The main concern with most urban infrastructure projects is maintaining the flow of the dynamic everyday life. Prolonged infrastructure projects like tunnels lead to traffic disruptions, which in turn result in business interruptions, commuter frustration, and indefinite road closures.
However, underground construction projects, especially tunnels, have become essential in modern cities. They facilitate the construction of metro systems, stormwater drainage, utility corridors, and underpasses, to name just a few.
Traditionally, a cut and cover approach was used to create these underground structures. Most modern projects, however, prefer precast concrete tunnels due to the time and cost savings that they offer.
This blog looks into both of these methods in depth. It highlights how these methods affect the smooth flow of traffic during construction. So, let’s get right into it.
- What Are Precast Concrete Tunnels?
- What are Traditional Cut and Cover Tunnels?
- Precast Concrete Tunnels vs Cut and Cover: Which is Better for Fewer Traffic Disruptions
What Are Precast Concrete Tunnels?
Precast concrete tunnels are a genius innovation in civil engineering. In this technology-driven approach, you construct tunnel segments in carefully controlled factory settings. Everything from concrete pouring to curing takes place in optimal conditions, which results in greater structural uniformity.
After curing, these segments arrive at the ready underground construction sites where you can install them quickly using Tunnel Boring Machines (TBMs) or micro tunneling systems.
One key benefit of this approach is that it requires minimal surface excavation, which reduces traffic disruptions. Precast concrete construction also leads to faster or more predictable timelines that are essential for minimizing traffic disruptions. Several studies suggest reduced traffic disruption and improved safety during infrastructure upgrades that involve a precast concrete approach.
Here is how this process works.
- The first step is the design and construction of precast concrete tunnel segments in factories.
- On the site, workers create shafts or small entry and exit points.
- Then, TBMs excavate the site while you simultaneously install precast tunnel segments.
- Finally, you install internal lining, waterproofing elements, and utilities to finish the job.
What are Traditional Cut and Cover Tunnels?
Cut-and-cover is a traditional tunnel construction approach where you excavate a trench in the surface, construct the tunnel, and cover it up with concrete. For this method to work, you have to either divert or close traffic, which affects the city’s flow for quite some time. This method comes with low upfront costs. This simple approach works perfectly for shallow tunnel projects.
Unlike with precast concrete products, cut and cover tunnels construction timelines can be much longer, which creates major surface disruptions.
Precast Concrete Tunnels vs Cut and Cover: Which is Better for Fewer Traffic Disruptions
The following are a few points that make it clear which of the two methods leads to less disruption in the flow of traffic in modern infrastructure projects.
1. Extent of Road Closures
Precast concrete tunnels require minimal road restrictions. The restrictions only apply to localized areas where you need to construct the shafts. Only roads that are directly above the tunnel alignment are closed for a short while. After installation, these roads become operational at once.
In the case of cut and cover approach, the roads remain closed along the entire length of the project. This leads to a lot of traffic disruption near the construction site. The disruption in the construction site also leads to more traffic pressure on other roads, which also leads to congestion.
2. Duration of Disruption
The duration of disruption is much shorter in the case of precast tunnels. Precast concrete construction is approximately 20% faster than traditional methods. Case studies also reveal there are schedule reductions of several weeks in projects that use these systems. In this case, both the excavation and the tunnel parts manufacturing take place simultaneously. This results in faster installation, which in turn leads to a shorter disruption window.
On the other hand, cut-and-cover tunnels involve sequential construction phases. These are also subject to weather or logistics delays. This results in extended traffic diversions.
3. Traffic Flow Management Complexity
In the case of precast construction, the traffic management is simpler. You only have to take a detour around the location of the shaft, which eliminates complexity.
Cut-and-cover tunnels need complex detour planning. In some cases, you need to erect temporary roads or bridges to manage the flow of traffic. This approach also needs you to continuously monitor and adjust traffic to prevent congestion, accidents, or general disruption.
4. Impact on Public Transportation
With precast concrete structural elements, public transportation, such as buses, emergency vehicles, etc., faces fewer disruptions. This is because there are no significant changes in daily commute routes when you use this approach.
Cut-and-cover tunnel construction requires you to reroute every public transport route nearby. This leads to unnecessary delays, which result in a lot of public frustration.
5. Pedestrian and Business Access
With a precast approach, the business locations, shops, or homes near the construction site remain accessible. This type of construction creates minimal interruption for foot traffic, which enhances the use of precast concrete in city landscaping as well as infrastructure development.
For cut-and-cover tunnels, authorities have to completely block pedestrian access. This has a significant impact on local businesses as well as pedestrians who live in the vicinity.
6. Environmental and Social Impact
Precast concrete construction of tunnels involves less on-site work. This reduces noise at the surface. The use of heavy machinery in a limited capacity also leads to fewer dust emissions as well as surface vibrations. This further reduces the impact on the traffic.
Cut-and-cover tunnel construction can disrupt communities to a great extent due to high dust levels, continuous construction noise pollution, and traffic congestion. This approach makes the entire area feel like a construction zone for a long time.
Conclusion
There is a significant difference in the extent of traffic disruption when you compare precast concrete tunnels with cut-and-cover construction. Precast construction leads to minimal disruption in the flow of the city. This results from factors like minimal on-site work, faster installation, and fewer weather delays.
Cut and cover construction takes much longer since you have to prepare the site, create the structure of the tunnel, and backfill the site all in a sequence. This translates into prolonged traffic congestion and a lot of inconvenience.
This makes precast concrete tunnels not just an alternative but a standard for building underground structures for modern infrastructure projects.
Visit us at Naran Precast Concrete Co. today to get premium quality precast concrete solutions that minimize traffic disruptions and enhance efficiency, safety, and project success rates in all city infrastructure applications.
FAQs
What are the major drawbacks of cut and cover tunnels?
In this case, you cannot restore the functioning of the road until the entire project finishes. These projects have more labor requirements, longer timelines, and more delays due to weather as well.
Which tunnel construction approach causes less traffic disruption?
Precast concrete tunnels lead to fewer disruptions. This is because a part of the construction takes place off-site. There is no need to excavate the site to dig a trench in this case, which makes it a much better approach than cut and cover tunnels.
What makes precast concrete tunnels costly?
This construction approach has high upfront costs, as there is specialized fabrication and construction machinery involved to make and install precast concrete tunnel segments.
How do cut-and-cover and precast concrete tunnels affect underground utilities?
There is minimal disruption to these utilities with precast tunnels, as you can construct them at greater depths. Cut and cover tunnels often have shallow depths, which requires you to relocate water, gas, or electrical utilities.