Reinforced Soil Slope at the Entrance of Gukeng Interchange, National Freeway No. 3, Taiwan

This project is located at the entrance ramp of Gukeng Interchange on the Northbound of National Freeway No.3. The site is close to a mountainous area with frequent intense heavy rainfall. The soil has been seriously eroded because the runoff on the slope cannot be efficiently removed. In addition, the trees and shrubs on the slope also presented significant root channeling, blocking the slope's drainage system, worsening the slope's drainage of the runoff, and thus further increasing the risk of the slope's instability. Considering these problems, the Authority of the National Freeway decided to take necessary and appropriate measures to restore the slope.

In addition to the problem of slope soil erosion caused by heavy rainfall, this project also encountered a more severe challenge - the site constraint to accommodate large equipment during construction. For such conditions, the project's construction must consider the site's restrictions and the construction method's practicality. During the construction period, the freeway will remain open for operation. Therefore, it is crucial to prioritize construction safety, including conducting a thorough safety assessment of the existing traffic flow and construction site. The contractor should develop an effective traffic control and management plan to ensure safety.

This project faced various challenges, such as site constraints and construction safety, along with the need to consider slope stability, eco-environment, and landscape aesthetics in its design. After evaluating several options, the owner and the designer finally decided to adopt the reinforced soil slope for construction.

Temporary retaining rail piles are installed before the slope excavation to avoid possible collapse risks. Thus, safeguard the safety of the freeway during the construction period. The slope was then excavated in stages, downward, to improve slope stability. Such excavation effectively reduced the earth pressure, providing larger space for efficient work by construction workers. Furthermore, equipment and tools can move around with greater ease, enhancing the overall productivity of the construction site. In addition, the excavated material was applied to the later reinforced slope, eliminating the need to dispose of it offsite. It reduced carbon emissions and conformed to the project's sustainability goals.

For the structural design, ACEGrid^® geogrid with a strength of 150 kN/m and reinforcement lengths ranging from 2.5 to 5 meters were selected. Considering the site constraints, the slope angle was set at 70 degrees, with its height varied from 3 to 6.5m.
To address the issues of slope erosion and poor vegetation growth on steep slope, high erosion-resistant bags, ACESandbag^TM EC, were used as the materials for wrapped around protection face for the slope. Their smaller openings and the inclusion of grass effectively reduced the risk of soil loss and specifically improved the erosion resistance of the slope surface.

A notable fact of this project involved preserving and restoring the current vertical and horizontal concrete drainage systems on-site. The project's goal was to achieve optimal results while minimizing costs. This practice showed that the reinforced soil slope construction could be satisfactorily adapted to local conditions while achieving an overall excellent performance of economic, safety, environmental friendliness, and landscape aesthetics.

The design and construction of this project comprehensively considered multiple requirements, including site constraints, construction safety, slope stability, slope anti-erosion, and landscape aesthetics. Using reinforced soil slope technique and adopting ACE materials, the restoration has achieved the desired results, ensuring cost-effectiveness and overall meritorious performance of the engineering and sustainable environmental contribution. It is also of great significance to traffic safety maintenance in the area. Through the implementation of this project,freeway users can obtain safer and more reliable driving conditions, and the eco-friendly vegetated slope also can integrate with the surrounding natural environment.