Shimizu Corporation, through a joint venture with Toa Corporation, is working on the safety measures and the reduction of environmental impact from blasting noise in the New Kobushi Tunnel of the Chuo Expressway (from Hachioji City, Tokyo to Sagamihara City, Kanagawa) within the narrow and dimly lit working space.

In the case of mountain tunnels, safety measures and the reduction of environmental impact become critical issues compared to other construction types. This is due to the narrow working space with the movement of numerous Heavy Equipment, the low visibility in the dim space, and the vibrations and noise from blasting propagating to the suburbs. At the New Kobushi Tunnel work site, various creative solutions are being implemented to address these challenges.

The key points of safety measures involve actively using lighting equipment to take advantage of the dimness and ensuring that measures do not require relocation of equipment. First, projection mapping displays traffic signs like "STOP" on the road surface, with red line illumination marking stop lines, and green lines indicating the Range of safe passage. The road surface markings provided by lighting are certainly recognizable by Heavy Equipment operators, and a benefit is that they do not get damaged or worn when vehicles pass over them. All lighting devices are installed on full-section slide forms (hereafter referred to as central), waterproof sheet laying carts, or traffic signs that must be placed on the road surface, so there is no need for the relocation of standalone lighting devices.

Additionally, for the narrow openings and heights of the vehicle passage in the tunnel, red tube lights are installed along the internal sides of the central and waterproof sheet laying carts to provide flashing indications. For the stairs leading to the central used by many workers, pink and white tube lights are installed on the handrails of the lower and upper stairs, respectively. All safety measures using lighting equipment have been evaluated positively by Heavy Equipment operators and workers as being effective in raising awareness.

On the other hand, for the low-frequency noise measures associated with blasting work, the paper-based low-frequency sound attenuation device "KAMIWAZA (sound-absorbing cylinder)" developed in collaboration with Oji Holdings Corporation has proven effective. The installed sound-absorbing cylinders have a diameter of 406 mm, a length of 3,000 mm, an intake opening of diameter 76 mm and length 350 mm, weighing 18 kg, targeting low-frequency sounds at 20 Hz, with a total of 250 units installed.

According to measured values of the sound-absorbing effect, against low-frequency sounds of 5-20 Hz that generate rattling in doors, there was an average reduction of 1.5 dB, 10 dB around 20 Hz, and 3 dB at around 8 Hz, where heavy soundproof doors find it difficult to cope. In terms of the energy amount of the noise, a reduction of 1.5 dB is equivalent to a decrease of 1/1.4 for the original low-frequency sound, a reduction of 10 dB equals 1/10, and a reduction of 3 dB equates to 1/2.

The company continues to promote technological development contributing to safety measures and environmental conservation, not limited to mountain tunnels.