长短桩复合地基室内模型试验研究
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摘要
近几年,随着复合地基理论和技术的发展,许多新型的复合地基被应用到工程的设计和实践中去,长短桩复合地基就是其中的一种。长短桩复合地基的优势就是通过褥垫层的应力协调作用充分发挥桩间土的承载力,从而最大限度的发挥复合地基的承载力,以减少桩量,并满足工程的承载力和沉降要求,因此具有良好的经济性。这种地基处理方式,实际上是我国的工程技术人员结合我国的国情,在不断总结以往的工程经验而发展起来的一种新型的地基处理方式。
鉴于此,本文依托国家自然科学基金资助项目“长短桩复合地基的变形性状分析及其试验研究”(项目号:50678110),通过在砂土中进行的一系列模型试验,包括不同桩数、不同桩间距、不同厚度的垫层,对长短桩复合地基的工作机理进行了研究,得到如下结论:
1.在本试验长短桩相间布置的情况下,复合地基承载变形特性主要体现在长桩上,长桩不仅在承载方面发挥重要作用,而且是控制沉降的主要构件。短桩作为辅助桩,其桩身变形较大,上部荷载不能有效地向下传递,与长桩相比在承担荷载及控制沉降方面的作用较小。
2.不同位置长桩与短桩桩身轴力的发挥程度,依次为角桩最大、边桩次之、中桩最小。
3.带褥垫层的复合地基,不同位置长桩与短桩桩侧负摩阻力的发挥程度为中桩最大,土反力的分布为中部大、边部小;而在无褥垫层的情况下,桩侧负摩阻力的发挥程度为角桩最大,土反力的分布为中部小、边部大。
4.随着桩间距的减小,复合地基的沉降、桩侧摩阻力和桩间土承担的荷载减小,长桩和短桩的桩身轴力、桩土应力比和桩的荷载分担比增大。
5.随着垫层厚度的增大,复合地基的沉降、桩侧摩阻力和桩间土承担的荷载增大,长桩桩身轴力、桩土应力比和荷载分担比减小,短桩桩身轴力、桩土应力比和荷载分担比先增大后减小。
Recently, with the theoretical and technologic development of composite foundation, many new types of composite foundation have been used in design and construction. The long-short-pile composite foundation is one of them. Its advantage is that, the capacity of soil between piles has been developed through the stress coordination of cushion, in turn, bearing capacity has been satisfied, the number of piles has been reduced, capability and settlement has been satisfied, so it is economic. As a new ground treatment method, it is developed by our engineer, according to local conditions and engineering experience.
In response to these circumstances, this subject relies on the National Natural Science Foundation Project " The Long-short-pile Composite Foundation Deformation Behavior Analysis and Experimental Study" (project number: 50678110), a series of model experiment on the sandy soil has been done, including a number of different piles, different pile spacing, different thickness of cushion, the long-short-pile composite foundation's work mechanism has been conducted, the following conclusions have been made.
1. In this experiment, the long pile plays an important role in the capability and deformation characteristics of long-short-pile composite foundation, it not only occupies an important position in the bearing capability, but also control settlement. As the auxiliary pile, short pile has more deformation, the upper load can not pass down effectively, compared with the long pile, short pile’s effect on bearing capability and settlement is small.
2. The axial force’s level of long pile and short pile with different position is different, the corner pile is biggest, the side pile is next, the center pile is smallest.
3. The negative skin friction’s level of long pile and short pile with different position of composite foundation with cushion is that, the center pile is biggest, and the distribution of soil stress of composite foundation with cushion is that, the middle of soil stress curve is big, side is small. But without cushion, the conclusion is opposite, the negative skin friction’s level is that, the corner pile is biggest, the distribution of soil stress is that, the middle of soil stress curve is small, side is big.
4. With the pile spacing decreases, the settlement of composite foundation, the skin friction and the soil between piles bearing capacity decrease; the axial force, the pile-soil stress ratio and pile-soil load-sharing ratio of long pile and short pile increase.
5. With the cushion thickness increases, the settlement of composite foundation, the skin friction and the soil between piles bearing capacity increase; the axial force, the pile-soil stress ratio and pile-soil load-sharing ratio of long pile decrease, these factors of short pile increase at the beginning and then decrease.
鉴于此,本文依托国家自然科学基金资助项目“长短桩复合地基的变形性状分析及其试验研究”(项目号:50678110),通过在砂土中进行的一系列模型试验,包括不同桩数、不同桩间距、不同厚度的垫层,对长短桩复合地基的工作机理进行了研究,得到如下结论:
1.在本试验长短桩相间布置的情况下,复合地基承载变形特性主要体现在长桩上,长桩不仅在承载方面发挥重要作用,而且是控制沉降的主要构件。短桩作为辅助桩,其桩身变形较大,上部荷载不能有效地向下传递,与长桩相比在承担荷载及控制沉降方面的作用较小。
2.不同位置长桩与短桩桩身轴力的发挥程度,依次为角桩最大、边桩次之、中桩最小。
3.带褥垫层的复合地基,不同位置长桩与短桩桩侧负摩阻力的发挥程度为中桩最大,土反力的分布为中部大、边部小;而在无褥垫层的情况下,桩侧负摩阻力的发挥程度为角桩最大,土反力的分布为中部小、边部大。
4.随着桩间距的减小,复合地基的沉降、桩侧摩阻力和桩间土承担的荷载减小,长桩和短桩的桩身轴力、桩土应力比和桩的荷载分担比增大。
5.随着垫层厚度的增大,复合地基的沉降、桩侧摩阻力和桩间土承担的荷载增大,长桩桩身轴力、桩土应力比和荷载分担比减小,短桩桩身轴力、桩土应力比和荷载分担比先增大后减小。
Recently, with the theoretical and technologic development of composite foundation, many new types of composite foundation have been used in design and construction. The long-short-pile composite foundation is one of them. Its advantage is that, the capacity of soil between piles has been developed through the stress coordination of cushion, in turn, bearing capacity has been satisfied, the number of piles has been reduced, capability and settlement has been satisfied, so it is economic. As a new ground treatment method, it is developed by our engineer, according to local conditions and engineering experience.
In response to these circumstances, this subject relies on the National Natural Science Foundation Project " The Long-short-pile Composite Foundation Deformation Behavior Analysis and Experimental Study" (project number: 50678110), a series of model experiment on the sandy soil has been done, including a number of different piles, different pile spacing, different thickness of cushion, the long-short-pile composite foundation's work mechanism has been conducted, the following conclusions have been made.
1. In this experiment, the long pile plays an important role in the capability and deformation characteristics of long-short-pile composite foundation, it not only occupies an important position in the bearing capability, but also control settlement. As the auxiliary pile, short pile has more deformation, the upper load can not pass down effectively, compared with the long pile, short pile’s effect on bearing capability and settlement is small.
2. The axial force’s level of long pile and short pile with different position is different, the corner pile is biggest, the side pile is next, the center pile is smallest.
3. The negative skin friction’s level of long pile and short pile with different position of composite foundation with cushion is that, the center pile is biggest, and the distribution of soil stress of composite foundation with cushion is that, the middle of soil stress curve is big, side is small. But without cushion, the conclusion is opposite, the negative skin friction’s level is that, the corner pile is biggest, the distribution of soil stress is that, the middle of soil stress curve is small, side is big.
4. With the pile spacing decreases, the settlement of composite foundation, the skin friction and the soil between piles bearing capacity decrease; the axial force, the pile-soil stress ratio and pile-soil load-sharing ratio of long pile and short pile increase.
5. With the cushion thickness increases, the settlement of composite foundation, the skin friction and the soil between piles bearing capacity increase; the axial force, the pile-soil stress ratio and pile-soil load-sharing ratio of long pile decrease, these factors of short pile increase at the beginning and then decrease.
引文
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[3]龚晓南.土塑性力学.浙江大学出版社,1998.
[4]龚晓南.地理处理手册(第二版).中国建筑工业出版社,2000.
[5]龚晓南.复合地基发展概况及其在高层建筑中的应用.土木工程学报,1999, 32 (6):8-10.
[6]《建筑地基处理技术规范》(JGJ79-2002).北京:中国建筑工业出版社,2002.
[7]《建筑桩基技术规范》(JGJ94-2008).北京:中国建筑工业出版社,2008.
[8] Burland,J.B.,Broms,B.B. and De Mello,V.H.B.(1977).Behabiour of foundations and struetures.Proe.9th ICSMFE,Vol.2.
[9] Hain,S.J. and Lee,I.K.(1974).Rational analysis of raft foundation. J.Geoteeh. Engrg. Div,ASCE,Vol.100,No.GT7.
[10] Oulos,H.G. and Davis,E.H. ( 1980 ) . Pile foundation analysis and design.John Wiley and Sons,New York.
[11]马骥,张东刚,张震,阎明礼.长短桩复合地基设计计算.岩土工程技术,2001年第二期: 86-91.
[12]王步云,赵秀芹.砂石桩与低强度混凝土桩组合型复合地基在软土地基中的应用(一).岩土工程技术,1997年第1期:8-14.
[13]王步云,赵秀芹.砂石桩与低强度混凝土桩组合型复合地基在软土地基中的应用(二).岩土工程技术,1997年第2期:3-5.
[14]党昱敬.CFG桩和沉管挤密碎石桩组合型复合地基的承载力.工业建筑,1997(3):13-18.
[15]解志浩,杨文志.三元复合地基在工程中的应用.山西建筑,2002(11):13-15.
[16]王昆泰,张丙印.二次复合地基在高层建筑中的应用.建筑技术,2003(3): 215-216.
[17]田志勇,史智飞,王文杰.挤密碎石桩与CFG桩复合地基技术的应用.市政技术,2003(5):156-162.
[18]刘海涛.刚柔性长短桩复合地基工程性状分析.杭州:浙江大学,2004.
[19]钱家欢,殷宗泽.土工原理与计算(第二版).北京:中国水利水电出版社,1996.
[20]吴建华,张涛.素砼桩、水泥土桩及土共同工作的复合地基设计.江苏建筑,1999(1):46-47.
[21]郑俊杰,刘志刚.石灰桩与深层搅拌桩联合加固杂填土地基.施工技术,1997(9):23-24.
[22]郑俊杰,袁内镇.石灰桩与深层搅拌桩联合加固深厚软土.岩土工程技术,1998年第2期:33-34,47.
[23]杨军龙,龚晓南,孙邦臣.长短桩复合地基沉降计算方法探讨.建筑结构,2002, 32(7):8-10.
[24]杨军龙,龚晓南.长短桩复合地基沉降计算方法探讨.建筑结构,2002(32):8-9.
[25]杨军龙.长短桩复合地基沉降计算.杭州,浙江大学,2002.
[26]葛忻声,龚晓南.长短桩复合地基设计计算方法的探讨.建筑结构,2002(7):3-4,7.
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