空沟对冲击荷载隔离的现场试验与数值模拟

在场地开挖了一条空沟，以落锤式弯沉仪（falling weight deflectometer，简写为FWD）的荷载模拟冲击荷载，通过FWD自带的传感器测得空沟后一定范围内的竖向位移。通过室内试验，获取试验场地的岩土参数，采用非线性动力有限元软件ABAQUS建立二维模型（将远处单元定义为无限单元来模拟吸收边界，从而避免振动波的来回反射）。以空沟中心线的现场测试数据为依据，校核有限元模型。通过分析不同工况模拟的竖向位移，研究得出空沟-荷载间距、沟深、沟宽等对隔振效果的影响。结果表明，(1) 空沟-荷载间距越小，隔振效果越好，但实际隔振工程中，为避免振动对空沟侧壁的稳定性的影响，空沟与振源不宜太近，因此可以不计空沟-荷载间距对隔振效果的影响；(2) 就提高隔振效果而言，增大沟深比增大沟宽更有效，而相同的隔振效果，窄-深沟的挖方量远小于宽-浅沟；(3) 在对冲击荷载进行隔振设计时，对于一般的民用和工业建筑，综合隔振效果、开挖和支护费用等因素，采用宽度为0.5～1.0 m，深度为2.0～2.5 m的空沟较为合理，与某工程实例进行比对，验证结论的合理性。

In-situ test and numerical simulation of isolation of impact loads by open trenches

An open trench was excavated at the field, the falling weight deflectometer (FWD)is adopted to replace the impact loads, and the vertical displaces in the near areas behind the trench are measured with the sensors of the FWD. The geotechnical parameters of the fields are in-door tested; the nonlinear dynamic finite element software of ABAQUS is adopted to establish a two-dimensional model, in which the far elements are defined as infinite to simulate the absorbing boundary; and so the vibration caused by wave bounces at the boundaries are avoided; and the FEM model is modified according to the in-situ tested vertical displacements. The vertical displacements of different conditions are simulated; the factors that influence the vibration isolation effects are analyzed; such as trench depth, trench width and distance between trench and impact loads. Some conclusions are drawn as follows. (1) The vibration isolation effects increase when the distance between trench and impact loads decrease; but in the actual vibration isolation engineering, the trench can not be constructed much near to the impact loads to guarantee the stability of the trench walls; so the distance between trench and impact loads should not be considered as an important factor in the vibration isolation design. (2) As to improve the vibration isolation effects, to increase the trench depth is much effective than the trench width, and a narrow and deep trench usually need much less excavation than a wide and shallow trench. (3) When designing the vibration isolation of normal civil and industrial buildings for impact loads, an open trench with 0.5-1.0 m width and 2.0-2.5 m depth is relatively reasonable by considering the isolation effects, excavation and maintenance fees; it is proved to be reasonable by comparing with one vibration isolation engineering.