Predicting Light-Rail Groundborne Noise and Vibration from Tunnels

The standard measurement procedure for vibration propagation measurements for subway testing is borehole testing prior to the construction of the subway tunnel. Borehole testing is completed by drilling a borehole to the depth of the subway and locating a force transducer at the bottom of a hole. Typically, a standard soil sampling hammer is used to impact the transducer and excite the ground at the bottom of the hole. However, this measurement procedure does not account for the attenuation provided by the tunnel structure and may result in the overprediction of vibration and groundborne noise levels. This paper looks at some measured vibration propagation data from boreholes and from inside a constructed subway tunnel along the same alignment, as well as numerical models to estimate the attenuation from the tunnel structure. The results indicate that the tunnel structure likely provides between 5 to 10 decibels of vibration reduction at frequencies above 40 Hz.