大直径扩底灌注桩的工作性能研究

发布时间：2018-04-12 19:30

本文选题：大直径扩底灌注桩 + 球孔扩张理论　；参考：《山东科技大学》2017年硕士论文

【摘要】：大直径扩底灌注桩具有承载力高、沉降小、稳定性好等优点,被广泛应用于大跨度桥梁、高耸结构中。迄今为止,大直径扩底灌注已在我国发展三十多年,在机械成孔和沉降计算方面均取得长足的进步,对于横向荷载作用下的动静力响应特性研究也在蓬勃发展;但由于扩大端的存在,其设计中机械成孔的扩孔压力大小,竖向荷载作用下的沉降计算及地震荷载作用下的抗震特性与等直径桩相比,存在较大差异。因此,本文对大直径扩底桩的球孔扩孔压力计算、竖向荷载作用下的沉降计算以及地震荷载作用下的动力响应分析等方面进行研究,以期完善大直径扩底灌注桩的设计计算理论。主要内容包括:(1)扩底桩扩孔压力的理论研究。基于空间准滑动面(SMP)准则,考虑塑性区弹性变形,从能量耗散的角度分析球孔扩张的全过程,利用应力不变量推导符合球孔扩张的屈服准则,分别导出弹塑性区应力、位移、应变表达式;利用体积守恒和能量守恒推导出扩孔压力的表达式,并给出扩孔压力P、塑性区半径R与扩孔半径a的关系。算例分析可知,本文方法计算的扩孔压力与现场试验得出的结果较好的吻合,塑性区半径和扩孔压力均随扩孔半径的增加而增大,但增幅逐渐减小而趋于稳定值,剪胀角对塑性区半径和扩孔压力影响显著,随着剪胀角的增加,塑性区半径和扩孔压力明显增加。(2)扩底桩的沉降计算方法。考虑压缩模量的深度效应,对已有的大直径扩底灌注桩沉降计算公式进行修正。取土体微单元进行受力分析,并引入深度对压缩模量的影响,建立室内压缩模量与变形模量的关系,代入扩底桩沉降计算公式,得出扩底桩沉降计算修正公式。分别采用修正前和修正后的计算公式对某工程实例进行沉降计算。结果表明,修正后的计算结果与实测数据吻合更好。同时,数值计算结果也表明,与压缩模量Es修正前的计算沉降相比,压缩模量Es修正后的计算沉降与实测沉降更加吻合。(3)扩底桩在地震荷载作用下的动力响应分析。桩周土采用Drucker-Prager弹塑性模型,以考虑土体的非线性;桩与桩周土之间设置接触以考虑桩—土接触非线性;通过借助ABAQUS有限元软件,分别建立地震荷载作用下扩底桩—土—结构和普通桩—土—结构相互作用体系的三维有限元动力模型。对两种桩基进行时域内的数值模拟研究,分析两种不同桩基的抗震性能差异,并探讨桩土模量比、阻尼比、软夹层、上部质量等因素对桩基相互作用问题的影响。
[Abstract]:Large diameter reamed cast-in-place piles with high bearing capacity, small settlement and good stability are widely used in long-span bridges and high-rise structures.Up to now, large diameter bottom filling has been developed in China for more than 30 years, and great progress has been made in the field of mechanical hole formation and settlement calculation, and the research on the dynamic and dynamic response characteristics under transverse loads is also booming.However, due to the existence of the enlarged end, there is a great difference between the pressure of the mechanical hole reaming, the settlement calculation under vertical load and the seismic characteristics under the earthquake load compared with the equal diameter pile.Therefore, in this paper, the calculation of pressure of bulbous hole, settlement calculation under vertical load and dynamic response analysis under earthquake load of large diameter belled pile are studied.The purpose of this paper is to perfect the design and calculation theory of large diameter reamed cast-in-place pile.The main contents include the theoretical study of reaming pressure of reamed pile.Based on the spatial quasi-sliding surface (SMP) criterion, considering elastic deformation in plastic zone, the whole process of spherical hole expansion is analyzed from the angle of energy dissipation. The yield criterion consistent with spherical hole expansion is derived by using stress invariant, and the stress and displacement in elastic-plastic zone are derived respectively.The expression of strain is derived by using volume conservation and energy conservation, and the relation between reaming pressure P, plastic radius R and reaming radius a is given.The analysis of example shows that the pressure calculated by this method is in good agreement with the result of field test. The radius of plastic zone and the pressure of reaming increase with the increase of the radius of reaming, but the increase decreases gradually and tends to be stable.The influence of expansion angle on the radius of plastic zone and the pressure of reaming hole is significant. With the increase of expansion angle, the radius of plastic zone and the pressure of reaming hole increase obviously.Considering the depth effect of compression modulus, the existing formulas for calculating settlement of large-diameter belled cast-in-place piles are modified.The relationship between compression modulus and deformation modulus is established by introducing the influence of depth on compression modulus, and the calculation formula of pile settlement is put in place, and the modified formula is obtained.The calculation formulas before and after modification are used to calculate the settlement of an engineering example.The results show that the calculated results are in better agreement with the measured data.At the same time, the numerical results also show that compared with the calculated settlement before the compression modulus es correction, the calculated settlement after the compression modulus es correction is more consistent with the measured settlement.The Drucker-Prager elastoplastic model is adopted to consider the nonlinearity of soil mass, the contact between pile and soil around pile is set to consider the nonlinearity of pile-soil contact, and the nonlinear contact between pile and soil is considered by means of ABAQUS finite element software.Three dimensional finite element dynamic models of pile-soil-structure and pile-soil-structure interaction systems under seismic loads are established respectively.In this paper, numerical simulation of two kinds of pile foundations in time domain is carried out. The difference of seismic behavior of two kinds of pile foundations is analyzed, and the effects of pile-soil modulus ratio, damping ratio, soft interlayer and upper mass on pile-foundation interaction are discussed.
【学位授予单位】：山东科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD350

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