【作者】 薛江炜；

【导师】 葛忻声；

【作者基本信息】 太原理工大学 ， 岩土工程， 2013， 博士

【摘要】 桩伴侣是中国发明专利桩头的箍与带箍的桩(200710160966.1)的俗称：桩头侧而上下一设定高度范围设置一闭合环形箍,箍的内径大于桩头的外径,箍与桩是分开的,桩与桩头的箍通过桩间土和垫层的传力来协同工作,组合成带箍的桩。：因其具有对桩竖向支承刚度简单灵活调整的属性,其专业学术名称为“变刚度桩”。为了深入了解桩伴侣的作用机理和承载性状,本文对该技术进行了初步研究。主要的研究成果、创新和结论包括：(1)人为地将桩土共同受力体的某些环节削弱或增强,可改变共同工作的方式,使承载和沉降性状向预定的方向发展,实现工程上可以接受的较大总体沉降与较小差异沉降和较小工后沉降,从而极大地促进岩土工程的技术进步和经济上的巨大节约。(2)以相对的深和浅来划分基础类型不尽合理,而用“直接基础”和“间接基础”的表述来划分基础类型更加合理,传统上“深基础”与“浅基础”的表述可以特指基础的埋深或相对埋深；直接基础可简单定义为能够直接将荷载传递到上层天然地基的基础；间接基础也可定义为穿过上部持力层将荷载传递到下部持力层并间接影响上层天然地基的基础。显然,这样一种分类方法同时包含了地基与地基两方面的因素,更客观地反映地基与基础之间之间相互依存、相互影响、相互作用的关系。(3)“用沉降量换承载力”的等价说法或具体解释是地基承载的良性循环,即“上部荷载增大→压实地基土→地基土性质改善→可以承担更大的荷载→进一步压实地基→地基土性质更加改善→……”，现有研究没有或没有充分考虑作用于滑移线上的附加应力对抵抗剪切滑动的贡献；桩伴侣可减小直接基础发生整体剪切破坏的风险。(4)选择适宜的滑移线可以将地基承载力问题转化为倾覆问题来研究；有桩伴侣的地基基础非常符合较小刚体位移的“圆弧滑动和向下冲剪”假设,滑移线是以基础底板宽度为直径的一个半圆，圆心位于基础底板的中心,基于莫尔库伦强度理论,以符拉蒙的附加应力解答推导出考虑附加应力和土自重的滑移线上土剪力对基底中心抵抗力矩的解析解，将所有的倾覆力矩归结为等效偏心,得到了评价地基承载力的等效偏心法,与通常的地基承载力的计算方法不同,等效偏心法不仅考虑上体性质、基础宽度、埋深等因素,同时考虑了上部结构的等效偏心来综合计价地基承载力,不同的等效偏心对应不同的地基承载力值,等效偏心越小则承载力越人,经初步对比,不考虑地震等水平荷载形成的等效偏心因素,在静力荷载下太沙基公式的极限承载力所对应的相对等效偏心ΔF/B在0.154左右,而承载力标准值所对应的相对等效偏心ΔF/B在0.188左左右：以等效偏心法分析了桩伴侣“止沉”与“止转”的计算思路,中桩对于“止转”力矩的贡献很小,基桩设置应当重点加强边桩、角桩。(5)论述了间接基础的缺点；进行了复合桩基优化设计对间接基础改进的局限分析；提出个别安全系数的概念解释和质疑常规变刚度调平“内强外弱”的结果,指出当只有基础底板沉降均匀这唯一的一个控制参数时,间接基础调平只能调整桩下部支承刚度的单一手段是产生变刚度调平优化设计调平的结果不符合常理的重要原因,是用降低个别安个系数为代价换取了基础底板沉降均匀；桩伴侣具有调整桩上部支承刚度的能力,可均匀布桩、甚至局部加强边桩、角桩,增大抵抗整体倾覆的能力,适当调整桩顶与基础底板的距离,即边桩、角桩预留沉降大一些，中桩预留沉降小些就可以实现变刚度调平。(6)比较分析了桩伴侣的类似技术,桩伴侣具有类似技术的优点，且减震隔震,同时起到向土传递水平力、对桩阻隔水平力的双重作用,并且增大了基础底板的刚度；应用刚性桩复合地基时,应当注意地下室井坑破坏隔震、褥垫层模量影响隔震对其抗弯、抗剪能力较低的桩的水平承载产：生的不利因素,此外,常规采用褥垫层的刚性桩复合地基还存在反力“被平均”、基础既不经济又不安全、“流动补偿”导致垫层流失等缺点(7)按照有限元收敛准则判断桩伴侣的极限承载力有不同程度的提高,但有限元模拟和现场实测证明伴侣对于按照传统方法判定承载力的无显著影响,桩伴侣承载力的提高依赖于沉降量的增大和土塑性的充分发挥,需要打破土原有的本构关系并建立新的体系,有限无软件本质上难以模拟出现“拐点”的“止沉”曲线,最好的方法还是试验；研究了刚柔桩复合地基静载荷试验时设置伴侣对桩土应力比的影响,设置伴侣后桩顶应力大幅度减小,伴侣附近桩间上的应力大幅度提高,证实伴侣较好地起到了替桩头分担荷载作用,伴侣的作用可解释为由于桩顶向上刺入垫层发生剪胀增大了垫层的内摩擦角,也可以理解为由于伴侣的约束作用增大了桩顶上方垫层上柱受到的被动土压力。(8)提出了整合复合地基和复合桩基的承载力计算公式并以位移调节装置试验的数据进行了验证,建议复合地基技术规范(征求意见稿)修改为：“仅采用褥垫层技术的刚性桩复合地基中的混凝土桩应采用摩擦型桩,如果有可靠措施能够保证桩上相继同时共同工作时,桩顶与基础底板之间的上或垫层不会发生整体剪切破坏或其他滑移型的破坏,则刚性桩复合地基中的混凝土桩应采用端承效果好的桩型,桩端尽量落在好土层上”；推导了桩伴侣的整体承载力安全系数,只要下部持力层稳定安全系数总能保证大于等于2,表明桩伴侣的安全度在合理的范围内；建议对于不同的抗震设防等级的建筑,采用不同的安全系数：建议用适度的不均匀沉降作为检验建筑工程实体质量的外部荷载,以“抵抗不均匀沉降指数”来衡量建筑工程的施工和设计质量水平；提出“最小配桩率”概念；桩伴侣具有“止沉”的沉降特性,沉降主要由上部地基上的压缩引起,影响深度小的直接原位压板试验得到的极限沉降量与最终沉降量可能会比较接近,可直接作为沉降量预测的依据,提出“整体倾斜”极限状态的概念做为变刚调平“概念设计”的实用方法；应用桩伴侣对某处理基桩缺陷事故案例合理方案进行优化,减薄承台,取消片石找平层,提出一项“桩姐妹”的方案,使作为直接基础的桩能够承受上拔拉力,提出了现浇伴侣的施工方法。(9)建议将承台与土之间的摩擦力小或地基土约束力差的低承台桩基称为“非典型高承台桩基”,将其从“典型的低承台桩基”中细分出来；当不改变直接基础的属性,有限元数值模拟桩伴侣的改进证实：伴侣是承台向地基土传递水平荷载的可靠媒介,即使承台与土之间摩擦力小,也可大幅度减小基桩的应力和位移，对于桩身范围地基土模量低的“非典型高承台桩基”的水平承载性状也有一定的改善；低承台桩基的水平承载性状本质上取决于桩间上抵抗水平荷载的能力；使用桩伴侣，桩顶与基础底板预留沉降空间就可以将传统的桩基础由间接基础改造为直接基础,有限元数值模拟表明：水平荷载作用下桩身应力大幅度降低；设置伴侣后可取消褥垫层；桩与承台脱离开,更加促进了伴侣作用的发挥：伴侣自身受到的内力较大,且较为复杂；罕遇地震时伴侣可作为耗能构件(?)先牺伴侣更多还原

【Abstract】 The Chinese invention patent "hoop of pile head&pile with hoop (200710160966.1):s commonly known as Pile Partner (or Partner Pile), which is closed ring hoop set around pile head up and down, the inner diameter of the pile head is larger than the outer diameter the hoop, hoops and piles are separated; piles and hoops of piles head work together by force transmission of soil and cushion, combining to piles with hoops. Because of its attributes of simple and flexible adjustment for pile top stiffness, its academic name should be "Variable Rigidity Pile". In order to deeply understand the action mechanism and the bearing properties of partner pile, pilot study has been carried out on the technology, and the main research results, innovation and conclusions include:(1) To weaken or enhance some parts of the community of pile and soil on purpose. can change the way of their collaboration, and make the characters of load and settlement to the concerted or predetermined direction.(2) It’s not rational to differentiate foundation type on relative deep or shallow. while the expressions of "direct foundation" or "indirect foundation" to classify foundation type seems to be more reasonable, and the traditional expressions of "deep foundation" and "shallow foundation" could only refers to the relative depth of the foundation. (3) The same meaning or specific explainion of "settlement exchange with capacity" is the "virtuous cycle" of foundation capability, which is:"loads increase→compact foundation soil→foundation soil improved→more load can be undertaken—further consolidate foundation soil→foundation soil improved more→......," whereas, almost all the current study have paid no or little adequate consideration on the contribution of subsidiary stress acted on the sliding surface which could resist shear sliding; Pile partner can reduce the risk of occurring the whole shearing destruction of the direct foundation.(4) The foundation with partner pile accord with the very realistic hypothesis of "Circular sliding and downward shearing" of rigid body displacement, the slip line is a semicircle, which diameter equai to the width of the foundation slab, and the centroid point of the foundation slab is the centre of the circle, based on the Coulomb and Moore strength theory, and the Flamant Additional Atress Solution, an analytical solution the resistance moment about the centroid point of the soil shear resistance on the assumed slip line could be deduced, which additional stress and the soil weight have been taken into consideration; meanwhile, take all tilting moments into an equivalent eccentric, and then get hold of a completely new method to evaluate foundation bearing capacity, which can be called the method of equivalent eccentric; According to the method of equivalent eccentric, the foundation bearing capacity is not only be determined by the characters of soil, the width and depth of the foundation, but also the equivalent eccentric, which is mostly influenced by the structure. smaller equivalent eccentric get larger bearing capacity and vice versa; Preliminary comparisons show that the Terzaghi’s ultimate bearing capacity is corresponding to about△F/B0.154, and the standard value is corresponding to about△F/B=0.188, not considering the earthquake and other horizontal load; Based on the method of equivalent eccentric, analyse "stop sinking" and "stop turning", and the optimized arrangement of piles.(5) The disadvantages of indirect foundation have been discussed; Put forward the concept of individual safety coefficient to explain and question the results of the conventional variable stiffness leveling optimal design, that is "outside weak and inside strong", for if foundation settlement uniform is only but one control parameter, and adjusting pile bottom stiffness is the single means of variable stiffness leveling optimization design for indirect foundation, as a sesult,"outside weak and inside strong", which is less rational (compare with legs of a table or chair), and the cost of the result is the lower of individual safely coefficient; However, pile partner has the ability of adjusting pile lop stiffness, so pile can be put evenly according to the load above, or even strengthen edge piles, increase the ability of resistance whole overturned, and its easy to realize the leveling of variable stiffness by adjusting the distance between pile top and foundation slab, such as side piles and comer piles more distance and center piles less.(6) Pile partner has almost all the advantages of similar technology, and and shock isolation, and serves the double purpose of delivering level force to soil and cutting off level force to pile, meanwhile, pile partner increase the stiffness of the foundation slab; On the application of the rigid pile composite foundation, attention shall be paid lo the basement well pit and destructing isolation, and the modulus of cushion influencing isolation, which are adverse factors and dangerous to the pile of low level bending and shear capacity, in addition, the conventional rigid pile composite foundation also has serveral shortcomings such as reaction force concentrated ("forced to average"), high cost of foundation base, and the "flow compensation" leading to the loss of the cushion.(7) Finite element calculation show that the ultimate bearing capacity of foundation increase greatly according to convergence criteria, it is necessary to relax the judge criteria according to static load test; Field tests confirm that partner play a good role to share load for pile, and improve the reaction force of soil between piles.(8) Put forward an integration bearing capacity calculation formulas of composite foundation and composite piled foundation, so suggest the composite foundation technique standard (drafts) should be amended as: if there is only cushion, the rigid concrete pile composite foundation must be cushion type pile, but if there are reliable measures to ensure that the pile and soil work together in succession, soil or cushion between pile head and bottom of foundation won’t have overall shear failure or other sliding model destroy, the concrete pile in the rigid pile composite foundation should be good at pile end, and tip of pile should put on the good soil; The overall bearing capacity safety coefficient of pile partner is deduced, which show that the safety degree of all foundations with pile partner arc within the scope of reasonable greater than2; suggest that different seismic fortification level buildings use different safety coefficient; suggest that the moderate uneven settlement can be treated as external load to test engineering construction quality, and the engineering design and construction quality level can be measured by the "resist uneven settlement index"; Put forward the concept of "minimum ratio of pile"; Partner pile has the settlement characteristic of "stop sinking", the main settlement is caused by compression of the upper foundation soil, so although the influence depth of situ static load test is shallow, the test result should be closed to the real fanial settlement, and can predict settlement directly, furthermore, put forward a practical method of "overall tilting" for variable stiffness leveling "concept design"; Put forward an optimal design to deal with a foundation pile defects accident case by pile partner, with reduction the depth of cap and cancel flag leveling course; and Put forward the other optimal design,"pile sister" plan, making direct foundation withstand pulled force.(9) when there’s few friction between pile caps and foundation soil, or the modulus of foundation soil around pile shaft are small enough, or combinations thereof, pile foundation with low cap is not a "typical pile foundation with low cap", and should be treated as "pile foundation with non-typical high cap" Keeping the construction of the pile foundation form with only extra pile partner is the "amend" improvement, and finite element model calculations show that: partner is a reliable medium that help cap deliver lateral load to soil. reducing the stress and displacement of a pile greatly even there’s few friction between pile caps and foundation soil, and also ease the stress and displacement when the modulus of foundation soil are small, so pile partner should be widely used for pile foundation with low cap; The horizontal bearing character of pile foundation with low cap depends on the horizontal load capacity of foundation soil under the cap or around the pile cssentially.As long as the pile break away from foundation slab to some distance, the traditional pile foundation will change from indirect to direct foundation, and realize the "revolutionary" improvement, the finite element numerical simulation show the exponentially reducing of stress of a pile; pillow is not necessary and can be cancelled in composite foundation when pile partner is applied; the separation between pile and foundation slab encourage parter to play a stronger roie, and the internal forces of pile partners are large and complicated.更多还原