【作者】 卢建平；

【导师】 金翔龙；

【作者基本信息】 浙江大学 ， 地质学， 2008， 博士

【摘要】 目前,我国正处于高速公路的飞速发展阶段,桥头跳车问题是当前高速公路建设的热点问题,现浇薄壁筒桩的发明为这一问题的解决提供了全新的方法,论文根据当前研究中存在的问题采用典型路段现场试验与模型分析相结合的方法重点开展研究,本论文是现浇砼薄壁筒桩技术问世以来最为全面系统的一次研究工作,通过研究,对薄壁筒桩加固桥头软基有了较为全面深刻的认识,为该技术的推广应用奠定了重要的理论基础。首先,本文对浙江省软土地基的工程地质特性与工程地质结构特征进行了科学的分析,首次根据薄壁筒桩处理软基效果的不同对土层结构进行了科学合理的划分,根据两种土层结构单元多种试验检测手段的综合分析,揭示了薄壁筒桩成桩工艺先进性与良好质量特征,得出了薄壁筒桩极限承载力标准值的计算公式,提出了薄壁筒桩成桩质量的控制方法;其次,论文率先揭示了土层对成桩过程的反映,充分证明了薄壁筒桩处理范围内土层物理力学性质、表层土的地基承载力有不同程度改善与提高。研究发现,由二元结构土层单元分析得出的上述结论,鉴于薄壁筒桩对相似地层的相似影响,可近似适用于三元地层结构单元的简单地层情况,因此结论具有广泛的适用性。论文首次用基底瞬时沉降模型试验来揭示基底瞬时沉降规律特征,进而通过基底的受力与变形试验来进行薄壁筒桩加固软基响应研究,揭示了桩间土土压力、桩土应力、桩间土孔隙水压力的影响因素及其随荷载变化的规律,剖析了三元结构土层单元的总沉降量小于二结构土层单元根本原因。其三,论文通过试验研究揭示了薄壁筒桩的技术特点:薄壁筒桩的桩体强度高,侧向挡土效果明显,限制了地基土体的侧向变形,减小了路基软土的挤出量,增强了地基土体的抗滑稳定与变形稳定;由于薄壁筒桩承载力高,大大提高了地基土体的强度,采用薄壁筒桩处理由“硬壳上层与厚淤泥下层”组成的二元土层结构时,深部淤泥层的压缩变形通过薄壁筒桩的侧摩阻力由上部硬壳层承担,其效果相当于增大硬壳层的厚度,大大降低软弱下卧层的变形,对减少路基的沉降有非常好的效果,在防治桥头跳车、桥台位移方面取得了很好的效果。其四,论文对盖板设置、土工格栅的加筋作用、过渡区设置等进行了相关分析,揭示了相关规律,提出了通过加大桩间距,减小桩数,增大盖板面积,增加桩体承受上部荷载的份额,充分发挥薄壁筒桩承载力,来减小桩间土受力面积,控制复合地基的沉降量,降低工程造价;提出了土工格栅与薄壁筒桩的有机结合,通过土工格栅的加筋作用,均化地基应力,减小差异沉降。为使薄壁筒桩加固后桥头软基避免二次跳车,设置过渡区非常必要,过渡区可通过改变桩长来实现,也可以改变桩间距进行过渡。论文还论述了薄壁筒桩加固软基与水冲级配碎石加同路堤相结合这一新思路,通过首次在杭州绕城高速公路南线工程上实际应用验证,效果良好。其五,论文从高速公路软基沉降标准分析与软基沉降计算方法分析入手,对薄壁筒桩加固高速公路桥头软基的沉降控制与计算方法进行研究,提出了薄壁筒桩加固软基沉降“桩土复合地基计算模型”;论文首次利用人工神经网络所具有的强大的学习功能、高度的非线性映射能力、以及自组织、自适应、高容错性、并行处理、分布式知识存储等优点,建立薄壁筒桩处理桥头软基沉降的BP人工神经网络模型,进而利用支持向量机模型在解决小样本、非线性及多维模式识别问题中表现出的特有的优势,解决桥头软基沉降的小样本、非线性及多维模式识别问题,并进行了初步验证。最后,论文对现浇混凝土薄壁筒桩进行了经济技术分析,分析认为,该技术有如下突出的优点:与塑板桩相比,薄壁筒桩加固软基,具有沉降少,无需预压,填筑期短等特点。从单位处理成本考虑,虽然薄壁筒桩成本较高,但对地基强度低、工后沉降要求高的路段,综合考虑施工工期、后期维护费用等方面的因素,薄壁筒桩处理软基具有明显的优势。与粉喷桩相比,薄壁筒桩的加固深度、沉降量、路基稳定等方面均优于粉喷桩,而且施工质量可靠,检测手段简单、快速,成本较粉喷桩低,特别在软土深度大于15m的地段,薄壁筒桩有着粉喷桩无法替代的作用。薄壁筒桩处理的软基强度和刚度大大增强,因而能适用于快速填筑,无需超载预压,具有粉喷桩和塑料排水板所无法比拟的优越性,经济效益和社会效益也十分明显。薄壁筒桩的试验研究充分证明了它的双重性能:良好的群桩基础承载性能和有效地防止软土地基的侧向滑移的抗滑性能。试验研究与应用实践证明:现浇砼薄壁筒桩属薄壁结构,具有成桩速度快、施工周期短、自动排土、无泥浆污染、节省混凝土材料、单桩承载力较高等优点,用该技术处理高填方桥头软基技术构思新颖、科学合理且易于实施,经该技术处理后的桥头路基工后沉降小,这一技术的发明使解决桥头跳车难题有了新的突破,为解决高等级公路软土地基桥头跳车及其他建筑物地基加固问题提供了一种全新的方法,具有普遍推广意义。在论文的最后提出了薄壁筒桩桩靴形状、变形控制理论、制定薄壁筒桩的技术规范、降低桩体混凝土设计强度、设备改进等进一步研究的课题。更多还原

【Abstract】 My country is in the stage of fast development of highway now, and the car-jumping problem of bridge approaches is important problem in highway construction, it is nearly impossible to resolve this problem completely by usual treating-methods. the invention of cast-in-situ thin wall tube pile provides a fully new method which solves the problem. basing on the problem existed in current research, the paper does priority studies by test-in-situ of typical road section together with the model analysis, the paper is the most systemic and all-sided research on the cast-in-situ thin wall tube pile technology since it appeared. Through the research, a fully and deeply comprehension on the technology of thin wall tube pile reinforcing soft base at the end of a brige is achived, and a important theoretical foundation is set for the promoting and the applying of this technology.First, this paper has carried on scientific analysis to the engineering geology characteristic and the engineering geology structural feature of soft bases in Zhejiang,it provides a scientific and reasonable division about soft bases structure according to the effect of soft base reinforced by the thin wall tube pile for the first time, there is a generalized analysis basing on many kinds of tests-in-situ at two different soil layer structural unit, the technology advance and the good quality character of cast-in-situ thin wall tube pile is promulgated, the calculation method and the formula of normal value of its limited load-bearing capacity are obtained, and the method of taking control of its quality is proposed.Next, the paper takes the lead to promulgate the reflection of the soil layer at the process of being a pile, it is proved fully that the soil layer’s physical mechanics characters and the facial soil layer’s load-bearing capacity have a varying degree improvement and enhancement after reinforced by the thin wall tube pile, this conclusion comes out of the studies in two layers soil structural unit, in view of the fact that thin wall tube pile has similar influence to similar stratum, the conclusion above is suitable approximately for three layers soil structural unit, that is to say, the conclusion above has widespread serviceability. The paper uses the basis instant subsidence model experiment to prompt the rule and characteristic of basis’ instant subsidence for the first time,then carries on the soft bases’ response to thin wall tube pile through the stress and the deformation testing of the basis reinforced by thin wall tube pile, it reveals the factors that influences the pressure of the earth between the piles, the pressure of the earth and the pile, and the pored water pressure of the earth between the piles, at the same time, it reveals the rules of it changing with load, and tells us the basic reason why the total settlement is less in three layers soil structural unit than in twos.Third, the paper promulgates the technical characteristic of the thin wall tube pile through the study on tests-in-situ: its body intensity is high, has a significant effect in lateral retaining, limites the lateral deformation of ground soil, reduces the squeezing of the road ground, enhances the anti-slide stability and the distortion stability of the ground soil. The thin wall tube pile’s load-bearing capacity is high, it will increase the strength of the ground soil greatly. When it is used in two Layers soil unit that is made up of "upper hard soil and lower thick mud", it will transfer the compressed deformation of lower thick mud into upper hard soil with the effect of the pile’s side friction, it is equal to increas the thickness of the upper hard soil, resultly, it reduces the deformation of the weak underlying stratum greatly, it has a sound effect to reduce the compressed deformation of the road ground, and the same to prevent car-jumping at the end of a bridge and prevent the displacement of the bridge stand.Fourth, the paper carries on correlation analysis on the establishment of the cover, the function of the geogrills, the establishment of transition region and so on, it reveals the relevant rules, proposes to enlarge the pile spacing, reduce the pile number, increase the cover area, in order to display the thin wall tube pile’s load-bearing capacity fully, more part of the load is withstanded by the pile body, while less part is withstanded by the earth between the pile, this action will result in reducing the subsidence of the compound ground, cutting down the cost of projects. On the work of thin wall tube pile together with geogrills , it can equalize the stress of the foundation, reduce the unequal settlement .In the author’s view, in order to avoid second car-jumping at the end of a bridge enhenced by thin wall tube pile, it is necessary to set a transition region, it can realize by changing the length of piles and the space between the piles. Besides, the paper propose a new way to reinforce the soft base by thin wall tube pile together with reinforce the road ground by graded gravels and sands using water-flushed, this thought is practiced for the first time in south Hangzhou highway,it is proved to be good.Fifth, starting with the standard analysis and the calculation method of the soft base’s subsidence, the paper carries on research on the subsidence controlling and calculation method, proposes the calculation model of compound ground reinforced by thin wall tube pile; the paper for the first time establishes the BP artificial neural networks model of the soft base’s subsidence reinforced by the thin wall tube pile, using the artificial neural networks which has the advantages such as the powerful learning property and high unlineal reflection capability , self-organization and self-suitability, high fault tolerance, parallel processing, distributional knowledge storage, then according to the SVM model’s advantage in small sample, unlineal and multi-dimensional pattern recognition question, the paper provides a new way to resolve the small sample, unlineal and multi-dimensional pattern recognition problem of the soft base’s subsidence at the end of a bridge, and this is proved tentatively.Finally, the paper carries on the economical and technical analysis to the cast-in-situ concrete thin wall tube pile, according to the analysis, this technology is proved to have the following merits: compared to the plastic plate pile, soft base reinforced by the thin-wall tube pile, with less settlement, no need of preloading, short period of filling and so on. Only talking about the unit cost of treating, the thin wall tube pile’s cost is high, but considering of the construction cycle and the maintenance cost while using, for the road sections with lower foundation strength and higher demand of settlement while using, the thin-wall tube pile is superior to reinforce the soft bases. Compared to powder-spurt pile, the thin-wall tube pile is superior in all sides such as reinforcement depth, settlement, boadbed’s stability, and its construction quality is reliable, means of detection is simple and rapid, the cost is lower, especially in the road sections where the soft base’s depth is more than 15 meters, the thin-wall tube pile play a irreplaceable role. The strength and stiffness of the soft base reinforced by the thin wall tube pile is greatly enhanced, so the thin wall tube pile is suit to the road sections needing rapid filling, no need of overloaded preloading, it has a incomparable superiority to the plastic plate pile and powder-spurt pile, its economic and social benefits is also very obvious. The tests of the thin wall tube pile fully demonstrate its double performance: a good carrying performance and effective in preventing the soft ground lateral slip.It is proved by experimental research and application that cast-in-situ concrete thin wall tube pile belongs to thin wall structure, the advantages of fast to be a pile, short construction period, automatic soil dump, no mud pollution, saving concrete materials, high capacity and so on. The technology of using the thin wall tube pile at the end of a bridge to treat high filling soft bases is novel, scientific and rational and easy to implement. The settlement of the soft base reinforced by the thin wall tube pile is small. The invention of this technology brings a new breakthrough to solve the problem of car-jumping at the end of a bridge, provides a new way to high-grade highway, as well as other buildings to strengthen the soft soil ground, it deserves widespread promotion.At the end of the paper, the author lists the issue to further study, such as the shape of pile boot, the theory of deformation controlling, developing the technical specifications of thin wall tube pile, reducing the design strength of concrete ,equipment improving and so on.更多还原