【作者】 杨庆光；

【导师】 张可能； 刘杰；

【作者基本信息】 中南大学 ， 地质工程， 2008， 博士

【摘要】 复合地基处理方法作为一种常见的地基处理方法,已经在软土地区得到了广泛的应用。在沿海深厚软土地区,由于建设工程的数量、规模和地基土本身的工程特性等因素影响,地基处理技术的难度变得越来越大,寻求理论上可靠、经济上合理和施工上可行的地基处理新技术对于沿海地区的建设十分重要。本文针对南沙地区深厚软土的地基处理,提出了水泥土长短桩复合地基与锥形桩复合地基的软基处理新技术。通过原位测试、室内模型试验和理论分析与计算相结合的方法,对南沙软土的工程特性、深厚软土中复合地基有效桩长计算方法、深厚软土中水泥土长短桩复合地基的作用机理和沉降理论、锥形桩单桩成桩效应、锥形桩单桩及其复合地基的作用机理等一些问题进行了深入的研究。本文的主要工作包括以下几方面:(1)广泛收集广州南沙地区典型地段的软土工程勘察,总结出了广州南沙地区软土的形成环境与微结构。对南沙地区深厚软土的物理力学性能指标进行了详细的分析和研究,验证了南沙地区软土的“三高三低”工程特性,并通过统计与回归相结合的方法建立了南沙地区软土物理力学性能指标间的回归关系,为南沙深厚软土的物理力学性能指标的取值合理性提供了一种直观便捷,行之有效的判定方法;(2)通过理论推导,得到了刚性基础下不考虑桩间土顶荷载的柔性桩复合地基、刚性基础下考虑桩间土顶荷载的柔性桩复合地基和柔性基础考虑桩间土顶荷载的柔性桩复合地基的有效桩长计算方法,并通过实例对比分析,研究了各种计算结果的合理性,为深厚软土中复合地基桩长设计计算提供了理论依据;(3)通过现场载荷试验和室内外试验相结合的方法,对设置褥垫层情况下单一桩型水泥搅拌桩复合地基作用机理和加固效果进行研究,并得到了考虑桩土和复合地基沉降之间关系的特征值取值方法。(4)通过现场大型载荷试验,对水泥土长短桩复合地基的荷载传递,长短桩桩身和桩间土应力随荷载水平变化等问题进行了研究,并推导出水泥土长短桩复合地基承载力特征值的计算方法,然后根据长桩、短桩和复合地基之间的沉降关系,建立了一套求解桩间土承载力发挥系数的方法,最后根据长短桩复合地基的受力特征,对水泥土长短桩复合地基进行竖向分区,并根据各区域各自的特征采用不同的附加应力求解方法,最后利用分层总和方法得到了水泥土长短桩复合地基沉降量计算方法;(5)利用室内模型试验,对不同锥角的锥形桩单桩和等截面桩压桩的挤土效应和承载特性进行了对比研究,然后基于复合地基的桩土变形协调关系,推导出了带垫层情况下锥形桩复合地基的桩土应力比理论解,最后通过室内试验,对锥形桩复合地基和等截面桩复合地基的承载性能进行了对比研究,并把复合地基桩土应力比试验结果同理论结果进行对比分析发现,计算结果同试验结果非常吻合。更多还原

【Abstract】 As a common method of soft ground improvement,composite foundation technology has been widly used to improve soft ground .In coastal deep soft soil region,with the improvement of amoumt and size of constuction and the reason of engineering properties of soft clay,using common ground treatment technology to improve soft ground has become more and more difficult.It is very important to look for new ground treatment technologies which should be credibility in theory、reasonable in economy and feasible in construction for the construction of coastal region.For improving deep soft soil in Nansha area,cement-soil long-short pile composite foundation new technology and tapered pile composite foundation new technology have been put forward in paper.By the means of in-situ tests、in-lab model test and theoretical and numerical analysis, engineering properties of Nansha soft soik effective pile length of composite foundation in deep soft soil、mechanism and displacement theory of cement-soil long-short pile composite foundation in deep soft soil、compacting effect of tapered single-pile and mechanism of tapered single-pile and tapered pile composite foundation have been studied in the paper.The main contributions are as follows.(1)The Nansha Area lies in the south of the Zhujiang Delta. The form circumstance and tiny structure of Nansha deep soft soil have been summarize by analyzing a great deal of investigation and test date.Base on carefully analyzing and studying on physics and mechanics indexs of Nansha deep soft soil, the typical characteristic of high water content、high viod ratio、high compressiblity、low intensity、low permeability and low bearing capacity have been found.Moreover,some relationships amonge physics and mechanics indexs which can help engineers to choose suitable physics and mechanics values have been gained by the means of statistics and regression analysis.(2) Base on different hypothesises,such as no load of soil top among piles under rigidity foundation, having load of soil top among piles under rigidity foundation and having load of soil top among piles under feasible foundation ,several calculation formulas for calculation effecitive pile length of composite foundation have been gained by theory analyse and formula deduction. The rationality of several methods has been comparably studied which can offer theory support for design of pile length of composite foundation in deep soft soil.(3) Base on static load test、in-situ tests and in-lab model test, mechanism and improvement effect of cement-soil single pile composite foundation under cushion have been studied.moreover,a calculation method has been acquired thinking of the displacement relationship between pile、soil and composite foundation.(4)Base on static load test, the mechanism of load transfer of cement -soil long-short pile composite foundation and the stress of pile and soil among piles with the change of load level of composite foundation have been studied in the paper. Moreover, a computational formulas for bearing capacity characteristic value and bearing capacity coefficient of cement-soil long-short piles composite foundation which have though of the relationship of pile、soil and composite foundation.Finally,according to the mechanism of long-short pile composite foundation,the overall displacement of long-short pile composite foundation is the summation of displacements of different distincts.(5)Base on in-lab model test of tapered pile,the compacting effect and mechanism of tapered piles with different taper angles and same section pile have been study.Then, according to the displacement compatibility equations of composite foundation,a formulas for pile-soil stress ratio of tapered pile composite foundation has been achieve.Finally,according to result of in-lab model test,it has been study that the mechanism of tapered piles and same section pile composite foundation by the method of comparable study and it has been found that the pile-soil stress ratio of calculation and test is very close.更多还原