Shimizu Construction Co., Ltd. is working to ensure safety in a narrow and dim work space and reduce the environmental impact of blasting noise on the surrounding area in the underground of the Chuo Expressway Shin-Kobutsu Tunnel* (Hachioji City, Tokyo to Sagamihara City, Kanagawa Prefecture) under construction by a JV with Toa Construction Industry Co., Ltd.

In the case of mountain tunnels, safety measures and reduction of environmental impact are more issues than other types of work. Reasons for this include the fact that a large number of heavy equipment runs in a cramped work space, low visibility in dim spaces, and vibration and noise caused by blasting propagate to the suburbs. At the Shin-Kobutsu Tunnel Workshop, we are dealing with such issues through various ingenuity.

The key points of safety measures are that lighting devices are actively used using dim light, and that relocation of equipment is unnecessary. First, traffic signs such as “stop” are displayed on the road surface with projection mapping, a stop line is displayed with the red line of line lighting, and the range of safety passages is displayed with a green line. Of course, the advantage of road surface display with lighting is that heavy equipment drivers can reliably recognize it, and it does not get dirty or worn even when a vehicle passes over the display. Since both lighting devices are installed on full-section slide forms (hereinafter referred to as centrals) used to place secondary concrete coatings, waterproof sheet trolleys, or traffic sign signs that always stand on the road surface, there is no relocation work for the lighting device alone.

Also, for centers and trolleys with waterproof sheets, which narrow the width and height of vehicle passages in the mine, red tube lights are installed and flashed in accordance with internal laws. Pink and white tube lights are installed on the handrails of the lower staircase and upper staircase, respectively, for the elevating stairs in the center, which are used by many workers. Any safety measures using lighting equipment have been evaluated by heavy equipment drivers and workers as leading to reminders.

Meanwhile, the paper low frequency sound attenuation device “KAMIWAZA (Sound Absorbing Cylinder),” which was jointly developed with Oji Holdings Co., Ltd., is showing its power as a countermeasure against low frequency noise associated with blasting work. The installed sound-absorbing cylinders have a diameter of 406 mm, a length of 3,000 mm, a suction port with a diameter of 76 mm, a length of 350 mm, a weight of 18 kg, and the sound absorption target is 20 Hz low frequency sound, and the number of units installed is 250.

According to actual measured values of sound absorption effects, there was an average reduction of 1.5 dB for low frequency sounds of 5 to 20 Hz that causes rattling in fittings, 10 dB around 20 Hz, and 3 dB around 8 Hz, which is difficult to handle even heavy soundproof doors. In terms of noise energy conversion, 1.5 dB reduction was reduced to 1/1.4, 10 dB reduction was 1/10, and 3 dB reduction was reduced to 1/2 compared to the original low frequency sound.

We will continue to promote technology development that contributes to safety measures and environmental conservation, not limited to mountain tunnels.