间歇性动荷载长期作用下滨海相软土的工程特性及变形机理研究

Because of the bad engineering properties of marine soft soil, the post-construction settlement of subway tunnels and others on such soft soil foundation can not be ignored, and it brings a lot of problems. So, it is carried out the research of the engineering properties and deformation mechanism of marine soft soil which is subjected to intermittent dynamic loads in this study. It is sure that the intermittent dynamic loads cause the spatial distribution of soil vibration by the theoretical analysis to specifically carry out the relevant tests. The mechanical response and the damage mechanism of marine soft soil subjected to intermittent dynamic loads are studied by the dynamic development of microstructure, porosity and macroscopic mechanical properties. The mechanical model of the marine soft soil is established, which considers the stress ratio, the vibration frequency, the loading and unloading time, and the number of times of loading and unloading. In model test, the microstructures, porosity, and mechanical properties of the soils at different spatial locations are tested; and the damage characteristics and recovery characteristics of deformation modulus and strength of marine soft soil subjected to intermittent loading are studied. Combined with numerical simulation, It will reveal the engineering characteristics and deformation mechanism of marine soft soil foundation subjected to intermittent dynamic loads, and put forward the method of predicting the deformation of marine soft soil foundation subjected to long-term intermittent dynamic loads; and it is verified by the measured data. By studying the project, it will deepen the understanding of dynamics characteristics of soil, and provide a theoretical basis and technical support for the design and construction of related projects, and promote development of the theory of soil mechanics.

滨海相软土不良的工程性质，使其地基上地铁车振荷载引起的隧道长期沉降不可忽视，并严重威胁地铁的安全运营。本项目针对地铁列车等荷载对滨海相软土地基的间歇性作用特点展开研究。通过理论分析，明确间歇性动荷载引起土体振动参数的空间分布特征，针对性开展相关试验；从微观结构、孔隙度和宏观力学性质的动态发展等方面研究间歇性动荷载作用下滨海相软土的力学响应及强度损伤机理，建立考虑应力比、振动频率、加-卸载时长以及加-卸载次数的滨海相软土力学模型；测试模型试验中不同空间位置处地基土的微观孔隙结构特征和力学性质，研究间歇性荷载作用下滨海相软土变形模量和强度的损伤及恢复特征；结合数值模拟，揭示间歇性动荷载长期作用下滨海相软土地基的工程特性及其变形机理，提出其长期作用下滨海相软土地基变形预测方法；并以实测数据对其加以验证、优化；本项目将在深化土动力学认识的基础上，为相关工程设计施工提供理论依据和技术支持。

地铁列车等荷载对滨海相软土地基的间歇性作用，使地铁车振荷载引起的隧道长期沉降不可忽视。当间歇性动荷载这类特殊的荷载作用于滨海相软土之上，其力学行为和变形特征具有其独特的性质。根据查阅文献和调研，设计了间歇性动荷载试验参数。滨海相软土的循环荷载试验与间歇性动荷载试验结果相似，超孔隙水压力随振动次数增长，趋势大致为：前期急剧增加，随后趋缓，最后趋于稳定。振动时长与间歇时长对超孔隙水压力和剪切模量的发展有重要影响。减少振动时间，土体动剪切模量衰减也越少和超孔隙水压力的累积也越少；间歇时间的增加能有效削弱超孔隙水压力的累积趋势，减少土体动剪切模量的衰减，从而对变形的控制起到了积极作用，有利于土的变形控制。振动频率对剪切模量软化指数的衰减有重要影响。振动频率越高，单位振动-间歇周期内的加载次数越多，超孔隙水压力积累值越大，土样强度衰减也越明显。动应力比越大，超孔隙水压力积累越快，累积应变也越大。排水条件下间歇性动荷载试验，加载期和间歇期都会产生超孔隙水压力的消散，提高土的抗剪强度，增大了试样的变形；而不排水条件下，间歇期只是削弱了超孔隙水压力的累积趋势，并不能消散动荷载作用下产生超孔隙水压力。排水条件对滨海相软土长期变形有重要影响，排水提高了土的强度和刚度，土的长期变形符合双曲线模型；次固结系数与固结压力有关和加载时间有关。根据模型试验结果表明，地基中振动的传播近似呈线性衰减规律。但结构性土的制备较困难，导致测试数据不稳定，结果关联性不强。研究过程中，虽然由于取样运输或实验技术等原因导致部分测试结果不理想，但是间歇性动荷载作用下滨海相软土的特殊性质仍得到了反映，仍得到了一些有益的成果。后期将根据试验反馈的不足进行改进，进一步开展间歇性荷载试验研究。通过上述研究成果，在丰富滨海相软土动力学研究的基础上，为滨海相软土地区相关工程建设提供重要的理论支持。