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, a clay soil with very high moisture content will inevitably become instable, 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, it will decompose, subsequently causing it to become unstable. This is because organic materials rapidly change form and mass as they decompose in 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, and 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.

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

As I said previously in my blog post Stop Erosion Through Your Seawall with Polyurethane:

When it comes to seawalls, there is a lot more to learn than meets the eye. Seawalls are like living, breathing things: especially in the way that they are designed to function. But like all living breathing things, they have a finite lifespan. For many of them, it's a mere 20 – 30 years. Depending on where you live, replacing a seawall can cost anywhere from $150 to $500 per foot. That's enough for some homeowners to choose to move instead of rebuilding their seawalls. Today however, signs of seawall distress can be solved before they get too bad through the application of polyurethane grouts to seal leaks, fill voids, and stabilize the surrounding soils.

Here's a glimpse of polyurethane seawall repair in action. Hang 'Em High Charters in Key Colony Beach, Florida discovered massive voids inside their seawall. Watch closely as they are repaired with AP Lift 475 foam...

Want more info on polyurethane seawall repair?

In a recent media interview, I was quoted as follows: “Ultimately, the customer is the property owner, somebody who’s got a problem. Even though we’re selling to contractors, we kind of all have to be on the same page.” That view has motivated us to pay close attention to what contractors, engineers AND property owners are most concerned about regarding the use of polyurethane. Over the years, we’ve noticed three main questions that arise over and over again:

1. Are the polymers strong enough?
2. Are they easy to install?
3. How quickly can the job be finished?

So we’re going to take a look at each of these three core issues in detail…

Powerful Polymers

Concrete Leveling Foams

In my blog post Slab Jacking With Polyurethane Foam – How Strong is Strong Enough?, I point out that the National Home Builders Association and the International Building Code list stiff clay as having a 4,000 lbs per square foot load bearing capacity and crystalline bedrock as having 12,000 lbs per square foot capacity. Our lifting foams have load bearing capacities of 7,200 to 14,000 lbs per square foot after curing in a free rise state. 

When Alchemy-Spetec foams cure in a confined state underground, that bearing capacity has been known to be even stronger. Testing data in the lab shows that our lifting foams will increase in compressive strength: In a space confined 25% by volume there will be an increase of 31% in psi and in a space confined by 75% there will be a 79% increase in the psi.

The Alchemy-Spetec lifting foams are used to level airport slabs supporting jumbo jets, heavy equipment, building slabs supporting tremendous loads, and even railway slabs supporting the heaviest freight trains.

Leak Seal Resins

Alchemy-Spetec leak seal resins have been used in many applications, including shutting down a 2-million gallon per day leak at a water treatment plant. The leak was reduced from 1,700 gallons per minute to just 10 gallons per minute (attributed to the many vintage valves and fittings that are still present at the plant). They are also used in other applications such as curtain wall grouting.

Soil Stabilization Resins

Unstable, eroded, or loose soil around infrastructure can result in settlement and damage to the structure. Voids can be filled, seawalls remediated, soil consolidated, and water migration halted by injecting the soil with Alchemy-Spetec soil stabilization resins. In my blog post Soil Stabilization Products Prevent Cave In Beneath Busy Intersection, I profiled a powerful example of AP Fill 700 in action. Inspectors in Orange County, Florida found a depression in the middle of a busy intersection that was due to an underground sewer line that wasn’t sealed. Water and eroding soil were infiltrating the sewer line causing the road to slowly settle. The resulting voids around the drainage structures had the potential to grow larger, eventually resulting in a complete cave-in of the roadway. A point repair was done from within the leaky pipe to stop the infiltration but they feared it was only a matter of time before the road gave way. We devised a solution for their crew to use the versatility of AP Fill 700 as both a permeation and void filling grout.  To keep the lane closure down to a bare minimum of time, the project was successfully completed on two separate Saturdays. The voids were filled, the loose soil was solidified, and only minor asphalt patching was required to make that area smooth for traffic again.

Orange County Utilities Supervisor Paul Morrison has been enthusiastic about AP 700 since the first time he tried it out on a severe manhole leak, when he had this to say…

“Based on our extensive prior experience, we expected to use at least five to ten pails to stop this leak. With Alchemy-Spetec material we were able to do the job with 1/10th of that amount. Their product will save our crews a lot of time and labor, and save the taxpayers of Orange County a lot of money.”

AP Soil 600 is one of the most versatile permeation grouting products on the market. It can be characterized by its single component, moisture activated, hydrophobic, and low viscosity qualities. It can fortify sandy soil to strengths approaching 2,000 psi.

Painless Procedures

As I never fail to point out, application procedures for Alchemy-Spetec products are relatively painless. The installation process is very clean compared to replacing the structure or repairing with cement grout.  Polyurethane is lighter than cement, so it doesn’t sink. Alchemy-Spetec products do not shrink after installation. The closed cell structure makes these resins impermeable. 

Rapid Results

Application of polyurethane is usually less expensive than replacement. Polyurethane concrete repair is also less time consuming. Any structure repaired with Alchemy-Spetec products is usually ready for use 45 minutes after application.

There you have it – the three most critical issues for contractors, engineers and property owners regarding polyurethane concrete repair. By staying focused on these concerns we constantly remind ourselves WHY we do what we do. We do it for YOU.

Want in-depth info on polyurethane infrastructure repair resins?

As a technical consultant, I often assist customers when they're put to the test with difficult jobs. That's why we go out of our way to provide the powerful polymers and painless procedures they need to achieve the rapid results those projects require. For an in-depth dive into what we mean by powerful, painless and rapid - see this blog post I wrote awhile back. Then watch the video below to see powerful polymers, painless procedures, and rapid results in action... 

Want more in-depth info on Alchemy-Spetec products?

Salt corrosion, tidal action, currents, boat wakes, storm surges and sometimes hurricanes all deliver a constant beating on the seawall. Contrary to popular opinion, many of the forces also come from the side of the wall facing the land. Did you realize that rainfall/storm events create more hydrostatic pressure than rising and falling tides? Every time it rains or the irrigation system runs, and every time the tide goes out; all of the groundwater above the waterline needs a place to vent or equalize. Massive pressure can build up if that water is trapped, making it impossible for it to drain into the sea or storm water system. That is a recipe for disaster which can easily be avoided with proper surveillance. Let's take a look at some of the external signs a seawall is in need of repair... 

Small Sinkholes Near the Wall

In landscaped areas, evidence of soil erosion is often quite obvious.  In this photo you can see that there is a small sinkhole developing at the inside corner of the seawall.  Some types of grass will actually keep larger sinkhole from being seen.  So check thoroughly.

Voids Near the Edge of the Wall

Obvious settling soil should have gotten the property owner’s attention in this case.  Too often, they ignore the warning signs until something more catastrophic occurs.

Cracking Concrete

Here, ground penetrating radar revealed loose soil zones beneath this concrete apron outside of a fish processing facility.  The steel sheet pile walls were losing soil and huge voids had developed.  Evidence of cracking concrete was not enough to get their attention as is often the case.  However, when a Lull forklift went through the slab, everything but foot traffic was prohibited from being on the apron.

Damage to Structures Up to 100 Feet Away

Capillary pathways of leakage can be found over 100 feet away from the visible leak, depending on the soil matrix.  The back of this pool deck had dropped about 6” already as the yard slumped towards the leaking seawall.

Causes of Seawall Damage – An Overview

Correct construction of a seawall will include a drainage system to handle the bulk of the water that comes from rain in addition to check valves, weep holes, or seams to handle the daily influx and outflow from tide and wave action. Although these systems are designed to retain the soil behind the seawall, over time the materials degrade or can be disturbed by settling.

This is a direct symptom of normal wear and tear from the natural environment and is unavoidable. The result is a loss of soil and the inevitable sinkholes and / or low spots that will occur along the wall. Other times, the weep holes and vents become clogged and the water has no way to escape except to force its way down and out from underneath the base of the wall. When this occurs there will again be sinkholes and sometimes wall failure.

Conclusion

When signs of sinking ground are observed, you can almost be sure there are voids below that are that are not seen from the above the surface easily and are indeed dangerous. Sometimes these voids can extend below an adjacent patio, dock, or pool deck, causing those to sink and crack as well. The key to keeping those problems at bay is to actively anticipate them.

If you live along the water, it is always going to be man against nature. That seawall is keeping your property from damage and from disappearing altogether. The key to extending the life of your seawall is the advanced polyurethane technology from Alchemy-Spetec. For more on the repair process itself, read An In-Depth Look at Polyurethane Seawall Repair. It's fast; clean, easy to install, and most of all, effective.

Want more in-depth info on polyurethane seawall repair?

In the previous post, An In-Depth Look at Polyurethane Seawall Repair – Part 1, we looked at causes of seawall deterioration, typical evidence of deterioration to look out for near seawalls, and the three most common seawall repair options: excavation, cement grout repair and polyurethane repair.

Now we’re going to take a deep dive into the qualities, applications and advantages AP Fill 700 – the Alchemy-Spetec product most typically used for seawall repair. We’ll also share a case study on a seawall crisis at an upscale marina that was resolved by contractors using AP Fill 700.

AP Fill 700 Advantages

AP Fill 700 is a single component, water activated, hydrophobic, low viscosity, closed cell polyurethane injection resin. In addition to seawalls, it’s a proven polyurethane concrete crack sealant for all types of structures. From our experience advising contractors, we’ve found it to be the most cost effective method for repairing seawalls.

Here are some of the advantages it has over other polyurethanes:

Lowest viscosity on market

AP Fill 700 has a viscosity of 110 to 130 cps. This allows for getting into thin cracks.

Closed cell, 0% permeability

The closed cell structure of this foam allows for ZERO percent permeability. No compromising of the repair material to worry about.

Adjustable set time

Adding various amounts of catalyst to adjust the set time allows for custom application of the material to address the specific nature of the seawall problem. A longer set time allows for the material to permeate and soak in around the structure before setting up. A shorter set time makes the material set up more immediately, which may be appropriate when there are large voids to fill or gushing leaks to stop.

Single component

This particular product does not require a “B” side to react with before setting up. This allows for simple, efficient installation.

Phthalate free

Some companies use phthalates in their polyurethanes. Because of their environmentally unfriendly nature, it’s not even legal to manufacture phthalates in the United States. Companies using them have to import them from overseas. Needless to say, AP Fill 700 does NOT contain phthalates – a known marine pollutant.

Approved for contact w/ drinking water

As mentioned in the previous post in this series, AP Fill 700 has been NSF certified for contact with drinking water. So, obviously installation in recreational or commercial bodies of water is no problem from an environmental perspective. Read more about NSF certification in the blog post Alchemy-Spetec's NSF Certification Spells Environmental Protection.

High bonding characteristics

Once AP 700 is installed, it’s NOT coming off. The adhesive qualities are unparalleled. This contributes to the vast advantage polyurethane has over cement grout when it comes to durability.

More about AP Fill 700

This material is designed to be efficiently delivered into all sized gaps and eroded depressions. It reacts with water or moisture in the soil and expands to fill the voids. It’s compatible with any seawall material: concrete, steel, vinyl, etc. And it permeates the most sandy of soils to form a solid, strong, watertight mass. It sets in less than 10 minutes. By being impermeable to water once in place, the likelihood of future erosion is vastly diminished. 

AP Fill 700 Applications

In addition to seawall repair, there are many other general applications for AP Fill 700. Here a few to keep in mind…

• Cutting off low and high flow leaks
• Concrete void / crack filling for all structures
• Cutting off underground water flows
• Soil stabilization
• Filling voids under concrete slabs
• Encapsulating contaminated soils

Durability

Leading experts in the polyurethane industry predict that this material lasts for hundreds of years once installed. Polyurethane is made from similar materials as plastic. There’s a reason why people campaign against the dumping of plastic waste in the middle of the ocean: it will be there forever. The edge of the ocean, properly installed as part of a seawall repair, is a much better place for it. And, yes, it tends to last forever.

Powerful

If needed, AP Fill 700 can quickly shut down leaks of thousands of gallons per minute. Rapid expansion makes it great for filling voids, wide cracks, pipe joints, pipe penetrations. Originally developed over 30 years ago, and continuously improved since, this technology has one of the longest histories of success in the field among uses of polyurethane foams

Efficient Installation

Results are immediately clear due to the visible exiting of sea water when the foam is injected. The low viscosity allows it to be injected into hairline, expansion joints and smaller cracks as well. AP Fill 700 is field proven in “curtain grouting” (earthen dam seepage protection), and consolidating loose soils.

Case Study

Let’s close out this two part series with a look at polyurethane seawall repair in action…

Situation

Owners of an upscale marina in Riviera Beach Florida noticed cracking in the slabs outside of their main boathouse. They also noticed that the slab had settled in several areas. The slabs in question were subject to heavy dynamic loads as a large forklift traversed the area, bringing 40' motor yachts in and out of the boathouse. Contractors came in and did a site evaluation, drilling holes to probe beneath the slab and also a sub surface investigation of the seawall to see if soils were being lost.

Solution

Most of the joints in the seawall were leaking sandy soil out - resulting in a void beneath the concrete slabs, which then cracked and settled. AP Fill 700 was specified to seal the concrete panel joints. It was injected behind the panels in the area of the joints, both vertically through the concrete, and horizontally from the water side of the panels. Proper venting was then installed to relieve hydrostatic pressure.

Results

The sandy soils have been stopped from escaping from behind the seawall. The concrete slabs were then lifted back into place with a combination of helical piles and AP Lift 475. There are no longer any voids beneath the slab so it is not flexing and cracking any longer. This marina was saved from a much larger, more catastrophic failure.

Want more info on polyurethane seawall repair?

Spanning the Pithlachascotee River in New Port Richey, Florida is the Madison Street Bridge. Built in 1985, this structure was buttressed with four semi-circular seawalls at the base of each footing in the year 2000.

Over the years, tide fluctuation caused soils to wash out from underneath the seawalls. This caused the heavily used sidewalks on top of the walls to crack and settle, allowing even rainwater in. Without an alternate way for pedestrians to traverse the bridge, this structural problem quickly became a critical public safety issue.

Powerful Polymer

To rapidly address the problem a certified contractor relied on AP Fill 700 and its NSF 61-5 certification (approved for contact with drinking water). The rapid expansive properties of this semi-rigid hydrophobic resin made it the optimal solution for painlessly filling the voids that had developed in the seawall and stopping the erosion beneath the sidewalks.

Painless Procedure

To rapidly address the problem a certified contractor relied on AP Fill 700 and its NSF 61-5 certification (approved for contact with drinking water). The rapid expansive properties of this semi-rigid hydrophobic resin made it the optimal solution for painlessly filling the voids that had developed in the seawall and stopping the erosion beneath the sidewalks.

Rapid Result

Stopping the leaks in all four seawalls only took a few days. More than a year later the seawalls are still as good as new.

Want in-depth info on polyurethane seawall repair?

Repair sea walls instead of replacing them by stopping high flow leaks, filling the voids behind concrete structures and binding loose soil with:

AP Fill 720 & AP Fill 700 — innovative, cost effective, water activated, low viscosity, simple to use closed cell polyurethane injection resins.

Proven Strength

• Because these foams are impermeable to water once in place, the likelihood of future erosion is vastly diminished versus other commonly used fill materials.
  
  
• Originally developed over 30 years ago, and continuously improved since, this technology has one of the longest histories of success in the field among engineering uses of polyurethane foams.

Environmentally Friendly

• Phthalate free.
• Approved for contact with drinking water.

Quick Set Time vs Cement Grout

• AP Fill 700 & 720 foams set in 10 minutes or less.
• Cement grout takes hours to days.

Differences Between 700 and 720

• 720 has a higher expansion ratio and is more flexible when cured.
• 700 has a lower viscosity, so it works better in cooler temperatures.

Want a complete technical breakdown of AP Fill 700 & 720 for seawall repair?

When it comes to seawalls, there is a lot more to learn than meets the eye. A seawall is like a living, breathing thing: especially in the way that it is designed to function. But like all living breathing things, they have a finite lifespan. For many of them, it's a mere 20 – 30 years. Depending on where you live, replacing a seawall can cost anywhere from $150 to $500 per foot. That's enough for some homeowners to choose to move instead of rebuilding their seawalls. Today however, signs of seawall distress can be solved before they get too bad through the application of polyurethane grouts to seal leaks, fill voids, and stabilize the surrounding soils.

Although seawalls are found around lakes and rivers, it is around the ocean that they are put to the most difficult test. Salt corrosion, tidal action, currents, boat wakes, storm surges and sometimes hurricanes all deliver a constant beating on the seawall. But many of the forces are also coming from the landward side of the wall. Every time it rains or the irrigation system runs, and every time the tide goes out; all of the groundwater above the waterline has to vent or equalize. Tremendous pressures can build up if that water is trapped and cannot make its way into the sea or the storm water system.

Correct construction of a seawall will include a drainage system to handle the bulk of the water that comes from rain in addition to check valves, weep holes, or seams to handle the daily influx and outflow from tide and wave action. Although these systems are designed to retain the soil behind the seawall, over time the materials degrade or can be disturbed by settling. The result is a loss of soil and the inevitable sinkholes and / or low spots that will occur along the wall. Other times, the weep holes and vents become clogged and the water has no way to escape except to force its way down and out from underneath the base of the wall. When this occurs there will again be sinkholes and sometimes wall failure.

When signs of sinking ground are observed, you can almost be sure there are voids below that are unseen and dangerous. Sometimes these voids can extend below an adjacent patio, dock, or pool deck, causing those to sink and crack. Anticipating those problems is key to keeping those problems at bay, and proper application of polyurethane injection is the solution. AP Fill 700 is a lightweight injection resin that can be injected along the wall where the settling is occurring and generate multiple benefits. It will seal any leaks along the wall, fill the voids that have occurred, and mix with the soil to form a solid, impermeable mass. Combined with proper drainage, this method can extend the life of your seawall.

If you live along the water, it is always going to be man against nature. That seawall is keeping your property from damage and from disappearing altogether. Advanced polyurethane technology from Alchemy-Spetec is a key to extending the life of your seawall. It's fast, clean, easy to install, and most of all, effective.

Want in-depth info on seawall repair procedures and products?