【作者】 鲁燕儿；

【导师】 郑俊杰；

【作者基本信息】 华中科技大学 ， 岩土工程， 2009， 博士

【摘要】 预应力混凝土管桩具有诸多优点，因此在全国各地得到了广泛的应用。但由于许多工程人员对其沉桩和承载机理认识不够充分，因此在设计和施工中难免出现一些问题，如选型不当、构造措施不妥、桩的挤土效应严重影响邻桩的承载力和周边建筑等。为解决这些问题，本文针对预应力混凝土管桩的特殊性，对预应力混凝土管桩的沉桩机理和承载力计算方法进行了系统的研究。首先，采用圆孔扩张理论研究了混凝土管桩沉桩挤土效应。基于不同模量弹性理论和非关联Mohr-Coulomb流动法则推导得到了球形孔和柱形孔扩张时弹性区和塑性区的应力、塑性区半径和扩张压力的表达式。通过参数分析探讨了不同拉压模量之比、拉压泊松比和剪胀角对球形孔和柱形孔扩张的扩张压力及塑性区半径的影响。结果表明这些参数对塑性区的发展和土体中的应力有很大的影响。随后引入土塞增长率来衡量开口管桩内土塞的闭塞程度，得到了包含土体拉压模量比和土塞增长率的塑性区半径和桩外壁处的扩张压力解答，并分析了开口管桩沉桩过程中土塞增长率对开口管桩沉桩挤土范围的影响，结果表明土塞增长率越小，开口管桩挤土效应越明显。其次，研究了沉桩后土体中超孔隙水压力的消散问题。采用对数坐标系中有效应力和孔隙率的关系以及渗透系数和孔隙率的关系考虑固结过程中压缩性和渗透性的变化，得到了渗透系数和压缩系数变化的径向固结控制方程，采用分离变量法和Bessel方程求得了径向固结控制方程的半解析解。然后通过实例计算验证了该方法的正确性，通过参数分析讨论了不同渗透指数和压缩指数对超孔隙水压力消散过程的影响。并且研究了开口管桩内土塞中的超孔隙水压力消散问题，将其简化为一维竖向固结问题，通过迭代法求解了竖向固结控制方程，该解答能真实反映土塞中超孔隙水压力消散过程中土体渗透性和压缩性的变化规律。然后，探讨了预应力混凝土管桩桩端端阻力的计算方法。分析了武汉地区预应力混凝土管桩静载荷试验结果，并将这些结果与按湖北省地方标准《建筑地基基础技术规范》计算得到的值进行对比，结果表明实测值大于设计值。然后基于双剪滑移线理论，考虑了岩土材料的拉伸强度和压缩强度的不等性，通过滑移线的应力传递公式得到了考虑中间主应力的桩端端阻力计算公式。总结了不同规范中管桩端阻力的计算公式，分析了土塞的受力性状，得到了完全排水条件和不排水条件下土塞的端阻，结果有效地反映了开口管桩的承载特性。最后，分析了预应力混凝土管桩水平承载特性。首先验算了管桩规程中给出的水平承载力特征值是否满足抗裂的要求。然后基于地基土为理想弹塑性材料的假设，求解了水平荷载作用下，部分桩前土体处于塑性状态时任一深度处桩的水平位移、转角、弯矩和剪力的解答。这些计算公式可应用于分析承受水平荷载为主且水平位移较大的桩基的水平承载特性。本文的研究成果对预应力混凝土管桩的设计与施工具有重要的参考价值。更多还原

【Abstract】 Prestressed concrete pipe piles are widely used in China owing to their advantages. However many engineers are not familiar with the mechanisms of the installation and bearing capacity of the prestressed concrete pipe piles. Thus there are a lot of problems existing in the design and construction of the prestressed concrete pipe piles, such as mischoosing pile types, unsuitable structures, and severe influences of the squeezing effect on the bearing capacity of adjacent piles and surrounding buildings during pile installation. This dissertation mainly deals with the installation mechanism and calculation method for bearing capacity of the prestressed concrete pipe piles consideraing their characteristics.Firstly, the squeezing effect of prestressed concrete pipe piles is studied with cavity expansion theory. Analyses of spherical and cylindrical cavity expansion in elasto-plastic soil are performed based on the elastic theory considering different moduli in tension and compression. The characteristics of dilation are taken into account by using the non-associated Mohr-Coulomb yield criterion. The analytical solutions for the stresses in elastic and plastic regions, maximum radii of the plastic regions and expansion pressures are obtained. Then the influences of different tension and compression moduli ratios, Poisson’s ratios and dilation angles on the expansion pressures and radii of plastic regions are discussed by parametric study. The results show that different ratios of tension and compression moduli, Poisson’s ratios and dilation angles have significant influences on the development of plastic regions and the stresses in the soil. Subsequently, the incremental filling ratio is introduced to quantify the degree of soil plugging in the open-ended pipe pile. The radii of plastic regions and the expansion pressures on the external wall are formulated including ratio of tension and compression moduli and incremental filling ratio. Moreover, the influences of incremental filling ratios on the squeezing areas induced by installation of open-ended pipe piles are investigated. The results of the parametric analyses show that the squeezing effects of the open-ended pipe piles with smaller incremental filling ratios are more severe than those with larger incremental filling ratios.Secondly, the dissipation of the excess pore water pressure after pile installation is studied. The dissipation of the excess pore pressure is analyzed by radial consolidation theory with a variable consolidation coefficient based on the linear responses of effective stress-void and permeability coefficient-void. The governing equation of the radial consolidation considering variable compressibility and permeability is solved by the variable separation method. Bessel functions are used to solve the differential equations for the time independent part. Then the accuracy of this method is validated by comparing calculated values with numerical results and field data observed from two project cases. And the influences of variable compressibility and permeability on the variation of consolidation coefficient and excess pore pressure dissipation are analyzed. Moreover, the dissipation of the excess pore water pressures in the soil plugs of open-ended pipe piles is analyzed by one-dimensional vertical consolidation theory. And the differential equation of vertical consolidation is solved with iterative method. The solutions obtained can effectively reflect the variation laws of permeability and compressibility of soils during excess pore pressure dissipation in soil plug.Thirdly, the calculation method of tip resistances of the prestressed concrete pipe piles is investigated. The results of static load tests of prestressed concrete pipe piles in Wuhan are accumulated and analyzed. These results are compared to the values obtained from local standard of Hubei province "Technical code for building foundation", which show that test data are larger than the calculation values. Then a method to evaluate the end bearing capacity of pile by twin shear slip-line theory is recommended. The difference between the tension strength and compression strength of soil is considered and the effect of intermediate principal stress is included in the formula. The stress transferring formula of the slip-line method is applied during the calculation process. Whereafter, the calculation methods of tip resistances of open-ended pipe piles in different specifications are summarized. The characteristics of the soil plugs are analyzed. And the tip resistances of soil plugs under fully drained and undrained conditions are obtained, which can reflect the characteristics of bearing capacities of open-ended pipe piles.Finally, the lateral bearing characteristics of prestressed concrete pipe piles are analyzed. The anti-crack requirements of prestressed concrete pipe piles are verified under the condition of lateral loads, which act on the top of the piles and takes the characteristic values of lateral bearing capacity. Then based on the assumption that the soil is elastic-perfectly plastic material, the theoretical solutions of deflection, rotation, moment and shear force at any depth of the pile under lateral force are obtained, which can be applied to analyze the lateral bearing capacity of the piles mainly exerted by lateral force and with large lateral deflection.The achievements in this dissertation can be valuable references for the design and construction of the prestressed concrete pipe piles.更多还原