Published in the May 2009 Coal USA Magazine

Changes in underground strata conditions occur constantly, affecting safety and production. Like elsewhere in the mine, ventilation seals and the surrounding earth continually shift, often creating air and water leaks in sealed areas.

To remediate these seals, Micon developed polyurethane grout injection techniques based on the same technology and expertise the company has used in roof control and other applications over the past 28 years.

“When proposing solutions to our customers, we always think in terms of potential savings from future problems,” company general manager of operations Blair Lamb said.

Each seal site is assessed for proper polyurethane grout placement in its problematic areas, and a Micon technician then injects grout under pressure into the strata.

During injection, the polyurethane remains liquid for a short time as it expands into fissures as small as 0.1mm. Within two minutes, the polyurethane cures into a high-density hard plastic grout to form a monolithic, continuous structure with the strata surrounding the seal.

The grout blocks both small and large passageways around the seal, eliminating later operational hurdles, such as leakage during barometer shifts, and containing nitrogen pumped into the gob area for inertion.

“Micon’s ring grouting allows operators with air leakage around ventilation seals to stay in production or get back in production in a timely manner,” noted Micon operations manager Bill Waxter.

Other common approaches for fixing seal leakage include the application of two-component, low-density foam packs or other approved non-shrink sealants. These products are typically applied by mine personnel.

Results and effectiveness vary based on conditions and the severity of the problem; however, off-the-shelf products often cannot meet the large nature of the problem at hand or can only stave off the situation temporarily.

Off-the-shelf foam products patch the surface of the crack, while polyurethane injection goes to the root of the problem by filling the entire length of a crack, Micon said.

“Seal remediation is a very complex process that requires a trained professional to assess the situation and effectively inject the grout,” operations manager Mike Zekas said.

Waxter concurred, adding that by contacting Micon as soon as a leak is detected, the most proactive measures can be performed.

Micon’s seal remediation will mitigate, or at least minimize, the effects of gas transference due to regular daily barometric variations forming either an explosive mixture behind seals or eluting high methane into the ventilation system. To prevent such scenarios, Micon draws from the organization’s depth and breadth of industry experience to provide comprehensive solutions to customers.

One measure Micon may also recommend is gas sampling and analysis by its sister company, Phoenix First Response. Laboratory-analyzed samples are interpreted by Phoenix’s technical staff and can provide specific knowledge of the gas conditions in sealed areas.

This knowledge will augment safety and production by providing an accurate picture of the potential for contamination of the mine’s ventilation system.

Micon said it focused on creating an effective solution for each customer, and complementary products and services were only recommended when beneficial to the operator. Above all, addressing ventilation and water control issues before reaching a critical point is the key to successful seal remediation.

Ventilation seal leakage can be caused by a variety of factors, such as seals that were not properly topped off at construction; seal cores that have shrunk; deteriorating ribs, roof or floor that have sloughed off; an increased difference in pressure between the sealed area and the mine’s ventilation; or ground movement that has disturbed the strata surrounding the seal.

“Some of the other leaks that we encounter are from bolt communication,” noted western project manager Casey Dagit. Bolt communication occurs when air leaks from one roof bolt inby the seals through broken strata and out through a bolt in the ventilated area.

“These leaks also affect a seal doing its job and are usually fixable through the grouting process,” he said.

Micon officials said operators should look out for situations that can cause seal leakage and indications that leakage has already occurred.

Occasionally, a seal may develop structural problems and its repairs must be designed by a structural engineer and approved by the US Mine Safety and Health Administration.

The Micon grouting can give mines increased safety and greater ventilation efficiency, and can aid in meeting MSHA requirements. The company also provides federally approved 120psi seals as well as low-psi ventilation seals and stoppings, polyurethane injection for strata control and pumpable cribs.