铁路动载对下伏现浇隧道混凝土性能影响和对策研究

According to the existing damage on early stage concrete cracks of an underlying tunnel caused by train vibration, laboratory test will be mainly relied on to study influence law on the post stage concrete mechanical properties and durability. In the meantime, data analysis, field test, numerical simulation and statistical analysis will also been applied in this study so that the standard and countermeasures can be provided as an outcome.The strategies to perform this study is: firstly, the tunnel vibration response spectrum will be studied by field test and numerical simulation with different dynamic load model, different stratum, different cross section and different buried depth ; secondly, typical vibration response spectrum will be chosen as input file in the dynamic tests for the early stage concrete specimens with standard curing condition and then the standard concrete properties test at age of 7 days and 28 days, and durability test at age of 28 days will be performed; finally, the comparison between the specimen of concrete affected by the vibration and the standard concrete specimens without vibration will be performed for mechanical properties and durability. Therefore, the effect of early stage concrete performance under vibration and corresponding influence standards will be obtained. Furthermore, resistance and reduction countermeasures to railway vibration can be studied accordingly. More study on concrete performance and the countermeasures of underlying cast-in-situ tunnels impacted by railway dynamic load, will help to develop damage theory of concrete vibration at early stage, and will be a guideline for constructions of a large number of cast-in-place tunnels undercrossing railway.

针对实际工程中下伏隧道早龄期混凝土在列车振动下出现裂损的现象，以室内试验为主，综合运用调查研究、现场测试、数值模拟、室内试验、统计分析等方法，对铁路动载下的下伏隧道结构混凝土后期力学性能和耐久性影响规律、标准和对策问题进行研究。首先采用现场测试和数值模拟方法，获得不同列车动载、地层、断面和埋深下的下伏隧道振动响应规律，然后，选取典型的振动响应谱作为试验输入，对标准养护下的早龄期混凝土试件进行振动试验，再进行7天和28天龄期的力学性能试验和28天龄期的耐久性试验。最后，将受振动影响的后期混凝土力学性能和耐久性测试结果与未经振动的标准组试件进行比较，从而得到下伏隧道早龄期混凝土受列车振动下的后期混凝土性能影响规律和相应标准，并进一步研究相应抗减振对策。深入地研究铁路动载对下伏现浇隧道混凝土性能影响及其对策，将有助于发展早龄期混凝土受振损伤理论，服务于大量下穿铁路现浇隧道工程施工。

下穿铁路的隧道工程大量涌现，其中许多采用矿山法施工。在矿山法隧道衬砌现浇施工时，铁路列车动载可能导致混凝土结构早龄期产生微裂缝，导致混凝土后期性能发展不利，影响隧道结构的安全性及耐久性。对于此类问题，目前研究并未针对隧道结构受列车间歇性动载影响的问题进行深入探讨，同时也缺乏对混凝土在早龄期阶段受列车间隙性振动后性能发展的研究，造成此类背景下混凝土工作性能和隧道结构的安全状态不明晰。本项目结合理论分析、数值计算、现场测试及室内试验等方法，对铁路动载下的下伏现浇隧道结构振动响应机理和混凝土性能变化规律进行了研究。主要成果如下：（1）考虑铁路动载的时域特性及轨道不平顺作用，模拟了列车荷载时程谱，建立了可模拟铁路动载影响的隧道-地层-轨道动力计算模型；阐明了隧道结构动力响应与工程因素之间的影响机理，提出了以混凝土动拉应力作为隧道结构安全判据，建立了下伏隧道结构动力响应与埋深之间的定量关系；（2）开展了混凝土早龄期（24小时内）的直剪实验，得到了混凝土早龄期的性能发展规律，揭示了混凝土浇筑后强度质变的时间点；开展了早龄期混凝土受铁路列车振动实验，通过不同龄期的力学性能及耐久性能的测试，得到了混凝土受铁路动载后的性能发展规律，揭示了混凝土强度受铁路动载影响先增益后损害的变化特征，进而指出以峰值0.2g作为影响性能变化的强度阈值，建立了下伏隧道现浇结构的动载损益影响区间；（3）分别从隧道减振结构设计、混凝土材料、施工保护等方面提出了相应的铁路动载下现浇结构施工的保护对策，为该类工程对策选择提供依据。上述研究成果可进一步完善早龄期混凝土受列车振动影响的相关理论，也可为列车动载下隧道现浇施工的混凝土性能保护提供理论与技术支撑，为相关规范和指南的制定提供参考。