筋土界面特性及软基上加筋路堤稳定性研究

发布时间：2018-03-14 02:00

本文选题：拉拔试验　切入点：筋-土界面特性　出处：《暨南大学》2014年硕士论文　论文类型：学位论文

【摘要】：软基上筑堤最棘手的问题便是软基处理和工期的矛盾，实践证明，土工织物加筋垫层联合竖向排水体处置软基路堤是行之有效的措施。开展筋-土界面特性研究是进行加筋结构设计、变形与稳定性分析的前期基础性工作，其中界面强度参数是最关键的技术指标。合理的计算方法及工程实践有赖于对加筋机理的认识，加筋垫层处置软基路堤的机理仍需进一步研究。传统极限平衡法存在明显的不合理性及保守性，考虑加筋机理的改进模型亟待提出。本文通过开展大量的室内试验和数值模拟工作研究了砂土强度特性、砂-筋界面特性以及软基上加筋路堤的加筋机理，并结合相关机理建立了改进的整体稳定计算模型，主要研究内容和成果如下：（1）砂土强度特性及筋土界面特性研究。利用常规直剪试验研究了填筑密度、剪切速率对砂土强度特性的影响。利用拉拔试验重点研究了拉拔速率对筋-土界面特性的影响规律和机理，对比了不同填料界面、筋材类型的加筋效果，讨论了内摩擦参数的选取。结果表明：密度越大，砂土应变软化现象越明显，而剪切速率对砂土强度特性基本无影响。砂-筋界面应力应变关系呈硬化型。界面特性受拉拔速率和法向应力的共同影响，其中拉拔速率的影响比较显著，与试验方法、填料性质和筋材类型等因素有关。试验结果同时表明，试验速率影响的是嵌锁、咬合、粘结作用，对摩擦作用基本无影响。与砂土试验结果相比，可知虽然砂-筋界面摩擦角小于填料本身摩擦角，但当存在较大界面“似黏聚力”时，界面抗剪强度在一定法向应力下可高于砂土。所以，进行加筋设计时须根据界面“似黏聚力”大小合理选择内摩擦参数。（2）基于筋-土界面特性的软基上加筋路堤变形与稳定性分析。采用有限元法对一典型软基路堤填筑过程进行了弹塑性固结分析，从应力应变场、筋材拉力和稳定性等角度考察了软基路堤填筑的变形发展规律和加筋垫层加固软基路堤的作用机理，，并对比了考虑大变形效应的计算结果，探讨了界面强度、填筑速度和考虑间接影响带机理对计算结果的影响。结果表明：加筋能有效约束地基软土的剪切变形进而约束路堤侧向变形，并提高其在固结阶段水平位移的“回笼”能力，能有效降低填筑阶段的路堤中心沉降量（但在降低最终沉降量方面不明显），并使最大竖向位移扩展至路堤中心。由于筋-土界面剪应力的存在，填筑阶段浅层地基土的超静孔压较无筋路堤明显上升，但随着固结逐步趋于一致。加筋后路堤的安全系数有明显提升，破坏模式发生改变，改变特征与筋材抗拉强度、界面强度以及地质条件等因素有关。考虑大变形特征后得到中心轴处沉降和坡脚水平位移较小变形结果均有明显降低。界面强度对界面剪应力水平和稳定性有影响，但对加筋路堤的总变形场及筋材拉力基本无影响。填筑速度对无筋路堤有显著影响，而加筋路堤则可快速填至预定高度。考虑间接影响带机理后筋材拉力及界面剪应力水平大幅度降低，路堤稳定性得到提高。（3）基于极限平衡条件的软基上加筋路堤的稳定性分析。在传统分析方法的基础上结合间接影响带机理建立了改进的加筋路堤整体稳定计算模型，对软基上加筋路堤进行了不同计算方法下的稳定性分析。结果表明：基于间接影响带机理的强度折减法和简化Bishop法可以体现加筋的作用。强度折减法与简化Bishop法有很好的一致性，而瑞典条分法的结果与之有明显差距，安全系数偏低且滑弧可信度不高。强度折减法与简化Bishop法更适合分析加筋对稳定性的贡献。
[Abstract]:On the soft foundation of embankment and the most difficult question is contradiction, soft foundation treatment and construction of practice has proved that the geotextile reinforced cushion with vertical drainage body disposal of embankment on soft ground are effective measures. To carry out the research on reinforcement soil interface properties is the design of the reinforced structure, pre deformation and stability analysis of the foundation work among them, the interface strength parameters are the key index. The calculation method is reasonable and practical depends on the understanding of the mechanism of reinforcement, mechanism of geosynthetic reinforced embankment on soft foundation disposal still needs further study. The traditional limit equilibrium method is not reasonable and conservative obviously, to put forward the improvement model considering the reinforcement mechanism this paper studies the strength characteristics of sand. Through laboratory experiment and numerical simulation of a lot of work, the mechanism of reinforced sand bars and the interface properties of reinforced embankment on soft foundation, and the establishment of the related mechanism The main contents and results of the improved overall stability calculation model are as follows:
(1) study on interfacial properties of strength characteristics of reinforced soil and sand. Using the conventional direct shear test on the filling density, the effects of shear rate on the strength characteristics of sand. The influence law and mechanism of drawing speed on the interface characteristics of reinforced soil pull-out test was used to compare different fillers on interface, the effect of reinforcement reinforcement type the discussion on how to select the internal friction parameters. The results show that the density and sand strain softening phenomenon is more obvious, and the shear rate on the strength characteristics of sand - sand bars. No effect interface stress-strain relationship is hardening. Interface characteristics by drawing rate and method to the common effect of stress, the effect of drawing the rate is significant, and the test method, the property of filling and reinforcement type and other factors. The experimental results also showed that the test rate is on the impact of interlocking, occlusion, bonding, this has no effect on the friction between the base and the sand. Compared with the soil test results, although the sand bar interface friction angle is less than the friction angle of filler itself, but when there is a "quasi cohesion interface", strength in a certain normal stress can be higher than that of the sand soil interface shear. Therefore, reinforcement design should be selected according to the interface "quasi cohesion" size the internal friction parameters.
(2) reinforced embankment on soft foundation reinforcement soil interface properties on the deformation and stability analysis. Based on the analysis of elastoplastic consolidation of a typical soft embankment process by finite element method, the stress and strain field, reinforcement tension and stability of the perspective of the mechanism of deformation of soft soil foundation development law embankment and reinforced by soft base embankment, and compared the calculation results considering large deformation, discusses the interface strength, filling speed and considering the indirect effect mechanism of effect on the calculation results. The results show that the reinforcement can constrain the lateral deformation of embankment and shear deformation of soft soil foundation and effective constraints, and increase in the consolidation stage of horizontal displacement of the "return" of ability, can effectively reduce the filling stage of the embankment settlement center (but the decrease in the final settlement is not obvious), and the maximum vertical displacement of embankment by the extended to the center. In the reinforcement soil interface shear stress exists during construction of the shallow layer soil pore pressure of reinforced embankment increased significantly, but with the gradual consolidation tended to be the same. Reinforced embankment safety coefficient is improved obviously, the failure mode changed, change characteristics and tensile strength of reinforcement, the strength and the interface geological conditions and other factors. Considering the large deformation characteristics obtained after the center shaft settlement and horizontal displacement of small slope deformation results were obviously decreased. The interfacial strength of shear stress level and influence on the stability of the interface, but the total deformation and reinforcement tension of reinforced embankment has no effect. The construction speed has a significant influence on gluten free the embankment and reinforced embankment can be quickly filled to a predetermined height. After the mechanism of reinforcement tension and interface shear stress level is greatly reduced considering indirect effects, improves the stability of the embankment.
(3) the stability analysis of soft foundation of limit equilibrium conditions of the reinforced embankment. Based on the traditional analysis method based on the combination of indirect effect mechanism of calculation model of the overall stability of reinforced embankment on soft foundation improvement of reinforced embankment is analyzed on the stability of the different calculation methods. The results show that the indirect effect of strength reduction mechanism and simplified Bishop method can reflect the reinforcement effect. Based on the strength reduction method and simplified Bishop method are in good agreement, and the Swedish slice method results have obvious difference with the safety coefficient is low and the reliability is not high. The sliding arc strength reduction method and simplified Bishop method more suitable for the analysis of contribution of reinforcement to stability.

【学位授予单位】：暨南大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U416.1

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