Alchatek Blog

This post is part of the Alchatek Contractor Lens series, featuring views, news & case studies written by our customers. This article was written by Jay Silver and originally posted on the Helicon blog.

When Excavation Gets Tight, Think Beyond Sheet Piles

Excavating near an existing structure — like a home, commercial building, or utility line — often requires soil support to avoid collapse or damage. For decades, the go-to solution has been sheet piling: driving steel sheets into the ground to create a temporary shoring wall.

But sheet piles come with serious downsides:

• High cost
• Vibration risks to nearby structures
• Heavy equipment needs
• Limited accessibility in tight areas

Today, there’s a smarter, faster, and more cost-effective alternative for excavation support: polyurethane injection permeation grouting.

What Is Polyurethane Grout Injection for Excavation Assist?

Helicon uses a permeation grout called AP Soil 600, a low-viscosity polyurethane resin, to stabilize soil and build a temporary underground wall. This non-expanding material seeps into fine-grained soils (like sand), then hardens into a concrete-like mass — turning unstable ground into a solid excavation shoring wall.

This “grout curtain” supports the soil adjacent to your dig site, providing excavation assist without the need for steel sheets or heavy machinery.

Common Use Cases for Polyurethane Shoring Walls

Excavations next to homes or commercial buildings

Tight-access job sites where pile driving equipment won’t fit

Urban infill projects with vibration-sensitive neighbors

Value-engineered alternatives to high-cost sheet pile installation

Projects with depth requirements up to ~15 feet

Sheet Piles vs. Polyurethane Injection

How It Works: The Grout Curtain Process

1. Plan and Mark
The contractor provides excavation depth and layout. Helicon’s team maps out injection lines using stakes or string to ensure precision.

2. Drill Injection Holes
Using compact equipment, injection rods are installed at a slight 3–5° angle away from the excavation. Rods are spaced 18″ apart, and for depths >8 feet, a second staggered row is added 18″ behind the first.

3. Inject AP Soil 600 Grout
Each rod is used to inject grout in 1-foot intervals from bottom to top:

• Start 2 feet below planned excavation depth
• Inject 1 gallon per vertical foot
• Grout permeates and hardens in ~2 minutes per foot
• Stops 1 foot below surface to avoid breakout

The non-expanding grout permeates the soil, turning it into a rigid, cohesive wall capable of holding back earth during excavation.

4. Excavate Safely
Once cured (typically within 24 hours), excavation can begin — but mechanical equipment must stay 2+ feet away from the grout wall. Final trim is done by hand or hydro-vac.

Soil Types That Work Best

AP Soil 600 is designed for permeation, not expansion. It’s ideal for:

✅ Sand
✅ Fine silts
✅ Granular soil types

⚠️ Less effective in:

• High plasticity clay (which resists permeation and may not need shoring)
• Organic material or very dense clay (which can fracture or lens)

That’s why soil boring reports or geotechnical testing are important for project design.

Depth Recommendations

Helicon’s polyurethane grout walls are most effective up to 15 feet. Beyond that, multiple injection rows become inefficient, and other structural shoring may be needed.

Cost Savings & ROI

Switching from sheet piles to Helicon’s polyurethane grout method can save:

• Tens of thousands on residential jobs
• Up to six figures on larger commercial projects

Savings come from:

• No need for steel or removal
• Smaller crews and equipment
• Shorter install times
• No costly vibration damage

Combine with Underpinning When Needed

When adjacent structures need more than soil support, Helicon can pair permeation grouting with:

• Push piers (steel-driven deep supports)
• Drilled piers (poured concrete or steel)

This hybrid approach is ideal for:

• Older buildings
• Structures with active settlement
• High-load foundations near deep excavation

Real-World Examples

On a commercial project, the contractor and engineer originally planned to use traditional sheet piles for shoring to support the foundation of a commercial building. Helicon collaborated with the engineer to develop a value-engineered alternative: a polyurethane grout curtain combined with steel push piers installed under the building’s foundation. The shoring wall and underpins were completed within five days, excavation proceeded safely, and the client saved over $300,000 compared to the original sheet pile proposal.

On a recent project with access constraints, Helicon installed a polyurethane grout curtain within 2 feet of a residential foundation. Traditional sheet piles weren’t an option due to equipment access and budget. The wall was in place within two days, excavation followed safely, and the client saved over $70,000 compared to a sheet pile proposal.

Safety Guidelines

• Injection starts 2’ below excavation depth
• Do not excavate within 24” of cured grout with equipment
• Always hand dig near the grout wall
• Excavation limit line should be marked 33” back from rods (accounting for rod angle)

Why Engineers and Contractors Choose Helicon

• Florida-based foundation experts
• Proven track record in geotechnical solutions
• Fast mobilization and project turnaround
• Seamless integration with GCs, engineers, and owners
• Full service: injection + underpinning + stabilization

Optimize Your Excavation Support Plan

If you’re a contractor, builder, or geotechnical engineer working on an excavation project in tight quarters, don’t default to sheet piles. Helicon’s polyurethane injection method is often:

• Faster
• Cheaper
• Cleaner
• More flexible

Helicon specializes in value-engineering shoring solutions that reduce project costs and risks while maintaining structural safety and soil integrity.

Let’s Put Your Excavation Project on Solid Ground

Have a project where you’re excavating near a structure? Let’s collaborate. Helicon offers:

• Free project consultations
• Soil review and injection layout planning
• Rapid response teams for tight timelines

Want more information on Alchatek's geotech solutions?

Gerace Construction undertook a gate replacement project at the Tom Miller Dam in Austin, Texas. While working on Large Gate #6, and after installing a needle beam cofferdam system to lower the water level, a continuous wet spot was discovered under the metal gate sill. This indicated a crack in the concrete extending under the sill plate. Sealing the leak was necessary to prepare and coat the steel sill plate, which was crucial for the overall gate replacement.

Initial Assessment

The primary challenge was water seeping through a crack, less than one linear foot in length, located in the concrete beneath the steel gate sill. The cofferdam system had created approximately 18 feet of head pressure upstream, with the water level pumped down about two feet below the sill. As per the project specifications, a dry surface was required to apply coatings to the steel sill plate.

Proposed Solution

Alchatek recommended Spetec PUR H100 to seal the crack. This hydrophobic polyurethane resin was chosen for its ability to rapidly seal cracks with reasonable water flow and minimal anticipated movement. The solution involved injecting the resin into the crack to create a watertight seal, allowing the steel surface to dry for coating application. Alchatek also provided an on-site representative during the injection process, as required by the project specifications.

Procedures

1. Preparation:

• The contractor established the cofferdam system and lowered the water level to expose the leaking area.
• Injection ports were installed along the crack at 12-inch centers on alternating sides.

2. Injection Process:

• Spetec PUR H100 mixed with Alchatek Gen Cat was injected into the crack using positive displacement equipment capable of maintaining a minimum pressure of 250 psi.
• Injection began at the lowest port and continued sequentially upward until grout filled the crack and seepage ceased.
• Inline pressure was monitored throughout to ensure it did not drop below 190 psi during injection.

3. Post-Injection:

• The injected resin was allowed to cure fully, forming a watertight seal.
• Excess surface seal material was removed, and the repaired area was inspected to confirm no further water intrusion.
• The injection ports were removed, and holes were patched flush with hydraulic cement as per project guidelines.

Results

The application of Spetec PUR H100 successfully sealed the leak under the steel gate sill, allowing Gerace Construction to proceed with surface preparation and coating application. The fast-reacting properties of Spetec PUR H100 minimized delays while ensuring long-term durability against water infiltration. The Lower Colorado River Authority (LCRA) engineering staff approved of the product, and the Alchatek representative provided the required on-site supervision ensured compliance with all quality assurance measures, resulting in a successful repair that restored functionality and structural integrity to Gate #6 at Tom Miller Dam.

Want more information on polyurethane leak seal materials?

The PX-7 incorporates a valving rod to mechanically purge the mixed material from the mixing module at the end of each shot; eliminates the need for solvent flushing or air purge. It comes standard with a precision machined coupling block made from high strength steel. Manufactured by Polyurethane Machinery Corporation.

Key Features

• Economically Priced
• Mechanically Self Cleaning
• Solvent Free
• Airless Atomization
• Internal Impingement
• Machined Coupling Block
• Precision Ground, Single Piece Valving Rod
• Rebuildable Manual Valves
• Stainless Steel Hardened Gun Block
• CE Certified

Want more information on the PX-7 Mechanical Purge Gun?

Gerace Construction was contracted for a project at the Pat Mayse Dam in Paris, Texas, to repair and seal leaks in the discharge conduit. The project involved addressing cracks and weeps within a concrete pipe structure. The United States Army Corps of Engineers (USACE) was overseeing the project, requiring strict adherence to specifications, including the presence of a manufacturer’s representative on-site during the grout injection process.

Initial Assessment

The primary challenge was to stop active water leaks within the concrete conduit pipe. A site visit identified the locations of cracks and weeps, as documented in the photo report included in the specification. The photos showed typical leaking monolith joints on the sides and top of the structure, as well as leaking monolith cracks. These leaks required a solution that could effectively seal actively flowing water in both vertical and horizontal orientations.

Proposed Solution

Alchatek proposed the use of Spetec PUR F400, a flexible polyurethane grout, to address the leaking cracks. This product was selected for its ability to penetrate narrow cracks, its flexibility to accommodate movement, and its compatibility with wet concrete surfaces. The plan included supplying the necessary materials, equipment, and a qualified manufacturer’s representative to supervise the installation.

Procedures

1. Preparation:

• Injection ports were installed along the identified cracks and weeps in the concrete pipe.
• Holes approximately 12 inches deep were drilled at a 45-degree angle.

2. Injection Process:

• Spetec PUR F400, along with Alchatek Gen Cat to control reaction time, was injected through the installed packers using a suitable pump.
• Injection began at the lowest packer for vertical joints or cracks, working upwards.
• The process continued until the grout traveled between packers, and the leaks were sealed.
• An approved epoxy adhesive paste was used to seal the surface of the cracks, allowing grout to travel.

3. Post-Injection:

• Re-injection was performed to ensure all voids were properly sealed off.
• Each installed packer was re-injected with a small amount of water to allow the resin in the drill hole to react.
• The injection ports were removed and cut flush, and packer holes were filled with approved epoxy paste.
• Once cured, the remaining materials were removed from the concrete surface with a wire brush or handheld grinder.

Results

The Alchatek solution, implemented by Gerace Construction, effectively sealed the cracks and stopped the leaks in the Pat Mayse Dam discharge conduit. The on-site presence of a qualified manufacturer’s representative ensured the proper application of the product, meeting the requirements of the USACE. The project was completed in accordance with the specifications, resulting in a successful repair and improved structural integrity of the dam’s discharge conduit.

Want more information on polyurethane leak seal materials?

The Cave Buttes Dam, located in Phoenix, Arizona, required modifications that involved installing a 60-inch diameter steel conduit pipe beneath the dam through bedrock. During tunneling operations, a 15-foot-wide fault zone containing water and composed of clay was encountered. After the excavation and grouting of the annular space between the pipe and the rock with cementitious grout, leaks began to emerge from some of the welded grout packer plugs. SSC Underground was the contractor for this project, with engineering oversight provided by AECOM and the U.S. Army Corps of Engineers.

Initial Assessment

The primary issue was leaking grout plugs, which were 2-inch diameter, straight-threaded plugs welded into place after the initial grouting process. These plugs exhibited varying degrees of water seepage, with flow rates estimated at a few gallons per minute. The leaks were attributed to anticipated movement between the steel pipe and the surrounding rock due to temperature changes and vibrations. Based on these conditions, a flexible chemical grout was determined to be the best solution to seal the leaks while accommodating future movement.

Proposed Solution

Alchatek recommended injecting Spetec PUR F400, a flexible polyurethane grout, to seal the leaks. This grout was selected because of its ability to bond effectively while maintaining flexibility to withstand differential movement between the steel pipe and surrounding materials. The plan involved drilling into the existing grout plugs and injecting Spetec PUR F400 through packers to confine the grout and ensure a complete seal. The project utilized packers for controlled injection and a Titan Impact 440 pump to deliver the grout. Alchatek Gen Cat was used to manage the grout’s reaction time based on the specific site conditions.

Procedures

1. Preparation:

• The team drilled into the center of each leaking grout plug to create access points for injection.
• Packers were installed into these drilled holes to facilitate the controlled injection of the grout.

2. Injection Process:

• Spetec PUR F400 was injected through the packers using a Titan Impact 440 pump.
• Alchatek Gen Cat was added to the grout mixture to adjust reaction times as needed.
• The injection process was monitored to ensure proper confinement of the grout within the leaking areas.

3. Post-Repair Monitoring:

• After sealing each leaking port, inspections were conducted to confirm the cessation of water infiltration.
• New leaks that emerged from previously sealed or new locations were identified for subsequent treatment.

Results and Conclusion

The initial injection process sealed most of the identified leaking grout ports, effectively stopping water infiltration at those locations. However, water subsequently found new paths, resulting in additional leaks from previously sealed ports. The team used the same materials and procedures to address these additional leaks through follow-up injections. Ultimately, all leaks were successfully sealed, restoring the integrity of the steel pipe installation.

Want more information on polyurethane leak seal materials?

Attention Engineers!

Alchatek is exhibiting at the International Conference on Transportation & Development and the International Airfield & Highway Pavements Conference, held at the Renaissance Phoenix Glendale Hotel & Conference Center, 9495 Entertainment Boulevard, Glendale, Arizona 85305, from June 8–11, 2025. Visit us at Booth 201 to explore our advanced polymer solutions, including two-component structural polyurethanes for concrete leveling and void fill and one-component polyurethanes for soil stabilization and leak seal, addressing infrastructure challenges like cracked pavement, sinking slabs, leaking culverts, and unstable soil for DOT and airport projects.

Learn How Alchatek Helps You

At Booth 201, you can meet with our experts to learn how Alchatek supports your infrastructure initiatives with our environmentally friendly NSF/ANSI/CAN 61-certified technologies.

We benefit engineers in three key ways:

• Connections with Experienced Contractors: We partner you with skilled, vetted contractors trained in our advanced polymer solutions for high-quality project execution.
• PDH Credit Lunch and Learn Presentations: We offer in-office presentations providing Professional Development Hours (PDH) credits, equipping your team with the latest geotechnical and infrastructure repair techniques.
• Assistance with Project Specifications: Our experts collaborate to develop precise, project-specific specifications, ensuring compliance and optimal performance.

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The City of Sand Springs, Oklahoma, identified a foundation leak in Bay 10 of the Shell Lake Dam, necessitating repairs to ensure the dam’s structural integrity. The city’s Public Works Department contracted with a qualified firm to address the issue, and Keithline Engineering Group was retained to provide engineering design and oversight for the project.

Initial Assessment

An inspection by Keithline Engineering revealed an active boil, or leak, in the concrete footing of Bay 10. The leak, measuring approximately 5” by 7”, exhibited increasing water movement and was deemed a priority for repair. The engineering team determined that the water was likely traveling between the concrete footing and the porous sandstone underlayment before exiting through the hole in the concrete. This leak was transporting a small amount of material under low pressure. It was also determined the owner had made prior unsuccessful attempts to seal the area with bentonite.

Proposed Solution

After consulting with Alchatek, Keithline Engineering specified a leak-sealing solution centered around the injection of Spetec PUR H100. Alchatek recommended this hydrophobic polyurethane grout for its ability to expand and create a dense, impermeable seal upon contact with water. The repair strategy involved drilling through the concrete and injecting the grout into the concrete/sandstone interface to create a grout curtain. This approach aimed to stop the leak at its source and prevent further water migration.

Procedures

1. Preparation:

• Hammer-drilled 1/2-inch injection ports were installed into the concrete foundation at designated locations.
• Saturated oakum rope or hydraulic cement was applied to temporarily plug the hole during the injection.

2. Injection Process:

• Spetec PUR H100 was injected through installed packers using positive displacement pumps.
• Injection proceeded until the grout formed a complete polyurethane barrier around the boil and stopped water infiltration.
• The process included monitoring grout expansion and ensuring proper confinement within the concrete/sandstone interface.

3. Post-Sealing:

• Following the injection, all nipples were removed, and drilled holes were patched with hydraulic cement to a minimum depth of 12 inches.

Results and Conclusion

The injection grouting successfully sealed the foundation leak in Bay 10 of Shell Lake Dam. Spetec PUR H100 formed a durable polyurethane barrier, effectively stopping water flow and preventing further erosion of material from beneath the dam footing. The swift and effective repair was achieved in a matter of hours. Restek, Inc. precisely executed the specifications. The result is a solution that preserves the long-term structural integrity of the Shell Lake Dam, showcasing the value of proactive maintenance in preserving critical water resources.

Want more information on polyurethane leak seal materials?

A Utah-based geotech specialist partnered with a general contractor to address a critical DOT infrastructure challenge involving the replacement of an existing culvert on a major roadway in Utah. The project involved the installation of precast concrete slabs on both sides of the box culvert, designed to create a seamless transition from the culvert to the compacted road base.

Site Investigation and Challenge

During the design phase, engineers identified that constructing a compacted road base beneath the slab would inevitably leave voids underneath. These voids posed a risk of uneven support and potential rocking of the slab when subjected to heavy traffic load.

Proposed Solution

To address this, ¾” holes were drilled four feet apart to allow for injection rods to be inserted through the slab. The foam selected for this slab was AP Lift 440 structural foam due to its rapid expansion and high strength needed for DOT projects. This foam expands 17-19 times its original volume within 8-10 seconds of injection, ensuring comprehensive void filling. Dial indicators were used to ensure that there was no vertical movement of the slab during the injection process.  

Results and Conclusion

The entire operation was executed in approximately three hours, utilizing about 400 lbs of structural foam. This successful application filled all of the voids, providing uniform support for the precast slabs and enhancing overall road stability. The rapid curing properties of the foam allowed for swift project completion with minimal disruption to traffic.

Want more information on stabilizing soil with polyurethane?

Mid South Concrete Lifting successfully executed an emergency repair operation at a Tennessee Valley Authority (TVA) lift station in New Johnsonville, Tennessee. What began as a new construction project quickly required an urgent repair when significant leakage was discovered at multiple joint locations immediately after installation. The contractor's rapid response and innovative solution prevented extensive water loss and potential environmental impacts.

Initial Assessment

The investigation began when facility managers discovered several critical issues:

• Structural weaknesses detected in multiple joint locations
• Massive water loss occurring within 24 hours of installation
• Thousands of gallons of water escaping through compromised joints
• Environmental concerns due to uncontrolled water discharge

The severity of the situation demanded emergency intervention to prevent continued water loss and potential damage to surrounding infrastructure.

Proposed Solution

After technical evaluation, Spetec PUR F400 was selected as the optimal solution due to its superior characteristics:

• Rapid-curing formulation for quick deployment
• Excellent adhesion properties for joint sealing
• Water-reactive chemistry suitable for wet conditions
• High structural strength for long-term durability
• Environmental compatibility for water infrastructure

Procedures

1. Complete dewatering of the lift station
2. Technical team rappelled into the structure
3. Systematic injection of Spetec F400 at all compromised joints
4. Progressive sealing to ensure complete joint stabilization

Results and Conclusion

The emergency repair proved successful on multiple fronts:

• Complete elimination of water loss through compromised joints
• Restoration of structural integrity to all sealed areas
• The system returned to full operational status within 24 hours
• Long-term solution achieved with minimal downtime
• Cost-effective resolution compared to alternative repair methods

The project demonstrated the effectiveness of chemical grout injection as a rapid response to critical infrastructure leaks. It successfully prevented ongoing water loss while providing a durable, long-term repair solution.

Want more information on sealing leaks with polyurethane?

Suburban Basement was hired to address significant voids beneath a slab foundation residence in Roseville, Michigan. The voids were suspected to have been caused by a compromised sewer line under the bathroom shower, resulting in extended leakage affecting a substantial portion of the home’s foundation. After plumbers discovered the issue, a local property restoration company managing the overall project engaged Suburban Basement.

Initial Assessment

The extent of the voids was assessed using 4-foot-tall plow markers as probes. The voids almost entirely engulfed these probes, indicating severe foundation undermining. The situation required a solution that could effectively fill large voids, bond with both soil and concrete, and perform well in wet environments.

Proposed Solution

Suburban Basement proposed using Alchatek's AP Lift 430 for the void filling. This material was chosen for its high expansion rate, making it cost-effective for large voids. Its ability to bond with soil and concrete, perform in wet conditions, and displace residual moisture from the plumbing leak made it ideal for this application.

Procedures

1. Drilled a systematic grid pattern of holes throughout the residence
2. Employed controlled injection shots to avoid excessive product usage and prevent lifting
3. Carefully filled all voids without causing any lifting of the foundation

Results

The project restored the foundation's integrity, filling all voids within a day. This efficient execution led to significant time and cost savings for all parties. The insurance company reduced relocation expenses, the restoration company delivered ahead of schedule, and the homeowners returned to their structurally sound homes earlier than expected. The outcome satisfied all stakeholders, demonstrating the effectiveness of the chosen solution in addressing complex foundation issues promptly and efficiently.

Want more information on geotechnical polyurethanes?