Soft spots in asphalt can quickly turn into depressions, cracks, potholes, and other pavement failures. Although the damage appears on the surface, the asphalt itself is not always the original cause. In many cases, the real problem is a weak, wet, or poorly compacted area beneath the pavement.
Identifying and repairing soft spots before installing new asphalt is an important part of building a stable, long-lasting pavement surface. Simply placing asphalt over unstable ground may temporarily hide the problem, but the weakness underneath will usually cause the new pavement to settle or fail.
This guide explains what causes soft spots in asphalt, how paving contractors locate them, how they are repaired, and what Utah property owners can do to help prevent them.
What Is a Soft Spot in Asphalt?
A soft spot is an unstable area within the soil, subgrade, aggregate base, or existing pavement structure. It may feel spongy, move under equipment, develop ruts, or fail to support the weight of vehicles and new asphalt.
Soft spots are sometimes discovered after the old pavement has been removed and the underlying surface is exposed. Other times, the warning signs appear after paving as localized sinking, cracking, rutting, or repeated potholes.
A pavement structure generally includes several layers:
- Compacted native soil or subgrade
- Aggregate base material
- One or more layers of asphalt pavement
Each layer depends on the stability of the layer beneath it. Even properly produced and compacted asphalt can fail when it is installed over an unstable foundation.
The Federal Highway Administration’s guidance on the geotechnical aspects of pavement explains how subgrade strength, soil properties, moisture, drainage, compaction, and base materials affect pavement performance.
An excavated soft spot reveals saturated soil and a failed aggregate base.
What Causes Soft Spots in Asphalt?
Soft spots can develop for several reasons. In many projects, more than one condition contributes to the problem.
Excess Moisture Beneath the Pavement
Water is one of the most common causes of pavement instability. When moisture enters the soil or aggregate base, it can reduce the material’s ability to support traffic loads.
Water may reach the pavement foundation through:
- Cracks in the asphalt
- Standing water and low areas
- Poorly directed roof or landscape drainage
- High groundwater
- Damaged drainage systems
- Snow and ice melting near the pavement
Once the underlying material becomes saturated, it may shift or pump under the weight of vehicles. This can lead to depressions, alligator cracking, potholes, and uneven pavement.
Properties with recurring water problems may need more than a surface repair. Correcting the slope or installing an appropriate parking lot drainage solution may be necessary to keep the repaired area stable.
Poorly Compacted Soil
Soil and aggregate base materials must be compacted properly before asphalt is installed. If the underlying material is loose, it can continue settling after construction.
Insufficient compaction may occur when material is placed in layers that are too thick, the wrong equipment is used, moisture levels are unsuitable, or adequate compaction testing is not completed. These problems can create isolated weak areas or affect a larger section of pavement.
Professional grading and base preparation help establish the elevation, slope, drainage, and compaction needed before asphalt paving begins.
Weak or Unsuitable Native Soil
Not every type of soil provides the same level of support. Clay, organic material, loose fill, expansive soil, and other unsuitable materials can become unstable when exposed to moisture or heavy loads.
Some properties also contain areas that were filled during previous construction. If that fill was not installed and compacted correctly, portions of the site may settle differently over time.
When unsuitable soil is discovered, the affected material may need to be excavated and replaced rather than covered with additional aggregate or asphalt.
Inadequate Aggregate Base
The aggregate base distributes weight and creates a stable platform for the asphalt. If the base is too thin, contaminated with soil, poorly graded, or improperly compacted, the pavement may not have enough structural support.
A thin base can be especially problematic in commercial parking lots, loading areas, private roads, and other locations that regularly support heavy trucks or equipment.
Underground Utility Work or Previous Excavation
Utility trenches are common locations for settlement and soft spots. After water, sewer, electrical, gas, or communication lines are installed, the trench must be backfilled and compacted correctly.
If the material settles after paving, a depression or crack may form along the trench. In some cases, the affected area must be reopened so the unstable material can be removed and reconstructed.
Freeze-Thaw Cycles
Utah’s changing seasonal conditions can make existing soft spots worse. Water that enters the pavement structure may freeze, expand, and move the surrounding material. When the ice melts, the soil can become wet, loose, or unsupported.
Repeated freeze-thaw cycles can gradually weaken the base and contribute to cracking, sinking, and pothole formation. Learn more about how seasonal conditions affect pavement in our guide to Utah weather and asphalt damage.
Heavy or Repeated Traffic Loads
A pavement section must be designed for the vehicles that will use it. Areas exposed to delivery trucks, garbage trucks, buses, trailers, or construction equipment may require a stronger base and thicker asphalt than standard areas.
When the pavement structure is not designed for the expected load, weak areas may begin to deform. Repeated pressure can create rutting, depressions, cracking, and base failure.
How Can You Identify a Soft Spot?
Soft spots may not be visible before a paving project begins. Contractors often find them while removing old asphalt, grading the site, or driving equipment across the exposed base.
Common warning signs include:
- Ground that moves, pumps, or deflects under equipment
- Deep tire impressions in the aggregate base
- Localized areas that remain wet
- Soil mixing into the aggregate
- Repeated cracking or potholes in the same location
- Depressions that collect standing water
- Uneven settlement along utility trenches
- Rutting in vehicle travel lanes
A soft spot should be evaluated based on its depth, size, moisture conditions, soil type, drainage, and expected traffic. The correct repair depends on what is causing the instability.
A sunken soft spot in an asphalt parking lot caused by an unstable base.
What Happens If You Pave Over a Soft Spot?
Paving over a soft spot does not make the foundation stronger. The new asphalt may initially appear smooth, but traffic loads will continue pressing against the unstable material underneath.
Over time, the pavement may begin to:
- Sink or develop a depression
- Crack around the weak area
- Form wheel ruts
- Collect standing water
- Break apart into a pothole
- Require repeated surface repairs
The Asphalt Institute’s guidance for repairing asphalt parking lots and driveways explains that when base failure occurs, the damaged pavement must be removed, the underlying weakness corrected, and the pavement replaced.
This is why experienced paving contractors address unstable areas before installing the final asphalt surface.
How Are Soft Spots in Asphalt Fixed?
Repairing a soft spot usually requires more than adding asphalt to the surface. The unstable material must be exposed and corrected so the repaired section has adequate support.
1. Identify the Weak Area
The contractor first determines the approximate boundaries of the soft spot. Equipment movement, visual inspection, test pits, probing, and observations during excavation may be used to evaluate the affected area.
The visible surface damage does not always show the full size of the problem. Excavation may reveal that the unstable material extends farther or deeper than expected.
2. Remove Unstable Material
The weak soil, contaminated aggregate, damaged asphalt, or saturated base is excavated. This process is sometimes called undercutting.
Excavation continues until stable material is reached. The required depth can vary significantly depending on the site conditions and cause of the failure.
3. Address the Source of Moisture
If water caused or contributed to the soft spot, the drainage problem should be corrected before rebuilding the pavement section. Depending on the property, this could involve adjusting the grade, improving surface drainage, repairing a damaged drain, redirecting runoff, or installing drainage materials.
Without correcting the moisture source, the repaired area may become saturated and fail again.
4. Install Suitable Replacement Material
The excavated area is filled with appropriate material, often compactable aggregate base. Depending on the soil conditions and project design, geotextile fabric, geogrid, stabilization material, or additional structural support may also be used.
The replacement material is generally installed in controlled lifts rather than being placed all at once.
5. Compact Each Layer
Each lift must be compacted to create a dense and stable foundation. Proper moisture content, lift thickness, equipment selection, and compaction effort all affect the finished result.
Careful compaction reduces future settlement and helps the repaired area support the new pavement.
6. Restore the Asphalt Surface
Once the base is stable and properly prepared, new asphalt can be installed and compacted. The thickness and number of asphalt lifts should be appropriate for the expected traffic and use of the property.
For existing pavement, the repaired area should be connected carefully to the surrounding asphalt. Our Utah asphalt repair services include solutions for localized pavement failures, damaged sections, potholes, cracking, and other asphalt problems.
Asphalt paving crew repairing a soft spot by removing unstable material.
Can Soft Spots Be Repaired with an Asphalt Overlay?
An asphalt overlay can restore the surface of pavement that remains structurally stable. However, an overlay is not usually enough to correct an active soft spot or base failure.
If the pavement continues moving underneath the overlay, the cracks, settlement, or rutting may eventually reflect through the new asphalt. The unstable section generally needs to be repaired before the overlay is installed.
A professional pavement evaluation can help determine whether a property needs localized base repair, patching, milling, an overlay, or complete reconstruction.
How Can Property Owners Help Prevent Soft Spots?
Not every soft spot can be prevented, especially when a property contains unsuitable native soil or undocumented fill. However, good pavement design and maintenance can reduce the risk.
Helpful preventive measures include:
- Preparing the subgrade properly
- Installing enough base for expected traffic
- Designing the pavement for commercial vehicle loads
- Creating adequate
- Repairing cracks before water reaches the base
- Correcting low areas that hold water
- Maintaining drains, gutters, and runoff paths
- Repairing small pavement failures before they spread
Property owners should also pay attention to pavement that becomes uneven or repeatedly fails in the same location. Our article about why parking lots become uneven explains additional causes of sinking, rutting, and settlement.
Why Proper Base Preparation Matters
Asphalt is only one part of a complete pavement system. Long-term performance also depends on soil stability, depth, grading, compaction, asphalt thickness, and the amount of traffic the surface receives.
Proper preparation may require more work at the beginning of a project, but it can reduce the likelihood of cracking, settlement, potholes, and costly repairs.
Eckles Paving provides professional asphalt paving services for commercial parking lots, private roads, driveways, industrial properties, HOAs, schools, and other properties throughout Utah. Our crews evaluate site conditions and prepare the pavement foundation before installing new asphalt.
A construction worker compacts new base to create a stable foundation.
Frequently Asked Questions About Asphalt Soft Spots
What does a soft spot in asphalt feel like?
A soft spot may feel spongy, flexible, or unstable under vehicles and equipment. It may also appear as a depression, rut, cracked area, or section that repeatedly develops potholes.
Can a soft spot be fixed without removing the asphalt?
Minor surface problems may have other repair options, but a true base or subgrade soft spot usually requires excavation. The asphalt and unstable material must be removed so the foundation can be rebuilt and compacted.
Does adding more asphalt fix a soft spot?
Adding asphalt alone generally does not correct an unstable foundation. The additional material may temporarily improve the appearance, but settlement and cracking can return if the weak base remains in place.
How deep does a soft spot repair need to be?
The repair must extend deep enough to reach stable supporting material. Some soft spots are limited to the base, while others extend into the native soil. The final depth is often determined during excavation.
Can poor drainage cause soft spots?
Yes. Water can weaken soil, reduce structural support, and contribute to settlement. Correcting the source of the water is an important part of many soft spot repairs.
Why does the same asphalt patch keep failing?
A patch may repeatedly fail when only the surface damage is repaired. If unstable soil, a weak base, poor drainage, or heavy traffic caused the original failure, that underlying condition must also be corrected.
Are soft spots common during new paving projects?
Soft spots are sometimes discovered after existing asphalt or soil has been removed. Finding one does not necessarily mean the entire site is unstable, but the affected area should be repaired before paving continues.
How can I tell whether my asphalt has a base failure?
Possible signs include cracking, sinking, rutting, standing water, repeated potholes, and movement under vehicle loads. A pavement contractor can inspect the area and recommend the appropriate repair.
Request an Asphalt Evaluation in Utah
Soft spots should be corrected at their source rather than covered with another temporary surface repair. Proper excavation, drainage, base installation, compaction, and paving can help create a stronger and more durable pavement section.
Eckles Paving provides asphalt paving, grading, drainage, patching, and pavement repair for commercial and residential properties throughout our Utah asphalt service areas.
Contact Eckles Paving to request a free estimate for your asphalt paving or repair project.
