【作者】 骆以道；

【导师】 杨光华； 何亚伯；

【作者基本信息】 武汉大学 ， 岩土工程， 2012， 博士

【摘要】 地基沉降计算一直是岩土工程研究中的重要课题,实际问题中由于计算方法的不合理及岩土参数取值的不准确等原因,沉降计算的准确性较差。尤其对于滨海软土地基,因其具有独特的排水固结、蠕变、沉降非线性等特性,常用的沉降计算方法难以准确描述地基沉降发展规律。开展海积软土变形特性及地基非线性沉降计算方法的研究具有重要的理论和现实意义。本文通过文献成果归纳、工程资料统计分析、理论公式推导、数值模拟分析、室内试验、现场监测等手段,重点对地基的非线性沉降计算及海积软土排水固结、蠕变变形特性等问题进行了研究,并用多个工程实例对研究成果的可行性和合理性进行了验证,主要研究内容如下：收集并分析了深圳西部沿海多个典型工程勘察资料,运用统计方法对近千个海积软土样本的物理力学性质指标进行了统计分析,分析得出了海积软土物理力学指标随地层深度的分布情况,各指标之间的相关关系特征,以及主、次固结指标随荷载变化的规律。由于不同地域软土工程特性具有较大差异,本文的统计分析成果对深圳滨海软土区工程建设具有借鉴意义。对常用的分层总和法的计算原理及步骤进行了剖析,指出用分层总和法计算地基沉降时的理论缺陷及存在问题；针对软土压缩的非线性问题,从魏汝龙、施建勇提出的压缩模量的增长与压力呈线性关系出发,提出了压缩试验e-p曲线的双曲线拟合模型,并通过大面积荷载下海积软土地基固结沉降分析实例对模型的合理性进行了验证。双曲线模型参数可通过多种方法确定,避免了常规方法中利用e-p曲线计算沉降时的作图、插值等繁琐过程,使沉降计算方法更加简便。基于邓肯-张本构模型的简化,提出了用工程中常规压缩试验资料确定简化邓肯-张模型参数,从而可以实现用增量方法解决软土地基非线性沉降的简化计算,简化方法较常规方法更适合软土地基沉降的非线性特性,且不需做特殊试验即可确定计算参数,更具实用性。运用提出的简化方法,对位于珠海的深厚软土地基上的大型化工储油罐地基沉降进行计算分析,并将沉降计算结果与分层总和法、黄文熙法的计算结果进行了比较。研究认为,用常规的分层总和法计算建筑物软土地基沉降与实际情况相差较大,黄文熙法在实际应用时存在计算参数取值困难的问题,本文提出的简化方法计算结果更符合实际情况。运用杨光华教授提出的原位土切线模量法对美国Texas A&M University大学河滨校区的5个压板试验的非线性沉降进行了分析,研究由原位试验确定切线模量法计算参数的方法。通过理论推导和实例分析,提出当地基土的性质随深度变化不均匀分布时由旁压试验指标计算初始切线模量的方法；根据静力触探试验过程的数值模拟结果,得到了砂土地基强度参数与比贯入阻力的幂函数相关关系,从而提出了由CPT试验数据确定分层地基强度参数的方法。基于以上原位试验确定的切线模量法计算参数,对地基的非线性沉降进行了实例分析,分析结果表明,用简单的原位试验确定切线模量法参数进行地基沉降计算方法可行,较常规方法更适宜地基的非线性沉降计算。研究海积软土固结过程中渗透性的变化规律,提出了一个新的软土固结过程中渗透系数变化规律计算的经验公式。在此基础上推导了固结过程中软土固结系数的变化规律,得出固结过程中固结系数的计算公式,编制实用差分计算程序实现了考虑固结系数变化时软土地基固结度计算。实例分析表明,考虑固结系数变化时进行软土固结分析较经典固结理论更为合理。考虑软土地基次固结沉降的有限性,在Buisuman公式的基础上,提出了改进的软土地基次固结沉降计算模型,并用工程实例中长时间的软基沉降监测数据对提出的次固结沉降计算模型的合理性进行了验证。对堆载预压排水固结软土地基处理工法中沉降曲线拟合、推算方法进行了研究,提出了分段拟合沉降曲线的地基沉降推算改进方法。改进方法考虑了主、次固结阶段沉降曲线的不同特征,更适合软土地基的长期沉降预测。典型工程中沉降板观测数据实例分析表明,改进方法较常规预测方法更符合实际情况。更多还原

【Abstract】 Ground settlement calculating is always an important subject in geotechnical engineering research, and, in actual engineering practice, settlement calculating results are quite inaccurate because of unreasonable methods and inexactness of soil parameter chosen. Especially for coastal soft ground, because of its special properties such as consolidating with drainage, creep deformation, nonlinear characteristics of settlement, et al, settlement calculating methods that commonly used can hardly describe the actual development rule of ground settlement. From angles of both theory and reality, it will be important and significant to take some researches on deformation properties of marine deposit clay and calculating methods of nonlinear ground settlement.In this dissertation, some questions as nonlinear settlement calculation, drainage and consolidation properties of marine deposit clay, and its creep deformation characteristics, and so on, will be studied with emphases through methods of summarizing research documents, collecting and analyzing actual project data, theoretical deducing, numerical analyzing, laboratory test, field monitoring, et al. And the rationality and feasibility of research results will be tested and verified in actual project examples. The main contents are included as follows:The geotechnical test data of typical projects on west coast Shenzhen region are collected, and nearly a thousand samples of marine deposit clay are analyzed with its physical and mechanical parameters using statistical method. As a result, the former research works draw conclusions such as distribution of physical and mechanical parameters of marine deposit clay with depth, characteristic of correlations between parameters, and the rule how indexes of consolidation or secondary consolidation vary with load. There are specific regional disparities in engineering properties of soft soil, and the statistical results in this paper have practical significance for construction in Shenzhen coastal soft soil region.Through considering carefully about the computation theory and processes of the stratified summation method which is commonly used, theoretical limitations and existing problems in applying the method to calculate ground settlement are pointed out. As for the problem of nonlinear compression characteristics for soft soil, starting from the linear relationship between compression modulus and pressure, which is advised by Wei Ru-Long and Shi Jian-Yong, the hyperbolic model for e-p curve of laboratory consolidation test is brought forward, and its reasonableness is testified by actual ground settlement analysis of marine clay subgrade in large area loading. As for the hyperbolic model, the calculation parameters can be determined through different ways, and the cockamamie process of plotting and interplotation in traditional methods, which use e-p curve to calculate settlement, can be avoided, and the settlement calculation becomes easier.Based on simplification of Duncan-Chang constitutive model, parameters of the simplified model can be obtained from laboratory compression test data in general projects, so the nonlinear soft ground settlements can be calculated with incremental approach. Compared to general method, the simplified method is more suitable for nonlinear characteristics of soft ground settlement, and no special test is needed to determine calculation parameters, and it provides a more practical way. The subgrade of a large oil tank on deep soft soil ground in Zhuhai region is analyzed by using the simplified method mentioned above, and the calculating result is compared with those obtained from stratified summation method and Huang Wen-Xi method. As a research result, calculation with the common stratified summation method for construction subgrade settlements in soft area will bring distinct error to actual situation. There is difficulty in taking calculation parameters when applying Huang Wen-Xi method in actual projects. Calculating results by using the simplified method advised in this paper will fit better to actual situation.With application of the tangent modulus method which is proposed by professor YANG Guang-Hua, the nonlinear settlement of five in-situ plate loading tests on Texas A&M University Riverside Campus in USA is analyzed, and how to determine calculation parameters of tangent modulus method through some in-situ tests is researched. Through theoretical deduction and actual example analysis, the method obtaining initial tangent modulus from pressuremeter test data is put forward when soil properties of subgrade vary unevenly with depth. According to numerical simulating results of cone penetration test (CPT), correlation of power function between strength parameter and specific penetration resistance for sandy soil subgrade is obtained, and this provides a way to gain strength parameters of different ground layers with CPT data. Based on calculating parameters of tangent modulus method obtained from the in-situ test mentioned above, nonlinear ground settlements are analyzed with actual examples. As an analysis result, the ground settlement calculation method, which uses some simple in-situ test to determine calculation parameters of the tangent modulus method, is feasible and more suitable for nonlinear ground settlement calculation than normal methods.The variation rules of permeability during consolidating process is studied about marine clay, and a new empirical formula is proposed to calculate seepage coefficient for soft soil in consolidating process. Based on the above work, the varying regulation of consolidation coefficient for soft soil is deducted, and an empirical formula for calculating the consolidation coefficient is obtained. A practical differential program is compiled to calculate consolidation degree of soft ground with considering the variation of consolidation coefficient. As actual example analysis shows, consolidation analysis with considering variable consolidation coefficient will be more reasonable than classical consolidation theary.Based on the Buisuman formula, an improved calculation model of secondary consolidation for soft ground settlement is provided with considering the limitation of secondary consolidation settlement, and the rationality of the calculation model is testified by long duration field monitoring data of soft ground settlement in actual project.Fitting and forecasting approaches of settlement curve are studied within ground treatment of preloading drainage consolidation method, and an improved method is advised to forecast ground settlement with segmented fitting curves. For the improved method considers the different characteristics of settlement curve between primary and secondary consolidation phases, it is more suitable for long term forecasting of soft ground settlement. According to the analysis of observational data of settlement plate with actual examples in typical project, the improved method is more correspond to actual situation than normal forecasting method.更多还原