【作者】 刘志方；

【导师】 洪振舜；

【作者基本信息】 东南大学 ， 岩土工程， 2006， 硕士

【摘要】 粉喷桩复合地基的沉降计算方法是实际工程中关心的一个重要问题,现行规范在假定桩土变形协调的基础上对复合地基沉降计算进行了简明规定,这种方法简称为规范法。实际经验表明规范法计算所得的粉喷桩复合地基沉降量与实测值经常存在一定的偏差。本文对规范法计算复合地基沉降可能存在的问题进行深入探讨,并对解决问题的方法进行了研究。主要工作如下:(1)总结分析了粉喷桩复合地基沉降计算方法的研究现状,并对规范法计算复合地基沉降的影响因素进行归纳,提出了需要解决的问题。(2)基于大量已建和在建高速公路的勘察、设计、检测和沉降观测资料,应用规范法对粉喷桩复合地基沉降进行计算,并与实测沉降对比,发现两者关系比较散乱,实测总沉降量基本上处于计算沉降量的0.2倍和3.5倍之间。(3)分别从桩体强度和土体强度两方面分析复合地基材料的压缩性状对沉降计算结果的影响,得出影响计算结果的主要因素是下卧层土体力学参数的取值。目前国内工程地质报告中提供的土层的压缩模量等力学参数值存在以下不足:一是计算土性压缩指标时没有考虑应力水平问题;二是取样扰动导致土体的压缩变形指标严重失真。(4)对土体取样扰动的影响因素及主要影响表现进行了阐述,对目前国内外定量评价土体取样扰动度的方法进行了对比分析,并通过连云港软粘土的室内扰动模拟试验,对其中的孔隙指数法进行了适用性和可行性验证,确定该方法作为本文定量评价土体扰动度的方法。(5)描述了天然沉积粘性土的原位压缩曲线的形式以及土体结构性对其原位压缩曲线性状的影响,并对几种比较经典的原位压缩曲线的做法进行总结归纳,在此基础上,结合上述扰动度的定量评价方法以及扰动度与固结屈服压力的线性关系,提出了修正Schmertmann法,并通过工程实例验证了修正Schmertmann法的适用性和可行性。(6)在土层的原位压缩曲线的基础上,考虑应力水平的影响,推导出在实际应力水平范围内土层原位状态下的压缩模量值的计算公式。修正后的压缩模量值比工程地质报告中提供的E1-2更能反映土层在外荷作用下的实际压缩变形情况。(7)将考虑应力水平和取样扰动影响得到的修正压缩模量应用于规范法计算粉喷桩复合地基下卧层土体的沉降,发现计算结果能较好的与实测沉降结果相吻合,两者之间的线性拟合度也较高,验证了该方法的可行性和合理性。(8)通过有限元数值模拟计算结合直接反分析法中的试错法,对土体压缩模量进行了反演优化分析,并将反演结果分别与前文计算所得的修正压缩模量以及工程地质报告中的E1-2进行了对比,前者关系较为稳定,而与E1-2的关系比较散乱,进一步证实了前文所提方法的准确性,也表明修正压缩模量真实反映了土体原位情况下在上覆荷载作用下的压缩性状。更多还原

【Abstract】 The settlement of composite ground is a key parameter for engineering design, and is generally calculated using the specification method. However, experiences indicated that the difference exist extensively between the calculated settlement of the composite ground which are calculated using the specification method with the field measured settlement. So, analysis of the influencing factors of the specification method is being significant sense. The main works as follows:(1)History and research status of calculation method of the settlement of the composite ground is reviewed. The influencing factors on calculating the settlement of Dry-Jet-Mixing composite ground with the specification method are analyzed and summarized. Then, the problems need to be solved in the paper are brought out.(2)Based on lots of investigation, design, testing and settlement data of constructed and constructing highways, the settlement of the Dry Jet Mixing composite ground are calculated with the specification method. Comparing the results with the measured settlement show that their relationship are very messy and calculated settlement are 0.2~3.5 times the measured settlement.(3)The effects of the strength of pile or soil on the calculated settlement of composite ground with the specification method are analyzed. It is found that the main influencing factor is the modulus of compressibility of sub-layer soil. Nowadays, the shortage of the modulus of compressibility of soil provided by the engineering geologic investigation report are summarized as follows: firstly, the modulus of compressibility of soil is calculated without considering the influence of stress level; secondly, the modulus of compressibility is distorted badly because of sample disturbance.(4)The influencing factors and main phenomenon of sample disturbance on nature sedimentary clay are summarized. The methods of quantitatively evaluate the degree of sample disturbance (Dsd) of soil are reviewed. Furthermore, one of those methods which named“pore index method”is validated by a series of consolidation tests which conducted on artificially disturbed samples of Lian Yungang soft clay in the laboratory, so as the linear relationship between the Dsd with the consolidation yield stress of disturbed samples.(5)Shape of original compression curves and the effect of soil structure on the natural sediment clay are described. Then, several classical methods of forming original compressing curve are summarized. Furthermore, a new method named“modified Schmertmann method”is proposed in the paper based on quantitatively evaluation of the Dsd and the linear relationship between the Dsd and consolidation yield stress. Later, an engineering example is used to validate its applicability and feasibility.(6)Based on the original compression curve of soil, and considering the effect of stress level, a calculating formula of the modified modulus of compressibility which represents the in-situ compression properties of nature sedimentary clay is deduced. The modulus can reflect the practical deformation character of soil better than E1-2 which provided by engineering geologic investigation report.(7)The modified moduli of compressibility of soil are applied in calculating the settlement of sub-layer of Dry-Jet-Mixing composite ground. Comparing the calculated settlement with the corresponding field measured settlement gets a high-quality fitting degree, which validate the applicability and reasonability of the method proposed in the paper.(8)Finite element method combined with trail-and-error method is used to back calculating the modulus of compressibility of soil. It is found that the relationship between the results of back calculating with the modified modulus of compressibility is much better than that between the results with E1-2, which confirm the veracity of the method proposed in the paper again.更多还原