模型箱约束对大变形破坏离心模型试验影响初探

Preliminary study on influences of model container constraint on large-deformation failure behaviors by centrifuge modeling

离心模型试验需要模型箱盛放模型,模型箱壁边界的摩擦和法向限位约束必然影响到模型的位移变形性状特别是大变形破坏性状。采用大型平面应变模型箱开展了离心模型试验,尝试再现某散货码头堆场地基的大变形推移破坏现象,先后两次模拟了试堆载过程,与第一次试验不同的是,第二次试验部分解除了模型箱端壁法向限位约束。两次试验测得的堆场地基极限承载力值很相近,但第一次试验中淤泥质黏土层最大位移是1 m量级,第二次试验中达5.5m量级,仍不及原型的20 m量级。前后两次试验位移量级的差异表明模型箱端部法向限位约束严重影响模型推移破坏程度,部分解除端部法向限位约束在一定程度上有助于模型产生大变形推移破坏。而大变形三维破坏问题被简化成二维平面问题模拟,宽度方向模拟范围有限隐藏着土体变形破坏过程中土料侧向补充严重不足,这进一步造成土体破坏整体推进的距离和严重程度不及原型,因此,进行大变形破坏离心模型试验和解读试验结果时,必须充分考虑模型箱箱壁摩擦和箱体长度与宽度有限三方面的约束影响。

In the centrifugal model tests,the scaled model must be placed in the model container to withstand the action of supergravity field.The friction of the container wall and the normal limit constraint must exert an undesired influence on the displacement and deformation behaviors,especially its large-deformation failure behaviors.A large plane strain model container is utilized in the centrifugal model tests in an attempt to represent a large-deformation lateral translation collapse,which occurs in a bulk cargo wharf yard ground during filling of ore heap on trial.The filling process of ore heap on trial is simulated twice,and the normal limit constraint on the left end wall is partially released in the second running.The ultimate bearing capacity of the storage yard ground measured by the two tests is close.However,it is found that the failure degree of lateral translation collapse is significantly different in the two tests.The maximum displacement of the first running is 1 m,and that of the second running is 5.5 m,but still smaller than the prototype 20 m.It is noticed that the normal limit constraint on the end wall seriously affects the model failure behaviors.Partially releasing the normal limit constraint on the end wall,to a certain extent,helps to reproduce large-deformation failure phenomena in prototype.The main cause for significant difference in failure degree between the model and the prototype is that a three-dimensional large-deformation damage problem in the prototype is simplified into a two-dimensional plane strain problem to be simulated.The length simulated by container width is much smaller than that of the prototype collapse,resulting in that the model soil failure lacks enough soil supply as in the prototype so that the advanced distance and severity of soil failure of the model is much less than those of the prototype.Therefore,the influences of the above constraints of the model container must be fully considered in the centrifugal model tests on large-deformation failure.