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The Owerri-Orlu Road in Imo State, Nigeria, is a crucial transportation artery, linking the capital city of Owerri with the vibrant commercial hub of Orlu. Recognizing its strategic importance, the government launched a major project to rehabilitate and dualize the road, aimed at enhancing regional connectivity and spurring economic growth. The local authority needed to find a technically sound solution with a limited budget that required little to no maintenance. The chosen solution had to both restore full economic activities to the region and have the ability to accommodate future population and economic growth.
The previous road infrastructure had been significantly compromised by severe gully erosion, which presented a grave threat to both the road’s stability and public safety. This erosion, exacerbated by the region’s hilly terrain, intense rainfall, and poor soil conditions, led to the collapse of several road sections and the destabilization of underlying foundations, making parts of the road impassable. These challenges underscored the need for an effective, sustainable solution to prevent further degradation and restore the road’s functionality.
To effectively mitigate the gully erosion and stabilize the affected section of the road, a comprehensive approach was adopted. The solution focused on constructing a Mechanically Stabilized Earth (MSE) wrap-around structure, which provided the necessary stability to the eroded slopes and facilitated the road’s rehabilitation. After a detailed assessment of the ground conditions using the Bishop’s Slip Circle Method, the engineering team designed a multi-tiered slope reinforcement system. The design incorporated three tiers, each standing 5 meters high, with a slope ratio of 1V: 0.2H. The ACEGrid® GG150-I geogrid was used to reinforce the soil mass, ensuring long-term stability.
An ACEGrid-reinforced soil slope about 80m (262.4 feet) long, 10m (32.8 feet) wide, and with the highest section at 15m (49.2 feet) was constructed to reclaim the slope and provide stable, usable land for pavement and drainage rehabilitation works. This type of retaining wall system required a much shorter construction time through the use of in-situ fill materials.
The MSE structure was constructed using a Wrap-Around Facing Reinforced Soil Structure, which combines in-situ soil and geosynthetic materials. These included ACEGrid® GG150-I PET (geogrids), ACETex® NW PP (geotextile), and geotextile bags (ACESandbags) as the facing to promote vegetation growth that helps stabilize the slope.
The successful application of geosynthetic materials along the Owerri-Orlu Road highlights the effectiveness of combining advanced geotechnical engineering solutions with sustainable practices. The integration of these materials significantly reduced project costs and construction time while providing a robust solution to the erosion problem.
PROJECT HIGHLIGHTS
Owerri-orlu road rehabilitation and dualization
LOCATION
Owerri, Imo State, Nigeria
OWNER
Imo State Government
GENERAL CONTRACTOR
Craneburg Construction Company
ENGINEERS AND INSTALLER
ACE & Willem Engineering Company LTD.
GEOSYNTHETIC PRODUCTS
ACEGrid® GG150-I, ACETex® NW,
ACESandbag™ EC
GEOSYNTHETIC MANUFACTURERS
ACE Geosynthetics