Project Profile: The Application of Non-Woven Geotextiles in the Riverside Highway Stabilization Project

1. Introduction

The "Riverside Highway Stabilization and Improvement Project" was initiated to address chronic issues of soil erosion, embankment instability, and poor drainage along a critical 10-kilometer stretch of roadway adjacent to a major river. The existing embankment was susceptible to saturation from both rainfall and capillary action from the river, leading to weakened subgrade, pavement cracking, and costly annual repairs. The primary engineering challenge was to implement a cost-effective and durable solution that would separate soil layers, facilitate drainage, and filter fine particles to ensure long-term stability. The selected solution was the integration of a high-performance non-woven geotextile.

2. Project Challenges

The site presented several significant geotechnical challenges:

Erosion: Flowing surface water and wave action from the river were washing away fine soil particles from the embankment slope.

Soil Mixing: The granular base course was mixing with the soft clay subsoil, reducing its load-bearing capacity and leading to pavement failure.

Poor Drainage: Water trapped within the soil structure created hydrostatic pressure, further destabilizing the embankment and promoting frost heave in colder months.

Unstable Subgrade: The native soil had low California Bearing Ratio (CBR) values, making it unsuitable for supporting direct loads from traffic.

3. The Solution: Non-Woven Geotextile

After thorough analysis, a needle-punched non-woven polypropylene geotextile was specified. This material was chosen for its three primary functions, which directly addressed the project's challenges:

Separation: The geotextile was placed between the native subgrade soil and the new granular base course. This physical barrier prevented the upward migration of fine clay particles into the stone base and the downward intrusion of aggregate into the soft subsoil, maintaining the integrity and design thickness of both layers.

Filtration: Positioned along the embankment slope facing the river, the geotextile acted as a filter. It allowed water to flow freely through its plane (in-plane drainage) while preventing the erosion of soil particles. This was critical for relieving pore water pressure and stabilizing the slope.

Drainage: The inherent thickness and porosity of the non-woven fabric provided a conduit for water to flow within its structure, directing it toward designed weep holes and drainage outlets, thus preventing water accumulation.

4. Material Specification

The selected geotextile had the following key properties:

Polymer: UV-stabilized polypropylene

Manufacturing Process: Needle-punched

Mass per Unit Area: 200 g/m²

Tensile Strength: ≥ 9 kN/m (as per ASTM D4632)

Elongation at Break: ≥ 50%

Apparent Opening Size (AOS): 70-100 (O90) – optimal for filtering the site-specific soils while maintaining permeability.

Permittivity (Ψ): ≥ 1.0 sec⁻¹ (as per ASTM D4491) – ensuring high water flow capacity.

5. Installation Methodology

The installation followed a strict quality assurance protocol:

Site Preparation: The existing failed pavement and base materials were removed. The subgrade was excavated to the required level, graded to a 2% cross-slope for drainage, and compacted to 95% of its maximum dry density (Standard Proctor).

Geotextile Placement: Rolls of the non-woven geotextile were deployed manually and mechanically along the prepared subgrade and slopes. Rolls were placed in the direction of the primary construction traffic.

Overlap and Seaming: Adjacent rolls were overlapped by a minimum of 300 mm. On critical slopes, overlaps were sewn together using a robust polyester thread to prevent displacement during aggregate placement.

Aggregate Placement: A 300mm thick layer of clean, crushed stone aggregate (50mm nominal size) was carefully placed directly onto the geotextile. Spreading was done from the center outwards to minimize fabric distortion. Dumping of materials from height directly onto the unprotected geotextile was strictly prohibited.

Compaction: The aggregate was compacted using a vibratory roller in multiple passes to achieve the specified density.

Paving: The final asphalt pavement layer was placed upon the stabilized and well-draining base course.

6. Quality Control and Testing

Throughout the project, quality was ensured through:

Material Certification: Review of mill certificates for each geotextile roll lot.

Field Tests: In-situ CBR tests on the prepared subgrade.

Installation Inspection: Continuous monitoring of overlap widths, seam integrity, and material handling to prevent damage.

7. Results and Benefits

The use of non-woven geotextile delivered exceptional results:

Increased Lifespan: The stabilized foundation is projected to extend the service life of the highway by over 15 years.

Reduced Maintenance: Elimination of soil migration and improved drainage has drastically reduced the need for annual maintenance and repairs.

Cost Savings: The project achieved a 20% cost saving compared to traditional excavation and replacement methods.

Sustainability: The solution minimized the need for virgin quarry materials and reduced the carbon footprint associated with frequent maintenance works.

8. Conclusion

The Riverside Highway Project stands as a testament to the critical role non-woven geotextiles play in modern civil engineering. By performing the essential functions of separation, filtration, and drainage, this versatile material provided an elegant, efficient, and economically superior solution to a complex geotechnical problem. The project's success underscores the importance of proper material selection, specification, and installation in ensuring the long-term performance and resilience of infrastructure.