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What are sinkholes and how are they formed?
A Sinkhole is a cave-in or natural depression in the land's surface caused by the chemical dissolution of carbonate rocks or by erosion of rocks or soil below the land's surface. Sinkholes commonly occur in areas where the rock beneath the land's surface consists of carbonate rock, limestone, salt beds, or other types of rock that have a tendency to dissolve with moving underground water. In Florida, the most significant factor in the development of Sinkholes is the dissolution of the limestone by acidic waters underneath the grounds surface. Limestone is a porous rock, capable of cracking, breaking, and dissolving. As water reaches the Limestone and slowly begins to dissolve the rock, it creates voids and cavities and the soil resting on top of the Limestone then collapses or subsides into the caverns and voids, resulting in a Sinkhole.
Methods to remediate your sinkhole?
Grouting and/or Underpinning are the techniques used by APT in the Sinkhole repair process. Grouting is a method of Sinkhole repair or remediation in which Grout, a form of concrete, is pumped under or into the ground. The purpose of the Grout injection program is to grout within and along the top surface of the Limestone around the Property to restrict and/or seal breaches in the surface of the Limestone that connect the soils that overlie the rock surface to suspected cavernous bedrock zones, thereby reducing the potential for future subsoil raveling and migration. Please review the picture in figure 1 to see the Grout installation.
Compaction grouting process
Grout injection pipe of three inches in diameter, will be placed in augured holes, and then drilled to limestone. The on-site project engineer will determine and locate injection points. Injection point locations may be subject to change due to field conditions such as utilities, water wells, lawn irrigation, and/or various other obstacles etc. Grouting will be performed utilizing a positive displacement grout pump capable of generating injection pressures necessary to displace soft material and fill voids. The proposed grout mix typically attains compressive strength in excess of 1500 psi in twenty-eight days. A retarding admixture may be added to the grout mix depending on temperature and weather conditions at time of injection. Initial injections will proceed as a compaction grouting program, with consistencies ranging from 4in. to 6in. slump. Depending on the success of initial grout intake using low slump mix, it may be necessary to use more fluid material based on field conditions. Therefore, consistencies may vary and changes will be determined by the on-site project engineer. Once initial grout take has been established, the grout mix may be altered to control grout volumes. Grout pressures will be monitored at the point of injection. Structure movement will be monitored by use of a survey level or laser level at various observation points to detect and measure movement. Grout injection will begin at the bottom of the injection point and proceed upward in 3-5 foot increments. The pipe will typically be raised to the next zone when one of the following three items occurs: (1) A rapid pressure increase is observed at the injection point, (2) a target quantity of grout material has been injected into the zone (target quantities to be established by project engineer) or (3) ground heave or structure movement is observed. Upon achieving one of these criteria, the injection pipe will be extracted to the next zone and the process is repeated until the entire injection point is complete. Please note that all work described above will be monitored, directed and signed off by the on-site Licensed Professional Engineer, not APT.
Chemical grouting process
The chemical grout process is designed for stabilization and densification of loose base and sub-base soils within the first ten feet beneath the property. The work will consist of furnishing all labor, equipment and materials required to inject polyurethane material to depths no greater than 10' below the base of the slab on grade. The procedure is intended to stabilize the near surface soils by densification and/or infilling. The material will consist of a closed cell, hydro-insensitive, high density polyurethane-forming mixture, having insoluble diluents that permit the formation of polyurethanes in excess water. The scope of the stabilization program includes vertical injection points. The total estimated quantities, depths, and locations will be listed under the "ITEMIZED COST OF PROJECT" section in this proposal. Proposed injection point locations are planned with a spacing of 3-5 feet on center, beneath the slab on grade. Alternative injection points may be required if directed by on-site project engineer due to field conditions. APT will establish the final injection locations under the direction and supervision of the project engineer. The polyurethane shall be injected at a rate and amount specified by the manufacturer. Continuous monitoring of pressure, volume, and slab movement will be observed and recorded. The injection process will be stopped if any of the following actions take place: (1) polyurethane overflow is observed from any of the injection holes, (2) excessive pumping pressures exceed acceptable values specified by the manufacturer or (3) concrete slab movement is greater than required for re-leveling.
Underpinning
Underpinning is a method of subsurface repair in which metal piers, called Underpins, are driven into the ground and imbedded in the earth. Underpinning can repair structures (like your home) that have been damaged or have settled from Sinkhole activity, buried organics, shrinking/swelling clay, etc. Underpinning supports the foundation of a structure by transferring the weight of the structure from the foundation, through the unstable soils, to a more stable material below. Once the Underpins are secured, they are then attached to the structure with brackets. Underpins are usually installed around the perimeter of the structure at set intervals determined by a certified Engineer. If needed, Underpins can also be placed under the interior of the structure, such as under the interior load bearing walls. Please review the picture in figure 2 to see the Underpin installation. If Underpinning is recommended in your remediation plan, we are able to offer you a Lifetime Warranty. This warranty is transferable and covers the Underpins and the Materials and Labor associated with APT's installation of the Underpins. Let's face it: your Property is in Florida! Settlement caused by Acts of God, casualty, acts of others, or damage to the slab, roof, walls, fixtures, and underground utilities is beyond APT's control and are not included in the Warranty. APT also does not warrant Cosmetic Issues above or outside of the foundation slab including (but not limited to): tile; pool decks; driveways; sidewalks; walls; ceilings; your sprinkler system; trees, shrubs, or other landscaping; etc. Please be advised that, in many cases, your home will experience movement and further cracking that is associated with wind shear or pressure, thermo-expansion and contraction, faulty construction, or other upwards and lateral movements naturally occurring in Florida or from Acts by Others. Our Lifetime Warranty also does not provide coverage for the stabilization of the soils or continued Raveling or Settlement of new founded soil issues. Cracks and changes in the soils are not always associated with Sinkholes, and your Lifetime Warranty extends only to the stabilization of the Foundation.
Exterior Underinning Process
The installation of pressure piers will be needed in order to accomplish proper stabilization of the structure. An access area of approximately 3' x 3' will be dug out from around the footer and the pier placement will be determined by the project engineer. Areas covered by concrete slabs will be cut out to an area of approximately 3' x 3' to allow for access to the footer. A foundation bracket will be attached to the footer at each recommended location. Seamless steel tubing of 3.000 x 2.760 will be either pushed hydraulically using 100 ton hydraulic rams or drilled through the bracket. Each pier is advanced to limestone or an equal load bearing strata as recommended by the project engineer. The piers are then capped/sealed off and pinned, the holes are backfilled and the entire work area is properly cleaned. Your structure is now on underground pilings/piers. Please be aware that partial pinning of a foundation will not remedy problems or potential problems that may exist in other areas of the structure and differential settlements of the structure may be possible. APT DOES NOT RECOMMEND PARTIAL UNDERPINNING OF ANY STRUCTURE.
Interior Underinning Process
Depending on the engineers recommendations, the installation of interior slab and/or footer supports could be needed in order to accomplish proper stabilization of the structure. If slab supports are needed, an access area of 6" in diameter will be drilled through the slab, in various locations throughout the structure, which will be pre-determined by the project engineer. If footer supports are needed, an access area of 3'x3' will be cut out around load bearing walls determined by the project engineer. Once all the areas are exposed, a bracket will be attached to the slab and/or footer at each recommended location. Seamless steel tubing of 3.000 x 2.760 will be either pushed hydraulically using 100 ton hydraulic rams, or drilled through the bracket. Each pier is then pushed to limestone or an equal load bearing strata as recommended by the project engineer. The piers are then capped/sealed off and pinned, the holes are backfilled, the 6" cores holes and/or 3' x 3' access areas are re-pored with concrete, and the entire work area is properly cleaned.
