Japan’s Civil Engineering Technology, Part I: Tunnels - Science View

Key Concepts

Tunneling Technology in Japan: Advanced techniques and methodologies for constructing tunnels, particularly in challenging geological conditions.
Seikan Tunnel: A historically significant railway tunnel in Japan, notable for its depth and length.
Earth Pressure and Rockbolts: Forces exerted by the surrounding earth and rock on a tunnel, and the use of steel rods (rockbolts) to reinforce tunnel walls against these forces.
NATM (New Austrian Tunneling Method): A tunneling method that utilizes sprayed concrete and rockbolts for ground support.
Geological Challenges in Japan: The complex geological formations in Japan due to tectonic plate activity, leading to varied rock hardness, fault zones, and groundwater issues.
Green Tough: A specific geological formation known to dissolve in water, posing a significant challenge in tunnel construction.
Explosive-Based Geological Survey: Using controlled explosions to generate seismic waves for analyzing underground structures, identifying groundwater, and fault zones.
Risk Management in Construction: Differences in safety approaches between Japan (zero risk) and Europe (risk tolerance).
Multiskilled vs. Specialized Workforce: The Japanese construction industry's reliance on multiskilled workers (多能工) versus the specialized roles common in other countries.
Automation in Tunnel Construction: Development of machinery for tasks like inserting rockbolts to address labor shortages and improve efficiency.
Post-Harvest Physiology and Technology: Scientific methods to extend the shelf life of fruits and vegetables by controlling their respiration and metabolic processes.
Controlled Atmosphere Storage: Modifying the gas composition (oxygen and carbon dioxide levels) within storage environments to slow down fruit ripening and spoilage.
Ethylene Gas: A plant hormone that promotes ripening and senescence in fruits.
Enzyme Activity and Browning: The role of enzymes in fruit discoloration, and how controlled atmospheres can inhibit their activity.

Tunnel Construction in Japan

Overview of Japanese Tunnels

Japan possesses a significant number of road tunnels, estimated at approximately 10,000 in number, spanning a total length of about 5,000 km. This length is comparable to the distance from Tokyo to Bangkok, Thailand.

Historical Significance: Seikan Tunnel

A landmark achievement in Japanese tunneling technology is the Seikan Tunnel, a railway tunnel connecting Honshu and Hokkaido. This tunnel has a seabed section of approximately 30 km. At its deepest point, the seabed is about 140 meters below sea level, with an additional 100 meters of rock and soil above the tunnel itself, making it a remarkably deep construction.

Technical Challenges and Solutions

The construction of deep tunnels like the Seikan Tunnel presents significant challenges, including managing water inflow and the immense pressure from both the sea and the surrounding rock. To address these, Japan has developed advanced technologies:

Chemical Injection (薬液注入): Used to solidify the ground and prevent water seepage.
Ground Stabilization Techniques: Methods to stabilize the excavated face (切り羽) of the tunnel.
Excavation Methods: A combination of mechanical excavation and controlled blasting (爆破) using explosives is employed.

Takamatsu Tunnel Case Study

A visit to the Takamatsu Tunnel under construction highlighted several key aspects of modern tunneling:

Excavation Process: Explosives are used to blast away rock, followed by the use of heavy machinery like loaders to remove the debris. Dump trucks transport the excavated material.
Support Systems:
- Erector: A specialized heavy machinery equipped with Japan's unique technology, designed to install steel frameworks that support the inner walls of the tunnel.
- Rockbolts (ロックボルト): Steel rods, typically 4 to 6 meters long, are inserted into drilled holes in the tunnel walls. These bolts reinforce the ground by clamping the rock layers together, preventing collapse due to earth pressure (土圧) – the downward force exerted by the weight of the overlying earth and rock. This system is a crucial component of methods like NATM (New Austrian Tunneling Method), also known as Nato in Japan or Sprayed Concrete Lining Method internationally. The rockbolts not only provide support but also increase friction between rock layers, preventing slippage.

Geological Complexity and Its Impact

Japan's location at the convergence of four tectonic plates results in highly complex geological conditions, characterized by intricate rock formations, fault lines, and varying rock hardness.

Interlayered Rock: The presence of alternating hard and soft rock layers makes excavation unpredictable and challenging.
Fault Fracture Zones (断層破砕帯): Areas where rock layers have ground against each other, leading to extreme instability.
Green Tough (グリーンタフ): A specific geological formation that dissolves in water. Contact with groundwater during construction can cause this rock to swell, compromising the tunnel's structural integrity and potentially leading to the destruction of water-soluble materials.

Advanced Survey and Mitigation Techniques

To overcome these geological hurdles, sophisticated survey methods are employed:

Explosive-Based Seismic Surveys: Similar to how seismologists study the Earth's interior, controlled explosions generate elastic waves. The returning signals reveal the presence of underground water streams (indicated in blue in the visual representation) or solid rock. This technology helps identify the scale and extent of groundwater flow.
Groundwater Drainage: Areas identified with significant groundwater flow are drained before excavation.
Chemical Injection for Unstable Soil: For unstable soil conditions, solidifying chemicals are injected to strengthen the ground before excavation.

Safety and Workforce Philosophies

Risk Management: A significant difference exists between Japanese and European approaches to safety. Japan prioritizes a "zero risk" (リスクをゼロにしよう) philosophy, leading to comprehensive safety measures. In contrast, Europe tends to adopt a "risk tolerance" (リスクを許容しながら) approach, planning safety measures within acceptable risk parameters. While the zero-risk approach can increase costs, it has also driven the development of advanced technologies.
Workforce Structure: In many overseas countries, construction projects are often carried out by specialized workers (単能工), each responsible for a specific role. In Japan, the industry often relies on multiskilled workers (多能工), who can perform a variety of tasks. This necessitates continuous training and skill development. The need for automation is also growing to address labor shortages and improve productivity.

Automation in Tunnel Construction

The development of automated machinery, such as the boom rock machine, is a significant advancement. This machine automates the insertion of rockbolts, a critical step in reinforcing tunnel walls. The drill's movement mimics the precise actions of a skilled worker, adapting to varying rock resistance. This automation aims to overcome labor shortages, reduce work-related accidents, and enhance productivity in the construction industry.

Future of Japanese Tunneling Technology

The future of Japanese tunneling technology lies in pushing the boundaries of "deeper and longer" (より深くより長く) constructions.

Linear Shinkansen: The development of the Linear Shinkansen (maglev train) involves tunneling at depths of around 100 meters in urban areas, showcasing the application of advanced tunneling techniques in city development.
Disaster Prevention Infrastructure: Tunneling technology can be further utilized for constructing underground river channels and floodways for disaster prevention purposes, beyond traditional road and rail applications.

The speaker concludes that technically, there is no limit to the size or length of tunnels that can be excavated, provided the geological properties of the mountain are thoroughly understood.

Post-Harvest Physiology and Technology

The Problem of Food Waste

Globally, a significant portion of food is lost after harvest. A UN survey indicates that approximately 13% of food is lost before reaching store shelves, and an additional 19% is wasted in food services and households.

Research at Tokyo University of Agriculture

The Laboratory of Post-Harvest Physiology and Technology at Tokyo University of Agriculture is dedicated to addressing this issue.

Extending Fruit Shelf Life: The Case of Pears

Respiration: Fruits, even after being cut, are living organisms that respire, consuming oxygen and releasing carbon dioxide. To extend their shelf life, the key is to suppress respiration (呼吸を抑える) or slow it down while keeping the fruit alive.
Controlled Atmosphere Storage: This technique involves modifying the gas composition within a storage environment.
- Normal Air: Typically contains about 20% oxygen and less than 1% carbon dioxide.
- Controlled Atmosphere for Pears: Researchers found that storing pears in an atmosphere of 40% oxygen and 40% carbon dioxide significantly extended their shelf life and prevented browning.
Mechanism of Browning: Browning in pears is caused by enzymes within the fruit. The specific gas environment in controlled atmosphere storage inhibits the activity of these enzymes, preserving the fruit's white color and delicious state.
Varied Gas Requirements: Different fruits have different optimal gas compositions. For example, pineapples require a different balance, such as 80% oxygen and 10% carbon dioxide.
Experimental Approach: The researchers emphasize the importance of experimentation, as unexpected results can arise, and what seems unpromising might prove successful.

Temperature and Fruit Preservation: The Case of Peaches

Warming Peaches: Surprisingly, peaches are sometimes warmed to around 39°C. This treatment can extend their shelf life by approximately one month, effectively doubling it for some varieties.
Consumer Awareness: A goal of this research is to ensure consumers experience the true, optimal taste of fruits, which may not be fully appreciated due to current preservation and distribution methods. The aim is to deliver fruits in their most delicious, or even enhanced, state.

The research in post-harvest physiology not only helps reduce food waste globally but also contributes to delivering higher quality produce to consumers.