摘要
预应力锚索抗滑桩是20世纪80年代开始应用及发展起来的一种新型支挡结构,由于它具有安全、经济、节约用地等优点,在公路、铁路及房屋建筑工程中的高边坡、深基坑治理中己获得了广泛应用。工程实践表明,目前桩锚支护结构设计中土压力传递模式还不能较好地反映其真实受力状况,有待进一步完善。
本文作者在工程实践及查阅国内外相关文献的基础上,借鉴桩承式路堤土压力传递方式,将其引入到锚拉桩设计中,提出了一种新的土压力计算模式——基于“三维土拱效应”的土压力传递模式,即桩板结构后的大部分土压力通过土体不均匀变形而形成的空间土拱直接传递到锚头,剩余部分的土压力才经桩板结构再传递到锚头。
为了论证该理论的正确性,论文依托重庆市科技攻关项目——基于三维土拱效应的预应力锚拉桩关键技术研究与应用(CSTC,2010AC0109),采用理论分析、室内模型试验、数值分析及工程监测等技术方法,对锚拉桩支护结构三维土拱效应是否存在、影响土拱效应的因素、锚拉桩荷载传递机理及桩板所受土压力大小等方面进行了深入研究,取得了以下阶段性成果:
①通过理论分析,论证了三维土拱效应存在的可能性,提出了形成三维土拱效应的基本条件,推导得到了形成土拱效应的锚点间距控制方程。在此基础上,推导得到了基于三维土拱效应的桩板土压力计算公式,探讨了影响桩板所受土压力大小的相关因素,并将计算结果与常规设计方法进行了对比分析,阐述了本文计算结果的合理性。
②通过室内模型试验,验证了土拱效应的存在,发现了土拱效应在支挡结构中部较其上部及坡脚部位要显著的分布规律。根据实验结果,将三维土拱拆分为4个两端直接支撑在锚头上的三棱形土拱及1个四边支撑在4个三棱形土拱上的壳体土拱。测试数据表明,土压力沿填土深度呈非均匀分布,桩背土压力呈反“B”字型,锚索位置处桩身土压力较大;挡板背后土压力呈正“B”字型,挡板土压力分布规律与桩身相反,即距锚头距离越大,土压力也较大。
③通过数值分析,进一步验证了土拱效应的存在,得到了与室内试验相同的土拱分布规律。分析了锚头间距、土体物理力学特性对土拱效应的影响,结果表明,抗剪强度参数c、φ及弹性模量E、泊松比μ对土体的成拱能力有显著影响,c、φ及E增大土拱效应增强而μ增大则土拱效应减弱。
④通过对一边坡工程桩板结构所受土压力进行监测,结果表明,三维土拱效应是存在的,进一步验证了理论分析及模型试验、数值分析的正确性。
⑤基于“三维土拱效应”理论研究成果,开发了一套锚拉桩设计计算软件,以应用于工程设计。
Pre-stressed anchor piles began to be used and developed as a new type of retaining structures in the1980s. It has been applied widely in the high slope and deep pit governance of highway, railway and housing construction because of its safety, economy, land conservation, etc. Engineering practice showed that pressure transmission mode of pile-anchor retaining structures can not better reflect its real force state, need to be further improved.
Based on the engineering practice and access to relevant literature, soil pressure transfer mode of pile-supported embankment was introduced to the pre-stressed anchor pile retaining structures, a new calculation model was proposed-based on "three-dimensional soil arching effect of soil pressure transfer model " in which most of its of the pile plate structure directly was transfered to the anchor head by soil arch effect formed on-uniform deformation of soil, the remaining portion of its was then passed to the anchor head by the pile and plate structure.
In order to demonstrate the correctness of the theory, the paper relied on scientific and technological project of Chongqing-based on three-dimensional soil arching effect pre-stressed anchor piles key technology research and application (CSTC,2010AC0109), and used theoretical analysis, indoor model test, numerical analysis and project monitoring and other technical methods, and carried out in-depth studies about three-dimensional soil arching effect exists, the factors that affect the soil arching effect, load transfer mechanism and the pile plate suffered earth pressure, and made the following achievements:
①Through theoretical analysis, The paper demonstrated the existence possibilities of three-dimensional soil arching effect, put forward to its basic form conditions, derived the anchor spacing control equation of form soil arching effect. On this basis, deduced soil pressure formula exerted on pile and plate of basing on three-dimensional of soil arching effect, discussed the impact of factors related to the size of soil pressure. Finally, the paper described the rationality of the calculated results which was compared with the conventional design method.
②Through the indoor model test, verified the existence of soil arching effect, discovered a significant distribution that the soil arching effect in the middle of retaining structures more apparent than its upper and lower. According to the experimental results, the three-dimensional soil arching was split into4three prismatic soil arch which its both ends directly supported in anchor head and a1shell soil arch which its Quadrilateral supported in three prismatic soil arch.
Test data showed that the earth pressure was non-uniform distribution along the depth of fill, Earth pressure exerted on pile is inversely "B" distribution, and it was larger the anchor head than other parts; On the contrary, Earth pressure exerted on baffle is positive "B" shape, and the greater the distance from the anchor head, the earth pressure as well.
③Through numerical analysis, the paper further verified the existence of soil arching effect, moreover, its distribution law was the same with Indoor test, finally, analyzed the anchor head spacing and soil physical and mechanical characteristics impact on soil arching effect, the results indicated that the shear strength parameters c、 φ, elastic modulus E, Poisson's ratio μ had a significant influence on soil arching effect, the soil arching effect was enhanced with c、φ and E increasing and u weakening.
④A slope engineering case monitoring results testified that three-dimensional soil arching effect was existed, and theoretical analysis and model test, numerical analvsis were corrected.
⑤Based on the " three-dimensional soil arching effect" theory and research results, developed a set of anchor pile design calculation software, to be applied to the engineering design.
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