Preparation and Rehabilitation of Permanent Ventilation Seals


Preparation and Rehabilitation of Permanent Ventilation Seals

Background of Sub-Technical Inc

A fifteen year old contracting company, specializing in Ground and Water control in the Mining and Civil Industries. Utilising a variety of proprietary Polyurethane Formulations. Over nine hundred projects completed to date, approximately half of them within Underground Coal.

Background in development, Installation and Rehabilitation of Permanent Ventilation Seals in Coal Mines

The Principals of Sub-Technical were deeply involved in the development and testing of a variety of explosion proof seals from the late nineteen eighties onward. Designs included steel sets with interlaced, imbedded rebar and an internal bladder filled with cementitous grout, (similar to the "Precision Seal", currently installed by Strata Services, Inc.).Additionally a variety of Composite Barrier Seals using Block walls to contain the core.

Being established in 1996 Sub-Technical undertook as an approved installer for the "Minova" "Plug Seal" for a number of years. In addition we were appointed by the "Mowlem Group, Plc." (Australia) to install and advise per Testing and Approval at the Lake LLyn Facility. These were also an imbedded steel/Rebar interlaced structure which was then Gunnited.

Our portfolio of projects related to Sealing also includes Bulkheads, deep under Lake Superior to contain Sulphuric Acid leaching solution. Also many Bulkheading projects for Coal Mining, in which we incorporated a proprietary “Burst Hose” installation, prior to filling of the forms. This system allows complete “ring grouting” once the cement is cured, (and shrunk), without ever drilling a hole.

Current and past materials used for Consolidation/Sealing in and around Ventilation Seals

"Hyperflex" as a grouting medium specifically as refers to Preparation of, or Rehabilitation of Permanent Ventilation Seals.
HYPERFLEX is a single component, water activated, Hydrophobic, Pre-Polymeric, Pre-Catalyzed, Polyurethane. It’s product is a low density, closed cell, flexible foam.

Technically Speaking,

Practically Speaking. We have as a company championed the cause of Single Component materials in the Mining Industry for most of our History, they have sat well with our other formulations to allow us a full range of offerings. Five years ago we were fortunate to engage the services of one of the Nation’s foremost Polyurethane Chemists, (ex-Mobay/Bayer) and have benefitted since. As a result all of our formulations have been improved to a finite degree, including of course HYPERFLEX.

Although we began use of this versatile material many years ago, its urgency of use in Coal Mining is increasing along with operators needs to remain in compliance in light of MSHA’s increased regulatory activity.

Applications for Seal areas prior to seal installation are to be honest understated, there have been many instances where the expense involved up front would have saved time and money when compared to retrofitting at a later date. This is understandable to some degree as the cost of a given seal has escalated significantly, since we left the use of the 20PSI and progressed to 50 and 120 PSI ratings for the units. Nevertheless a more thorough examination of the sites and some predictive engineering as relates to future mining plans and the effect they will or may have on Ground conditions in these critical areas could well save the time and expense of a reactive approach brought about by regulation at a later date.

This being said current reality is that the majority of our work in Seal areas takes place at a point where significant gaseous exchange is occurring, often the leakage has progressed to the point where Roof, Interface and floor are all incompetent to a greater or lesser degree. In addition there is often need for supplementary support in the adjacent entry way, sometimes beyond.

Generally if apparent the worst zone receives primary injection but in instances where it is not obvious we begin with the roof unit and progress downward, there are instances where both injection and some supplementary spot bolting is required although the properties of Hyperflex most often make the latter unnecessary.

Mechanical Strengths

Although as mentioned previously the stated strengths of Hyperflex are measured in a “free rise” situation, the reality of pumping these materials means that when pumped under pressure, they can not expand fully and the density of the cured material increases. For example the free rise density of Hyperflex would be 2.25 #PCF, this gives a compressive strength of 25 PSI, Shear 28 PSI, Tensile 30 PSI. Whereas at 08 #PCF, compressive 70 PSI, Shear 80 PSI, Tensile 85 PSI. So physical strength characteristics as may be expected increase along with Density.

Pumping tests performed in roof strata, where crack systems are well defined, with an input pressure of 1,000 PSI (having subtracted pumping losses); give an average cured in place Density of 40 # PCF, which provides a compressive strength in the region of 2,000 PSI, with very high adhesion values. This provides very competent support in unstable roof conditions while still allowing a large margin for movement without "Compromising the materials sealing ability".

Hyperflex's advantages as a Sealing/Support Medium.

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