楔形劲芯水泥土复合桩成桩特性研究

发布时间：2018-01-11 19:18

本文关键词：楔形劲芯水泥土复合桩成桩特性研究　出处：《湖南工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：基于对混凝土劲芯桩、楔形桩的分析与总结,课题组提出了一种软土地基加固新技术——楔形劲芯水泥土复合桩。本文采用室内土工试验、大尺寸模型试验与数值模拟相结合的方法,较为系统的研究楔形劲芯水泥土复合桩成桩特性,分析水泥土表面位移、内芯和水泥土外桩桩身应变以及压桩贯入力等的变化规律,主要研究工作与成果包括:1、进行室内抗压强度试验,研究夯实水泥土无侧限抗压强度的发展规律。结果表明:夯实水泥土强度随着龄期、掺入比的增加而增加,并通过回归分析得出三者间的数量关系;夯实水泥土轴向应力随应变先增大后减小,轴向峰值应力随掺入比、龄期的增加而增加;同时,掺入比、龄期影响和改变水泥土的破坏方式。当水泥用量偏低时,早期水泥土强度较低,发生塑性破坏,随着掺入比、养护龄期的增加,破坏方式慢慢转变成脆性破坏。2、基于相似理论,设计模型试验,研究楔形劲芯水泥土复合桩成桩特性。研究表明:1)贯入力受桩型、楔角和置换率等因素的影响。其他条件相同时,贯入力随水泥土含水率的增大而减小,随内芯置换率、楔角和平均直径的增大而增大,同等条件下压入楔形内芯所需的贯入力比等截面内芯的较大;2)等截面内芯压入时,水泥土桩表面会出现“隆起”,内芯直径与置换率越大,“隆起”现象越明显,且最大地表隆起量出现在1d~2d范围内,约为桩径的1%~1.5%;楔形内芯压入时,水泥土桩表位移不断增加,且增加的幅度随楔角、置换率和水泥土含水率的增加而增大;3)水泥土桩桩底压力、内芯桩端压力均随内芯竖向位移的增加而增加,与置换率、水泥土含水率和桩型有关;4)水泥土桩身应变随深度的增加而先增大后减小,在某一桩深处出现峰值,且峰值应变不断增加;对于等截面内芯,出现峰值应变的深度随内芯的沉入而不断下移,且始终在距离内芯桩端约10cm以内范围;对比楔形和等截面内芯,相同条件下压入楔形内芯时出现的应变较大。3、基于模型试验结果,采用PFC2D软件进行数值分析,讨论置换率和内芯桩型对成桩特性的影响。分析表明:内芯压入使水泥土发生侧向变形,置换率相同时内芯直径(或平均直径)越大,侧向变形量越大,且与等截面内芯相比,楔形内芯使水泥土产生的侧向变形更大,成桩效果更显著;内芯所受阻力由桩端阻力和桩侧阻力组成,二者在成桩过程中均随内芯竖向位移的增加而增加;楔形内芯压入过程中桩侧阻力所占比例(约为80%~95%)远大于桩端阻力。
[Abstract]:Based on the analysis and summary of the concrete core pile and wedge-shaped pile, a new technology of strengthening soft soil foundation, wedge-shaped cement-soil composite pile, is put forward in this paper. In this paper, the laboratory geotechnical test is carried out. Based on the method of large-scale model test and numerical simulation, the characteristics of cement-soil composite pile with wedge-shaped rigid core are studied systematically, and the surface displacement of cement-soil is analyzed. The internal core and cement soil outside pile body strain and pressure pile penetration law, the main research work and results include: 1, the indoor compressive strength test. The development rule of unconfined compressive strength of rammed cement-soil is studied. The results show that the strength of compacted cement-soil increases with the increase of age and ratio, and the quantitative relationship among them is obtained by regression analysis. The axial stress of compacted cement-soil increases first and then decreases with strain, and the axial peak stress increases with the ratio of cement to soil and the age of the compacted cement-soil. At the same time, mixing ratio, age influence and change the failure mode of cement-soil. When the cement content is low, the strength of early cement-soil is lower, plastic failure occurs, and the curing age increases with the ratio of cement to soil. The failure mode slowly changed to brittle failure. Based on the similarity theory, the model test was designed to study the pile-forming characteristics of wedge-shaped cement-soil composite pile with strong core. The research shows that the penetration force is subjected to pile type. When the other conditions are the same, the penetration force decreases with the increase of water content of cement soil, and increases with the increase of core replacement ratio, wedge angle and mean diameter. Under the same conditions, the penetration force required to press the wedge core is larger than that of the equal section core. 2) when the inner core of the same section is pressed, the surface of the cement soil pile will appear "uplift". The larger the diameter of the core and the replacement rate, the more obvious the "uplift" phenomenon is, and the maximum surface uplift amount appears in the range of 1 d ~ 2 d. About 1 / 1. 5 of the diameter of the pile; The displacement of cement soil pile surface increases with the increase of wedge angle, replacement ratio and moisture content of cement soil. 3) the pressure on the bottom of cement-soil pile and the pressure at the end of the core pile increase with the increase of the vertical displacement of the core, which is related to the replacement rate, the moisture content of the cement soil and the pile type. 4) the strain of cement-soil pile firstly increases and then decreases with the increase of depth, and the peak value appears in a certain pile, and the peak strain increases constantly. For the inner core of the constant section, the depth of peak strain is continuously moving down with the inner core sinking, and always within 10 cm from the end of the inner core pile. Compared with the wedge core and the equal section inner core, under the same conditions, the strain in the wedge core is larger. 3. Based on the model test results, the numerical analysis is carried out by PFC2D software. The influence of displacement rate and core pile type on pile forming characteristics is discussed. The results show that the lateral deformation of cement-soil is caused by internal core indentation. The larger the core diameter (or average diameter) is when the replacement rate is the same, the larger the lateral deformation is. Compared with the inner core of the same section, the wedge-shaped core makes the lateral deformation of the cement soil larger, and the piling effect is more remarkable. The resistance of inner core is composed of pile tip resistance and pile side resistance, both of which increase with the increase of vertical displacement of inner core in the process of pile formation. The proportion of pile side resistance (about 80 / 95) is much larger than that of pile tip.
【学位授予单位】：湖南工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

【参考文献】