【作者】 李鑫；

【导师】 白明洲；

【作者基本信息】 北京交通大学 ， 道路与铁道工程， 2022， 博士

【摘要】 岩溶地质在我国分布较广,隐伏洞穴的发育对途经铁路路基的稳定及安全性造成隐患,而重载铁路大重量、高目标、长编组的货运特性加大了风险事故发生的可能。岩溶隐伏土洞的形成具有一定随机性,且发育时间较长,部分设计较早、等级较低、地基处理不够彻底或注浆效果不理想的岩溶区铁路路段,土洞隐患不能保证完全根除,随着铁路轴重的增大、铁路服役时间的增长、自然气候与地下水的长期影响,薄弱区域依旧存在地下岩溶洞穴的形成隐患。因此,为深化研究岩溶区重载铁路在隐伏土洞情况下路基的受力特性并给出安全评价与相关指导,本文从岩溶形成环境、致灾因素、地基土性质、土洞发育过程与监测预警和土洞路基稳定性及受力响应等角度展开针对性综合研究。通过室内试验方法,以岩溶地区重载铁路路段土洞发育地基土层为研究对象,从土体的物理化学性质、干湿循环下的静三轴试验力学特性的角度展开研究。采用现场综合监测技术,对研究区内一处典型岩溶土洞塌陷开展现场监测试验,分析降雨因素下土洞周边不同深度土壤水土参数的变化特征并建立预警系统及其阈值。在对背景环境、土洞扩展特性及土壤参数充分分析的基础上,运用离散元及离散元-有限差分耦合建模方法,对隐伏土洞路基在流-固耦合及不同类型荷载下的水土细观特性深入探讨并对不同工况下土洞的发育过程、路基的稳定性及受力响应进行模拟分析和风险评价。主要创新性研究成果如下:(1)收集岩溶区重载铁路段附近不同深度范围的土体,系统开展了不同压实度、初始含水率、干湿循环次数、土体埋深下的细角砾土不排水不固结三轴试验与电镜扫描试验,基于三轴试验结果,引入干湿循环强度残余比的概念,构建了考虑围压与干湿循环作用的细角砾土归一化应力-应变模型。(2)提出了细角砾土力学性能与微观结构对应关系,通过图像信息提取技术,将不同试验条件下细角砾土的微观特征参数与力学性能指标建立对应关联,并给出地基土填筑指标建议。(3)基于试验区土洞发育多因素现场监测试验,获得了降雨诱发的土洞发育多参数综合变化特征,通过多重逻辑数据遍历搜索,提出基于多因素综合判据的土洞发育综合风险二级预警体系及相应阈值。基于含水率监测数据,以现场土洞塌陷监测点为模拟原型,构建了二维流体模型,并提出土壤水力学反演参数。(4)基于离散元流-固耦合理论、离散元-有限差分耦合理论分别构建了流-固场与动荷载作用下的离散介质、连续-离散介质三维仿真模型,实现了渗流与路基自重荷载、列车动荷载作用下,不同路基结构、土洞特征与荷载特征下的重载铁路隐伏土洞路基细观特性与宏观响应的精细模拟与分析。(5)运用双指标体系与正交分析法,揭示了不同因素对土洞路基性能的影响性强弱并对其排序,同时结合模糊综合评价法提出了运营期隐伏土洞铁路路基失稳易发性评价体系,对不同情况的运营期隐伏土洞铁路路基进行了风险评价。更多还原

【Abstract】 Karst geology is widely distributed in China.The development of hidden caves causes hidden dangers to the stability and safety of railway subgrades.The heavy haul railway are characterized by large weight,high target and long marshalling,which increases the possibility of risk accidents.The formation of hidden soil caves in karst areas is random and has a long development time.For some railway sections in karst areas with early design,a low grade,incomplete foundation treatment,or an unsatisfactory grouting effect,the hidden dangers of soil caves cannot be completely eradicated.With the increase in railway axle load,increase in railway service time,and long-term impact of natural climate and groundwater,the hidden dangers of underground karst caves still exist in weak areas.Therefore,to further the research on the stress characteristics of the subgrades of heavy-haul railways in karst areas with hidden soil holes,evaluate safety,and provide relevant guidance,targeted comprehensive research was conducted from the perspectives of the karst formation environment,disaster causing factors,foundation soil properties,soil hole development process,monitoring and early warning,soil hole subgrade stability,and stress response.Through laboratory tests and taking the buried soil tunnel subgrade of a heavy-duty railway in a karst area as the research object,the physical and chemical properties of the soil for the subgrade filler under a dry–wet cycle were examined,and the mechanical properties were investigated through a static triaxial test.Using on-site comprehensive monitoring technology,experiments were carried out on the collapse of a typical karst soil cave in the study area,and the variation characteristics of the soil water and the soil parameters at different depths around a soil cave under rainfall conditions were analyzed.The background environment,soil cave expansion mechanism,and soil parameters were analyzed fully.Based on the results,the discrete-element and discrete-element––finite-difference coupled modeling methods were used to analyze the soil and water fineness of the subgrades of hidden soil caves under fluid–structure coupling conditions and different types of load.The characteristics of the soil cavity were studied in depth,and a simulation analysis and risk assessment of the development of the soil cave,the stability of the roadbed,and the stress response were performed under different working conditions.The most important and innovative research results are as follows.(1)An undrained unconsolidated triaxial test and scanning electron microscopy test of fine breccia soil under different degrees of compactness,initial moisture contents,dry–wet cycle times,and soil burial depths were systematically performed using soil collected at different depths near a heavy-haul railway section in a karst area in Jiangxi Province,China.Based on the triaxial test results,the concept of the dry–wet cycle strength residual ratio was introduced,and a normalized stress–strain model of fine breccia soil considering the effects of the confining pressure and dry–wet cycle was constructed.(2)The corresponding relationship between the mechanical properties and microstructure of fine breccia soil in Jiangxi Province was examined.Through image information extraction technology,the micro characteristic parameters of fine breccia soil under different test conditions were correlated with mechanical property indices.Suggestions for the filling indices of subgrade fill are provided.(3)Based on a multifactor field monitoring test of soil cave development in the test area,the comprehensive change characteristics of parameters of soil cave development induced by rainfall were obtained.As a result of a multiple logical data traversal search,a two-level early warning system and the corresponding threshold of comprehensive risk of soil cave development based on multifactor comprehensive criteria are proposed.Based on water content monitoring data,a two-dimensional fluid model was constructed using the soil cave collapse monitoring points as the simulation prototype,and the soil hydraulic inversion parameters were determined.(4)Based on the discrete-element fluid–solid coupling theory and the discrete-element–finite-difference coupling theory,three-dimensional simulation models of a discrete medium and continuous discrete medium under the action of a fluid–solid field and dynamic load were constructed,respectively.The fine simulation and analysis of the meso characteristics and macro response of the concealed soil tunnel subgrade of a heavy-haul railway under the action of seepage,subgrade dead weight load,train dynamic load,different subgrade structures,various soil tunnel characteristics,and different load characteristics were examined.(5)Through the use of the double index system and orthogonal analysis method,the influences of different factors on the performance of a soil tunnel subgrade were revealed and ranked.The fuzzy comprehensive evaluation method was employed to develop a risk evaluation system for hidden soil tunnels for railway subgrades in operation periods,and the risk was evaluated under different conditions.更多还原