Road Tunnel Maintenance Handbook (Civil and Structure Edition) published.

1. Introduction

  The Road Tunnel Maintenance Handbook was originally published in 1993 (hereinafter referred to as the original handbook) as a practical reference for maintaining road tunnels.

  In December 2012, the ceiling panels of the Sasago Tunnel fell down. This accident made society recognize anew the importance of maintaining social infrastructure and eventually led to the revision of the Road Act and promulgation and enforcement of the relevant cabinet and ministerial ordinances. With this in mind, MLIT issued the Guideline for Periodical Inspection of Road Tunnels in June 2014. In these revisions, inspection methods including a close visual inspection and diagnosis are specified as mandatory.

  Considering these changes, a new set of handbooks, the “Road Tunnel Maintenance Handbook (Civil and Structure Edition)” (hereinafter referred to as new Handbook) was compiled by incorporating the new knowledge obtained after publication of the original handbook. In particular, the latest technology and updated case examples on maintaining tunnels, to provide the latest information on specific methods of road tunnel maintenance.

2. Commentary on the Methods of Periodic Inspection

  Following the revision of the Road Act, etc., it is now specified as a standard procedure with respect to road tunnels that inspection by performing a close visual inspection at an interval of once in five years is to be conducted. This is to be done for not only tunnel main structure including the lining and or portals but also to examine the conditions of jointing members for tunnel facilities such as jet fans. It is also provided that the results of diagnosis be classified based on the standardized scale with four stages from I to IV. In addition, it is stipulated that it is important to properly take measures when any defects are found and conduct maintenance according to the maintenance cycle from inspection to diagnosis, and take measures and recording including the records of inspection results. The new Handbook provides specific descriptions including points of intensive inspection so that engineers can appropriately handle the situations they face on site.

3. Commentary on Judgment Case Examples

  Defects of road tunnels are very complicated as they occur due to various factors and emerge in the form of wide-ranging phenomena. In order to continue appropriately maintaining road tunnels, it is necessary to conduct detailed surveys necessary to cope with those defects and make the right judgment on the degree of the defects. The new Handbook provides easy-to-understand commentaries that serve as references for judging defects using actual case examples, figures and photos. The book also provides detailed descriptions of the specific survey methods based on updated technical knowledge, points to note about judgment, and the guideline and principle of judgment, using schematic illustrations and photos.

4. Commentary on the Measures

  Whenever any defects occur in a road tunnel, some measures must be taken. Measures to cope with such defects include repair work aiming to mainly restore or maintain the functions degraded by deteriorated materials of the lining or water leakage, and reinforcing work aiming to mainly maintain the structural stability of the lining. When measures are taken, it is necessary to estimate the causes of condition changes and select the measures that fit them. The new Handbook explains the selection methods of measures, and provides information on specific application cases, referring outcome studied by PWRI.

5. Conclusion

  The new Handbook describes examples of inspection records, the basic principle about monitoring taken as one of the actions against defects, and updated technology on measures.

  We hope the new Handbook will be useful for appropriately maintaining road tunnels in the future and keeping them safe.

(Contact: Tunnel Research Team)

Will Efficiency-oriented Rice Cultivation Cause Irrigation Water Requirements to Change?

Background of the Study: Expansion in the Area of Directly Seeded Rice Cultivation in Hokkaido

  Over the past few years, the increase in farm sizes has continued in paddy rice cultivation regions across Hokkaido, and transplant cultivation is common in those regions, a method in which most of the rice seeds are grown in greenhouses before being planted in paddy fields. Transplant cultivation is suitable for paddy fields of up to 20 ha. For fields larger than that, however, a single farming household has trouble growing rice only with this method, because of labor shortages, particularly in spring when intensive farming work is required. In response to the labor shortage, some regions in Hokkaido have adopted direct seeding cultivation, a rice cultivation method in which rice seeds, instead of seedlings, are sown. Direct seeding cultivation does not require the pre-raising and transplanting of seedlings, thereby mitigating the workload in springtime. Direct seeding cultivation used to afford less stable yields than transplant cultivation. Nevertheless, research on breeding/cultivation methods, as well as farmers' efforts to acquire the skill for direct seeding, have overcome the issues. In municipalities of Hokkaido where direct seeding cultivation has expanded rapidly, rice fields with direct seeding cultivation have increased to account for 10% of all rice fields. This trend is likely to continue.

Difference in Soil Management between Transplant Cultivation and Direct Seeding Cultivation

  Soil management methods differ between transplant cultivation and direct seeding cultivation. Transplant cultivation necessitates puddling prior to rice seedling planting (Photo 1). During this work, soil clods are harrowed in the flooded field and mixed with water to settle. This work is intended to (1) inhibit the growth of weeds, (2) level the paddy field ground, and (3) fill the cracks in the ground surface so that the field controls the infiltration capacity and allows water to be well stored. In transplant cultivation, puddling is also intended to enable the puddled, watery soil to cover and fix the seedling root to the field ground. Direct seeding cultivation is performed at well-drained paddy fields and submerged fields. When it is performed at well-drained paddy fields, puddling is not necessary. Puddling is sometimes omitted when seeding is performing at submerged fields, too, because direct seeding cultivation does not require the soil to be watery to take care of the roots. Additionally, herbicides and laser level bulldozers are available for achieving the above-mentioned (1) and (2), respectively. The amount of water needed for a rice field depends on the infiltration capacity of the field. If direct seeding cultivation begins to be performed at a larger area of rice field and thus puddling is omitted at those fields, the above-mentioned (3) may not be achieved. Accordingly, the irrigation water requirement will increase across the area, which may cause water shortages.

Will the Irrigation Requirements of Paddy Rice Fields Change with Increases in the Area of Direct Seeding Cultivation?

  The Irrigation and Drainage Facilities Research Team of CERI has been surveying the irrigation requirements of a large paddy field (approx. 2 ha) in Moseushi Town in Sorachi region since FY 2011. This is intended to compare the volume of irrigation water required for transplant cultivation, direct seeding cultivation in well-drained paddy fields, and direct seeding cultivation in submerged fields (Figure 1). Puddling was not performed at the fields where direct seeding cultivation is applied. This is a rare case of research in that irrigation requirements have been compared among three different cultivation methods consistently at the same rice field. The findings indicate that the irrigation requirements of direct seeding and transplant cultivation are similar. The soil of Moseushi is peaty, and the groundwater level is relatively shallow. Under such conditions, the infiltration capacity of the ground is smaller beneath the paddy field than for the ground surface soil. This causes a field with highly permeable surface soil to allow a similar amount of water to infiltrate through the ground surface whichever cultivation method is performed. Consequently, the irrigation requirements were similar among the three cultivation methods. Further research will be conducted in other regions, and the data will be used for forecasting the irrigation requirements of paddy rice cultivation areas in the future and for examining methods for stabilizing irrigation water distribution.

(Contact: Irrigation and Drainage Facilities Research Team, Civil Engineering Research Institute for Cold Region)