Unveiling the Underground: Access Tunnel Construction Techniques
Access Tunnel Construction Techniques
Urban explorers are constantly on the lookout for hidden and mysterious places to explore. One of the most captivating and intriguing locations that draw their attention is access tunnels. These underground passages provide a unique opportunity to discover hidden secrets beneath our cities. In this article, we will delve into the various construction techniques used in creating these fascinating access tunnels.
1. Cut-and-Cover Method:
The cut-and-cover method is one of the oldest and most common techniques used in tunnel construction. It involves excavating a trench, constructing the tunnel walls using concrete or steel, and then covering it back with soil or other materials. This technique is typically employed when building shorter access tunnels beneath roads or buildings.
2. Boring Machines:
For longer and deeper access tunnels, boring machines come into play. These massive machines are capable of drilling through different types of soil without disturbing the surface above. The process starts by installing a launching pit where the machine begins its excavation journey underground while simultaneously lining it with concrete segments as it progresses forward.
3. Drill and Blast Method:
In situations where rock formations pose challenges for conventional digging methods, drill and blast technique comes to rescue. Explosives are used to break down rocks into smaller fragments which can then be removed by machinery or manual labor. This method requires skilled engineers who calculate precise drilling patterns to ensure controlled blasts.
4. Shield Tunnelling:
Shield tunnelling is commonly employed when constructing access tunnels under water bodies or areas with unstable soil conditions such as marshes or clayey terrain. A shield, consisting of hydraulic jacks and bulkhead doors, protects workers from potential cave-ins while they excavate manually behind it.
5. Microtunneling:
Microtunneling is an innovative technique that involves remotely controlled miniaturized boring machines known as microtunnel boring machines (MTBMs). These machines dig small diameter tunnels typically ranging from 0.6 meters to 3 meters. Microtunneling is often used when constructing access tunnels for utility pipes or sewage systems.
6. Sequential Excavation Method (SEM):
The sequential excavation method, also known as the New Austrian Tunnelling Method (NATM), is a flexible technique that adapts to varying ground conditions encountered during tunnel construction. It involves excavating small sections of the tunnel at a time and then supporting it with sprayed concrete or other reinforcement methods.
Access tunnels provide an exciting opportunity for urban explorers to uncover hidden aspects of cities. From simple cut-and-cover techniques to advanced drilling machines, there are various methods employed in their construction. Each technique offers its own advantages and challenges depending on factors such as soil conditions, length, depth, and purpose of the tunnel. So next time you step into an access tunnel, take a moment to appreciate the engineering marvel behind its construction.