Geotech….What you need to know
By: Jeff Philbin, Helicon Marketing Director
According to the United States Geological Survey (USGS), 20% of the United States lies in areas susceptible to sinkhole events. The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. And unfortunately we live in area coined “Sinkhole Alley” but a negative connotation does not need to be all doom and gloom as there options to help you gain piece of mind from a trusted ally.
How do Sinkholes Form?
Sinkholes can form anywhere there is soluble rock underground. This is referred to as“karst terrain“. The most common types of soluble rock are limestone or dolomite.
Florida has more sinkholes than any other state in the nation because the entire state of Florida is underlain by limestone. Limestone is common in Florida because limestone forms over very long periods of time from the accumulation of seashells, coral, and algae in regions with warm shallow seas.
What Causes a Sinkhole?
Dissolution: Limestone dissolves slowly when it comes into contact with carbonic acid, a mild acid. Carbonic acid is created when rainwater absorbs carbon dioxide from the atmosphere and soil. In addition, the burning of fossil fuels from cars and industrial production can produce carbon dioxide that can further contribute to the dissolution of limestone bedrock.
(CO2 + H2O → H2CO3) (Carbon Dioxide + Water = Carbonic Acid)
Over time, this dissolution forms cracks and crevices large enough to create caves, tunnels, cavities, and most notably sinkholes.
Naturally Occurring Sinkholes
▪ Heavy rainfall: Without proper drainage, rainwater will pool underground, become acidic, and escalate the formation of sinkholes.
▪ Drought: A drought will cause the water table to drop and loss stability. Also, when limestone dissolves, it forms a claylike soil, which holds a lot of water. When the clay soil dries, it loses its cohesive bond, which could potentially cause the ground to drop.
▪ Leaky faucet, old mine shafts and sewage malfunctions all can add to the development of sinkholes.
▪ Aging sewage and water main pipes – as water soaks into the ground, it can dissolve and erode the aging pipits, creating caverns, which can develop into sinkholes.
Warning Signs a Sinkholes May Occur
It can be difficult to detect when a sinkhole is about to occur, particularly if it is covered with ground cover, however there are a few signs you can look for:
▪ Doors and Windows fail to close properly
▪ Slumping, sagging or slanting fence posts, trees or other objects
▪ Vegetation dying due to underlying streams that feed the plants draining into the sinkhole
▪ Polluted or muddied well water
▪ Formation of new ponds or small collection of water
According to the Southwest Florida Water Management District, if a sinkhole appears on your property or a portion of your home has shifted or sunk, take these steps immediately:
▪ Provide for the personal safety of your family. Evacuate if necessary.
▪ Secure or move your valuable possessions if you can do so safely.
▪ Notify your insurance company or agent.
▪ Notify your city or county building inspection department.
▪ Mark the sinkhole or property with fencing, rope or tape to warn others of the danger. You could be held liable if someone is injured in the sinkhole.
Do You Need to Protect Your Home or Future Home Against Sinkholes?
If you plan to build or you already own a home or building in an area that is underlain with carbonate rocks, such as limestone and dolostone, you may be at risk of a sinkhole forming. An inspector that is a licensed professional geologist and is trained to recognize sinkhole activity is best suited to determine if a sinkhole exists, or if the property has the potential for developing a sinkhole. In our state of Florida, it is the responsibility of the home/building owner to contact an inspector because building contractors are not required to provide sinkhole testing on private home sites; however, in some cases public building construction sites in sinkhole areas may be tested and reinforced as needed for safety and liability reasons.
Does Florida Homeowners Insurance cover Sinkhole Damage?
Here in Florida, having catastrophic ground cover collapse insurance does not guarantee you will be covered for damage due to sinkhole activity
Florida Statute 627.706 requires every insurer authorized to sell property insurance in Florida to also provide coverage for catastrophic ground cover collapse.
However, sinkhole damage may not be covered by your homeowner’s insurance policy because the law defines sinkhole damage differently from catastrophic ground cover collapse.
Florida law defines catastrophic ground cover collapse as “geological activity that results in all the following:
1. The abrupt collapse of the ground cover;
2. A depression in the ground cover clearly visible to the naked eye;
3. Structural damage to the building, including the foundation; and
4. The insured structure being condemned and ordered to be vacated by the governmental agency authorized by law to issue such an order for that structure.
If your home is damaged due to sinkhole activity, your claim must meet all four criteria for catastrophic ground cover collapse otherwise your insurance company can legally refuse to pay your claim. All insurance companies licensed to do business in Florida offer sinkhole coverage, and an additional cost.
How is commercial sinkhole insurance different than residential?
The coverage itself is usually quite similar. Remember that the sinkhole insurance offered here in Florida is written by Statute so all domestic insurance companies follow the same guidelines. Big differences in the coverage can arise when you have surplus lines carriers, which often are the only options for a large, riskier commercial property. (Commercial properties will still have to prove the presence of structural damage and sinkhole activity. In our experience structural damage is more common to find at a commercial building than residential. When you consider the increased amount traffic coming in and out of the building, the different ingress and egress flows and code requirements and ADA restrictions, etc. safety hazards are much more common. Commercial properties can also have very unique issues you would never see at a residence. For example, performing sinkhole repairs at a gas station is a task that can take some real time and creativity to work on. Also, many commercial structures are multi-story and sometimes multi-unit, allowing for more ways for damage to express itself in the structure.
The biggest differences in commercial projects usually are procedural due to the sheer volume of money, time and people involved. Apartment complexes for example require a ton of time in just scheduling alone to be able to inspect the different units. Often these types of properties are overseen by property management companies and homeowners associations, which can create a different dynamic as far as communication goes. Having a smooth system of interfacing with everybody involved is critical. Finally, the amount of money necessary to properly work a larger case up can be daunting sometimes. In short, if you have a large commercial property or a property with very unique issues make sure you hire a firm with the financial resources to take on the task and with the time and attorney resources to properly work it up.
Why it’s important to have a sub-surface soil evaluation done before you build
In some parts of the state you can’t drive down the road these days without seeing a billboard or hear a radio spot advertising a law firm offering their services in the event your home has suffered structural settling due to a sinkhole. Truth be told, many cases aren’t always sinkhole-related, but instead are caused by other subsurface, soil-related issues.
“Soils are the most important construction material you’ll have on any job site,” says Hal Barrineau, a structural engineer with HW Barrineau & Associates, Inc. in Ocala. The weight of all materials of construction incorporated into a building, i.e. walls, floors, roofs, ceilings and stairways are loads known as “dead loads”. For structures below ground, the soil and hydrostatic pressure from ground water are also considered dead loads. Likewise, the loads generated by wind, rain, snow, earthquake and flood are considered “live loads”. Both dead and live loads are forces that must be accounted for in the structure design. These forces are transferred to the underlying soils, which must be sufficiently adequate to support the structure. If the underlying soils are not adequate then structural distress is imminent and can even occur prior to completion of construction. Taking a proactive approach and evaluating the sub-surface soil conditions determines whether the soil is capable of sufficiently supporting the loads imposed by the structure. “Often the importance of soil as a construction material is overlooked. If the integrity of the soil is problematic, then that’s going to manifest itself after the loads are applied in the way of problems with the structure,” says Barrineau, an engineer in Florida since 1993.”
When Houses Settle
If you see signs of stress in your structure, such as cracks in the foundation and walls, or uneven floors, the usual protocol is to call your insurance company. In accordance with Florida Statutes, the insurance company must determine whether or not the damage is the result of sinkhole activity. The insurance company sends out a claims adjuster and the adjuster makes a determination on whether the company should retain the services of a geotechnical engineer to do an investigation. The insurance company usually bears the cost of paying for the investigation, which can be substantial.
The investigating engineer will prepare a report of his findings and render an opinion as to whether or not the damage is sinkhole related. If he believes it is then the report will include recommendations for remediation of the sub-surface soils. If not, this is usually where the insurance company’s participation ends. If soil remediation within 10 to 15 feet below the surface is called for, one potential solution is chemical grouting, also known as permeation grouting, which is used to increase the integrity/bearing capacity of the underlying soils immediately beneath the structure’s foundation. This method is usually done as part of a comprehensive remediation plan, which also may include deep cement grouting and underpinning. For remediation deeper than 15 feet, cement grouting- also known as pressure grouting- is used.
This method of injecting cement grout into the voids and fractures of the underlying limestone formation and/or weak soil strata is the most common solution. After remediation of the underlying soils the structure also must be supported, Barrineau says. A structural engineer can design a solution to remediate the foundation which may requires the underpinning of the structure. Installing piers or piles under the existing foundation to stabilize the structure does this. Identifying the right solution for the right soils before construction can save owners a lot of stress and discomfort of post-construction remediation, not to mention the added cost of cosmetic repairs after the foundation has been stabilized.
Sub-Surface Soil Evaluation Methods
Soil testing methods fall into two categories: lab tests and field tests. Lab tests are performed on concrete and soils to determine compressive strength. Barrineau compares the proper mixture of cement to making a cake according to its recipe. Concrete requires the right amount of sand, rock, cement and water. If you mess up any of the ingredients, the concrete isn’t going to perform as it should. Soil samples pulled from deep borings are tested to identify their properties, such as gradation and natural moisture content. If clay is present, the plasticity and the liquid limit of it must be determined. All of these factors contribute to the projected performance of the soils.
Many insurance companies today refuse to issue homeowner policies in certain zip codes due to increased sinkhole claims in those regions. The Florida Office of Insurance Regulation has reported steady increases of sinkhole and settling claims over the last few years. A 2010 report, “Report on Review of the 2010 Sinkhole Data Call, November 8, 2010, Florida Office of Insurance Regulation,” stated that total sinkhole costs increased from $209 million in 2006 to $406 million in 2009. The total of reported claims rose from 2,360 in 2006 to 6,694 through the first nine months of 2010. Of the total number of sinkhole claims in Florida, Marion County is fifth in the state behind Hernando, Pasco, Hillsborough and Pinellas counties.
Don’t be a Statistic
Bad soil conditions can have a huge effect on the overall construction budget, so we recommend doing geotechnical testing before you build and perhaps even before you buy the property. Doing your homework up front by performing proper testing is the best insurance you can buy.
Protecting Your Home or Building from Sinkholes
What are Pre-Construction Piers?
A Pre-Construction pier is a type of structural pier, which is installed below the structure before it is built. The pier is tied into the footer of the structure to keep the structure from moving due to weak or compromised soils. Normally this consists of a type of multi lead helical pier that is driven with precision deep into the ground until it rests soundly upon the underlying load-bearing strata.
The helical piers are embedded within the foundation via a custom footer bracket. When the building contractor places the concrete foundation, the bracket is essentially embedded into the footer by twisting the rebar into the top bracket thus making the Pre-Construction piers an essential part of the foundation once the concrete has cured.
More and more architects, engineers, and construction professionals are paying closer attention to the potential of soil issues such as buried debris, clay, and muck and sinkhole damage. These professionals are taking precautionary measures to prevent the problem before damage begins. By installing a deep foundation system prior to building you can ensure the structure will rest on a solid base for years to come.
Pre-Construction piers are easy to install, only taking 2-3 days to drive and weld a whole house. They are also cost effective when compared to other retrofitted soil improvement systems and all Pre-Construction piers come with Helicon Property Restoration Lifetime Warranty on workmanship completely protecting you with the most comprehensive warranty in the industry and you could easily save thousands of dollars in sinkhole coverage premiums by using Helicon for your restoration project.
What is the installation method of Pre Construction Piers?
▪ Your engineer’s installation design is reviewed and installation points are marked off in cooperation with your building contractor.
▪ The Helical Piers are hydraulically torque driven into the soils to the specified depths.
▪ Excess pipe is cut at the bottom of the proposed footer and pipe is made ready for the top bracket.
▪ The top bracket is welded to the top of the pier.
▪ Process continues until all the Pre Construction Piers are installed.
▪ Work site is cleaned up.
How do pre-construction piers work?
Pre-construction helical piers are installed prior to pouring footings as specified by the engineer’s installation design. (These are the same piers that have long been used to stabilize and often lift the foundations of existing homes that have settled.)
Rugged steel tube sections are hydraulically driven until they reach the depths of competent load-bearing soil strata or bedrock. The top of the pier is then cut to the footing elevation and a footing bracket or plate cap is welded to it. Rebar is added and the footing is poured, making the pier and bracket assembly integral to the foundation.
Your foundation rests upon these piers, not potentially unstable soils closer to the surface. This precaution ensures that your new home will not settle due to weak soil conditions or sinkhole activity.
Advantages of our pre-construction helical piers
▪ Can be installed year-round
▪ Round shaft has a high resistance to bending
▪ Galvanized steel resists corrosion for long life
▪ Cannot be seen after installation
▪ Can be installed in tight spaces
▪ Minimizes the seismic activity and ultimate noise of pounding into the rock layer
▪ Load is transferred through problematic soils to bedrock.
▪ The drilling process ensures the pier is seated in the rock.
▪ Calculation of the load is simple. No need to use a complicated load-bearing calculation that may or may not be accurate. 100% of the load is seated in bedrock.
▪ The piles are easy to handle and are available in multiple lengths.
▪ Can be drilled through dense layers. The lateral displacement of the soil during driving is low.
▪ Can be driven in hard soil conditions and to greater depth
▪ Higher load capacity
▪ Faster and easier installation, and lower overall cost.
▪ Can be encased in concrete, if required.
▪ Greater design flexibility for the engineer. Many design options available
▪ Lifetime warranty
Limitations against its current competitor – Timber Piles
▪ Salt-water corrosion limits life of piles.
▪ Pile Cap installation costs are greatly increased due to deep excavation requirements where sub-soil water level is very low.
▪ Low joint strength limits the depth of the timber piles.
▪ Lower load-bearing capacity.
▪ Timber piles must be cut off below the permanent ground water level to prevent decay. If the water table at a site is at a greater depth, extra cost of excavation needed to provide the pile cap may render the choice uneconomical.
▪ Increased safety concerns during installation in filled-in ground.
Pre-Construction Protection Against Sinkholes
Chemical grouting is one of the best ways to repair a shallow sinkhole (exists within 15 feet of the surface) under your home. Chemical grouting uses a low-pressure injection technique to fill narrow crevices, pores, and loose soils that could cause sinkhole activity. In addition to repairing foundations affected by shallow sinkhole activity, chemical grouting is also used to repair sensitive areas like pools, decks, driveways, and sidewalks.
The compaction grouting method of sinkhole repair caps and seals the limestone’s surface, fills voids and pushes into the loose, weak soil, compacting and strengthening it. It is the best way to repair sinkholes that are characterized by a downward shift of soil particles.
The injection process actually makes the soil much more compact and dense. The injection piers utilize a process that injects or pumps a grout solution through the perforated pipes of the pier. Thus, the power of underpinning is combined with the stabilization of compaction grouting to ensure a rock-solid foundation. The injection pier system is a true combination of compaction grouting and underpinning.
Time to bring in professional assistance
The lasting effects from the threat of a sinkhole can be daunting if you think you should be doing it alone but there is help out there. Helicon is the premier geotech construction company in Florida. Based out of Tampa, FL. we are a licensed general contractor leading the industry in full-service geotech work We are experts in pre-construction, sinkhole repair, and reconstruction & general contracting and ready to serve our customer with 24 hours a day, 7 days a week readiness. As the premier provider of geotech construction throughout Florida for over a decade, Helicon prides itself on providing high quality service, for both insurance companies and private customers in the short term with boarding up your property, removing water and mitigating damages to longer term projects with handling all repairs and construction work after the storm. We strive to exceed everyone’s expectations. Helicon has successfully completed thousands of restoration and remediation projects in the Tampa Bay metropolitan area, including the surrounding counties of Hillsborough, Pinellas, Hernando, Polk, Citrus and Marion counties. Our professional Helicon Teams are trained and equipped with the tools and expertise needed to execute a flawless and professional repair experience. We invest in our teams ensuring they remain up to date on the latest industry technology and training. Our Office Teams will answer all your questions, provide professional service, give knowledgeable advice, and execute a project that will fully satisfy our customers.