筋土界面静、动剪切特性试验研究

发布时间：2018-06-25 08:13

本文选题：加筋土 + 筋土界面　；参考：《上海大学》2013年硕士论文

【摘要】：加筋土技术从20世纪60年代问世以来，因其技术经济效益十分显著，可节约工程造价25％~65％，施工快速、外形美观、节约土地等优点，得到了广泛应用。筋土界面的相互作用特性直接影响着加筋土结构的稳定性，界面强度参数对加筋土工程结构的设计起着至关重要的作用。本文通过室内大型直剪试验，对几种工程中常用的土工合成材料与砂土填料的界面特性进行了较为详细的研究，，主要工作如下： 1.为了研究填土与土工合成材料相互作用时筋土界面的抗剪强度以及剪胀特性，采用三种不同级配的砂土分别与土工格栅和土工织物进行了室内大型直剪试验。研究了不同颗粒级配、密实度、筋材种类以及竖向应力对界面剪切特性的影响，并对界面剪胀系数进行了分析。结果表明：粗砂和细砂与筋材的界面剪切强度要明显大于粗细混合砂；松砂剪切过程中只有剪缩效应的存在，但密实砂土表现出了明显的剪胀过程；当竖向应力较大时，筋土界面达到峰值剪切强度所需的剪切位移比低应力水平时大；粗砂与土工格栅作用时达到峰值剪切强度所需的剪切位移比与土工织物作用时大，而细砂则相反。 2.采用室内大型直剪试验，系统地分析了格栅横肋与纵肋以及格栅几何尺寸对于筋土界面强度特性的影响。试验结果表明：格栅的横肋与纵肋在界面强度中均发挥了较大的作用，两者表现为不同的作用机理，当剪切位移较小时格栅横肋的被动阻力和纵肋的摩阻力起到共同承担荷载的作用；而随着剪切位移的增大，横肋的被动阻力进一步提升，纵肋则发挥了较为显著的提高筋材刚度的框架作用。因此，格栅的纵横肋需要协调作用才能发挥出较大的筋土界面强度。 3.为了研究砂土与土工合成材料相互作用的动力特性，进行了一系列室内大型界面循环剪切与单调剪切试验。研究了不同竖向应力、循环剪切幅值、剪切次数等因素对于界面抗剪强度以及剪胀性的影响，并与单调剪切试验条件下的试验结果对比，分析了循环后的界面特性。试验结果表明：竖向应力的值越大，循环剪切强度的增长幅度越平缓，即低应力下循环剪切强度的增幅较为明显；界面剪胀剪缩性能随着剪切幅值的增加而增强；随着循环次数的增加，界面的强度有了一定的提高，同时竖向位移变化也较大。 4.在试验基础上提出了一种能够描述筋土界面力学性能的组合本构模型，该模型包含四个关系式：(1)峰值、残余强度包络线；(2)强度峰值前的双曲线模型；(3)强度峰值后的位移软化模型；(4)反映剪胀特性的界面剪胀模型。该组合模型的预测结果与验证试验的结果能够较好的吻合，表明所提模型是合理的。
[Abstract]:Since the advent of reinforced earth technology in the 1960s, it has been widely used because of its remarkable technical and economic benefits, the advantages of saving engineering cost by 25 and 65, rapid construction, beautiful appearance and saving land. The interaction characteristics of the reinforced soil interface directly affect the stability of the reinforced soil structure, and the interface strength parameters play an important role in the design of the reinforced soil engineering structure. In this paper, the interfacial characteristics of geosynthetics and sand fillers, which are commonly used in engineering, are studied in detail through large direct shear tests. The main work is as follows: 1. In order to study the shear strength and shear dilatancy of reinforced soil interface under the interaction of fill and geosynthetics, three kinds of sand with different gradation, geogrid and geotextile were used in the laboratory direct shear tests. The effects of particle gradation, compactness, reinforcement type and vertical stress on the interfacial shear properties were studied, and the shear expansion coefficient of the interface was analyzed. The results show that the interfacial shear strength of coarse sand and fine sand and steel bar is obviously greater than that of coarse sand, the shear shrinkage effect exists only in loose sand shear process, but the shear expansion process is obvious in dense sand, and when the vertical stress is large, The shear displacement required to reach the peak shear strength of the reinforced soil interface is larger than that of the low stress level, and the shear displacement required to reach the peak shear strength between coarse sand and geogrid is greater than that of geotextile, whereas the shear displacement of fine sand is opposite to that of geotextile. In this paper, the influence of transverse rib, longitudinal rib and geometric size of grid on the strength characteristics of reinforced soil interface is systematically analyzed by large direct shear test. The experimental results show that the transverse rib and longitudinal rib play a significant role in the interfacial strength, and the two play different mechanisms. When the shear displacement is small, the passive resistance of the transverse rib and the friction resistance of the longitudinal rib bear the load together, but with the increase of the shear displacement, the passive resistance of the transverse rib increases further. Longitudinal ribs play a more significant role in improving the stiffness of steel frame. Therefore, the longitudinal and transverse ribs of the grille need to be coordinated in order to play a larger reinforced soil interface strength. 3. In order to study the dynamic characteristics of the interaction between sand and geosynthetics, a series of laboratory tests on cyclic shear and monotone shear were carried out. The effects of different vertical stress, cyclic shear amplitude and shear times on the shear strength and dilatancy of the interface were studied. Compared with the experimental results under monotonic shear test, the characteristics of the interface after cycling were analyzed. The experimental results show that the increasing amplitude of cyclic shear strength is more gentle with the increase of vertical stress, that is, the increase of cyclic shear strength is obvious under low stress, and the expansion and shrinkage properties of interfacial shear increase with the increase of shear amplitude. With the increase of cycle times, the strength of the interface increases to a certain extent, and the vertical displacement changes greatly. 4. 4. On the basis of experiments, a combined constitutive model is proposed, which can describe the mechanical properties of the interface between reinforcement and soil. The model consists of four relations: (1) peak value, envelope of residual strength, (2) hyperbolic model before peak strength; (3) displacement softening model after peak strength and (4) interfacial shear dilatation model reflecting shear dilatancy. The prediction results of the combined model are in good agreement with the results of the verification test, which indicates that the proposed model is reasonable.
【学位授予单位】：上海大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU41

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