北京西六环膨胀岩（土）中加筋拉拔试验及其数值仿真
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摘要
柔性支护技术首次用于治理北京西六环沉积型膨胀岩(土)堑坡已获成功,支护体中土工格栅与膨胀土填料间摩擦、U型钉锚固及上下格栅反包连接构成边坡整体强度,而拉拔试验是确定其相互作用的最好方法。为获得膨胀土中加筋作用机理、界面参数并优化设计方法,本文开展西六环膨胀岩(土)中加筋拉拔试验研究及其数值仿真。
为确定CS-LB01大型数控拉拔试验系统进行筋土界面试验的合适条件,以西六环三种膨胀土为填料,采用两种格栅加筋,通过改变上覆荷载、拉拔速率、土样含水率及固结时间完成了33组拉拔试验,获得各因素的影响程度,基于此并考虑实际工况,分析提出合适的试验条件。
为探讨拉拔力与格栅强度、几何特性间关系,用湖北力特生产的五种格栅及2#土样为材料,进行了系列试验,得到拉拔力不仅与筋材强度有关,而且还与相同埋入长度时的横肋数有关,实施柔性支护时,加筋材料的选择应综合考虑这两方面因素。
为模拟柔性支护的实际工况,还设计并开展了格栅尾部用两种钢钉固定的拉拔试验,结果表明,拉拔力较未加钉固定的测试值有较大提高,说明U型钉锚固对提高柔性支护整体强度发挥了重要作用。
最后,采用FLAC3D模拟了膨胀土中加筋的拉拔试验过程,格栅采用FLAC特有的Geogrid结构单元,土样选用摩尔—库伦本构模型,获得的拉拔力与位移曲线形状与试验时机器自动绘图相差无几,同时还得到格栅发生有效拔出时土体的位移场分布、竖向应力分布、筋土界面水平向应力分布以及界面摩擦阻力分布,可为加筋作用机理、界面参数分析提供参考。
It was a huge success that flexible supporting technology was firstly used in the Beijing Western Sixth Ring Highway depositional expansive rock/soil cutting slope. The overall strength of cutting slope included the friction between geogrid and expansive soil, the anchoring geogrid using U-shaped nail and the folding connection of geogrid. Pullout test is the best method for studying on this interaction. In order to obtain reinforcement mechanism of expansive soil, interface parameters and optimize the flexible supporting design, the research on pullout tests of the Beijing Western Sixth Ring Highway reinforced expansive rock/soil and numerical analysis were carried out.
To gain the interface appropriate testing conditions of reinforced soil, a large-scale pullout test system‘CS-LB01’was used. Three expansive soil samples from Beijing Sixth Ring Highway and two kinds of geogrids were utilized to research the influence degree by different factors such as various overlying loads, sample moisture contents, pullout rates of geogrid, consolidation times and types of reinforcement material. Totally, thirty-three groups of pullout tests were performed. Based on the results and actual working conditions, the appropriate testing condition was proposed.
In order to research on the relation between geogrid drawing force and its strength and geometric characteristics, five kinds of geogrids manufactured by Hubei Nete Geosynthetics Ltd and expansive soil (sample 2) were utilized to perform the pullout tests. The drawing force was related with not only the strength of reinforcement material, but also the number of horizontal rib with the same length of geogrid in the soil. When flexible supporting technology was implemented, these two factors were synthetically considered when reinforcement materials were selected.
In order to simulate the practical situation of flexible supporting, pullout tests were carried out with geogrid tail fixed by two types of reinforcement nails. The results showed that drawing force increased considerably than that without reinforcement nails. U-shaped nail played an important role in increasing flexible supporting body’s overall strength.
Finally, the pullout test between geogrid and expansive soil was simulated by the finite difference FLAC3D software. Geogrid structure unit built-in FLAC3D was adopted for stimulating reinforcement material and Mohr-Coulomb Model was adopted for the constitutive model of expansive soil. The curve of between drawing force and displacement agree very well with the automatic computer testing graphics. When the geogird was effectively drawn out, these that included displacement field distribution, vertical stress distribution, interface horizontal stress distribution and interface frictional resistance distribution were obtained. These provided reference for analyzing on reinforcement mechanism and interfacial interaction parameters.
为确定CS-LB01大型数控拉拔试验系统进行筋土界面试验的合适条件,以西六环三种膨胀土为填料,采用两种格栅加筋,通过改变上覆荷载、拉拔速率、土样含水率及固结时间完成了33组拉拔试验,获得各因素的影响程度,基于此并考虑实际工况,分析提出合适的试验条件。
为探讨拉拔力与格栅强度、几何特性间关系,用湖北力特生产的五种格栅及2#土样为材料,进行了系列试验,得到拉拔力不仅与筋材强度有关,而且还与相同埋入长度时的横肋数有关,实施柔性支护时,加筋材料的选择应综合考虑这两方面因素。
为模拟柔性支护的实际工况,还设计并开展了格栅尾部用两种钢钉固定的拉拔试验,结果表明,拉拔力较未加钉固定的测试值有较大提高,说明U型钉锚固对提高柔性支护整体强度发挥了重要作用。
最后,采用FLAC3D模拟了膨胀土中加筋的拉拔试验过程,格栅采用FLAC特有的Geogrid结构单元,土样选用摩尔—库伦本构模型,获得的拉拔力与位移曲线形状与试验时机器自动绘图相差无几,同时还得到格栅发生有效拔出时土体的位移场分布、竖向应力分布、筋土界面水平向应力分布以及界面摩擦阻力分布,可为加筋作用机理、界面参数分析提供参考。
It was a huge success that flexible supporting technology was firstly used in the Beijing Western Sixth Ring Highway depositional expansive rock/soil cutting slope. The overall strength of cutting slope included the friction between geogrid and expansive soil, the anchoring geogrid using U-shaped nail and the folding connection of geogrid. Pullout test is the best method for studying on this interaction. In order to obtain reinforcement mechanism of expansive soil, interface parameters and optimize the flexible supporting design, the research on pullout tests of the Beijing Western Sixth Ring Highway reinforced expansive rock/soil and numerical analysis were carried out.
To gain the interface appropriate testing conditions of reinforced soil, a large-scale pullout test system‘CS-LB01’was used. Three expansive soil samples from Beijing Sixth Ring Highway and two kinds of geogrids were utilized to research the influence degree by different factors such as various overlying loads, sample moisture contents, pullout rates of geogrid, consolidation times and types of reinforcement material. Totally, thirty-three groups of pullout tests were performed. Based on the results and actual working conditions, the appropriate testing condition was proposed.
In order to research on the relation between geogrid drawing force and its strength and geometric characteristics, five kinds of geogrids manufactured by Hubei Nete Geosynthetics Ltd and expansive soil (sample 2) were utilized to perform the pullout tests. The drawing force was related with not only the strength of reinforcement material, but also the number of horizontal rib with the same length of geogrid in the soil. When flexible supporting technology was implemented, these two factors were synthetically considered when reinforcement materials were selected.
In order to simulate the practical situation of flexible supporting, pullout tests were carried out with geogrid tail fixed by two types of reinforcement nails. The results showed that drawing force increased considerably than that without reinforcement nails. U-shaped nail played an important role in increasing flexible supporting body’s overall strength.
Finally, the pullout test between geogrid and expansive soil was simulated by the finite difference FLAC3D software. Geogrid structure unit built-in FLAC3D was adopted for stimulating reinforcement material and Mohr-Coulomb Model was adopted for the constitutive model of expansive soil. The curve of between drawing force and displacement agree very well with the automatic computer testing graphics. When the geogird was effectively drawn out, these that included displacement field distribution, vertical stress distribution, interface horizontal stress distribution and interface frictional resistance distribution were obtained. These provided reference for analyzing on reinforcement mechanism and interfacial interaction parameters.
引文
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[2] Fredlund D.G, Chen Z Y.China-Canada Cooperative Research Program on Expansive Soils.Report Summited to International Development Research Centre (IDRC).1988.
[3] D.G Fredlund and Rahardjo著,陈仲颐等译.非饱和土土力学.北京:中国建筑工业出版社,1997.8.
[4]包承纲.土工合成材料应用原理与工程实践.北京:中国水利水电出版社,2008.
[5]周志刚,郑健龙.公路土工合成材料设计原理及工程应用.北京:人民交通出版社,2001.
[6]肖桂彰.道路复合材料.北京:人民交通出版社,1999.
[7]雷胜友.现代加筋土理论与技术.北京:人民交通出版社,2001.
[8]包承纲.土工合成材料界面特性的研究和试验验证.岩石力学与工程学报,2006,9,1735-1744.
[9] Bauer C E, Zhao Y J. Effect of soil dilatancy on shear strength of reinforced composites.In:Proc.of International Conference on Geotextiles[C].[s.I.]: [s.n],1994.369-372
[10]南京水利科学研究院.土工合成材料测试手册.北京:水利电力出版社,1991.
[11]土工合成材料工程应用手册编写委员会.土工合成材料工程应用手册(第二版).北京:中国建筑工业出版社,2000.
[12]马时冬.土工格栅与土的界面摩擦特性试验研究.长江科学院院报,2004,21(1):11-13.
[13]徐超,赵春风,叶观宝.关于土与土工合成材料界面的试验研究.同济大学学报,2004,32(3):307-311.
[14]陈榕,栾茂田,赵维等.土工格栅拉拔试验及筋材摩擦受力特性研究.岩土力学,2009,30(4):960-964.
[15]张文慧,王保田,张福海等.含水率对经编土工格栅与土界面作用特性的影响.中南公路工程,2007,32(3):24-26.
[16]杨和平,万亮,谭波.土工格栅拉拔试验研究的现状与发展.长沙交通学院学报,2006,22(1):36-41.
[17] Khalid Farrag,Yalcin B.Acar & Ilan Juran.Pull-out Resisitance of Geogrid Reinforcement.Geotextiles and Geomembranes.1993,133-159.
[18] M.L.Lopes,M.Ladeira.Influence ofthe confinement,soil density and displacement rate on soil-geogrid interaction.Geotextiles and Genmembranes,1996,14,543-554.
[19]魏红卫,喻泽红,邹银生.土工合成材料加筋土抗剪作用的试验研究.水利学报,2005,36(5).
[20]丁建明,张波.土工合成材料与粘土接触面直剪试验研究.华中科技大学学报(城市科学版),2005,22(2).
[21]孟凡祥.筋土之间直剪试验和拉拔试验的对比分析[同济大学硕士学位论文].上海:同济大学,2009.3.
[22]徐晓艳.土工格栅拉拔特性的试验研究[大连理工大学硕士学位论文].大连:大连理工大学2007.6.
[23]施有志.土工合成材料界面直剪摩擦试验研究.中外公路,2006,26(3):255-258.
[24]吴景海.土工合成材料界面作用特性的拉拔试验研究.岩土力学,2006,27(4):581-585.
[25]邹静蓉,刘拓瑜,冷伍明.土与土工格栅相互作用的模型试验研究.铁道科学与工程学报,2005,2(3):51-55.
[26]张波,石名磊.粘土与筋带直剪试验与拉拔试验对比分析.岩土力学,2005,26(Supp):61-64.
[27]魏红卫,喻泽红,尹华伟.土工合成材料加筋粘性土的三轴试验研究.工程力学,2007,24(5):107-113.
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