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► Auger: A corkscrew-like drill tool designed to remove the soil from a drill hole without using air or water. This method does not require vibration or impact to create the drill hole.
► Bentonite: A clay material that is mined in the mid-west and typically ground into a powder. Bentonite is normally used in test drilling to prevent the drill hole from caving. It is also used in cosmetics and even some candy bars.
► Compaction Grouting: The typical method of grouting used to stabilize cover-subsidence sinkholes. The primary difference between this technique and pressure grouting is that the grout material for compaction grouting is a thick, mortar-like material that is designed to displace soft soils and fill voids.
► Cover-Collapse Sinkhole: The most graphic of sinkhole conditions. These conditions result when the “roof” of a limestone dome will no longer support the weight of the soil and/or what is located above the surface of the ground. This is the most rare sinkhole condition.
► Cover-Subsidence Sinkhole: The most common type of sinkhole condition. Unlike the cover-collapse sinkhole, this type of sinkhole typically moves slowly over a period of time. A passageway in the limestone allows soil particles to flow into a larger void or opening, similar to the way sand from an hourglass passes from the top to the bottom. Like in the hourglass, a depression or subsidence occurs at the surface when enough sand or soil moves into the deeper void.
► CPT Abbreviation for Cone Penetration Test. Similar to the SPT in that it is used to determine the density of subsurface soils. This test uses a metal rod or tube fitted with a special point that is equipped with sensors that measure the resistance that is required to advance the point through the soil as it is hydraulically forced into the ground. This technique is very common in Europe.
► Fly Ash: A fine powered ash material that is a by-product of the coal burned in an electric power plant. This material is added to the grout mixture to fill the small voids between the sand particles to produce a well-graded mixture. This is important when pumping the grout material underground.
► Foundation: The structural system constructed below a building that transfers the weight of the building to the ground on which it stands.
► Geotechnical: Dealing with soils beneath the surface of the ground.
► Geotechnical Report: A compilation of test data and opinions prepared by a specialty engineering company or geotechnical engineer. This report will typically contain the results of soil borings (SPT borings), ground-penetrating radar analysis and other specific tests related to the site-specific soil conditions.
► Geotechnical Engineer: A degreed engineer that specializes in subsurface soil conditions.
► Grout: A cement-based material similar to the mortar that is used to lay bricks. A specially designed mixture that utilizes portland cement, fine sand, fly ash and water. Small-diameter stone may also be added to the mixture, depending on the particular project. This material is typically delivered to the site by local concrete suppliers on residential stabilization projects. Grout material used in residential stabilization projects usually reaches about 1000 psi of compressive strength in 28 days. It will typically reach an initial set in about two hours.
► Grout Casing Injection Pipe: A high-strength steel pipe, usually about three inches in diameter. It is very important that a specially designed, flush-joint (internally threaded) grout casing be used for this purpose. Standard threaded and coupled pipe should not be used for this purpose. This casing will initially be installed to the top of the limestone and will then be withdrawn as the grout-injection process proceeds.
► Grout Design Mix: This is the actual "recipe" of the grout mixture. For most residential compaction grouting projects, a blend of cement, fine sand, fly ash, water, and sometimes small gravel is used. Grout design mixes will sometimes vary between contractors.
► Grout Injection Point: A hole drilled for the purpose of injecting grout material. For most sinkhole stabilization projects, this hole is drilled to the top of the competent or firm limestone. This depth can vary dramatically depending on local conditions. The hole can initially be advanced with continuous flight augers or installed by spinning a steel pipe into the ground while using a drilling fluid. In either case, it is important that a steel flush joint casing be installed the entire depth of the hole. The casing will ultimately be used to inject the grout material. Remember… The actual amount of Grout Material and Injection Hole Drilling will be dictated by each individual project.
► Grout Monitor: Typically an employee of the engineering company that has been retained to watch over or monitor the stabilization project. This technician will normally record and document drill depths, grout takes and other specific information regarding the project.
► Grout Take: The volume of grout material that is required to treat a particular zone or project. Grout takes are typically estimated during the proposal phase of a project, but the actual amount of grout required will only be determined after the project is completed.
► Heave: The upward movement of the ground. This can be a result of several conditions. For the purpose of residential soil stabilization, typical causes would be:
- Clay… When highly active, plastic clay absorbs enough moisture that the clay can expand and possibly lift or heave structures or concrete situated above.
- Grout… When injecting grout into the soil, a hydraulic action may be experienced, causing the surface soils to rise. This type of heave is often used in an effort to re-level structures that have settled. When grouting around an existing structure, it should always be monitored with a survey instrument to detect heave.
- Organic Soil…Soil that includes a substantial amount of decayed or decaying plant matter, wood, peat, roots, etc. As time passes, the organic matter will continue to decay, and the soil will experience a decrease in volume. If organic laden soil is under a structure or concrete slab, the decrease in soil volume may cause settlement or subsidence.
► Highly Active I Plastic Clay: Oftentimes referred to as Shrink I Swell Clay. This type of clay has the ability to work like a sponge; it shrinks when it becomes dehydrated, due to lack of moisture from the surface or from a decrease in the groundwater table; or it expands or swells when fully saturated. Structures that are built with a foundation system that is within the influence of these types of soils are subject to upward and downward movement as soil moisture levels fluctuate. This movement can vary from heave in wet conditions to settlement in dry conditions.
► Karst: a geologic term that refers to an area where limestone lies beneath the surface. Karst Geology refers to soils underlain by limestone material that is partially dissolved by groundwater. The resulting voids in the rock provide paths through which water can travel, taking erodible soil with it.
► Limestone: The bedrock layer that typically lies beneath central Florida. This rock layer also contains the two major aquifers in Florida: The Floridian, which extends across the entire state, and the Biscayne, which is found only in South Florida. The Floridian aquifer is a confined Artesian aquifer. The upper part of the Floridian is used as a water supply in north and central Florida. The lower part is mostly found to be in salty coastal areas.
► Lump Sum: The total price charged for a particular bid item. This would be typical for bid items such as Mobilization.
► Professional Engineer: A licensed engineer that has the authority to design certain activities or projects.
► Proposal: A document presented by a contracting company for the services that will be required for stabilization. This proposal must follow the design and recommendations detailed in a geotechnical report or project specifications. The proposal for stabilization grouting will typically contain an ESTIMATED number of Lineal Feet of Drilling and Cubic yards of Grout Material that a particular contractor feels will be required to complete the stabilization work.
► Settlement: The downward movement of the ground surface of a structure or element situated on the surface.
► Sinkhole: a subsurface condition resulting from the softening or dissolving of limestone over geologic time; a depression caused by the soil and other materials subsiding into an open hole or void below the ground surface. Typically classified as either Cover-Collapse or Cover-Subsidence Sinkholes.
► SPT Abbreviation for Standard Penetration Test. This is an industry-standard test that is used to determine the density of subsurface soils. This test documents the number of “blows” required to advance a steel test spoon one foot by dropping a 140-pound hammer thirty inches. The recorded number of blows is referred to as an "N Value."
► Subsidence Settlement: The downward movement of the ground. This can be a result of several conditions:
- Clay… When highly active, plastic clay loses moisture, and the clay will shrink and lose soil volume. Significant volume change can result in serious settlement problems.
- Organics… Decaying organic matter such as plants, wood, roots, peat, etc., that cause the soil to decrease in volume. Organic-laden soils can result in serious settlement problems.
- Poorly Compacted Soils… Prior to the construction of a building or the placement of concrete slabs, the soil must be properly compacted. If the soil is not compacted, it will compress beneath the weight of what has been placed on top of it.
- Sub-standard Construction Techniques… Poorly designed or poorly-constructed structures or concrete work may settle or crack, due to inadequate construction techniques. Oftentimes, additions to an existing home are built without proper foundations. Concrete is sometimes poured too wet or without proper control joints to allow expansion and contraction.
- Sinkholes: In Florida, the limestone bedrock that lies beneath the soil contains many openings, fractures and cavities that have resulted from the percolation and flow of mildly acidic water from the surface. This surface water slowly erodes or dissolves the calcium carbonate of the limestone, enlarging the paths along which the water flows. Once the pathways are large enough, soil also begins to move downward with the water. The result is a gradual downward movement of the land surface and development of a depression that collects increasing amounts of surface water.
► Target Quantity: This is the pre-determined quantity of grout material that is placed in a particular zone or injection point.
► Underpinning: A process by which the weight or load of a structure is transferred through a problematic soil condition to a suitable load-bearing- strata, such as rock. Underpinning usually involves the installation of small-diameter (usually three-inch) steel pipe sections directly adjacent to the foundation. The pipe sections are typically hydraulically jacked or drilled down to the bearing zone. A foundation attachment or bracket is then mounted to the top of the pier and situated to transfer the weight of the foundation section to the pier. The piers are typically spaced from 4 to 8 feet on center across the affected area, depending on structure loads. Underpinning plans should be designed by a Professional Engineer.
► Unit Price: The actual cost of each Cubic Yard of Grout Material or each Lineal Foot of Injection Hole Drilling. These are the fixed prices that are submitted by the contractor.
► Water Table: distance below the ground surface at which the soil is completely saturated with water.