Predicting ground-borne train vibration using vibration propagation testing I:Procedures for obtaining valid data under unfavorable field conditions

摘要

The standard approaches for predicting ground-vibration for environmental studies of North American rail transit systems rely on empirical data.A test using an impact hammer is the most common method of determining site-specific vibration propagation characteristics.This procedure is recommended in the Federal Transit Administration(FTA)manual Transit Noise and Vibration Impact Assessment~1,2 for“Detailed Vibration Assessments”.The test consists of exciting ground waves with an impulse(typically a dropped weight)and measuring the transfer function between the exciting force and the resulting ground vibration.For surface tests,impacts are performed at regular intervals along a line at the location where the tracks will be located. The most vital element of the test procedure is obtaining a valid relationship between the exciting force and the ground response.Problems such as unfavorable field conditions, background vibration,bouncing of the impact hammer,radio frequency interference,and equipment problems often will degrade the test results.In this paper we present several case studies to evaluate the sensitivity of the test results and the resulting vibration predictions to variations in the test conditions.The specific issues investigated are the effect of using different materials for the hammer tip,the degree to which bouncing affects the test results,adjusting the force signal because of RF interference or other problems,and approximating for missed intervals in surface tests.