地下增层条件下既有受荷基桩承载特性研究

发布时间：2018-09-07 17:44

【摘要】：既有建筑下挖增层改造将改变既有桩及托换桩基础的承载性状。首先,结合浙江饭店地下车库扩建工程,分别分析下挖增层改造对既有单桩基础及群桩基础沉降性状的影响。随着增层下挖深度的增加,桩周土体对基桩的约束逐渐减小,基桩有可能发生屈曲失稳破坏。之后,结合浙江饭店地下车库扩建工程及甘水巷3号组团地下室建设工程,研究下挖增层工况下嵌岩桩及非嵌岩桩的屈曲稳定临界荷载;在此基础上,研究基桩两端不同约束对嵌岩桩及非嵌岩桩屈曲稳定的影响。最后,结合甘水巷3号组团地下室建设工程的现场实测资料及有限元三维数值模型,分析既有建筑下挖增层改造对上部结构沉降性状,托换桩及新增地下室结构柱承载性状的影响。本文主要工作和成果如下:(1)利用荷载传递法建立下挖增层工况下单桩的受力模型并得到其控制方程,通过侧阻软化模型及端阻双曲线模型分别模拟开挖工况下的桩侧及桩端阻力荷载传递性状,得出下挖深度对桩端极限阻力影响不大,而对桩侧极限阻力影响较大;既有单桩基础桩顶沉降量随下挖深度不断增大。假定托换桩基础与既有桩基础截面尺寸保持一致,考虑既有桩与托换桩之间存在的桩-桩相互作用,结合混合法研究下挖增层改造对群桩基础沉降性状的影响,得出随着下挖深度的增加,方形承台中心桩桩顶沉降量不断增大;在同一开挖深度时,角桩桩顶沉降量最大,边桩次之,中心桩最小;不同布桩形式会对群桩基础中心桩桩顶沉降量产生一定的影响;下挖深度对圆形布桩中心桩桩顶沉降量影响最大,方形次之,菱形最小;(2)由甘水巷3号组团地下室建设工程托换桩载荷试验可知,当反力架所提供的反力达到极限值时,对应的桩顶沉降量为1.61 mm;当桩顶荷载卸载至零时,托换桩桩顶残余沉降量为1.22 mm;当桩顶荷载超过150 kN时,上部土层发生侧阻软化效应。结合甘水巷3号组团地下室建设工程现场实测资料,可知托换桩桩身轴力随开挖深度的增加而逐渐增大,随入土深度的增加而缓慢减小;桩侧摩阻力至上而下逐步发挥,在整个下挖增层改造过程中,桩端阻力始终为零;上部结构沉降量随时间而缓慢增大,但在截桩工序中,上部结构沉降量急剧增大;结构柱轴力随托换桩截除数量的增加而急剧增大,特别是③号托换桩截除时,结构柱轴力增量达到最大值;相邻承台截桩对结构柱轴力的影响可忽略不计;(3)结合浙江饭店地下车库扩建工程和甘水巷3号组团地下室建设工程,通过能量法建立嵌岩桩及非嵌岩桩桩-土体系总势能方程,利用最小势能原理,导出桩身屈曲稳定临界荷载表达式,并分析下挖增层改造对嵌岩桩及非嵌岩桩屈曲稳定临界荷载的影响;之后,分析不同桩顶约束对下挖增层工况下的嵌岩桩及非嵌岩桩屈曲稳定临界荷载的影响。表明,随着半波数的增加,嵌岩桩与非嵌岩桩的屈曲稳定临界荷载急剧收敛,且桩顶固定时的收敛速度最快,铰接次之,弹性嵌固最慢;桩侧摩阻力及桩身自重对非嵌岩桩屈曲稳定临界荷载的影响不明显;非嵌岩桩的屈曲稳定临界荷载随比例系数m值的增大而增加,但当下挖深度大于4.0m时,m值对非嵌岩桩的屈曲稳定临界荷载的影响可忽略不计;嵌岩桩与非嵌岩桩的屈曲稳定临界荷载随下挖深度的增加而急剧减小;不同桩顶约束对桩基础屈曲稳定临界荷载比影响不同,在同一开挖深度时,桩顶固定时,临界荷载比最大,弹性嵌固次之,铰接最小;随着下挖深度的增加,桩顶固定时的临界荷载比缓慢减小,而桩顶嵌固及铰接时的临界荷载比急剧降低;(4)利用Plaxis 3D有限元软件建立甘水巷3号组团地下室建设工程中7C承台的三维实体模型,分析下挖增层改造对7C承台沉降、托换桩及新增地下室结构柱承载性状的影响。可知托换桩施工结束后,土层下挖对7C承台沉降性状的影响较基础托换施工之前小;当下挖至指定标高时,浇筑新增地下室底板对上部结构沉降性状影响较大。基础托换及浇筑结构柱对上部结构沉降性状的影响可忽略不计。不同的截桩顺序对结构柱轴力会有一定的影响。
[Abstract]:First of all, combined with the extension project of Zhejiang Hotel underground garage, the influence of excavation and layering on the settlement behavior of existing single pile foundation and pile group foundation is analyzed. After that, the critical buckling load of rock-socketed pile and non-rock-socketed pile under the condition of digging and adding layers is studied. On this basis, the buckling stability of rock-socketed pile and non-rock-socketed pile under different constraints at both ends is studied. Finally, combined with the in-situ measured data of the basement construction project of Ganshui Lane Group 3 and the finite element three-dimensional numerical model, this paper analyzes the influence of the excavation and storey addition on the settlement behavior of the superstructure, underpinning piles and the bearing behavior of the new basement columns. The load transfer behavior of pile side resistance and pile tip resistance under excavation is simulated by side resistance softening model and end resistance hyperbolic model respectively. It is concluded that the depth of excavation has little effect on the ultimate resistance of pile tip, but has great influence on the ultimate resistance of pile side. The top settlement increases with the depth of excavation. Assuming that the section size of underpinning pile foundation is consistent with that of existing pile foundation, considering the interaction between existing pile and underpinning pile, combined with the hybrid method, this paper studies the influence of layered excavation on the settlement behavior of pile group foundation. At the same excavation depth, the top settlement of corner pile is the largest, the side pile is the second, and the center pile is the smallest; different forms of pile arrangement will have a certain impact on the top settlement of pile group foundation; the bottom excavation depth has the greatest impact on the top settlement of circular pile center, followed by square, the diamond is the smallest; (2) Ganshui Lane 3. Load test of underpinning pile in No.1 group basement construction project shows that when the reaction force provided by the reaction frame reaches the limit value, the corresponding settlement of pile top is 1.61 mm; when the load of pile top is unloaded to zero, the residual settlement of underpinning pile top is 1.22 mm; when the load of pile top exceeds 150 kN, the lateral resistance softening effect occurs in the upper soil layer. The measured data of the basement construction project of Group No. 1 show that the axial force of underpinning pile increases gradually with the increase of excavation depth and decreases slowly with the increase of excavation depth; the friction resistance of pile side is gradually exerted from top to bottom, and the resistance of pile tip is always zero during the whole process of the downward excavation and layering; the settlement of superstructure is slowly with time. The axial force of the structural column increases sharply with the increase of the number of underpinned piles, especially when the number of underpinned piles is cut off, the axial force increment of the structural column reaches the maximum value; the influence of the adjacent pile cap on the axial force of the structural column can be neglected; (3) The expansion of the underground garage of Zhejiang Hotel can be considered; (3) The influence of the adjacent pile cap on the axial force of the structural column can be neglected. The total potential energy equation of rock-socketed pile and non-rock-socketed pile-soil system is established by energy method. The expression of critical load for buckling stability of pile body is derived by using the principle of minimum potential energy. The influence of excavation and layering increase on critical load of rock-socketed pile and non-rock-socketed pile is analyzed. The results show that the critical buckling load of rock-socketed and non-rock-socketed piles converges sharply with the increase of half wave number, and the convergence speed is the fastest when the top of the pile is fixed, followed by the hinge, and the elastic embedding is the slowest. The critical buckling load of non-rock-socketed piles is not obvious; the critical buckling load of non-rock-socketed piles increases with the increase of the ratio coefficient m, but when the excavation depth is greater than 4.0 m, the influence of m on the critical buckling load of non-rock-socketed piles can be neglected; the critical buckling load of rock-socketed piles and non-rock-socketed piles can be neglected; the critical buckling load of rock-socketed piles The critical load ratio decreases sharply with the increase of the depth of excavation, and decreases slowly with the increase of the depth of excavation, but decreases slowly with the increase of the depth of excavation, while the critical load ratio decreases with the increase of the depth of excavation. The critical load ratio decreases sharply. (4) Using Plaxis 3D finite element software, a three-dimensional solid model of 7C pile cap in Ganshuixiang Group 3 basement construction project is established, and the influence of excavation and storey addition on the settlement of 7C pile cap, underpinning pile and the bearing behavior of new basement structural column is analyzed. The influence of foundation underpinning and pouring structural columns on the settlement behavior of superstructure can be neglected. The axial force of structural columns can be affected by different pile cutting sequence.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU473.1

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