高土石坝地震响应的弹塑性分析方法研究

The equivalent linear method is widely used in analyzing the seismic responses of earth-rock dams. In this method the stress-strain behaviour of dam materials is simulated by a viscoelastic model, and the hysteresis behaviour and the strain accumlations are considered in a separate way. Indirect consideration of the permanet strains in this method inevitably makes it impossible to obtain the real evolution of the permanent deformation of the dams and the damage processes of the water tight systems. The keystone for solving this problem is establishing a rational dynamical elastoplastic constitutive model for dam materials based on experiments. In this study, dynamical triaxial experiments and cyclic simple shearing experiments will be carried out on rockfill materials used in dam engineering. The elastic behaviour, the shear dilation (contraction) properties and the hardening behaviour will be investigated on the basis of experimental findings. Then, By vitue of the concept of generalize plasticity, an elastoplastic constitutive model that takes all the loading, unloading and reloading phases as elastoplastic processes will be constructed by defining the plastic flow direction, the loading direction and the representations for tangential moduli, elastic moduli and plastic moduli at different stages. The cyclic constitutive model will be embedded into an existing procedure and a computer program will be developped for the seismic responses of earth-rock dams.Afterward, verification of the constitutive model and the program will be perfomed by simulating the dynamical behaviour of a typical rockfill dam that were attacked by Wenchuan earthquake. Studying the above subjects will deepen the understanding of the properties of rockfill materials during cyclic loading and enrich the dynamical constitutive theories of soils. In additon, the elastoplastic analysis method is expected to be effectively used in practical high earth-rock dams for the prediction of seismic responses.

土石坝地震响应分析广泛运用基于粘弹性模型的等效线性化方法，将坝料应力应变滞回效应与永久变形分开考虑，通常无法获取坝体地震变形的真实发展过程及防渗体损伤过程。解决这一难题的根本途径是在试验基础上建立更合理的土石料动力弹塑性本构模型。本项目运用动三轴仪和动单剪仪对筑坝堆石料进行循环加载试验，研究加载、卸载及再加载过程中堆石料的弹性性质、剪胀（缩）及硬化特性。在广义塑性理论框架下，定义塑性流动方向和加载方向张量；建立不同加载阶段切线模量、弹性模量及塑性模量的表达式，从而提出一个将加载、卸载和再加载均作为弹塑性过程的动力本构模型，实现应力应变滞回效应与应变积累特性的统一描述。开发土石坝地震响应的弹塑性计算程序，并对遭受过汶川地震的典型堆石坝进行震害模拟，检验本构模型的合理性及计算程序的可靠性。本项目研究可以加深对堆石料循环加载特性的认识；丰富土石料的动力本构理论；实现高土石坝地震响应的弹塑性分析。

我国地处环太平洋地震带和地中海-喜马拉雅山地震带之间，是地球上中、强地震活动最频繁的区域之一。另一方面，我国已建、在建和拟建的近百座百米级以上高土石坝大多位于高地震烈度区，这些高坝大库一旦因地震失事，后果将是灾难性的。因此，加强高土石坝地震灾变领域的研究工作，确保高坝大库的地震安全意义十分重大。本项目运用动三轴仪和动单剪仪对筑坝堆石料进行了循环加载试验，研究了筑坝堆石料在循环荷载作用下的应力变形特性；在此基础上定义提出了一个将加载、卸载和再加载均作为弹塑性过程的广义塑性本构模型；开发了高土石坝地震响应的弹塑性计算程序，并对遭受过汶川地震的紫坪铺面板堆石坝进行了震害模拟；研究了紫坪铺面板堆石坝的加速度响应、地震残余变形分布、面板脱空过程以及面板水平施工缝错台机理。

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