【作者】 田小娟；

【导师】 曹文贵；

【作者基本信息】 湖南大学 ， 岩土工程， 2010， 硕士

【摘要】 地基沉降是土力学的主要研究课题之一。从现有沉降计算方法来看,分层总和法由于具有简便实用的特点,目前仍是工程设计中的主流方法。但是该方法所采用的计算指标一般是由有侧限压缩的试验来测定,不能较好地反映应力状态对变形参数的影响。而土体具有很强的孔隙性和体积压缩性,致使土体在不同附加应力水平和应力历史条件下的变形力学参数尤其是变形或压缩模量变化显著,因而,地基沉降或变形呈高度非线性变化特征。于是,如何考虑地基土体力学参数变化的影响成为地基非线性沉降计算方法建立的关键。鉴于此,本文在传统分层总和法的基础上,引入分级加载的思想,对条形基础下地基的非线性沉降计算方法进行了研究和改进,主要成果和结论如下：首先,针对地基土体孔隙的压缩性导致其变形力学参数变化的特征,深入探讨附加应力和应力历史对地基土体模量影响的力学机制,分别建立出地基土体模量随附加应力和应力历史变化的分析模型。根据虎克定律,提出了条形基础下地基非线性弹性沉降计算方法。该方法不仅反映了地基土体变形力学参数随附加荷载变化的特征,也反映了地基土体由于初始应力水平或应力历史不同而引起的土体模量不同对地基沉降计算的影响,而且,有效地避免了地基沉降计算中压缩试验曲线的使用。其次,将本文所建立的改进非线性弹性模型与莫尔—库伦塑性模型结合起来,以取代后者关于弹性区的线弹性假设,形成土体非线性弹性—塑性模型。将其运用到地基沉降计算中,从而形成了基于弹塑性理论的地基非线性沉降计算方法。该方法既有常规分层总和法简单、便于理解运用的优点,又能考虑土体的弹性非线性以及塑性变形特性,同时还能考虑土体三向应力对其变形的影响。最后,采用本文提出的两种沉降计算方法分别进行工程实例分析,并与实测沉降值和其他方法计算结果进行比较,表明本文方法的合理性与可行性。更多还原

【Abstract】 The subsoil settlement is one of the main research subjects in soil mechanics. From the existing methods of settlement calculation, layerwise summation method is still the mainstream of engineering designs currently because of simplicity and practicability. However, such method adopts calculation indexes generally measured by confined compression test, which can not be better to reflect the effect of stress condition on deformation parameters. The soil has strong porosity and voluminal compressibility, resulting in deformation mechanic parameters changing obviously under different conditions of stress level and stress history, especially the deformation modulus or compression modulus. Therefore, foundation settlement or deformation present highly nonlinear variation. Upon that, how to think about the impacts of soil parameters change is the key to establish nonlinear calculation methods of foundation settlement. In view of this, the nonlinear settlement calculation method of strip foundation was studied and improved in this paper, in which the traditional layerwise summation method and an idea for step loading were incorporated. Main results and conclusions are as follows:Firstly, according to the variation characteristics of deformation mechanical parameters caused by the interstitial compressibility of foundation soils, this paper further studied the mechanical mechanism about the effect of additional stress and stress history to foundation soil modulus, and the analysis models that reflect the deformation mechanical parameters of foundation soils which changing with additional stress and stress history were established respectively. A new nonlinear elastic computational method for settlement of strip foundation was put forward based on the Hooke’s law. This method not only reflects the characteristics that deformation mechanical parameters of foundation soils change with additional loads, but also the effect of different soil modulus induced by different initial stress level or different stress history on foundation settlement computation. Moreover, the using of the compression test curves in foundation settlement calculation is avoided efficiently.Next, combining the improved nonlinear elastic model established in this text with the Mohr-Coulomb plastic model to form a new inelasto-plastic constitutive model, so as to replace the latter on the assumption that elastic zone was linear elasticity. The new model was applied to the calculation of foundation settlement, and then proposed the method of settlement calculation based on elastoplastic theory. The theory has the advantage of layerwise summation method, it can consider the character of elastic nonlinearity and plastic deformation of soil, what is more, the effect of 3-D stress on deformation can be taken into account also.Finally, by comparing the computation and analysis of two engineering examples with actually measured and calculated settlement results by other methods, it shows that the proposed methods in this text are reasonable and feasible.更多还原