【作者】 潘军刚；

【导师】 李大勇；

【作者基本信息】 山东科技大学 ， 岩土工程， 2007， 硕士

【摘要】 在城市中进行隧道开挖会对已有建筑物、地下管线等产生不良影响。当隧道近接或穿越建筑物桩基而向前推进时，引起的地层移动会对邻近桩基施加轴向力或侧向力，会降低桩基承载力，增加桩基的不均匀沉降，进而影响到上部结构的正常使用。因此，研究隧道开挖对邻近桩基的影响显得尤为重要。本文利用有限差分程序，建立了三维模型，验证了一个实例(Chen1999)，然后在实例模型和参数的基础上，研究了盾构隧道近接施工所引起单桩和群桩的内力和变形响应，所取得的成果对工程实际具有一定的参考价值和指导意义。研究内容如下：1．研究了隧道开挖对邻近既有单桩的影响，考虑的影响因素有：桩顶荷载、地层分布、隧道纵坡、双孔隧道、桩体弹性模量、桩径等。研究表明：①随着桩顶荷载的增大，桩身轴力和竖向沉降逐渐增大，桩身弯矩和水平位移变化不大。②隧道3倍洞径范围内的土层强度对桩的内力和变形影响较大。当隧道开挖可能对邻近桩体产生不利影响时，可以提前加固此部分土层(如注浆加固、锚杆支护等)来改善桩的受力性能，从而保证桩及上部结构的安全。③有纵坡隧道开挖比无纵坡隧道开挖所引起的桩身沉降要小的多。④双孔隧道开挖对邻近桩的竖向承载力和竖向沉降相当不利，而对桩的水平变形和弯矩比较有利。⑤当桩体弹性模量或桩径增大时，桩身轴力和弯矩随之增大，桩身抵抗侧向变形的能力会相应增加，桩项与桩端的差异沉降减小。2．分析了隧道开挖对邻近既有群桩的影响，考虑了桩长、桩与隧道间的水平距离、高低承台等因素变化时桩及桩间土不同响应。研究表明：①当承台上部荷载一定时，随着桩长的增加，桩身轴力、水平位移和弯矩逐渐增大，桩身沉降和桩间土竖向应力逐渐减小。②随着桩与隧道之间距离的增大，桩身轴力、弯矩、水平位移、竖向沉降和桩间土竖向应力等均有不同程度减小。③在桩身轴力和竖向沉降方面，高承台桩大于低承台桩；在水平位移和竖向沉降的变化规律方面，高承台桩与低承台桩基本相同。④由于受前排桩“遮拦作用”的影响，后排桩受隧道开挖影响较小，但后排桩的轴力明显大于前排桩的轴力。3．总结分析了隧道近接既有桩基施工时几种常见的保护措施，并以隔断墙为例，通过尺寸研究得出了最为经济合理的桩基保护方案。更多还原

【Abstract】 The existing buildings and buried pipelines will be affected inevitably by tunneling in urban areas. When the tunnel excavation under or adjacent to the pile foundations of buildings, stratum movements caused by tunneling will exert axial and lateral forces on adjacent piles, which may reduce the bearing capacity of piles and increase the differential settlement, thus superstructure is influenced. Obviously, it is important to study the responses of piles to nearby tunneling.In this paper, finite difference code is adopted and three-dimensional model is created. Though verifying an example proposed in Chen’s paper, the model put forward by the author is available. Thereafter, the responses of single pile and pile groups to adjacent shield tunneling is investigated, some useful conclusions have been obtained, which can be used to guide practical engineering. The contents of this paper are outlined in details as the following:1. The responses of single pile to tunneling are analyzed with parameters, such as loads on the top of a pile, soil layers, longitudinal slop of a tunnel, double-tube-tunnel, elastic modulus of pile and pile diameter. It shows:①The axial force and vertical settlement along a pile increase with the increasing of the load on the top of a pile.②The internal force and deflection of a pile is apparently affected by the strength of soil in the region of three-hole-diameter-of-the-tunnel. Soil strength around the tunnel can be enhanced by some reinforce measures (such as grout and anchor), which can improve the force performance of the pile and ensure the safety of building structure.③The settlement of pile caused by the tunnel with gradient is smaller than that of pile caused the tunnel without gradient.④The excavation of double tunnel is adverse to the vertical bearing capacity and settlement of a pile, but it is advantageous to the lateral deflection and bending moment of the pile.⑤With the increasing of elastic modulus and diameters of the piles, axial force and bending moment of a pile will increase, then the capability to resist deflection of the pile is strengthened, and the differential settlement of the top and bottom of the pile is reduced.2. The responses of pile groups to tunneling are also studied with parameters, such as pile length, the horizontal distance between the tunnel and the pile, and the height of the cap of the pile. Research indicates:①When the load on the cap of the pile is definite, the axial force, horizontal movement and moments of the pile will increase as the increase of pile strength, and the settlement of the pile and vertical stress of soil under the cap of the pile will decrease.②The response of piles and soil between the piles to tunneling will decrease with the increasing of the horizontal distance between the tunnel and the pile.③The axial force and vertical settlement of the high cap pile is larger than that of the low cap pile, the horizontal movement and moments of the high cap pile is similar to that of the low cap pile.④Due to the "barrier effect" of the front pile, the responses of back pile to tunneling is smaller than the front pile, the axial force of back pile is larger than the axial force of front pile.Finally, some protection measures of pile foundations engineering are summed up and analyzed, then the partition wall is taken into consideration, an optimal scheme is gained through research on the size of the partition wall.更多还原