Abstract: 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.

Key words: open trench, impact loads, vibration isolation effects, in-situ test, numerical simulation