复合桩基差异沉降控制优化设计方法的研究
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摘要
对于软弱地基上的桩基础来说,基础沉降控制是设计的关键。常规设计认为荷载全部由桩承担,不考虑桩间土的承载能力。本文在总结前人研究的基础上,深入研究了复合桩基差异沉降控制优化设计方法,该方法通过调整地基土刚度和桩基支承刚度的分布,使建筑物的差异沉降得到较好的控制,平均沉降和整体承载力满足规范的要求,且降低基础工程的造价。主要研究内容如下:
①本文采用有限元方法,系统地分析了桩长、桩径、桩间土及桩端土模量、承台宽度、垫层厚度和垫层模量等参数对单桩沉降的影响。特别是模拟了桩-土非线性共同作用的全过程,得出了一些有益的结论,为群桩的分析研究做铺垫。
②对圆形筏板下复合桩基的差异沉降进行了数值模拟和分析,通过对所建模型的桩长、桩径、桩距、地基土模量及布桩形式调整的分析与对比,得到变桩长布桩、以及调整地基土刚度后仅在中心区域布桩是控制基础差异沉降的两种最为有效、简便的布桩方法的结论。这一分析过程也给出了以零差异沉降优化桩筏基础非线性设计的一般方法与程序。
③对地基土刚度调整后的中心布桩复合桩基土中附加应力的分布进行了有限元模拟。由于布桩方式的不同,将其土中附加应力分布特征与等长布桩的复合桩基一样简化为梯形,有欠缺之处,仍需做进一步的研究。
④结合某油罐基础的工程实测资料,对其桩筏基础的变桩长设计进行了有限元模拟;并按照复合桩基差异沉降控制优化设计方法,采用中心等长布桩,结合地基土刚度的调整进行设计计算,说明了本文所提出的调整地基土刚度和桩基支承刚度的方法是控制基础差异沉降的一种切实可行的方法。分析结果表明,该优化方案完全达到了控制甚至消除差异沉降的目的,且与常规桩基设计相比大大减少了用桩数量,节约了基础工程造价,做到了技术与经济效益的最佳结合,从而实现了复合桩基沉降控制优化设计的目的。
For the pile foundation on the soft soil, settlement control is the design key. The general design requires that loads are born entirely by piles, regretting the bearing capacity of soil between the piles. Based on the former researches, the Balanced Settlement Optimum Design Method is presented in this paper. According to this method, the differential settlement can be better reduced by adjusting the rigidity of both the foundation soil and the piles. Meanwhile, the average settlement and the whole bearing capacity all satisfy the code request, and the cost of foundation can also be reduced. The main contents are as the followings:
①The finite-element method is adopted in this paper to analyze the influence factors to the settlement of single pile, which are pile length, pile diameter,soil elastic modulus, cap width, cushion thickness and cushion elastic modulus etc. Especially, the whole course of the non-linear interaction on pile foundation-soil is simulated and some useful conclusions are given to be the reference of the pile group analysis.
②The numerical simulation are carried through to analyze the composite pile foundation under the circular raft. By adjusting several main factors such as pile length, pile space and soil elastic modulus in the finite-element model, a conclusion can be drew that pile length adjusted method and central locating piles combining with soil elastic modulus modulation method are two most effective ways to reduce the differential settlement of composite pile foundation. Beside, this analysis process also gives out the common non-linear design method of pile-raft foundation which aims to reduce the differential settlement to zero.
③Meanwhile, the distributions of additional stress of the composite pile foundation with equal pile length and the composite pile foundation with the adjusted soil rigidity. The research shows that: the additional stress distributions of the composite pile foundation with the adjusted soil rigidity cannot be easily predigested to be a trapezoid as the composite pile foundation with equal pile length because of the different pile disposal. Thus, it needs some more discussion.
④Combining with the actual settlement data of pile raft foundation from one oil storage tank, its pile length variation design is simulated by finite-element method. Beside, the finite-element model of central locating piles combining with soil elastic modulus modulation
①本文采用有限元方法,系统地分析了桩长、桩径、桩间土及桩端土模量、承台宽度、垫层厚度和垫层模量等参数对单桩沉降的影响。特别是模拟了桩-土非线性共同作用的全过程,得出了一些有益的结论,为群桩的分析研究做铺垫。
②对圆形筏板下复合桩基的差异沉降进行了数值模拟和分析,通过对所建模型的桩长、桩径、桩距、地基土模量及布桩形式调整的分析与对比,得到变桩长布桩、以及调整地基土刚度后仅在中心区域布桩是控制基础差异沉降的两种最为有效、简便的布桩方法的结论。这一分析过程也给出了以零差异沉降优化桩筏基础非线性设计的一般方法与程序。
③对地基土刚度调整后的中心布桩复合桩基土中附加应力的分布进行了有限元模拟。由于布桩方式的不同,将其土中附加应力分布特征与等长布桩的复合桩基一样简化为梯形,有欠缺之处,仍需做进一步的研究。
④结合某油罐基础的工程实测资料,对其桩筏基础的变桩长设计进行了有限元模拟;并按照复合桩基差异沉降控制优化设计方法,采用中心等长布桩,结合地基土刚度的调整进行设计计算,说明了本文所提出的调整地基土刚度和桩基支承刚度的方法是控制基础差异沉降的一种切实可行的方法。分析结果表明,该优化方案完全达到了控制甚至消除差异沉降的目的,且与常规桩基设计相比大大减少了用桩数量,节约了基础工程造价,做到了技术与经济效益的最佳结合,从而实现了复合桩基沉降控制优化设计的目的。
For the pile foundation on the soft soil, settlement control is the design key. The general design requires that loads are born entirely by piles, regretting the bearing capacity of soil between the piles. Based on the former researches, the Balanced Settlement Optimum Design Method is presented in this paper. According to this method, the differential settlement can be better reduced by adjusting the rigidity of both the foundation soil and the piles. Meanwhile, the average settlement and the whole bearing capacity all satisfy the code request, and the cost of foundation can also be reduced. The main contents are as the followings:
①The finite-element method is adopted in this paper to analyze the influence factors to the settlement of single pile, which are pile length, pile diameter,soil elastic modulus, cap width, cushion thickness and cushion elastic modulus etc. Especially, the whole course of the non-linear interaction on pile foundation-soil is simulated and some useful conclusions are given to be the reference of the pile group analysis.
②The numerical simulation are carried through to analyze the composite pile foundation under the circular raft. By adjusting several main factors such as pile length, pile space and soil elastic modulus in the finite-element model, a conclusion can be drew that pile length adjusted method and central locating piles combining with soil elastic modulus modulation method are two most effective ways to reduce the differential settlement of composite pile foundation. Beside, this analysis process also gives out the common non-linear design method of pile-raft foundation which aims to reduce the differential settlement to zero.
③Meanwhile, the distributions of additional stress of the composite pile foundation with equal pile length and the composite pile foundation with the adjusted soil rigidity. The research shows that: the additional stress distributions of the composite pile foundation with the adjusted soil rigidity cannot be easily predigested to be a trapezoid as the composite pile foundation with equal pile length because of the different pile disposal. Thus, it needs some more discussion.
④Combining with the actual settlement data of pile raft foundation from one oil storage tank, its pile length variation design is simulated by finite-element method. Beside, the finite-element model of central locating piles combining with soil elastic modulus modulation
引文
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[18] Horikoshi, K. and Randolph, M.F. A contribution to optimmn design of piled rafts [J].Geotechnique, 1998:Vo1.48,No.3,301-317.
[19] 宰金珉.复合桩基沉降计算方法研究[J].南京建筑工程学院学报.2001(4).
[20] 宰金珉.复合桩基沉降计算的最终应力法及其应用[J].土木工程学报.2002(2).
[21] 宰金珉.塑性支承桩-卸荷减沉桩的概念及其工程应用[J].岩土工程学报,2001(3):273 -278.
[22] 凌华.考虑筏板刚度的桩筏非线性共同作用分析[D].南京工业大学硕士学位论文, 2002.
[23] 余闯.复合桩基沉降计算和差异沉降控制研究[D].南京工业大学硕士学位论文,2003.
[24] 宰金珉.复合桩基理论与应用[M].知识产权出版社,中国水利水电出版社,2004:198- 214.
[25] 李雄威.复合桩基非线性工作机理模型试验研究与分析[D].南京工业大学硕士学位论文,2005.
[26] 黄绍铭,裴捷,贾宗元,魏汝南.软土中桩基沉降计算.第四届全国土力学及基础工程学术会议论文集.中国建筑工业出版社,1983.
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