Alchatek Blog

Unstable soils present significant challenges in civil engineering projects. Whether caused by erosion, improper compaction, freeze-thaw action, or decay of buried organic matter, loose and shifting soils undermine structural integrity. Together, these mechanisms prevent soil from remaining firmly in place. This necessitates methods to stabilize and strengthen the matrix. Geotechnical engineers must find solutions to reinforce the substrate and restore load-bearing capacity.

Polymer injection grouting offers an innovative approach, transforming loose soil into a strong, consolidated mass. These polymeric resins permeate porous soils and compact denser soils, then expand and cure in place. The resulting soil-polymer matrix has high compressive strength, stopping subsidence, erosion, and migration of fines. Alchatek's standard soil stabilization products and deep soil stabilization products provide specification-grade stabilization.

Polymer Foam Stabilization Mechanisms

• Permeation of loose sediments, gluing them into a firm matrix
• Displacement of water from eroded zones, reversing further erosion
• Filling of void spaces from decayed organics or poor compaction
• Adhesion to soil particles creates a strong substrate

Additionally, these foams are NSF/ANSI/CAN 61 certified for contact with potable water supplies. This enables environmentally safe use.

Performance Characteristics

Polymeric foams provide exceptional soil stabilization and foundational reinforcement. Key advantages include:

• Ability to permeate and treat loose or unstable soils in situ without excavation
• Ability to compact dense soils such as clay
• High compressive and shear strength, restoring structural load capacity
• Permanent stabilization without ongoing maintenance requirements
• Mitigation of subsidence or erosion with bonded soil matrix

When applied correctly, polymeric foams offer lasting soil stabilization and ground improvement. Alchatek case studies document successful performance for applications including commercial, industrial, new construction, and other geotechnical engineering projects.

Additional Guidance for Geotechnical Engineers

Specify these advanced soil grouting products to permanently resolve instability issues. They deliver rapid installation, minimal invasive work, and results that last. Let us provide guidance on product selection, specs, and installation techniques for your next soil stabilization project. Polymer grouting is an innovative, low-impact way to reinforce unstable ground.

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Polyurethane grouting is an essential process in construction and infrastructure projects with the need to lift structures, fill voids, and stabilize soil. While polyurethane grouting has been utilized for decades, advancements in technology and technique have enabled a new level of precision and control in modern grouting applications. Innovations in polyurethane injection methods and equipment allow design and construction teams to achieve highly accurate, consistent injections for maximum strength and longevity. 

Precision is critical in polyurethane grouting applications. Inadequate filling of voids or inconsistent distribution of grout can lead to structural instability, settlement, and even collapse. Precise injections ensure that soil is saturated, voids are filled, and slabs are leveled accurately. This provides uniform load distribution and protection against shifting, vibration, and erosion. Precision also prevents wasted materials and rework due to incorrect amounts or placement of grout. 

Modern polyurethane grouting equipment and techniques enable accurate monitoring and adjustment of grout injection rates, depths, pressures, and consistency. Some examples of modern technology include: 

• Hydraulic and Electric Pumps: Modern polyurethane injection equipment includes hydraulic or electric pumps. These pumps provide precise control over pressure and flow, ensuring a more uniform injection of grout material.
• High-Pressure Injection: Modern equipment can handle high-pressure injection, making it suitable for stabilizing deep structures and addressing challenging soil conditions. High-pressure injection ensures better penetration of the polyurethane grout.
• Remote Monitoring and Data Logging: Advanced systems come with remote monitoring and data logging capabilities when necessary. Operators can monitor the injection process remotely and collect data on pressure, flow, and other parameters for quality control and documentation.
• Compact and Portable Systems: Some advanced injection grouting systems are designed to be compact and portable, making them easier to transport to job sites and set up quickly.
• Safety Features: Modern equipment includes safety features such as shut-off valves and pressure relief mechanisms to protect both operators and the equipment itself.

Modern polyurethane grouting equipment has revolutionized construction and infrastructure project challenges, offering engineers and design teams an array of precision-driven advantages. The evolution of polyurethane injection equipment, including hydraulic pumps, pneumatic pumps, and computerized control systems has empowered design teams and application technicians to achieve precise outcomes.

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The terms hydrophobic and hydrophilic may not mean anything to the average person. But, to a contractor, these terms can mean a world of difference. Hydro means water while phobic means “to fear” and philic means “to love”. Alchatek offers both hydrophobic and hydrophilic polyurethanes, so it is important to be aware of the differences between the two types.  

Hydrophobic Polyurethanes

Hydrophobic polyurethanes naturally repel water (similar to the way oil would repel water and stay separate if you were trying to mix them in a glass). These products push water out of the area in question as they expand. Hydrophobics are used with catalysts which allow you to adjust the set time. They also have zero shrinkage after curing.

Check out these hydrophobic polyurethanes:

• Spetec PUR HighFoamer 
• Spetec PUR F400
• Spetec PUR H100 
• Spetec PUR H200 
• AP Fill 420
• AP Deep Lift® 420
• AP Lift 430
• AP Lift 435
• AP Lift 440
• AP Lift 475
• AP Soil 600 
• AP Fill 700
  
• AP Fill 720

Hydrophilic Polyurethanes

Hydrophilic polyurethanes naturally mix with water before curing (similar to the way gin and tonic mix thoroughly in a glass). This characteristic allows for a very strong chemical and mechanical bond, as water helps pull the material into the pores of the concrete. These products do not require a catalyst. You can pump them straight out of the pail.

Check out these hydrophilic polyurethanes:

• Spetec PUR GT350
• Spetec PUR GT380
• Spetec PUR GT500

Don't Oversimplify These Concepts

Don't get caught in the trap of oversimplifying hydrophilic vs. hydrophobic.  There are varying degrees of each (see chart below for more information on how this is measured).  

Some hydrophilic materials will keep absorbing water (10-15 times their original volume).  Others (such as Spetec PUR GT500) only absorb as much water as is necessary for their reaction and then they reject the rest.  Yes, hydrophilic gels will shrink like crazy in the absence of water, but Spetec PUR GT500 won't.  It is completely safe to use in a dry environment.

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When the residue of plants or animals is converted into soil, the process is known as decomposition. Bacteria, fungi, and worms break down this residue, taking nutrients from them and leaving the remaining portion. Organic molecules are broken down into simpler inorganic molecules. This biological process changes the makeup of the soil and can therefore lead to soil instability.

What are the causes of decomposition?

When soil has a high concentration of organic materials, the soil will naturally begin to decompose. Throughout this process of decomposition, the mass and form of these organic materials will change. Up to 90 percent of organic material will actually disappear over the course of the decomposition process, which means the mass of the soil will decrease substantially, reducing the quantity of available soil. The causes of decomposition can be broken into two main groups: manmade and natural. Trash pits or buried construction debris can cause manmade decomposition, while tree stumps and peat content can cause natural decomposition. 

What are the signs of decomposition?

Sinkholes, unstable soil, and low spots are all indications of soil decomposition. When soil begins to decompose and shift, it can compromise the integrity of buildings, foundations, and other manmade structures. 

How can decomposition be addressed?

In some cases, it is possible to dig up the cause of decomposition. For example, it might be possible to extricate a trash pit or old construction debris from the soil. However, in other cases, this simply isn’t feasible. You can’t easily extricate a trash pit after you have already built on top of it. If removal isn’t an option, the best solution is to envelop the area with polyurethane soil stabilization material. This process is known as encapsulation, and it essentially works to compact the area and reduce the amount of oxygen and water that can get to it, thereby helping to slow decomposition.

Want in-depth info on soil stabilization procedures and products?

What is freezing and thawing?

As the name suggests, a freezing and thawing cycle refers to a natural phenomenon in which soil freezes in cold weather and then thaws out again once the temperature warms up. Freezing and thawing in northern climates is good news for farmers, as it helps to loosen up the soil and reduce compaction, which makes it easier for crop roots to grow. However, for construction engineers and contractors, this process can prove to be incredibly problematic, especially if they are building on fine-grained soils with silt or clay factions, which are more prone to freezing and thawing.

What are the problems associated with freezing and thawing?

Essentially, freezing and thawing cycles accelerate soil instability. Soil with pores containing small particles of frozen water is known as permafrost. Building on permafrost is fine, as long as the soil stays frozen, but things become problematic once the permafrost begins to thaw. Freezing and thawing of permafrost cause soil to become soft and less compact. Subsequently, this causes structures, such as roadways, railways, foundations, and pipeline supports, to sink. Obviously, this can cause major headaches.

How can the problem of freezing and thawing be mitigated?

Alchatek soil stabilization products can be used to compact the ground and displace water particles in the soil pores. Depending on the soil type, this could prevent frost heave, resulting in a stronger, more consistent base to build on.

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Many types of infrastructure, including roads, bridges, and buildings, depend on compacted soil in order to stay in place. Therefore, in order for these structures to last, a specific degree of compaction must be achieved. When soil does not adequately compact, the problem is known as poor compaction, and that can lead to more serious issues. Concrete repair contractors always need to be on the lookout for signs of poor compaction which include settling slabs, cracking foundations, and dips in roadways and railroads.

What causes poor soil compaction?

There are a variety of causes of poor soil compaction. However, much of it boils down to soil texture and soil properties. Some soils are more prone to compaction than others. Excess soil salt content, high clay fraction soils, low pH soils, and soils with high water content tend to compact less favorably. It should also be noted that decisions made by construction contractors and their teams can also influence soil compaction. For example, failure to select proper compaction equipment or compaction materials can contribute to poor compaction. Furthermore, some areas are more prone to poor compaction than others, such as portions of soil set against a foundation.

How can poor soil compaction be corrected?

Luckily, poor compaction can be corrected. The solution is to strengthen the soil until it is properly compacted. As mentioned in the previous post, voids can be filled, soil consolidated, and water migration halted with Alchatek soil stabilization products. Once the bearing capacity of the soil has been increased with this process, then the structure can be lifted if necessary.

Want in-depth info on soil stabilization procedures and products?

What is erosion?

In geological terms, erosion can be defined as an exogenic process that moves a portion of the earth’s crust from one location to another. This includes a range of different processes, including water flow, wind, and even human action, that move dirt, soil, rock, etc. They are called exogenic processes because they originate outside of the earth’s crust, or externally. In more practical terms, erosion can best be described as the way in which the earth is worn away by water, wind, or ice. So when a river carves a canyon out of stone (such as when the Colorado River carved out the Grand Canyon in Arizona over the course of so many years), that is an example of erosion. The formation of sand dunes by the wind moving across the desert is also an example of erosion, as are changes in rocks along a shoreline due to the constant thrashing of waves. 

Why does erosion cause unstable soil?

You’ve probably heard that erosion is dangerous because it causes unstable soil. It is important to remember that the consequences of erosion can potentially be dramatic, causing landslides and structural damage. After investing money in the construction of a building, the last thing you want is for unstable soil to put the whole project at risk. 

How can erosion be repaired?

Voids can be filled, soil consolidated, and water migration halted with Alchatek soil stabilization products. Once the bearing capacity of the soil has been increased with this process, then the structure can be lifted if necessary.

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Unstable soil can be defined as soil that will not stay in place on its own and therefore requires extra support. It should be noted that unstable soil can threaten the stability, security, and safety of infrastructure and can damage, degrade, and even destroy a number of structures, such as buildings, bridges, and roads.

Let's look at the four main causes of unstable soil...

Erosion

Erosion refers to processes in which external elements (wind, water, etc.) remove soil or rock from a certain location and transport it to another location. There are a variety of different erosion types, including river and gull erosion, wind erosion, and erosion attributed to human activity. Erosion ultimately destabilizes soil and can lead to landslides and sinkholes.

Poor Compaction

One of the most common causes of unstable soil is poor compaction. In some cases, certain types of soil are simply very loose and subsequently not compact. The cause of this is typically an imbalance of mineral pieces, organic matter, air, and water. For example, clay soil with very high moisture content will inevitably become unstable, as it will be incredibly difficult to compact. Similarly, soils with high sand content will be difficult to compact.

Freeze/Thaw

Processes of freezing and thawing essentially accelerate erosion processes. Cold weather freezes moisture trapped in tiny cracks. When this water freezes, it expands, subsequently pushing on the rocks and breaking them into smaller pieces. As processes of freezing and thawing continue, rock and sediment are continually broken down.

Decomposition

When soils contain a high concentration of organic materials, such as topsoil and plant matter, they will decompose, subsequently causing them to become unstable. This is because organic materials rapidly change form and mass as they decompose in the soil. In fact, up to 90 percent of organic material will disappear over the course of the decomposition process.

Fortunately, stability can be restored to soil with ultra-low viscosity polyurethane resins. Foaming and permeation polyurethanes can mitigate the damage done by processes of erosion, decomposition, freezing, and thawing, as well as help to rectify compaction problems. When it comes to unstable soil, you can’t afford to take a risk. Stable soil is crucial to maintaining secure structures.

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An Oakwood, Georgia corrugated metal pipe rehab job, involving the replacement of the end caps, resulted in soil migration through the new joints. This in turn led to depressions in the asphalt road above. The City of Oakwood public works department called in Atlanta-based geotech specialists LiftitRite to assess and repair the pipe and the soil.

Powerful Polymer

Alchatek's AP Fill 700 was an easy choice for this project. AP Fill 700 is a single-component, water-activated, hydrophobic polyurethane resin that is highly effective in cutting off high-flow underground leaks, filling voids, and stabilizing soil. It is also NSF/ANSI/CAN 61 approved for contact with drinking water.

Painless Procedure

The technicians began by stuffing the larger joints with resin-soaked Oakum to create an impermeable gasket. Then, injection ports were installed adjacent to the joint in a clock pattern. The crew injected AP Fill 700 until the joints were fully sealed and permeation of the surrounding soils was achieved.

Wanting to ensure a “belt and suspenders” repair was done, they opted to inject AP Fill 700 through the top of the road as well via injection probes. The probes were driven down to depths coinciding with the tops and sides of the culvert pipes. These injections ensured that all voids and shifted soils caused by the pipe infiltration were filled, permeated, and stabilized - thus preventing any future road depressions or dropouts.

Rapid Result

City of Oakwood officials were extremely pleased to see this issue remedied in just 2 days via an effective and affordable solution that involved minimal traffic disruption and zero excavation. 

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As a geotechnical engineer, you understand the importance of stable supporting soil around structures. When the supporting soil becomes unstable, the stability of the structure is at risk. Common causes of unstable soil include erosion, poor compaction, freeze/thaw cycles, and decomposition of organic materials within the soil. Fortunately, soil can be stabilized with high-strength polyurethane. Whether you need a product recommendation for soil stabilization specs, or you're seeking accredited continuing education on this subject, Alchatek has you covered.

Product Recommendations for Soil Stabilization Specs

Experienced members of the Alchatek technical support team consult with engineers on a regular basis. When you call for assistance, you'll be connected to someone with extensive product knowledge and years of on-the-job experience out in the field. If you need a product recommendation for polyurethane soil stabilization specifications, call 404-618-0438 and ask for a geotechnical expert. 

Accredited Presentations

Alchatek offers one-hour CE/PDH accredited presentations on a variety of subjects, including geotechnical applications for polyurethane. These presentations are available online via videoconferencing or in person in a lunch-and-learn context. Geotechnical presentations are always given by an experienced expert who can field pretty much any question your team may have on the subject.

Click the button below and fill out the form to request an accredited presentation.