地震和波浪联合作用下砂质海床沉管隧道灾害机理及演化过程研究

The earthquake disaster prevention and mitigation technologies of subsea tunnels have become an urgent research topic in the field of earthquake engineering to meet the demand of the high development strategies for the coastal regions of eastern China. Silty-sand soils are widely distributed throughout China’s offshore. Based on the advanced cyclic triaxial testing system, extensive experimental studies on the dynamic behavior of saturated silty sand are carried out under complex initial stress conditions and cyclic loading patterns for simulating the combined action of earthquake and wave. Accordingly, a constitutive model for the liquefiable silty sand is given, which intends to describe the behavior of silty sand under complex loading path associated with continuous rotation of principal stress axes. Then, a completely numerical model is built in which the immersed tunnel and the liquefiable seabed are taken into account as well as their interactions under the combined action of earthquake and wave. The dynamic effective stress analysis is applied by implementation of Biot dynamic consolidation theory. Since then, extensive simulations are performed to study the dynamic response of the immersed tunnel and the surrounding seabed under the combined action of earthquake and wave, as well as the behavior of the liquefied site. Last, according to the systematic numerical modeling, the main factors such as wave loading, local site conditions and the structural characteristics of the tunnel are analyzed to reveal their influence on the seismic response of the immersed tunnel in sandy seabed, so that the seismic hazards and evolution mechanism of the immersed tunnel in sandy seabed can be realized. The achievements of this research can provide theoretical basis and a noval analysis method for the seismic response analysis and safety evaluation of the immersed tunnels and the pipelines, which have similar buried conditions.

随着我国东部沿海重大发展战略的需要，海底隧道的防震减灾问题已成为地震工程领域的研究热点。首先以广泛分布于我国近海海域的饱和粉砂为研究对象，基于循环三轴试验系统，模拟地震和波浪联合作用的循环加载模式和应力路径，研究复杂初始应力条件下海洋饱和粉砂的动力学特性，建立能够描述主应力幅值和应力主轴耦合变化特性的饱和粉砂液化大变形本构模型；其次，采用基于Biot动力固结理论的有效应力分析方法，建立沉管结构-砂质海床动力耦合效应分析模型和计算方法，研究地震和波浪联合作用下砂质海床沉管隧道动力响应特性，以及周围海床的动力响应和场地液化特性；最后，基于系统的数值模拟和理论分析，研究波浪荷载、局部场地条件和沉管结构特征对砂质海床中沉管隧道地震反应特性的影响规律，揭示海底沉管隧道地震灾害机理及演化过程。研究成果将为海底沉管隧道以及与之埋置条件相似的海底管线地震反应分析和安全评价提供重要科学依据和具体分析方法。

海底隧道建设工期长且耗资巨大，如发生地震破坏，其后果不堪设想。波浪是常遇的海洋环境作用，研究地震和波浪联合作用下海床-沉管隧道体系灾害机理及演化过程具有重要的科学意义与工程应用价值。以海底隧道的防震减灾为研究背景，对地震与波浪联合作用下砂质海床中沉管隧道灾害机理及演化过程进行了系统研究，首先模拟地震和波浪联合作用的加载模式和应力路径，通过轴向-扭转耦合循环的南京细砂均等固结排水试验，揭示了饱和砂土累积体应变的发展规律，以等效循环应力比ESR作为表征复杂应力路径下动应力大小的物理指标，提出了可考虑应力路径影响的累积体应变增量模型；其次，采用适宜于将一维应力–应变关系向三维空间扩展的等效剪应变算法和加卸载判据，构造了三维应力空间中的Davidenkov本构模型，通过摩尔库伦准则对Davidenkov骨架曲线进行塑性修正，；基于Biot动力固结方程以及对剪应力和正应力差耦合剪切引起的不可逆性体应变的数学描述，建立了一个可描述可液化地基中土-地下结构相互作用的有效应力分析方法。基于FLAC3D软件平台，实现了该有效应力算法，适用于大规模二维和三维可液化场地土-地下结构体系非线性地震效应分析，并在单元、场地和土-结构体系三个尺度上验证了该方法的有效性。最后，数值模拟了地震和波浪联合作用下砂质海床中沉管隧道结构的内力反应特征以及沉管结构周围海床的动孔隙水压力、位移和加速度时空分布规律、液化区分布特性和应力路径演化特征。当地震和波浪联合作用时，隧道周围海床的剪应力差和应力主轴偏转程度较仅有地震作用时显著增大，从而加速沉管隧道周围海床累积残余孔压的增长和渐进液化进程，扩大沉管隧道周围海床的液化范围和沉管隧道上浮量。研究成果可为海底沉管隧道以及与之埋置条件相似的海底管线地震反应分析和安全评价提供重要科学依据和具体分析方法。