DX嵌岩桩承载特性及失效机制试验研究

发布时间：2018-07-07 21:42

本文选题：DX嵌岩桩 + 承载特性　；参考：《北京交通大学》2017年硕士论文

【摘要】：随着经济迅速发展,现代化工程建设规模日益增大,对地基基础提出了严格的要求。桩基作为常见的基础形式,取得长足的进展,向大直径、超长、变截面等方向发展。然而,当桩径和桩长过大时,钻进难度相应增大,桩身质量亦难以保证。三岔双向挤扩灌注桩(简称DX桩)作为新桩型的代表,具有工艺先进、施工简便和成桩可靠的特点,能大幅度提高单桩及群桩承载力,减小桩顶沉降量,近年来广泛应用到超高层建筑基础、大型工业建筑、LNG储罐、铁路、高速公路桥梁等基础工程中。在此基础上,首次采用DX嵌岩桩来替代直孔嵌岩桩,通过在强风化泥质粉沙岩层中设置承力盘,将桩端置于中风化泥质粉砂岩表层,在满足承载力及沉降的要求下,减小桩径和桩长,并成功应用到广东、广西等桩基工程中,取得了良好的经济效益。国内学者针对土层中DX桩承载性能作了大量分析,而DX嵌岩桩的相关研究尚属空白。如何尽快全面探索新型DX嵌岩桩的承载机理及沉降特性,建立科学的设计方法,尤其当前我国高速铁路、公路、超高层建筑等工程中超长桩基越来越多,加强DX嵌岩桩的承载特性及失效机制的研究,成为当前推广应用新型桩基结构时工程界迫切需要解决的科学问题。为进一步揭示DX嵌岩桩荷载传递特性等基本规律,本文依托于防城港钢铁基地原料厂项目,通过一系列现场试验、模型试验与数值模拟手段,对DX嵌岩桩承载特性及失效机制进行研究,主要结论如下:(1)DX嵌岩桩Q-s曲线平缓变化,至加载末期桩顶未呈现明显加速变形趋势;卸除荷载后,桩顶残余沉降值较小,卸荷回弹量小,回弹率低,表明在强风化泥质粉砂岩层设置承力盘、桩端置于中风化泥质粉砂岩表层,能显著提高单桩承载力,且DX嵌岩桩桩身压缩性低、差异沉降小、抵抗沉降能力优异;(2)模型试验表明DX嵌岩桩Q-s曲线呈缓变型,而直孔嵌岩桩在加载后期桩顶沉降急剧增加;桩径、桩长及桩端嵌岩情况相同时:DX嵌岩桩极限承载力较直孔嵌岩桩zka提高118～131%;当直孔嵌岩桩达到承载极限时,等荷载水平下DX嵌岩桩桩顶沉降较直桩zka减小80～86%;当直孔桩zkb嵌岩深度增加(2～3d)时,DX嵌岩桩承载力仍较其提高56～64%;当直孔嵌岩桩达到承载极限时,等荷载水平下DX嵌岩桩沉降值较等桩径直桩zkb减小63～66%,充分表明DX嵌岩桩承载性能优异、控制桩顶沉降性效果显著;(3)DX嵌岩桩侧阻力、盘阻力及端阻力同步发挥,仅需桩顶发生较小沉降:当桩顶荷载较小时,侧阻力盘阻力端阻力;随着荷载增加,侧阻力、盘阻力及端阻力占总承载力百分比保持稳定;当荷载进一步增大时,盘阻力占总承载力百分比有所减小,端阻力所占总荷载百分比逐渐增大,端阻力盘阻力;(4)DX嵌岩桩属于摩擦端承桩:承力盘在加载初期能有效承担荷载,控制桩顶沉降,随着荷载增加,盘底岩体发生局部渐进性剪切破坏,多余荷载由桩端承担,盘阻力与端阻力占总承载力百分比呈此消彼长趋势,桩端承载力能进一步发挥,桩身各部分协调工作,保证承载体系稳定性;(5)承力盘底部岩体附加应力非均匀分布,外缘处较高,由于应力集中岩体局部剪切破裂始于此处,随荷载增大不断向桩根发展;桩端岩体附加应力最大,增长速率最快,随深度增加不断衰减,当盘底岩体产生剪切破裂带后,桩底应力显著增大。(6)根据模型DX嵌岩桩Q-s曲线、承力盘底部岩体及桩底岩体附加应力增长规律、数值模拟结果,将DX嵌岩桩失效过程分为四个阶段,即:弹性阶段、屈服前塑性阶段、屈服后塑性阶段及破坏阶段。
[Abstract]:With the rapid development of economy, the construction scale of modern engineering is increasing, and the foundation of foundation is strictly required. As a common foundation form, pile foundation has made great progress, and it develops to large diameter, super long and cross section. However, when the pile diameter and pile length are too large, the difficulty of drilling is increased, and the quality of the pile is also difficult to guarantee. Three As the representative of the new type of pile, DX pile, which is a new type of pile, has the characteristics of advanced technology, simple construction and reliable pile formation. It can greatly improve the bearing capacity of single pile and pile group and reduce the settlement of pile top. In recent years, it has been widely applied to the foundation of super high-rise building, large industrial building, LNG storage tank, railway, highway bridge and other basic engineering. On this basis, the DX rock socketed pile is used for the first time to replace the straight hole rock socketed pile, and the pile end is placed on the surface of the medium weathered muddy siltstone by setting the bearing plate in the strong weathered muddy sand rock layer. The pile diameter and pile length are reduced under the requirements of bearing capacity and settlement, and the good results should be achieved in Guangdong, Guangxi and other pile foundation projects. The domestic scholars have made a great deal of analysis on the bearing capacity of the DX pile in the soil layer, and the related research on the DX rock socketed pile is still a blank. How to explore the bearing mechanism and the settlement characteristics of the new DX rock socketed pile as soon as possible, and establish a scientific design method, especially the super long Zhuang Jiyue in the high speed railway, highway and super high rise building in China In order to further reveal the basic law of the load transfer characteristics of the DX rock socketed pile, this paper relies on the project of the raw material plant of the steel base of the Fangchenggang iron and steel base, through a series of field tests, and the research on the bearing characteristics and failure mechanism of the rock socketed pile has become an urgent problem to be solved in the engineering field. The model test and numerical simulation method are used to study the bearing characteristics and failure mechanism of DX rock socketed pile. The main conclusions are as follows: (1) the Q-s curve of DX rock socketed pile is slow change, and the pile top has no obvious accelerating deformation trend at the end of loading; after unloading the load, the residual settlement value of pile top is small, the unloading rebound is small, and the rebound rate is low, indicating the strong weathering mud quality. The bearing plate of the silt rock is set, the pile end is placed on the surface of the medium weathered muddy siltstone, and the bearing capacity of the single pile can be improved significantly. And the DX rock socketed pile body has low compressibility, small difference settlement, and excellent resistance to settlement. (2) the model test shows that the Q-s curve of the DX rock socketed pile is slowly variable, and the vertical hole rock socketed pile increases sharply in the later stage of the pile, pile diameter and pile. At the same time, the ultimate bearing capacity of DX rock socketed pile is increased by 118 ~ 131% than that of straight hole rock socketed pile zka; when the vertical hole rock socketed pile reaches the bearing limit, the settlement of the pile top settlement of the DX rock socketed pile is 80 to 86% lower than that of the straight pile under the same load level; when the zkb rock socketed depth increases (2 to 3D), the bearing capacity of the DX rock socketed pile is still higher than that of 56 to 64%; when the zkb rock socketed pile is increased by 56 to 64%. When the vertical hole rock socketed pile reaches the bearing limit, the settlement value of DX rock socketed pile under equal load is reduced by 63 to 66% than that of the same pile zkb, which fully indicates that the bearing performance of the DX rock socketed pile is excellent, and the settlement effect of the pile top is remarkable. (3) the side resistance of the rock pile, the disc resistance and the end resistance are synchronous, only the small settlement of the pile top is needed, when the pile top load is small When the load increases, the percentage of the total bearing capacity decreases as the load increases. When the load is further increased, the percentage of the total bearing capacity decreases, the total load percentage of the end resistance increases gradually and the end resistance disk resistance; (4) DX rock socketed pile belongs to the friction end bearing pile: bearing pile. At the initial stage of loading, the force can be effectively loaded and the settlement of the pile top is controlled. With the increase of load, the rock mass in the bottom is partially progressive shear failure. The excess load is assumed by the pile end, the disc resistance and the end resistance account for the percentage of the total bearing capacity, and the bearing capacity of the pile ends can be brought into play in one step, and the pile body parts coordinate work and guarantee the bearing body. (5) the additional stress in the bottom rock mass of the bearing plate is nonuniform distribution, the outer edge is higher, because the local shear fracture of the stress concentration rock begins to develop with the load increasing. The maximum additional stress of the rock mass, the fastest increase rate and the constant attenuation with the depth, when the rock bottom rock produces the shear fracture zone, the pile bottom The stress increases significantly. (6) according to the Q-s curve of the model DX rock socketed pile, the additional stress growth law of the bottom rock mass and the bottom rock mass of the bearing disc, the failure process of the DX rock socketed pile is divided into four stages, that is, the elastic stage, the pre yield plastic stage, the post yield plastic stage and the failure stage.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

【参考文献】