Determination of Soil Properties for In-Flight Models Using Bender Elements

一种近似模拟地震荷载对全尺寸土工结构（如土坝或挡土墙）影响的方法是在土工离心机上摇动飞行中的土工结构的物理模型。各种可用的物理模拟方法都是对现实的近似，清楚地理解这些近似是什么很重要。离心机实验数据可用于研究复杂问题中涉及的物理机制，也可用于验证数值程序，并评估新的设计方法。然而，离心机建模是一种复杂的实验方法。建模技术中存在一些不确定性，需要进一步研究，以建立对模拟精度的信心。其中一个最重要的不确定因素涉及离心机飞行（旋转）过程中模型中的土壤特性。在飞行前或飞行后测量特性是公认的做法，这可能与飞行中存在的特性有很大不同。一般也假定土样均匀且各向同性，主要是因为实际均匀度和各向同性难以测量。还有其他的近似值，也需要检验。首席研究员正在通过使用“弯曲”元素（一种相对较新的技术）来测量土壤的剪切模量来解决模拟的准确性。这是一种非常有前途的方法，有望使人们更好地理解在离心机上模拟地球结构上的地震载荷所固有的近似。

One method to simulate approximately the effects of earthquake loading on a full-size earth structure, such as an earth dam or a retaining wall, is to shake a physical model of the soil structure in-flight on a geotechnical centrifuge. The various physical simulation methods available are all approximations to reality, and it is important to understand clearly what these approximations are.Data from centrifuge experiments can be used to study the physical mechanisms involved in complex problems, as well as to verify numerical procedures, and to evaluate new design approaches. However centrifuge modeling is a complex experimental method. There are some uncertainties in modeling techniques that need further study so as to establish confidence in the accuracy of the simulation. One of the most significant uncertainties involves the soil properties in a model during the flight (rotation) of the centrifuge. It has been accepted practice to measure the properties prior to or after flight, which can be significantly different from the properties that exist during flight. It is also generally assumed that the soil samples are uniform and isotropic, basically because of the difficulty in measuring the actual degree of uniformity and isotropy. There are other approximations, which also need to be examined.The principal investigator is addressing the accuracy of the simulation by using "bender" elements (a relatively new technique) to measure the shear modulus of soil. This is a very promising approach that is expected to lead to an improved understanding of the approximations inherent in simulating on a centrifuge the earthquake loading on an earth structure.