The rapid urbanization of cities has brought an increasing demand for underground spaces to accommodate parking and transit facilities. As cities grow, these spaces are becoming indispensable for managing traffic congestion and ensuring efficient public transportation systems. However, the construction of underground facilities comes with significant challenges, including stability, water ingress, and space constraints. One solution that has gained prominence in addressing these issues is the use of diaphragm walls.
In this blog, we explore how diaphragm walls play a critical role in the construction of underground parking and transit facilities. We will discuss their benefits, construction methods, and why they are preferred over other retaining systems in these complex projects.
What Are Diaphragm Walls?
They are deep, reinforced concrete walls constructed in the ground to provide earth retention and waterproofing. They are typically used in large-scale construction projects requiring excavation in confined or sensitive areas, such as underground parking lots, metro stations, tunnels, and basements.
Built using advanced excavation and concreting techniques, they serve both as temporary retaining structures during excavation and as permanent walls in the final structure. Their ability to handle high loads and withstand water pressure makes them ideal for underground applications.
Advantages of Diaphragm Walls for Underground Parking and Transit Facilities
1. Structural Stability in Deep Excavations
Underground parking and transit facilities often require deep excavation, which can compromise the stability of surrounding structures. They provide robust support by acting as retaining walls during excavation. Their strength and rigidity ensure minimal ground movement, reducing the risk of damage to adjacent buildings or infrastructure.
2. Effective Waterproofing
Water ingress is a common challenge in underground construction. Diaphragm walls are designed to be watertight, making them a reliable solution for projects in areas with a high water table. By preventing water seepage, they protect the structural integrity of underground facilities and reduce long-term maintenance costs.
3. Space Optimization
In dense urban environments, space is often at a premium. Diaphragm walls require minimal footprint during installation, making them suitable for construction in confined spaces. This is particularly advantageous for underground parking and transit facilities, where maximizing usable space is a priority.
4. Dual Functionality
One of the key advantages of diaphragm walls is their dual functionality. They serve as both temporary retaining structures during excavation and permanent walls in the final construction. This eliminates the need for additional construction steps, saving time and reducing costs.
The Role of Diaphragm Walls in Underground Parking Facilities
Underground parking facilities are essential for urban areas where above-ground parking is limited. These facilities often extend several levels below ground, requiring strong retaining structures to prevent soil collapse and water ingress.
1. Supporting Multilevel Parking Structures
Diaphragm walls are capable of bearing the high loads associated with multilevel underground parking facilities. They ensure that the excavation process is safe and that the final structure is stable, even under heavy traffic loads.
2. Seamless Integration with Building Design
In many cases, underground parking is integrated into larger developments, such as shopping malls or office complexes. Diaphragm walls allow for seamless integration, acting as permanent perimeter walls that align with the overall architectural and structural design.
3. Enhancing User Safety and Comfort
Waterproof diaphragm walls help maintain a dry and secure environment within underground parking facilities. This not only protects vehicles from water damage but also enhances the overall user experience.
Diaphragm Walls in Transit Facilities
Transit facilities like metro stations, bus terminals, and train depots are critical for urban mobility. Constructing these facilities underground often involves navigating complex geological conditions and minimizing disruptions to surface-level activities.
1. Minimizing Disruptions During Construction
Transit facilities are often built in busy urban areas, where construction can cause significant disruption to daily life. Diaphragm walls allow for deep excavation with minimal noise and vibration, ensuring that surface activities, such as traffic and pedestrian movement, remain largely unaffected.
2. Ensuring Structural Integrity in Seismic Zones
In areas prone to earthquakes, diaphragm walls provide the stability needed to protect transit facilities. Their ability to absorb and distribute seismic forces reduces the risk of structural failure, ensuring the safety of passengers and equipment.
3. Facilitating Complex Designs
Modern transit facilities often feature intricate designs, such as multiple underground levels, interconnecting tunnels, and expansive platforms. Diaphragm walls can be constructed to meet these complex design requirements, providing flexibility in planning and execution.
Construction Process for Diaphragm Walls
The construction of diaphragm walls involves several key steps, ensuring precision and reliability:
- Site Preparation
The area is cleared, and guide walls are constructed to define the alignment of the diaphragm wall. - Excavation
Trenching is carried out using specialized equipment such as grab excavators or hydrofraise machines. Bentonite slurry or polymer solutions are used to stabilize the trench walls during excavation. - Reinforcement Installation
Steel reinforcement cages are prefabricated and lowered into the trench. These cages provide the structural strength required for the wall. - Concreting
Concrete is poured into the trench using tremie pipes to ensure a continuous, void-free structure. The bentonite slurry is displaced as the concrete is placed, leaving behind a solid wall. - Joint Sealing
Special care is taken to seal joints between panels, ensuring waterproofing and structural integrity.
Comparing Diaphragm Walls with Other Retaining Systems
While diaphragm walls are highly effective, they are not the only retaining system used in underground construction. Other options include:
- Secant Pile Walls: These involve overlapping piles and are often used for temporary retention. However, they may not provide the same level of waterproofing as diaphragm walls.
- Sheet Pile Walls: Suitable for shallow excavations, sheet piles are less durable and less effective in deep or high-water-table conditions.
- Soldier Pile and Lagging: Common for temporary applications, this system lacks the structural strength and waterproofing required for permanent underground facilities.
Compared to these systems, diaphragm walls offer superior strength, durability, and versatility, making them the preferred choice for underground parking and transit projects.
Challenges in Using Diaphragm Walls
Despite their advantages, diaphragm walls come with certain challenges:
- High Initial Costs: The equipment and expertise required for diaphragm wall construction can be costly.
- Complex Installation: Building diaphragm walls demands precise planning and execution, often requiring specialized contractors.
- Time-Intensive: The construction process can be time-consuming, especially for large-scale projects.
However, the long-term benefits of using diaphragm walls, such as reduced maintenance costs and enhanced durability, often outweigh these challenges.
Conclusion
Diaphragm walls have revolutionized the construction of underground parking and transit facilities, providing unmatched stability, waterproofing, and versatility. Their ability to support deep excavations, minimize disruptions, and integrate seamlessly into complex designs makes them indispensable in modern urban development.
As cities continue to grow, the demand for efficient underground spaces will only increase, further cementing the role of diaphragm walls in shaping the infrastructure of the future. By overcoming challenges and leveraging advanced construction techniques, diaphragm walls will remain at the forefront of underground construction innovation.
