Alchatek Blog

For structural and geotechnical engineers, general contractors, and soil stabilization specialists working on urban infill or renovation projects where conventional foundation equipment simply won't fit.

A new elevator shaft is not a place to guess about soil conditions. It carries a structural load every single day, and if the soil underneath it settles unevenly, the consequences show up in cracked finishes, misaligned rails, and, in the worst case, an elevator system that's out of service. The problem is that a lot of the buildings that need new elevator shafts are old buildings, and old buildings were not built with equipment access in mind. Narrow doorways, low ceilings, and tight interior footprints rule out the pile-driving rigs and excavation equipment that soil stabilization has traditionally relied on. That leaves engineers and contractors with a hard question: how do you densify loose, sandy soil under a structural load without bringing in equipment that can't get to the work?

The Access Problem Is a Structural Problem

Tampa Bay's urban core sits on a lot of loose, granular sand. It drains well, but it also shifts under load, which is exactly the wrong quality to have underneath a structure that will carry vibration and weight every time the elevator runs. A general contractor expanding an existing building doesn't get to relocate the shaft to easier ground. The soil under the planned footprint has to be dealt with as it is, and that usually means one of two paths.

The first path is conventional. Piering, underpinning, or heavy compaction equipment gets brought in, which typically means demolition or widening of existing openings just to get the machinery on site. In a downtown building with narrow entryways and low overhead clearance, that can mean tearing into structure that has nothing to do with the actual repair, just to make room for the rig.

The second path is permeation grouting. A low-viscosity resin gets pumped through small-diameter injection rods on a grid pattern, penetrating the loose soil and binding it into a dense, load-bearing mass, without ever requiring equipment larger than what fits through a standard doorway.

Cost of Access vs. Cost of the Repair Itself

On a tight-access job, the equipment mobilization problem is often the bigger cost driver than the soil work itself. Bringing in heavy piering or compaction equipment to a confined urban site can mean partial demolition to create equipment access, temporary shoring, and a longer project timeline before soil work even starts. Low-mobilization permeation grouting uses compact pumps and hand-portable injection rods, which generally means a smaller crew footprint and a shorter path from mobilization to injection.

The tradeoff isn't automatic. Permeation grouting is a strong fit for loose, granular, sandy soils. It is not the right call for dense clay or highly cohesive soils, where the resin can't permeate effectively, and it's not a substitute for deep piering when the load or depth requirements exceed what soil densification alone can support. The right approach depends on the soil profile, the load the shaft will carry, the depth of the problem layer, and what the site's access constraints actually allow. A geotechnical evaluation, not a general rule of thumb, should drive that decision on any given project.

Case Study: Elevator Shaft Foundation, Downtown Tampa

Valley National Bank needed a new elevator shaft as part of a building expansion inside an existing downtown structure. Before construction could move forward, the foundation soil beneath the planned shaft had to be confirmed capable of handling the long-term load and vibration of daily elevator operation.

Helicon, a Florida-based foundation and soil stabilization contractor, evaluated the site and found two problems working against each other. The shaft location sat inside an older building with narrow entryways and low overhead clearance, which ruled out traditional foundation equipment. And the subsurface soil was loose, granular sand, the kind that shifts under sustained load if it isn't addressed first.

Helicon selected AP Soil 600, a one-part, low-viscosity polyurethane permeation grout built for sandy soil stabilization. The low viscosity lets the material penetrate deep into loose soil without adding significant weight, and it's engineered to bind soil particles together into a stable, load-bearing mass while resisting water infiltration, a relevant property in Florida's wet climate.

The crew designed a grid of 14 injection points across the shaft footprint, drilling each to 5 to 6 feet, targeting the soil layers most at risk of movement. AP Soil 600 was injected through the full grid to ensure coverage without gaps, permeating the sand and locking it into a dense mass. Uniform support was confirmed across the foundation before vertical construction began.

The result was a stable base for both the static weight of the shaft and the dynamic forces of daily elevator operation, with voids and weak points eliminated and soil density and shear strength increased. The work went in quickly and cleanly, with minimal disruption to the surrounding building, and it kept the construction schedule intact by treating the soil before vertical work began instead of dealing with settlement after the fact.

Why Contractors Turn to Alchatek for Tight-Access Soil Work

Sandy, granular soil under a structural load is not a problem that solves itself, and it's not a problem that waits for convenient equipment access. Alchatek's AP Soil 600 is built specifically for this kind of work: a single-component, moisture-activated, hydrophobic, low-viscosity resin designed to permeate loose sand and soil and cure into a dense, load-bearing mass. It carries NSF/ANSI 61 certification for contact with drinking water, which matters on sites where groundwater or potable water lines are nearby.

The chemistry has to match the soil and the site. AP Soil 600 is engineered for permeation into non-cohesive, granular material like sand and fine silts. It is not the right choice for dense clay or organic soils, where a different approach is called for. That's why a geotechnical evaluation belongs at the front of any project like this, not an assumption that one product or method fits every soil condition.

For trained contractors working urban infill, renovation, or new construction projects with real access constraints, permeation grouting offers a way to address soil stabilization without the mobilization burden of heavy equipment, and without asking the client to accept demolition just to make room for a repair.

Related Reading

• Case Study: Stabilizing a 5.75 Million Pound Space Launch System (slug inferred, verify before publishing)
• Excavation Assist Using Polyurethane Grout: A Smarter Alternative to Sheet Piles (slug inferred, verify before publishing)
• Geotech Solutions for New Construction Series: Zero Lot Line Excavation (slug inferred, verify before publishing)

Talk to a Specialist Before You Break Ground

If your project has soil conditions you're not certain about, or access constraints that rule out conventional equipment, get a site evaluation before the schedule forces a decision. Call an Alchatek specialist at (404) 618-0438, or find a trained contractor near you.

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For DOT maintenance teams, municipalities, public works departments, bridge maintenance engineers, and the contractors who perform concrete lifting, void filling, and soil stabilization work — what an unstable approach slab really costs, and why the bump is rarely the actual problem.

A bridge approach slab does not fail all at once. It shows up as a bump, then a dip, then a crack along the joint where the slab meets the deck. Crews patch it, grind it smooth, and move on. A few months later, the same spot is back on the list.

That cycle is why this problem is easy to underestimate. Each patch looks cheap on its own. It's the repeated mobilizations, the lane closures, and the eventual heavier repair that add up. Most of that cost has nothing to do with the asphalt on top. It's driven by what's happening in the soil underneath.

The Real Cost Driver Isn't the Patch

A single patch is inexpensive. What's expensive is the pattern: mobilizing a crew, setting traffic control, closing a lane, and grinding or filling the same joint — repeatedly, at the same location, because the cause was never addressed. Traffic control and mobilization alone often cost more than the patch material itself, and that overhead repeats with every visit.

Left long enough, the condition can progress from the slab into the structure itself. At that point, repair moves into abutment or wing wall territory, where structural work runs $500–$1,200 per square foot.

Actual costs vary by region, traffic control requirements, agency specifications, slab condition, drainage, soil conditions, access, and severity.

This gradual progression is the point: money spent patching the same location, over and over, without resolving the underlying condition — until it's no longer just a slab problem.

The Bump Is the Symptom. The Void Is the Problem.

An approach slab bridges two systems that behave very differently. The bridge itself sits on a foundation — an abutment, piles, drilled shafts, footings bearing on stable material. The approach slab sits on compacted fill and native soil. Those two systems settle at different rates, and that difference is where the trouble starts.

Common causes include:

• Fill settlement — backfill behind the abutment consolidates over time, especially if it wasn't compacted to spec.
• Erosion and soil loss — water finds a path under the slab or through a failed joint and carries fines out, leaving a void.
• Failed drainage — deck drains or approach drainage that no longer function concentrate water exactly where it does the most damage.
• Voids beneath the slab — once soil is lost, the slab spans open space instead of bearing on support, and traffic loading accelerates the cracking.

None of this is visible from the driving surface. What's visible is the bump — the downstream symptom of a support problem that started below grade.

Why Repeated Patching Doesn't Fix It

Asphalt patching and grinding improve ride quality fast, which is why they're usually the first response. But if there's a void or ongoing erosion beneath the slab, the patch sits on the same unsupported base that caused the original settlement. Traffic keeps flexing the slab over the void, the patch cracks again, and the crew returns on a schedule that tends to compress rather than stretch out.

Where Polyurethane Injection Fits

When the cause is loss of support — a void, settled fill, or eroded soil — polyurethane injection addresses that condition directly, without full slab removal. Small-diameter ports are drilled through the slab or pavement, and high-density polyurethane resin is pumped beneath it. The material expands to fill the void, densify loose soil, and in appropriate cases lift the slab enough to close the joint differential.

If a soil boring or dynamic cone penetrometer (DCP) test indicates weaker soils at greater depth, those layers can be targeted first with polyurethane injected several feet into the ground using Alchatek's Deep Lock® process — addressing the soil density issue driving the settlement before the slab itself is lifted.

This isn't a fit for every situation. It addresses void and soil support — not a structurally deficient slab, a failed expansion joint, or drainage that's actively delivering water to the site. Site conditions, soil type, drainage, and the extent of the void all factor into whether injection is appropriate.

Why Contractors and Agencies Work With Alchatek

Alchatek manufactures high-strength polyurethane systems for void filling, soil stabilization, and concrete lifting on roadway, bridge, and transportation infrastructure. For contractors working under DOT or municipal specifications, that means products engineered for wet conditions, rapid cure, and traffic-ready turnaround, backed by technical support from a team familiar with public infrastructure estimating and application questions.

The right approach depends on the cause of the settlement, the soil conditions, and the condition of the slab — not a one-size-fits-all fix.

Related Reading

• 5 Warning Signs a Structure May Need Slab Lifting or Stabilization
• A Trusted Polyurethane Soil Stabilization Resource for Engineers
• AP Fill 700 – Polyurethane for Pipe Repair

Talk to a Specialist

If an approach slab on your system is showing repeated settlement, the first step is understanding what's happening beneath it. Call an Alchatek specialist at (404) 618-0438, or find a trained contractor near you.

The structural repair range in this article is confirmed via Alchatek's Cost Reference Library. Actual costs vary by site conditions, region, traffic control requirements, agency requirements, slab condition, drainage, soil conditions, access, and severity of settlement.

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An interior elevator pit needed for ADA retrofit in a multi‑level building, inside an old stairwell beside a load‑bearing wall on sandy soils. Conventional shoring wasn’t feasible indoors with tight footprint and headroom limits.​ Stable Soils of Florida was called in to assess and remedy the situation.

Initial Assessment

• Sandy, below‑water‑table soils at a planned 7 ft pit depth.​

• Footing and slab at risk of undermining if excavated untreated.​

• No practical option for sheet piling, slurry wall, or trench box.​

Proposed Solution

Engineers designed a perimeter grout “box” using AP Soil 600, a low‑viscosity, single‑component permeation resin that bonds wet sands into a rock‑like, load‑bearing mass.

Procedures

1. Lay out pit and grout‑box perimeter around the planned excavation.​

2. Drill and set probes to depths below the final pit grade.​

3. Inject AP Soil 600 while slowly extracting probes to form overlapping treated columns.​

4. Allow cure, then excavate the pit inside the treated zone.​

5. Grind exposed treated face flat and use it as the outer form for the concrete pit.​

Results

Stable excavation adjacent to the load‑bearing wall with no observed soil loss.​
Interior elevator pit completed without conventional shoring or large equipment.​
Enabled ADA‑compliant vertical access using permeation‑stabilized in‑place soils.

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In Cape Canaveral, Florida, a heavily loaded slap stand structure was planned for construction along a transfer aisle in the Vehicle Assembly Building (VAB). This slap stand would be critical in servicing the proposed Space Launch System vehicle (SLS). However, the project faced a significant challenge when it was discovered that the near-surface subsoils consisted of loose fill materials susceptible to further densification and volume loss due to vibrations and water infiltration. With the slap stand tentatively designed to bear directly upon the ground-level floor slab of the VAB, the degree of subsoil support beneath the floor slab section became a critical concern.

Powerful Polymers

To address this issue, the geotechnical engineer of record recommended a ground improvement solution using permeation grout. Helicon, a leading soil stabilization contractor, worked alongside the geotechnical design team to develop a permeation grout program that would meet the building code load criteria. AP Soil 600, a high-strength, hydro-insensitive structural polyurethane foam, was selected as the ideal product for this project due to its exceptional ability to support heavy structures.

Painless Procedure

Helicon’s technicians installed permeation grout injection pipes on a center-to-center spacing of approximately 2 feet across each of the slap stand areas. The injection points were driven to a depth of at least 5 feet below the floor slab grade. Grout was injected at a relatively low pressure (less than 50 psi), and grout needles were slowly withdrawn during pumping to ensure a uniform distribution of grout to about 3 feet below the bottom of the slab level. The amount of grout used was carefully controlled, with less than 15 gallons per foot per injection point.

Rapid Result

The permeation grout project was a resounding success, effectively improving the load-bearing capacity of the existing soils at the site. The precise application of AP Soil 600 ensured that the slap stand structure would have a stable and reliable foundation, allowing for the safe and efficient servicing of the Space Launch System vehicle. Thanks to Helicon’s expertise and the power AP Soil 600, this piece of critical infrastructure in Cape Canaveral was reinforced and readied for countless future space exploration missions.

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Developers working on a new CVS Pharmacy in Orlando, Florida, encountered critical soil stability issues during the construction process. The project managers faced a significant challenge when geotechnical testing revealed unsuitable soil conditions between 5 and 10 feet below the surface, posing a threat to the structural integrity of the planned parking lot. This issue was discovered after site preparation had already begun, adding urgency to finding an effective solution that would allow construction to proceed on schedule.

Initial Assessment

A geotechnical analysis revealed that although the upper soil layers had been replaced, a layer of muck remained at depth, posing significant risks of settlement and potential structural failure in the parking lot. The site required comprehensive soil stabilization to proceed with construction. Traditional methods of excavation and replacement were deemed too time-consuming and costly, necessitating an alternative approach.

Proposed Solution

A comprehensive soil stabilization plan utilizing AP Lift 475, a two-component polyurethane foam, was proposed. This solution was chosen for its ability to:

• Consolidate soil throughout the parking lot area.
• Provide a stable foundation for the structure.
• Avoid extensive excavation and soil replacement.

AP Lift 475 was selected for its high strength and excellent expansion properties, which would allow it to effectively fill voids and stabilize the muck layer without adding significant weight to the unstable soil.

Procedures

1. Establish a 5-foot grid pattern across the entire parking lot area.
2. At each grid point, inject 25 pounds of AP Lift 475 at a depth of 10 feet.
3. Inject an additional 25 pounds at a depth of 5 feet at each point.
4. Monitor soil consolidation and adjust injection amounts as needed.
5. Perform post-injection testing to confirm soil stability.

Results

The polyurethane injection solution proved highly effective, successfully stabilizing the soil without the need for extensive excavation. This approach allowed the construction schedule to be maintained, avoiding costly delays that would have been incurred with traditional soil replacement methods. Post-injection testing confirmed that the treated area passed all required stability tests, demonstrating the effectiveness of polyurethane injection for large-scale soil stabilization projects in commercial construction.

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A public park in New York had critical erosion issues at its waterfront staircase and adjacent beach, which were built over a landfill. Over the years, natural erosion pulled back sand, exposing uneven foundation areas and creating safety hazards for visitors. The partially buried concrete staircase exhibited significant subsidence and shifting soil, posing a threat to structural collapse. The New York City Parks Department required a rapid solution to stabilize the site before further degradation occurred.

Initial Assessment

The staircase and surrounding sand exhibited signs of differential settlement, likely due to uneven soil compaction and erosion. Technicians identified voids beneath the stairs and along the beachfront, with sand migration exacerbating instability. Traditional excavation or pier-and-casing methods were impractical due to limited access and the need to avoid displacing adjacent structures.

Proposed Solution

The team selected AP Fill 720 (a single-component polyurethane) for soil compaction/stabilization and AP 430 (a two-component foam) for structural void filling. AP Fill 720 addressed loose sand through permeation and consolidation, while AP Lift 430 filled critical voids beneath the staircase, providing lift and support.

Procedures

1. Stabilization Pattern: Injected AP Fill 720 every 4 feet at 6–8 feet depth to bond sand particles and prevent further migration.
2. Structural Foam Injection: Applied AP Lift 430 directly beneath the staircase’s granite slabs through strategic ports, filling void spaces with approximately 1 gallon per linear foot.
3. Final Treatment: Reserved excess AP Fill 720 to seal surface gaps around the staircase, preventing sand washout.

Results

The dual-material injection rapidly stabilized the waterfront staircase, eliminating soil migration and structural risk without closing the park. Compared to traditional heavy reconstruction, the approach cut costs by an estimated 97% and completed the work in under two weeks with minimal marine or community disruption. Post-repair inspections confirmed lasting results with no recurrence of erosion.

Want more information on stabilizing soil with polyurethane?

Initial Assessment

The management team at a corn syrup plant faced significant challenges with sinking concrete slabs supporting critical infrastructure, including water tanks and raw material tanks. The uneven slabs posed risks of tank instability and potential structural failure. A geotech contractor was engaged to perform void filling and stabilize the affected areas, ensuring a solid foundation for plant operations.

Proposed Solution

The technical team recommended using AP Lift 475, a two-component polyurethane foam that is ideal for void filling and slab stabilization. This material was selected for its high compressive strength, controlled expansion, and ability to effectively fill voids while providing robust support for heavy loads. The approach ensured minimal disruption, as it required no extensive excavation.

Procedures

1. Established a grid pattern to guide the placement of injection points in the affected areas beneath and around the water and raw material tanks.
2. Drilled holes through the concrete slabs at predetermined injection points to access the voids beneath.
3. Injected AP Lift 475 polyurethane foam into the drilled holes to fill voids and stabilize the soil beneath the slabs, ensuring comprehensive void coverage.
4. Patched drilled holes to restore the surface integrity of the concrete slabs.

Results

The void-filling project at the corn syrup plant was a success. The application of AP Lift 475 effectively filled all identified voids, stabilizing the concrete slabs and restoring a solid foundation. The stabilized areas now securely support the water and raw material tanks, eliminating concerns about sinking or tipping. The facility can resume full operations with confidence in the structural integrity of the tank foundations.

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In this episode of Groundworks' Stability Matters podcast, host Justin Bryant sits down with Alchatek CEO Stephen Barton and VP of Sales Andy Powell in Atlanta to discuss polyurethane solutions for geotechnical and leak seal issues. Stephen shares his journey from young concrete repair worker to industry leader, while Andy recounts the story of his career pivot to polyurethane expertise. They cover Alchatek’s product evolution, significant projects, and the importance of engineer outreach - offering insights on many industry challenges and key topics.

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Fifteen, two‑unit condominium buildings exhibited differential settlement and interior slab movement from loose organics and voiding, risking structural performance and livability. Continuous occupancy required a rapid, low‑disruption remediation strategy that delivered durable lift and stabilization. The job was completed by foundation repair specialists at Helicon.

Investigations confirmed loose to very loose near‑surface soils, voids at 3–8 ft below the surface, and active settlement beneath slabs and footings under service loads; full replacement was not viable due to resident displacement, extended schedules, and higher cost risk.

Proposed Solution

The experts at Helicon selected AP Lift 440 for its hydro‑insensitivity, rapid reaction, and ~80 psi compressive strength to permeate, densify, and lift with minimal downtime.

Procedures

1. Grid the interiors; mark piles, grout points, and quality control benchmarks.
2. Inject low‑mobility compaction grout to seal limestone and pre‑densify.
3. Install underpinning to ~36 ft, using predrill/sleeves to bypass clays.
4. Inject AP Lift 440 at 8/5/3 ft below land surface to lift slabs and encapsulate organics.
5. Monitor elevations/pressures; proof‑load and video‑verify.

Results

• Restored slab elevations and footing support with no resident displacement.
• Completion in days to weeks vs months for replacement.
• Approximately 80-90% cost savings versus full demolition/rebuild approaches.
• Durable, closed‑cell, water‑resistant stabilization for long‑term performance.

Want more information on polyurethane slab lifting?

Attention Geotech Professionals!

Alchatek is exhibiting at the DFI 50 conference in Nashville.

Where: Gaylord Opryland Resort & Convention Center

When: October 20-23, 2025

Click Here for Registration Info

Visit us at Booth 227 to explore our advanced polymer solutions, including single and two-component polyurethanes for soil stabilization, groundwater control, and deep foundation support, addressing challenges like unstable slopes, soft ground, and deep excavation shoring for geotechnical projects.

Learn How Alchatek Helps You

At Booth 227, you can meet with our experts to learn how Alchatek empowers your geotechnical projects with cutting-edge technologies.

We support geotech professionals in three key ways:

• Innovative Polymer Solutions: Our advanced polyurethane grouts and foams provide robust solutions for curtain grouting, point grouting, and ground improvement, ensuring stability for slopes, excavations, and deep foundations.
• Expert Technical Support: We offer comprehensive training and ongoing assistance, leveraging our proven track record with industry leaders to optimize your project outcomes.
• Environmentally Safe Materials: Our NSF/ANSI/CAN 61-certified, chemically inert polymers ensure safety and compliance in sensitive environmental areas.

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