【作者】 王磊；

【导师】 苗永红；

【作者基本信息】 江苏大学 ， 建筑与土木工程（专业学位）， 2021， 硕士

【摘要】 2021年国务院最新发布的《国家综合立体交通网规划纲要》中指出,到本世纪中叶我国应加快建成交通强国,努力建成社会主义现代化与现代化经济体系。沿海沿江城市带作为我国现代化建设的“领头羊”,高速铁路、大型机场、地下铁路等基础工程亟需得到满足。然而,这些城市带包含我国大部分东南沿海区域,该区域广布工程性质较差的软弱土层,属于典型的软土地基。而软土地基具有低承载力、高压缩性、低渗透性、高含水量等特殊的物理力学性质易引发严重的工程隐患。因此,对软土地基进行有效的加固处理,不仅是工程建设的需要,也是我国改革开放不断深化、经济发展稳步推进的有效保障。目前,软土地基的加固处理包括换填垫层法、真空预压法、堆载预压法、水泥加筋土、动力排水固结法等,但大多数方法仅仅满足其在静态加载条件下的有效性。而现代交通系统多对软土地基产生交通荷载的动力作用,为保证软土地基长期稳定性,有必要研究软土地基在动态加载条件下的加固处理特性。同时,交通工程中的荷载形式多体现为周期性循环荷载,这有别于动力排水固结法中的冲击荷载。因此,本课题组提出利用循环荷载替代动力排水固结法中的冲击荷载从而对地基进行加固,即“振动排水固结法”。本文通过考虑时效性对软土试样开展室内振动排水固结试验,分析其考虑时间效应影响的排水固结特性、塑性应变发展特性;并尝试从微观角度探讨软土振动排水固结机理,为振动排水固结法应用于实践提供有价值的研究基础。本文主要研究成果如下:(1)对软土进行室内振动排水固结的时效性分析,发现时效性对软土排水量和竖向应变皆具显著影响。结果表明考虑时效性影响的振动荷载能明显提高试样的排水固结效果;能增大竖向应变在趋稳后的排水量占比;时效性对排水效果和竖向应变的影响程度随着围压的增大而减小;存在排水效果最好的最佳时间间隔。(2)依据多孔介质理论并结合振动采油过程中两相基质的受力状态变化,从微观角度建立了饱和软土在振动荷载作用下单元受力状态,并在不同条件下结合微观受力状态分析了软土振动排水条件,最终结合室内试验结果分析并验证了荷载大小与荷载类型、振幅和时间间隔等因素对振动排水影响的机理探讨。(3)基于Monismith经典模型,考虑振动荷载加载过程中的围压、频率和时间间隔等因素对软土在循环荷载下累积塑性应变进行了模型修正,试验结果表明修改的模型能够合理预测围压、频率和时间间隔对软土累积塑性应变的影响并对该模型的有效性性进行了验证。更多还原

【Abstract】 In 2021,the State Council issued the outline of national comprehensive three-dimensional transportation network planning,which pointed out that by the middle of this century.As the "leader" of China’s economic construction,the coastal cities along the Yangtze River urgently need to meet the needs of high-speed railways,large airport,underground railway and other infrastructure projects.However,the urban belt contains most of the southeast coastal areas in China,which is a typical soft soil foundation.The soft soil foundation has special physical and mechanical properties such as low bearing capacity,high compressibility,low permeability and high water content,which is easy to cause serious engineering problems.Therefore,effective reinforcement of soft soil foundation is not only a requirement of engineering construction,but also the basic guarantee of the deepening of China’s reform and opening up and the steady progress of economic development.At present,there are many reinforcement methods for soft soil foundation,such as replacement cushion method,vacuum preloading method,surcharge preloading method,cement reinforced soil,dynamic drainage consolidation method and so on,but most of them only meet the effectiveness under static loading conditions.In order to ensure the stability of the soft soil foundation after reinforcement,it is necessary to study the mechanical properties of the soft soil foundation after dynamic load reinforcement.At the same time,the form of load in traffic system is periodic cyclic load,while the dynamic load in dynamic drainage consolidation method is impact load.Therefore,the project team proposed to use cyclic load instead of impact load in dynamic drainage consolidation method to reinforce the foundation,namely "vibration drainage consolidation method".In this paper,through the indoor vibration drainage consolidation test of soft soil samples,the drainage consolidation characteristics and plastic strain development characteristics were analyzed,and the vibration drainage consolidation mechanism of soft soil was discussed from the micro perspective,which provides a valuable research basis for the application of vibration drainage consolidation method in practice.The main research results are as follows:(1)It was found that the time effect has a significant effect on the displacement and vertical strain of soft soil.The results showed that the vibration load considering the time interval could significantly improve the drainage consolidation effect of the sample;it could increase the proportion of the displacement of the vertical strain after stabilization;the influence decreased with the increase of the confining pressure;and there was the best time interval for the best drainage effect.(2)According to the porous media theory and the stress state changes of two-phase matrix in the process of vibration oil recovery,the unit stress state of saturated soft soil under vibration load was established from the microscopic point of view,and the vibration drainage conditions of soft soil were determined according to the microscopic stress state.Finally,the load size and load type,amplitude and time interval were analyzed and verified combined with the indoor test results The mechanism of vibration drainage was discussed.(3)Based on the classic Monismith model,considering the factors of confining pressure,frequency and time interval of the vibration loading process factors,the model was modified to predict the cumulative plastic strain on the confining pressure and the time interval;the effect of frequency and time interval under cyclic loading Soft soil,and verified the accuracy of the model.更多还原