Research outline

Dust Reduction Technology for Mechanical Excavation in Mountain Tunneling Work

Fig. 1 (a) Outside view of experimental facility and fan blower

Fig. 1 (b) Inside of experimental facility

Fig. 2 excavation of mockup bedrock (concrete)

Fig. 3 Outline of local dust collection system

Fig. 4 Outline of Elastic ventilation ducting

Dust Generated from Tunnel Excavation
When road is constructed in mountainous area, tunnel may need to be built. However, when a tunnel is excavated through a mountain, dust is generated. Dust has various negative effects, including reduction in work efficiency and the danger of pneumoconiosis (lung disease) resulting from inhalation over a period of many years. The development of technology to tackle the dust problem associated with tunneling work is now urgently required.
Working together with the private sector, PWRI conducted experiments to verify the validity of a technique for reducing dust emission in tunnel excavation.

Experimental Facility and Excavation Experiment
The experiment was conducted in the construction environment laboratory, located in the PWRI compound. As shown in Fig. 1, the facility is a simulated tunnel measuring 8 m high, 13 m wide and 100 m long, and the internal space is designed as for a two-lane tunnel. The facility has a fan blower to pump in fresh air from the outside, and a large dust collector to suck out generated dust.
In a tunneling project, machinery as shown in Fig. 2 is used to excavate the bedrock. However, since it is difficult to bring such bedrock to the facility, dust was generated by excavating concrete, which was used in place of bedrock. Next, measurement was made of the concentration of the dust generated and of the size of the particles etc.
A comparison was made for the dust concentration and other data between the case in which the dust reduction technology was used and that in which it was not, in order to verify the validity of the technology.

Dust Reduction Technology and Experimental Results
The effects of the following dust reducing technology were verified as follows:
(1) Local dust collection system
As shown in Fig. 3, this system sucks in and removes dust through the suction ducts extending to the excavation point.
(2) Elastic ventilation ducting system
As shown in Fig. 4, this system collects dust through a flexible pipe (Elastic ventilation ducting) of around 1 m in diameter extending to the vicinity of the excavation point.
(3) Surfactant solution dispersal system
This system reduces scattering of dust by spraying a surfactant solution (foam) at the rock excavation point, absorbing the dust particles and causing them to fall.

On testing these techniques, it was confirmed that those are effective in reducing dust emission. If they are applied, it is highly likely that dust concentration at tunneling work sites will satisfy the target level.
Verification of the validity of these techniques at actual tunneling worksites represents a future task.

(Contact: Construction Technology Research Team)

Changes in Causes of Heavy Rainfall in the Abashiri and Tokachi Areas

Fig. 1 Changes in causes of heavy rain by year

Fig. 2 Transition patterns and frequency of typhoons and rain fronts

Appropriate management of drainage facilities is indispensable for farming operations in the large-scale upland farming areas of eastern Hokkaido, such as Abashiri and Tokachi. In these areas, open channel drainage projects have been conducted under direct government control for over 50 years, in order to construct and improve drainage canals. Recently, however, damage due to inadequate function of drainage has been occurring once every few years. Possible causes of inadequate function of drainage are changes in land use or changes in rainfall characteristics, etc. Against this background, the Irrigation and Drainage Facilities Research Team is engaged in "research on the function of drainage systems in large-scale upland farming areas". As one example of its research regarding the nature of the rainfall in both the Abashiri and Tokachi subprefectures, the trend of changes in meteorological conditions causing heavy rainfall during farming periods over the recent years is explained here.
The data used for this research is that for rainfall precipitation from May to October, in the years from 1976 to 2007, recorded at meteorological agency facilities and AMEDAS points in the two subprefectures. Heavy rainfall was judged to have occurred when one or more of the 68 observation points in the two subprefectures recorded a maximum hourly rainfall within the day of 30 mm or more, or a daily rainfall of 80 mm or more. In accordance with these criteria, a total of 102 heavy rainfall incidents were identified.
These are categorized by the year and the meteorological conditions causing them, and the numbers of incidents in each category were compared as in Fig. 1. An extratropical cyclone (typhoon) is a meteorological phenomenon characterized by an area of low atmospheric pressure that has changed from being a typhoon or a tropical cyclone. The figure shows that there was an increase in the number of heavy rainfall incidents caused by fronts in and after 1987 compared to the years from 1976 to 1986, and that there was a tendency for heavy rainfall induced by typhoons to increase in frequency.
Fig. 2 shows patterns for the passage of typhoons and fronts bringing heavy rainfall. Typhoons mainly passed through southeastern Hokkaido in the years from 1976 to 1986, but in recent years, an increasing number are passing through northwestern Hokkaido. In general, strong winds blow east of the center for typhoons moving northward. Given this fact, recent changes in the course of typhoons results in an increasing number of cases where the area of strong wind passes through eastern Hokkaido. There are an increasing number of rain fronts conforming to a pattern in which the front stays stagnant at latitude corresponding to central or southern Hokkaido.
Do these tendencies correspond to the recent perceptions of our readers?
In the future, we plan to investigate data relating to the frequency of occurrence of localized torrential downpours.

(Contact: Irrigation and Drainage Facilities Research Team, CERI)