CO₂ is now at the center of a major shift in how engineers build tunnels, especially in cities and mountainous regions where homes, schools, and critical infrastructure sit directly above construction zones. Traditional blasting with explosives such as TNT can break rock quickly, but it also creates loud noise, strong vibrations, and flying debris that may damage nearby buildings. To address these risks, Chinese engineers have developed a revolutionary method that relies on carbon dioxide instead of chemical explosives. This approach allows tunnel construction to proceed in a safer, quieter, and more controlled manner.
Why conventional blasting causes problems
For decades, engineers have relied on explosives to break rock efficiently. When TNT detonates, it releases energy almost instantly, sending shock waves far beyond the blast site. These waves can crack walls, damage pipelines, and destabilize older buildings.
In open areas, blasting is usually safe. But modern tunnels increasingly pass under busy cities, where even minor vibrations can harm wooden houses or delicate structures. Moreover, the loud noise from explosions can disturb residents and even force construction projects to pause during certain hours.
Because of these risks, authorities strictly limit the level of vibrations and noise that construction sites can generate. As a result, engineers need innovative methods that can break rock safely while keeping disturbances to a minimum.
How CO₂ can break rock without explosions
The new CO₂ method works by harnessing physics instead of chemical reactions. Engineers start by drilling small holes into the rock, just like in traditional blasting. Then, they insert special CO₂ devices filled with liquid carbon dioxide under high pressure.
When triggered, an internal membrane inside the device breaks, causing the liquid CO₂ to expand into gas almost instantly. This expansion increases the volume about tenfold, creating hundreds of megapascals of pressure inside the borehole.
Unlike an explosion, this process does not create a sharp shock wave. Instead, the pressure pushes the rock gently but forcefully, splitting it along its natural weak points. As a result, the rock breaks efficiently without loud noise, flying fragments, or long-range vibrations. This controlled approach makes it ideal for tunnels under residential or sensitive areas.
Real tests confirm safety and efficiency
Until recently, engineers relied on trial and error to estimate the CO₂ method’s power. They knew it worked, but they lacked precise measurements. In a recent study, researchers calculated the energy released during the CO₂ phase transition for the first time.
They examined a standard 1.5-liter CO₂ device with a burst pressure of 280 megapascals. The energy released was about 1,190 kilojoules, roughly equivalent to 281 grams of TNT. By converting CO₂ energy to a TNT equivalent, engineers can now compare it directly to conventional blasting methods and apply existing safety regulations.
The method was tested in a real water tunnel under a mountainous area. This tunnel ran below residential buildings, including older wooden structures sensitive to vibrations. Regulations require that ground vibrations near such buildings remain below 1 centimeter per second.
Calculations showed that the CO₂ devices would produce only 20 percent of the maximum allowable vibration. Instrument measurements confirmed this prediction. The highest vibration recorded near the nearest buildings was just 0.18 centimeters per second, far below the safety limit. The result demonstrated that CO₂ could safely break rock without endangering structures above.
Based on these findings, engineers recommend that future projects calculate CO₂ energy and its TNT equivalent before starting construction. They also emphasize continuous vibration monitoring and regular inspections using drones, especially near residential areas.
By combining precise calculations with real-time monitoring, this CO₂ method allows engineers to construct tunnels efficiently while keeping buildings and residents safe. Moreover, it represents a significant step toward more sustainable and controlled underground construction.
