Deep Injection for Sinkholes


The URETEK Deep Injection© Method offers customers a time and money saving solution for sinkhole repairs.

  • Weather events in regions with rain and floods have caused an extreme amount of sinkhole issues.
  • When initiating a sinkhole repair, the objective is to prevent further movement of loose material and remove the triggering mechanism that causes the sinkhole.
  • Repair methods are varied depending on the economics and location of the sinkhole.
  • Many sinkhole remediation options can be costly and time-intensive – requiring the use of heavy machinery, a wide range of repair materials, and much manpower.

Causes of Sinkholes

Sinkholes can result from the collapse of the roof of a cave (called cover collapse) but typically it is the piping of unconsolidated material from one location to another that causes most sinkhole events. This means that underground soil particles erode and wash through channels in the subsoil down through the Karst drains (Karst: a geologic formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite). Water is generally the primary triggering mechanism for sinkholes. Below is an infographic to common origins of sinkhole formation.

Traditional Sinkhole Repair Methods

Repair methods are varied, and the method used depends largely on economics and the location of the sinkhole. The method and materials needed to fill in a small sinkhole in a backyard or in a rural area can be quite different from those needed to repair a sinkhole in the middle of a street or under an occupied home or business in a highly urbanized area. Repair tools and material vary greatly as well. The two primary goals of sinkhole repair are:

  • Stabilization Area – By stopping loose material from flushing down into the drain (a fissure in the bedrock that returns water to the aquifer)
  • Prevent Recurrence – By removing the triggering mechanism and its source. It is important to understand why the failure occurred so that a durable repair can be made.

During repair, the sinkhole’s triggering mechanism must be addressed in order to minimize additional soil settlement or sinking. As water is generally the primary triggering mechanism, it is necessary to identify and remove to the extent the possible source of the water that may have caused the sinkhole. It is better to construct the plug (drain stopper) directly at the location of the bedrock drain. This allows the plug to be in direct contact with the bedrock, providing a better seal.

Sinkholes in which no bedrock is encountered, and where the soil cover is thick, require careful geologic analysis followed by various costly repair methods, ranging from pressure grouting (also called permeation grouting) in the subsurface, to driven piles having concrete caps and gravel-mat backfilling.

Inverted Filter Approach

The inverted filter approach is often used for sinkhole repair, especially when the sinkhole is not located near structures that require advanced, engineered support. Under this method, the sinkhole area is excavated to expose either bedrock or the throat of the sinkhole. A course of rock large enough to bridge the throat of the sinkhole is placed at the bottom of the excavation. Courses of progressively finer rock and gravel are compacted above the base course. A geotextile fabric may be placed above the finest gravel course to prevent excessive loss of the uppermost course, which may consist of sand and/or soil. One benefit of the inverted filter method is to provide filtration treatment of storm water and to permit controlled infiltration and groundwater recharge (the drain is still unplugged but water flow is controlled).

Compaction Grouting

This sinkhole repair technique may consist of excavation to bedrock, placement of low-slump mix (such as cementitious grout) in the excavation, and placement of compacted fill to grade level. This approach should be taken with caution, because grout loss may be excessive if the underlying solution conduits are large (the hollow nature of karst terrain provides conduits through which underground streams flow through). In 1997, a contractor in central Pennsylvania attempted to grout cavernous rock at a roadway project and found that the cavernous area took an enormous quantity of grout (4-5 truckloads). Within hours, the job site was visited by the Pennsylvania Fish and Boat Commission who was called to investigate an extensive fish kill at a nearby wild trout stream. In this case, the grout flowed readily through bedrock openings into a major, water-filled karst conduit and then to the nearby stream. Typically, compaction grouting is the injection of a very stiff, pumpable cementitious grout mixture at very high pressure into specific areas in the soil. The expanding globular mass of grout then compacts the soil around each point of discharge. Compaction grouting is most commonly done in stages, working from the bottom up, since this is the fastest method. It is generally used for pre-construction site improvement, to halt foundation settlements, rectify sinkhole problems, and to lift and level slabs and foundations. Advanced grouting techniques, such as compaction grouting, may be used for more demanding sinkhole repairs. The grout consistency, pressure of grout delivery, and grout placement strategy are important aspects of these more advanced methods. Consideration should be given to the potential for interference with groundwater circulation and induced flooding due to the sinkhole repair. Sinkhole repairs should include active measures to limit the exposure of the repaired area to storm water, if feasible. This is related more to high volume cementitious grout blocking the subterranean natural path of runoff.

Permeation Grouting

Permeation methods are effectively used to fill voids, cracks, fractures, cavities, and to create barriers to the movement of liquids through the ground. Permeation grouting is the direct pressure injection of a fluid grout (chemical or cementitious) into the ground to fill the spaces between particles. Pressure grout methods are used for preventing water flow, stabilizing granular material, encapsulating organic material, and improving the physical properties of soil or rock. Structural chemical grouting, when used in granular soils, permeates the spaces between the soil particles, binds the particles together, and improves the soil’s bearing capacity. This process is not necessarily intended to restrict water but when injection points are laid-out in a well-designed grid pattern, these masses interconnect to form an underground structure or curtain that inhibits fluid migration from moving through the soil. The process is quite flexible, can be designed to cause minimal disruption at the surface and therefore, is advantageous for use in urban areas or areas of limited access.

Traditional Sinkhole Remediation Methods & Challenges

There are many challenges associated with sinkholes and the traditional methods that are used to repair them:

  • Heavy machinery is often required to repair sinkholes. This equipment can require a lot of manpower to get it to the site and to operate it.
  • A wide variety of materials and mixes are typically needed for a repair, including concrete, soil, grout, synthetic filter fabrics, and various sizes and mixtures of crushed stone.
  • Injection holes for the repair materials are large and very invasive.
  • High pressure is required to pump the heavy grout to the location of the repair.
  • There is no expansion strength in the repair materials used, so over lift occurs to compensate for any shrinkage that may occur.
  • More water is introduced when using a cementitious grout – adding more weight (approx 135 lbs per cubic foot) to already distressed soils.

The Best Solution: URETEK’s Deep Injection© Process

The URETEK Deep Injection© Process is one of the best ways to repair a shallow sinkhole. Because severe structural damage can result from shallow sinkholes, immediate and conclusive sinkhole repair is critical.

URETEK Deep Injection is a combination of chemical, compaction and permeation grouting that will not cause environmental damage, stabilizes the soil at perimeter of the throat, can fill and plug the throat, and can cap the soil pipes, filling the voids and micro-fissures within the soil at the injection site. The unique URETEK geo-polymer is the key factor in the repair.

While traditional chemical grouting fills the soil cavities and pores with a waterproof material, it does not have expansion characteristics of the URETEK process.

The URETEK Deep Injection© Process gives long-term stability to the area affected by the shallow sinkhole and is the best solution for shallow sinkholes and sinkholes that occur close to the surface where compaction grouting is not an option. The URETEK Deep Injection© Process is the safest and most accurate method of filling sinkhole voids and densifying loose soils that exist within 15 feet of the surface.

The Deep Injection© Advantage

  • Fast–the unique repair process requires no digging, and projects can often be completed in hours or days. With traditional sinkhole repair methods, additional digging can be required and the time required for project completion can last weeks.
  • Effective – The URETEK geo-polymer has been used to successfully complete over 85,000 projects nationwide. The lightweight, expansive geo-polymer material not only realigns concrete liabilities but also addresses the problem at the source – giving the customer a long-lasting solution.
  • Economical – The repair process is priced consistently below alternative repair methodsand implementing repairs significantly reduces the chance for further repair costs down the road.
  • Minimally Disruptive – Unlike other repair methods, the URETEK process is minimally disruptive to the surrounding elements – which could be home residents, building workers, or vehicle traffic (depending on sinkhole location).
  • Durable – The URETEK geo-polymer that is used in the repair process is specially formulated for stability and strength – even in the harshest environmentsThe URETEK geo-polymer is moisture resistive, and the Deep Injection process is guaranteed against loss of dimensional stability or deterioration.
  • Safe – Liability risk is greatly reduced by the repair process, as a result of a safer environment. The process and material are eco-friendly and meet today’s high environmental standards.

Understanding The URETEK Deep Injection© Process

The goal of any sinkhole repair is to quickly and effectively achieve a stabilized environment with minimal intrusion on the affected property. A properly executed sinkhole repair requires the expertise of URETEK ICR Affiliates. URETEK ICR Affiliates specializes in stabilization applications, with the use of its revolutionary URETEK geo-polymer.

The URETEK geo-polymer technology was developed through a partnership with leading chemists at Bayer Material Science. The geo-polymer material is formulated to be lightweight yet have powerful lifting and stabilization features, and maintains impressive compressive strength under the heaviest of loads. The geo-polymer is also proven effective and environmentally safe in over 85,000 projects worldwide over the past 25 years.

The Choice is Clear

RETEK’s Deep Injection® Process provides a cost effective, fast, and safe solution to for sinkhole remediation. As the pioneer and patented holder of the Deep Injection Process, URETEK ICR offers a proven, long-term solution for residential, commercial, industrial, and infrastructure sinkhole repair. The end result is a properly repaired sinkhole environment with stabilized strata that is durable and will provide maximum efficiency for years to come. URETEK ICR network of affiliates are exclusive applicators of The URETEK Deep Injection© Process.

URETEK ICR is associated with an international network of URETEK companies located in 80 countries, with exclusive rights in the United States to international patented technologies. Globally, URETEK companies have completed over 100,000 successful jobs, and utilize over 30 years of real world project experience. URETEK ICR focuses on resolving complex concrete lifting, soil stabilization and infra­structure rehabilitation projects for industrial, commercial, and residential properties, infrastructures, and assets.

In addition to sinkhole repair, the Deep Injection Process is an effective solution for infrastructure sealing and repairs, including emergency restoration. The versatility of the URETEK geo-polymer makes it ideal for repairs involving manholes, sewer systems, dams and levees.

Watch Now: Deep Injection Animation

Excavated soil showing how URETEK polymer bonds and compacts weak soil in saturated environments.