Ho W.,Wilson Acoustics Ltd WAL |
Cheng M.,Wilson Acoustics Ltd WAL |
Cao J.,Wilson Acoustics Ltd WAL |
Wong K.,Nishimatsu Construction Co. NCC
21st International Congress on Sound and Vibration 2014, ICSV 2014 | Year: 2014
Gap sealing of traditional blast cover is easily damaged by daily opening operation and blast overpressure such that high noise insulation of blast cover is difficult to achieve, especially for large area cover. An operable blast cover has been installed on top of a vertical shaft of 750m2 cross-sectional area to be excavated to 83. 6m deep for railway tunnel construction of MTR South Island Line. 24-hour drill and blast excavation is employed. The blast cover is required to be opened for moving in and out of heavy equipment and removal of excavation rubble, and closed for blasting protection and noise insulation for daily operation. The shaft is located at lOm from British Council and 40m from Shangri-La Hotel. Blast overpressure is required to control below 168dBL (5kPa) at the blast cover and 12OdBL at residences. Apart from blasting noise, rock drilling and breaking is the noisiest activity, where predicted noise levels without noise enclosure are 1 O2dB (A) at British Council and 82dB (A) at Shangri-La Hotel. The operable blast cover is required to provide minimum 4OdB (A) noise insulation to achieve the statutory criteria, and finally it provided 44dB (A) insulation by specific cover closing and gap sealing mechanism, material selection and good workmanship. With shaft entrance double door system, checklist record and regular noise monitoring to ensure the overall noise insulation performance, the 24-hour drill and blast excavation was improved from 2 to 3 blasts per week and the shaft excavation process was completed within 8 months.