【作者】 董彦莉；

【导师】 白晓红；

【作者基本信息】 太原理工大学 ， 岩土工程， 2011， 博士

【摘要】 作为一种刚刚引进市场不久的新型土工格栅,三角形土工格栅有着更稳定的网格结构,可以在各个方向提供更均匀的约束。目前世界上各国对于该土工格栅的基础理论研究和应用技术刚刚起步,研究数据还非常有限。因此很有必要开展三角形土工格栅加筋地基的试验、理论及应用的研究,加快我国对新产品研究应用的步伐,缩短与国际间的差距,更好地为工程实践服务。利用美国堪萨斯大学、建筑与环境学院设计制造的直剪仪进行了三角形土工格栅加筋砂土的室内直剪试验,研究了三角形土工格栅与砂土的界面特性；通过室内载荷试验,研究了三角形土工格栅加筋砂土的承载力性状；采用FLAC数值模拟,分析了三角形土工格栅在不同方向拉力作用下的张拉性能,同时对施工损伤下的强度损失也作了一些探讨,为三角形土工格栅进一步在工程中推广应用提供了试验和理论研究基础。结合现场原位载荷试验结果,讨论了加筋地基承载力计算方法。本文获得主要结论如下：(1)采用室内直剪试验,首次对新型三角形士工格栅与砂土的界面特性进行了研究,探讨了影响土工格栅筋土界面特性的因素,引入摩擦系数比,对三角形土工格栅筋土界面特性进行评价。试验表明,三角形土工格栅和双向土工格栅加筋砂土的剪切应力与剪切位移的关系曲线变化规律基本相同,剪应力与垂直荷载间存在线性关系,可用莫尔库伦抗剪强度公式表示。峰值强度条件下,双向土工格栅和砂土界面摩擦角与砂土的内摩擦角基本相等,筋土界面抗剪强度较砂土抗剪强度的提高主要决定于格栅肋条上下表面与砂土颗粒的摩擦作用和格栅肋条对砂土颗粒的“嵌固”作用使颗粒间的“咬合力”提高引起的似粘聚力增加；三角形土工格栅和砂土的摩擦角大于砂土的内摩擦角,筋土界面抗剪强度的提高除考虑似粘聚力提高外,需适当考虑摩擦角增量的贡献。这是由于三角形格栅的形状优势,对砂土颗粒提供了更大的侧向约束和“嵌固”作用,不仅使筋土界面的似粘聚力提高,同时也引起摩擦角的明显增大。引入栅孔形状参数,分析了栅孔形状对筋土界面相互作用的影响,验证了三角形土工格栅三角形栅孔的优越性,同时从四个阶段简要分析了土工格栅与砂土界面破坏的机理。(2)首次采用模拟的方法,提出简化分析模型,分析了三角形土工格栅和双向土工格栅在不同方向拉力作用下的张拉性能,研究了抗拉强度和抗拉刚度的分布受栅格形状,肋条截面积,肋条弹性模量变化的影响规律。通过模拟分析发现,双向土工格栅的抗拉强度和抗拉刚度极大程度上与单向拉力的方向有关,而三角形土工格栅抗拉强度和抗拉刚度受拉力方向影响较小。肋条弹性模量和截面积的增加均会引起三角形土工格栅抗拉强度和抗拉刚度的增加。(3)将施工损伤的概念引入数值模拟模型中,模拟分析了土工格栅不同损伤程度下的抗拉强度变化。结果发现,随着损伤程度的增加,两种格栅的强度近似呈线性递减,30。方向抗拉强度变化较其它方向变化大。双向土工格栅极限抗拉强度受施工损伤的影响较三角形土工格栅敏感。建议三角形七工格栅的施工损伤折减系数以30。方向下25%-75%损伤范围内取值。(4)利用室内模型试验方法,首次对三角形土工格栅加筋砂土开展载荷试验研究。试验表明,三角形土工格栅或双向土工格栅加筋,均可提高砂土地基的极限承载力和刚度,同时可提高加筋地基的模量。三角形土工格栅首层加筋间距为1/3倍的基础宽度时,加筋效果最好。单层加筋时,在地基允许变形范围内,筋材抗拉强度接近的条件下,三角形土工格栅较双向土工格栅更能有效地发挥作用。引入承重比的概念,从经济方面研究了三角形土工格栅的优越性。选用土工格栅进行地基加筋时,需结合工程实际,选择合适的格栅类型、格栅型号和加筋参数。(5)比较和分析了改进的Terzaghi公式和Binquet公式这两种方法的不足之处,结合现场原位载荷试验结果,在筋材拉力计算中引入了筋材抗拉强度发挥系数,提出修正的加筋地基的实用计算方法,与工程实测数据吻合良好,为《建筑地基处理技术规范》的修订提供参考。更多还原

【Abstract】 The new triangular geogrid products with a triangular aperture shape recently introduced into the market are expected to have a more stable grid structure, which can provide more uniform resistance in all directions. However, limited test data related to triangular geogrid-reinforced bases has been published so far. Therefore, tests are needed to evaluate their behavior and mechanisms when used in the reinforced bases. Laboratory direct shear and plate load tests were conducted in the apparatus designed and fabricated at Department of Civil, Environmental, and Architectural Engineering at the University of Kansas to investigate the behavior and mechanisms of triangular geogrid reinforced sand bases. The tensile behavior of the geogrids with triangular and rectangular apertures under different uniaxial tensions was modeled using the numerical software-FLAC2D. The effects of installation damage on the geogrid under uniaxial tensions were also investigated. A simplified method for calculating the bearing capacity of geosynthetic reinforced bases was proposed, which can provide the reference data for the revision of the Technical Code for Ground Treatment of Buildings. The main conclusions can be drawn out from this study as follows:(1) It was the first time using the direct shear test method to study the interface strengthbetween the new triangular geogrid and Kansas River sand. The ratio of frictional coefficients was introduced to evaluate the interface properties. As obtained from the test data, the relationships between shear stress versus shear displacement are nearly the same and the shear strength increased linearly with the increase of vertical stress. The friction angles between biaxial geogrid and the sand are nearly equal to the internal friction angle of the sand. The increment of interface shear strength between biaxial geogrid and sand was mainly due to interlocking between geogrid and sand. Indition to the interlocking between geogrid and sand, the contribution of aperture shape on the increase of the friction angle was considered for the triangular geogrid. The shape parameters of geogrid were introduced to analyze the effect of the aperture shape on the interface action between geogrid and sand. The interface failure mechanisms between geogrid and sand were investigated from four stages.(2) It is the first time using the numerical software-FLAC2D to model the tensile behavior of the geogrid with triangular and rectangular apertures under different uniaxial tensions. In addition to the loading direction, this study studied the influence of the following factors on the tensile stiffness of the geogrids:aperture shape, elastic modulus, and cross-section area of geogrid ribs. The tensile strength and stiffness of the geogrid with rectangular apertures were highly dependent on the direction of the uniaxial tension relative to the orientation of ribs. The tensile strength and stiffness of the geogrid with triangular apertures were relatively uniform at all the loading directions relative to the orientation of ribs even though those at the 45°loading were slightly lower. An increase of the elastic modulus and/or cross-sectional area of ribs increased the tensile stiffness of the geogrid with triangular apertures.(3) As discovered from the numerical results, it was found that the tensile strength decreased linerly with the increase of the extent of damage. The extent of damage was referred to the tensile strength loss in the middle ribs at 0°direction. The reduction of the tensile strengths under 30°tension was significant than other directions. The ultimate tensile strengths of the biaxial geogrid are more sensitive to the installation damage than the triangular geogrid. An installation damage reduction factor of the triangular geogrid based on the tensile strength reduction under 30°tensions was given for reference.(4) The plate load tests were performed to study the behaviors of triangular geogrid reinforced sand. An unreinforced base and biaxial geogrid reinforced sand base were also tested for the comparasion purpose. The reinforced sections were found to perform better than the unreinforced sections when the geogrid was placed at 5 or 10cm. The triangular geogrid at the depth of 1/3 to the width of base performed the best. At the range of effective displacement of base, single layer reinforcement, with a similar tensile strength, the triaxial geogrids had a higher interface shear resistance than biaxial geogrids. The bearing capacity to weight ratio was introduced to investigate the advantages of triangular geogrid. According to the actual site conditions, the types, aperture shape, reinforcement parameters should be considered when geogrid is chosen for reinforcement. The bearing capacity rario was suggested for reference.(5) The modified Terzaghi method and Binquet method were compared first. Based on the site conditions of the reinforced projects, a coefficient of tensile strength of geosynthetic was introduced for calculation. A simplified method to calculate the bearing capacity of geosynthetics-reinforced base by forms of characteristics value method and modified Terzaghi method was given in this paper. The formulations were found to match the test data reseasonably well.更多还原