Poor subgrade conditions don't have to derail a project. Geogrid can help stabilize working surfaces over weak or variable soils while reducing the need for undercut and excessive aggregate. But while geogrid installation is relatively straightforward, success often comes down to the details.

Most geogrid-related issues in the field are not caused by the geogrid itself. They result from avoidable installation mistakes that can impact constructability, performance, and project efficiency. Here are seven common geogrid installation mistakes and practical ways to avoid them.

Mistake #1: Inadequate Geogrid Overlaps

Proper overlap between adjacent geogrid rolls is essential to maintaining continuity throughout the stabilized section. One of the most common installation mistakes is using insufficient overlap, particularly when working over soft or unstable subgrades.

As soil conditions become weaker, overlap requirements become increasingly important. On extremely soft soils, temporary ties may also be used during construction to help maintain overlap lengths as aggregate is placed.

How to avoid it: Follow project-specific overlap requirements and verify that overlaps remain properly aligned throughout installation and aggregate placement.

Mistake #2: Improper Aggregate Placement

Even when the geogrid is installed correctly, poor aggregate placement practices can create problems.

Geogrid overlaps should be shingled in the direction of aggregate placement so advancing fill travels over the overlap rather than against it. When aggregate is pushed into an overlap, the geogrid can lift, shift, or become misaligned.

Another common issue occurs when crews push aggregate from opposite directions. As the advancing piles meet, the geogrid can be pulled in opposing directions, creating slack or wrinkles that can slow the installation process.

How to avoid it: Establish the aggregate placement direction before construction begins and advance aggregate in a consistent and uniform direction across the entire section.

Mistake #3: Using an Initial Lift That's Too Thin

The initial aggregate lift plays a critical role in protecting the subgrade and supporting construction traffic.

If the lift is too thin for site conditions, excessive rutting and deformation can occur before the stabilized section is fully established. In very soft conditions, thicker initial lifts may be necessary to distribute loads and reduce stress on the underlying soils.

Compaction is equally important. Inadequate compaction can lead to rutting under wheel loads, reducing the effective thickness of the aggregate layer and placing additional stress on the subgrade. However, excessive compaction over weak, moisture-sensitive soils can also be problematic, potentially weakening the subgrade or causing additional deformation.

How to avoid it: Follow project-specific lift thickness requirements. Closely observe the subgrade's response and work with the local Geotechnical Engineer to adjust compaction efforts as needed based on site conditions.

Mistake #4: Driving Equipment on Exposed Geogrid

Geogrid is designed to work as part of a composite mechanically stabilized layer (MSL) system, not as a stand-alone driving surface.

A common field mistake is allowing equipment to drive directly on exposed geogrid before sufficient aggregate cover has been placed. Depending on the equipment type, speeds, and site conditions, direct trafficking can disrupt a perfect geogrid layer installation.

Sharp turns and sudden movements can further increase the potential for displacement.

How to avoid it: Place the required aggregate lift before allowing construction traffic and follow project-specific guidance regarding equipment operations.

Mistake #5: Treating Utilities as an Afterthought

Utilities can have a significant impact on how a stabilized section is constructed.

Existing pipes, conduit, culverts, and other underground infrastructure may limit excavation depth or affect construction sequencing. Future utility crossings, posts, and piers may also require modifications to the stabilized section after installation.

Fortunately, geogrid systems can be excavated or penetrated when needed. Once utility work is complete, new geogrid can be installed as necessary to restore continuity within the section.

How to avoid it: Identify utility conflicts early and incorporate them into the stabilization plan before construction begins.

Mistake #6: Automatically Choosing Dig-and-Replace

When contractors encounter peat, organics, or other poor soils, the instinct is often to excavate and replace the unsuitable material.

While undercut may be appropriate in some situations, it is not always the only solution. Excessive excavation can increase costs, add hauling requirements, and extend schedules.

In many cases, geogrid-stabilized working platforms and access roads can be constructed over very weak soils while minimizing excavation and reducing aggregate requirements. On some sites, preserving existing vegetation and root mat structure may also help maintain a workable platform rather than unnecessarily disturbing or completely failing an existing weakened subgrade.

For example, on the Bixby Residential Development project in Oklahoma, mechanical stabilization with geogrid helped mitigate weak subgrade conditions and eliminated the need for excavation while creating a stable construction platform.

How to avoid it: Evaluate site conditions carefully before assuming excavation and replacement is the best approach.

Mistake #7: Overlooking Drainage

Even a properly installed geogrid section can experience performance issues if drainage is ignored.

Water that accumulates within the aggregate layer can migrate to the subgrade and create soft conditions and reduce the effectiveness of the section. Geogrid, aggregate, subgrade, and drainage all work together as part of a comprehensive system.

The most successful installations account for water management from the beginning rather than addressing drainage concerns after problems appear.

How to avoid it: Incorporate drainage into both the design and construction plan to help maintain long-term performance.

Field Conditions Don't Always Match the Plan

No two jobsites are exactly alike. Unexpected soft spots, buried utilities, groundwater, and changing soil and site conditions can require adjustments during construction.

The most successful geogrid installations are typically those where crews recognize changing conditions early and adapt their approach accordingly. Paying attention to overlaps, aggregate placement, lift thickness, equipment traffic, utilities, and drainage can help prevent costly rework and keep projects moving.

Because when it comes to geogrid installation, most problems are not caused by the geogrid itself. They're caused by small field decisions that become much bigger construction challenges later.