Using Geogrids to Remediate Pavement and Infrastructure Failures

When unfavorable soil conditions are encountered beneath pavement structures, engineers must look beyond conventional over-excavation and aggregate layer enhancement. Geogrids have emerged as a powerful solution for stiffening sub-bases and reinforcing asphaltic layers, enabling reduced section thickness, shorter construction timelines, and significant cost savings. This article examines how geogrids help remediate common failure scenarios, drawing on field-tested methods and real-world applications from Orange County, Florida. Understanding these techniques is essential for anyone studying Structural Failures in Concrete Structures and broader infrastructure remediation strategies.

Understanding Geogrid Reinforcement Mechanisms

How Geogrids Work in Pavement Structures

Geogrids are geosynthetic materials with an open grid structure that interlocks with surrounding soil or aggregate. Their primary function is mechanical stabilization through three key mechanisms:

1. Lateral confinement: The geogrid restrains lateral movement of aggregate particles, creating a stiffened platform that distributes loads more evenly across the subgrade.
2. Tensile reinforcement: The geogrid carries tensile stresses that unbound granular layers cannot sustain alone, effectively bridging weak zones in the subgrade.
3. Load transfer enhancement: By improving composite action between the base and subgrade, geogrids enable more efficient transfer of traffic loads to the underlying soil layers.

When used in a composite asphaltic sandwich configuration with glass grids, the reinforcement becomes even more effective. Glass grids placed between asphalt lifts create a tension-resistant layer that controls reflective cracking and adds structural strength to the entire pavement system.

Key Benefits Over Conventional Remediation Methods

Traditional remediation of weak subgrades requires over-excavation of unsuitable material and replacement with imported aggregate, often to considerable depths. Geogrid reinforcement offers several advantages:

• Reduced sub-base thickness: With geogrid reinforcement, the required aggregate layer can be reduced by 30 to 50 percent while maintaining equivalent structural performance.
• Faster construction: Eliminating deep excavation reduces construction time and minimizes road closure durations, which is critical in high-traffic urban areas.
• Lower material costs: Less imported aggregate means lower material procurement and transportation expenses, directly improving project budgets.
• Improved long-term performance: The reinforced section resists differential settlement and rutting better than unreinforced sections of greater thickness.

Types of Geogrids and Their Applications

Each geogrid type serves a distinct role. Biaxial and triaxial geogrids are most common for sub-base stabilization beneath pavements, while glass grids are specified for reinforcing the asphaltic wearing course itself. Selection depends on the failure mechanism being addressed and site-specific soil conditions.

Kelly Park Road Tearing Failure and Reconstruction

Failure Mechanism

Following two days of heavy rainfall, a 100-foot section of Kelly Park Road developed a crack pattern resembling tearing across the pavement surface. Notably, this crack did not manifest as differential settlement of the underlying soil, and no perched water table suggested a seepage slope. Investigation revealed that the pavement crack resulted from a northward pull of the underlying fill along a plane of weakness. The plane was created by improper joining of new fill against the original road embankment.

The roadway had been widened by filling against pre-widened slopes without a proper box-cut procedure. Infiltrated rainfall increased the weight of the soil, initiating movement along this weak interface. This type of failure parallels Formwork Failures where inadequate interface preparation compromises structural integrity.

Remediation Approach with Dual Geogrid Layers

The affected pavement and portion of the soil-cement base were milled and reconstructed using a two-layer geogrid reinforcement system:

1. Milling of damaged pavement and soil-cement base down to sound material.
2. Placement of the first geogrid layer directly on the prepared subgrade surface.
3. Placement of limerock base material over the first geogrid layer.
4. Installation of a second geogrid layer within the base section.
5. Construction of multiple asphalt lifts to restore the finished pavement surface.

The dual-geogrid system provided tensile reinforcement across the weak interface zone. By distributing tensile stresses that would otherwise concentrate at the joint between old and new fill sections, the system prevented recurrence of the tearing failure pattern.

Settlement over Organic Soils and Rotational Bank Failure

Organic Soil Settlement at South Lake Pleasant Road

South Lake Pleasant Road traversed a natural wetland and exhibited significant settlement distress across its alignment. Geotechnical evaluation revealed that the settlement resulted from compression of thick deposits of buried organic soils beneath the roadway embankment. These organic deposits, exceeding 100 feet in thickness, occur naturally within wetland slough channels and present unique challenges for pavement support.

The distress was aggravated by a declining water table resulting from a record cumulative rainfall deficit in 2007. As water table levels drop, effective stress in the soil increases because buoyancy support is reduced. This increased load compresses buried layers of muck and peat, causing progressive surface settlement. Recognizing Types of Failures Experienced By Different Construction Materials helps engineers anticipate such behavior when organic soils underlie critical infrastructure.

Remediation Design for Settlement Bridging

Based on the severity of distress, the remediation plan included a multi-layer reconstruction approach:

• Removal of 4 inches of existing asphalt and deteriorated base material.
• Construction of a 1-inch thick leveling course to restore uniform grade.
• Placement of a geogrid layer over the leveling course to facilitate settlement bridging and load transfer.
• Construction of 3 inches of asphalt overlay in two separate lifts.
• Incorporation of a Pavetrac asphalt additive for additional structural reinforcement.

The geogrid played a critical role by bridging localized settlement zones and transferring loads to less compressible areas. This prevented the new overlay from reflecting cracks as underlying organic soils continued to consolidate under their own weight.

Canal Bank Rotational Failure

A separate failure scenario involved rotational sliding on a segment of a major canal bank during backfilling restoration. The failed slope segment was excavated to determine the failure plane geometry. Reconstruction used geogrid reinforcement placed in a series of stair-step cuts into the undisturbed soil. Each geogrid layer was anchored into competent material beyond the failure plane, providing tensile resistance against rotational moment. This technique, known as geogrid-wrapped slope reconstruction, effectively stabilizes slopes where conventional grading alone would not provide sufficient factor of safety.

Lake Underhill Road Reconstruction and Glass Grid Asphalt Reinforcement

Full-Depth Pavement Failure Analysis

In a highly residential and commercial neighborhood, a segment of Lake Underhill Roadway continued to exhibit severe and recurring pavement failures. The root cause was a deficient base and subgrade material that had lost inherent strength over time due to material disintegration under repeated traffic loading. The design capacity of this roadway had been compromised by cumulative load cycles exceeding original specifications.

The initial approach specified removal of existing pavements to subgrade level and full-depth reconstruction at selected locations, extending down to 25 inches. However, due to roadway traffic delay concerns in this busy corridor, the approach was modified to a partial-depth reconstruction enhanced with geosynthetic reinforcement.

Composite Geogrid and Glass Grid Reinforcement

The optimized remediation involved two distinct reinforcement strategies working together:

1. Subgrade stabilization: Unsuitable soils below the subgrade were removed and backfilled with sand, then reinforced with geogrid to provide a stable working platform and distribute loads across the weak zone.
2. Asphaltic composite reinforcement: The asphalt layer was reinforced with glass grid, sandwiched between two 2-inch thick layers of Superpave 12.5 mm asphalt. This created a composite asphaltic layer with substantially enhanced tensile strength.

The glass grid serves a fundamentally different function than subgrade geogrid. Glass grids have high tensile modulus and low elongation (3 to 4 percent), making them ideal for intercepting and dissipating tensile stresses within the asphalt layer itself. This prevents reflective cracking from propagating through new overlays and extends pavement service life significantly.

Construction Lessons for Glass Grid Placement

Field experience from Bates Road and similar projects provided valuable construction lessons. Orange County Public Works relied on Geotextile Apparatus Co.’s Grizzly Cub fabric and grid installation machine, attached to a motor grader, to properly place geogrid on its projects. Several critical challenges emerged during glass grid installation:

1. Tack coat optimization: Selecting the correct type and application rate of tack coat to hold the glass grid in place without bleeding through grid openings required field trials.
2. Construction traffic management: Minimizing tack coat pickup from asphalt delivery truck movements was essential to prevent grid displacement before the overlay was placed.

Proper tack density for geogrids and thorough knowledge of bonding techniques are essential skills for crews working with these materials. For further reading on geosynthetic product types and design considerations, see the dedicated resource on Geogrids.

Summary of Applications and Benefits

Geogrids and glass grids offer versatile and cost-effective solutions for remediating a wide range of infrastructure failures. As demonstrated across the case studies from Orange County, these geosynthetic reinforcements enable:

• A stiffer subgrade layer with reduced aggregate thickness and lower construction cost.
• Effective settlement bridging over compressible organic soils where deep excavation is impractical.
• Rotational stability in slope and bank failures through anchored tensile reinforcement.
• Composite asphaltic pavement sections with enhanced fatigue resistance and extended service life.

Whether addressing tearing failures from improper fill joining, settlement over deep organic deposits, rotational slides in canal banks, or full-depth pavement disintegration, geogrids provide tensile reinforcement that conventional granular remediation alone cannot match. The combination of subgrade geogrids for base stabilization and glass grids for asphalt reinforcement represents a comprehensive approach to extending infrastructure service life while keeping construction costs and timelines under control. Deodat Budhu, P.E., is manager of Florida’s Orange County Roads & Drainage Division.