海底岩土交界段隧道结构地震响应机制

Heave rolling bedrock in coastal zone makes the routine of undersea tunnel fluctuate between soil and rock strata. The lining structure would vary to adapt to the construction in different strata, complicated lining of connection emerged when tunneling to transitional portion. Two issues to be considered in the earthquake engineering of underground construction: (1) the characteristics of near ground motion at tunnel location around transitional portion, and (2) seismic response of tunnel linings around connection zone. The proposed research will try to set up a numerical model to simulate the propagation of earthquake wave, and then summaries the characteristics of bedrock motion for the site to reveal the non-uniform excitation from geological condition. Analyze the seismic response of tunnel linings (such as composite lining, segmental lining, and the combination of both, etc.) under elevated earthquake intensity (such as fortified earthquake, rare earthquake, and huge earthquake) could be taken, by means of multiscale dynamic method and shaking-table tests based on the previous input of bedrock motion. The design methodology for the connection lining to withstand strong earthquake (both rare and huge one) can be developed with multiple measures.

近海地层基岩起伏变化大，海底隧道线路必然在土层和岩层中穿行。地层不同隧道建设工法有别，衬砌结构类型也随之而变，工法交接段衔接结构也有差异。于是，在地下工程抗震方面带来两个难题：场地类别变化的土-岩交界区隧址的地震动特征；隧道衬砌结构刚度变化段地震响应机制。本项目拟以连续介质波动理论为基础，采用数值模拟方法研究土-岩交界区段的波动传播规律（反射、折射、散射）及其与地层特性的关系，分析归纳这类场地的地震动响应特征以揭示地层差异所致场地差动效应；以此为隧道基岩地震动输入条件，采用多尺度结构动力分析方法和结构振动台模型试验，研究海底隧道交接段典型结构型式（复合衬砌、装配式管片环、管片环复合内衬、复合衬砌套接管片环等）在多个地震水平（设防地震、罕遇地震、巨震）作用下的地震响应机制及强震破坏机理；在评价强震危害性的基础上，提出隧道交接段衬砌结构抗震与减震设计方法。

近海地层基岩起伏变化大，海底隧道线路必然在土层和岩层中穿行。地层不同隧道建设工法有别，衬砌结构类型也随之而变，工法交接段衔接结构也有差异。于是，在地下工程抗震方面带来两个难题：场地类别变化的土-岩交界区隧道的地震响应特征；隧道衬砌结构刚度变化段的地震响应机制。本项目以连续介质波动理论为基础，采用数值模拟方法研究了土-岩交界面倾角、土-岩地层剪切波速比等因素对隧道地震响应的影响规律；明确了隧道结构的抗震最不利位置；揭示了土岩交接段场地对隧道地震响应的作用机制。基于弹性地基梁理论，推导了均质地层中变刚度隧道以及土岩变化地层中长隧道在任意地震动作用下地震动力响应的解析表达式，提出了面向工程设计的地层变刚度以及隧道变刚度纵向抗震简化分析方法；通过参数敏感性分析，揭示了结构刚度、地层剪切波速比等关键因素对隧道结构地震响应的影响规律。建立了基于几何相似比1:10的大比尺岩石隧道变刚度段振动台模型动力相似比理论；提出了围岩-结构相对刚度等效设计原则，合理模拟了实际地震动过程中围岩与衬砌之间的动力相互作用关系；研制了可满足动力相似关系以及围岩-结构相对刚度的围岩和衬砌相似材料；采用多种测量仪器全面地捕捉了地震动过程中变刚度隧道各区段的地震动响应特征。针对隧道变刚度段的特点，结合岩石隧道变刚度段大比尺振动台模型试验技术，开展了隧道变刚度段振动台模型试验；研究了变刚度隧道各区段的地震动响应特征；揭示了衬砌刚度变化对隧道结构地震动响应的影响规律；通过逐级增大输入地震动强度，模拟了变刚度隧道在强震作用下的渐进式破坏过程，揭示了隧道衬砌破坏前后动力响应的差异性。