加筋路堤土拱效应现场试验[J]. 长安大学学报(自然科学版), 2016, 36: 41-7

[79] Xue S, Chen Y, Liu H. Model test study on the influence of train speed on the dynamic response of an X-section pile-net composite foundation[J]. Shock and Vibration, 2019, 2019.

[80] 蒋泽中, 肖宏, 蒋关鲁, 等. 桩网结构加固土质路基的离心机模型试验研究[J]. 铁道工程学报, 2013: 18-22+56

[81] 朱学敏, 崔晓艳. 桩承式加筋路堤中土工格栅加筋效应的室内试验研究[J]. 河北工程大学学报(自然科学版), 2020, 37(01): 35-40.

[82] Han J, Gabr M. Numerical analysis of geosynthetic-reinforced and pile-supported earth platforms over soft soil[J]. Journal of geotechnical and geoenvironmental engineering, 2002, 128(1): 44-53.

[83] Zhang J, Liu S-W, Pu H-F. Evaluation of an improved technique for geosynthetic-reinforced and pile-supported embankment[J]. Advances in Materials Science and Engineering, 2015, 2015.

[84] 许朝阳, 周健, 完绍金. 桩承式路堤承载特性的颗粒流模拟[J]. 岩土力学, 2013, 34(S1): 501-7.

[85] 赖汉江, 郑俊杰, 章荣军, 等. 桩承式路堤土拱形成及荷载传递机制离散元分析[J]. 岩土力学, 2015, 36: 646-50

[86] 杨涛, 盛志成, 陆振荣. 加筋对桩承式路堤荷载传递影响的三维有限元模拟[J]. 上海理工大学学报, 2020, 42(04): 361-7.

[87] 铁道第一勘察设计院.TB 10001-2005. 铁路路基设计规范[S]. 北京: 中国铁道出版社, 2005.

[88] GB/T 50123-2019. 土工试验方法标准[S]. 北京: 中华人民共和国住房和城乡建设部;国家市场监督管理总局, 2019.

[89] 汤智钧. 基坑开挖对近接地铁高架嵌岩桥桩影响的模型试验研究[D]. 广州: 华南理工大学, 2022.

[90] 邓友生, 李令涛, 彭程谱, 等. 静动荷载下桩网结构路基模型试验研究[J]. 岩土力学, 2022, 43: 2149-56

[91] GB/T 1936.2-1991. 木材抗弯弹性模量测定方法[S]. 北京: 国家技术监督局, 1991.

[92] GB 50007-2011. 建筑地基基础设计规范[S]. 北京: 中国建筑工业出版社, 2011.

[93] JGJ 106-2014 建筑桩基检测技术规范[S]. 北京: 中国建筑工业出版社, 2014.

[94] 李鑫, 李昌龙, 白明洲, 等. 桩间距和布桩形式对微型桩受力的影响[J]. 北京交通大学学报, 2017, 41: 47-54