Sinkhole Terminology

  • Sinkhole: a subsurface condition resulting from the softening or dissolving of limestone over geologic time. Definition.. "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.
    • There are three types of sinkholes that can form:
      • Dissolution or solution sinkhole: In this type of sinkhole, there is little soil or vegetation over the limestone or other bedrock. Water from rain and runoff slowly trickles through crevices in the bedrock, dissolving it. As a result, a depression gradually forms. Dissolution sinkholes happen slowly and are generally not dangerous, but one that becomes a pond can drain suddenly if water makes it through the protective bottom layer.
      • Cover-subsidence sinkhole: These sinkholes happen in areas where sand covers the bedrock. The sand filters down into openings in the rock, gradually causing the land surface to sink. Continued erosion increases the size of the depression. Like dissolution sinkholes, cover-subsidence sinkholes happen slowly.
      • Cover-collapse sinkhole: In these cases, the bedrock is covered by a layer of clay. Beneath this ground cover, however, water dissolves an underground cavern. Gradually, ground sediments begin to erode, or spall, into the cavern from the bottom. The ground continues to crumble from beneath until only a thin layer remains between the surface and the underground opening. When that layer collapses, the sinkhole opens up suddenly, swallowing any structures on top.
         
  • Foundation: The structural system constructed below a building which transfers the weight of the building to the ground on which it stands.
     
  • Settlement: The downward movement of the ground surface of a structure or element situated on the surface.
     
  • Erosion: Erosion is the process of weathering and transport of solids in the natural environment or their source and deposits them elsewhere. It usually occurs due to transport by wind, water, or ice; by down-slope creep of soil and other material under the force of gravity; or by living organisms, such as burrowing animals.  Erosion is a natural process, but it has been increased dramatically by human land use, especially industrial agriculture, deforestation, and urban sprawl.
     
  • Geotechnical Engineering: Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering includes investigating existing subsurface conditions and materials; determining the relevant physical/mechanical and chemical properties of these materials; evaluating stability of natural slopes and man-made soil deposits; assessing risks posed by site conditions; designing earthworks and structure foundations; and monitoring site conditions, earthwork and foundation construction.
     
  • 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.
     
  • Groundwater: Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations
     
  • Karst: a geologic term that refers to an area where limestone lies beneath the surface. Karst Geology is where soils are underlain by limestone material, which 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 salty in coastal areas.

  • Auger: A cork screw 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.
     
  • 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.
     
  • Displacement Pile: A pile that is installed by displacing existing material.
     
  • Ductile Iron Pile: Driven pile system, utilizing high strength ductile cast iron. Pile sections are connected together by a unique spigot and socket joint, which offers speed of connection together with a high degree of stiffness.
     
  • Fly Ash: A fine powered ash material that is a by-product of coal that is burned in 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.
     
  • Geotechnical: Dealing with soils beneath the surface of the ground.
     
  • 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 reach about 1000 psi of compressive strength in 28 days. It will typically reach an initial set in about 2 hours.
     
  • Grout Casing I 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 the 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 are 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 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 intd 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.
     
  • 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, however, 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 a highly active, plastic clay absorbs enough moisture 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 which would cause the surface soils rise. This type of Heave is often used in an effort to relevel 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: Often times 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 type 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 is where soils are underlain by limestone material, which 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 salty in coastal areas.
     
  • Lump Sum: The total price charged for a particular bid item. This would be typical for bid items such as Mobilization.
     
  • Micro Piles: Twelve inch (305mm) or less bored, grouted-in-place piles incorporating steel pipe (casing) and/or steel reinforcement.
     
  • 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. Estimated quantities of Grout Material may vary significantly between contractors. The reality is that if you only ask for proposals from highly qualified contractors with many years of experience, the final grout quantities should be the same regardless of the original estimate.
     
  • Replacement Pile: Pile that is installed by removal and replacement of material.
     
  • Settlement: The downward movement of the ground surface of a structure or element situated on the surface.
     
  • 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 I Settlement: The downward movement of the ground. This can be a result of several conditions:
    • Clay... When a highly active, plastic clay losses moisture 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 reduce soil 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 constructed structures or concrete work may settle or crack due to inadequate construction techniques. Often times, additions to an existing home are built without proper foundations. Concrete is sometimes poured to wet or without proper control joints to allow expansion and contraction.
       
  • Steel Piering: A process by which the weight or load of a structure is transferred through a problematic soil condition to a suitable bearing strata such as rock. In regards to Residential Steel Piering, this 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 mini pile and situated to transfer the weight of the foundation section to the mini pile. The mini piles are typically spaced from 4 - 8 feet on center across the affected area depending on structure loads. Steel Piering systems should be designed by a Professional Engineer.
     
  • Stone Columns: Process of introducing addition materials (typically stone) in the constant volume (earth), or process of decreasing the total volume occupied by in-situ materials by means of inserting a vibrating probe “vibroflot”.
     
  • Target Quantity: This is the pre-determined quantity of grout material that is placed in a particular zone or injection point.
     
  • 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.
     
  • Vibrating Hammer: A pile-driving hammer normally weighing from three to five tons, with rapid vibrations. The rapid vibrations cause the soil around the pile to change to a liquid state. The weight of the hammer then slips the pile down through the soil.
     
  • Vibratory Probe: A vibrating device, which produces an axial (vertical) vibration throughout the length of a continuous tube.
     
  • Vibro Compaction: Densification of existing cohesionless granular soils by means of inserting a vibrating probe “vibroflot”.
     
  • Vibro flotation: A process used to stabilize and otherwise improve soil for building by compacting loose granular soils. The trade name for a geotechnical process that uses vibration to compact clean sands and gravels. The vibration is combined with a water jet to give a high degree of compaction by means of inserting a vibrating probe “vibroflot”.
     
  • Water Table: The distance below the ground surface at which the soil is completely saturated with water.