As a result of a proposal to reconstruct part of a dual three-lane carriageway trunk road in the form of a cut and cover tunnel and subsequently to build residential accommodation above, it was necessary to assess the likely amplitude of traffic induced vibrations on the ground surface above the tunnel. As little relevant data existed it was necessary to commission some measurements. At the five tunnels tested, measurements of vibration levels were made at the kerb, at the centre of the roof, and at several positions at ground level and in nearby buildings. The highest levels were caused by heavy commercial vehicles; the highest level measured above ground in the tests was 0.045 mm/s at a frequency of 8 Hz, which is at least three times smaller than the threshold of human perception. An acoustically generated vibration at about 63 hz produced the largest kerbside amplitude (0.23 mm/s) but this was heavily attenuated by the time it reached ground level. In the tunnels with rectangular cross sections comparable with the proposed tunnel, the vibration amplitude at the centre of the roof beam was up to 1.7 times greater than at the kerb at a frequency of about 10 Hz, making it inadvisable to attach building foundations to the structure at this position.(a)
Samenvatting