8/18/2019 Airtight.pdf

1/4

A ventilation seal is a barrier

that separates a remote or

abandoned area of an

underground mine from the

current active area where miners and

equipment routinely work and travel.

Ventilation seals improve safety for the

workers, reduce the hazards associated

with accumulations of noxious and

explosive gases, improve the efciency

of the mine ventilation system and

reduce the area of the undergroundmine that needs to be maintained or

monitored by mine personnel. The

underground mine ventilation seal

system is therefore a line of defense that

separates a potentially hazardous

environment and provides safety for the

workers in the underground operation.

The mine ventilation seal system has

evolved dramatically. As mining

operations have increased in size in

conjunction with the advancements in

mining methods and mechanised

mining equipment, mining regulatory

agencies have recognised that allworked out or abandoned areas of

underground mines need to be

AirtightROBERT BOLINGER, MINOVA NORTH AMERICA,

US, DISCUSSES THE RECENT EVOLUTION OFUNDERGROUND MINE VENTILATION SEALS.

Reprinted from June 2011  |  World Coal | Reprinted from June 2011  |  World Coal | 

8/18/2019 Airtight.pdf

2/4

8/18/2019 Airtight.pdf

3/4

 l A professional engineer must examine and certify theseal location and installation of the ventilation seals.

 l All seals must be designed, constructed and maintainedto meet the following criteria:

 x Withstand a 50 psi instantaneous overpressure andmaintain this overpressure for a specified interval.For a 50 psi ventilation seal, the sealed area must bemonitored and maintained inert.

 x Sealed areas that do not require monitoring ormaintained inert after the approved ventilation sealhas reached their required strength must withstanda 120 psi instantaneous overpressure and maintain

this overpressure for a specified interval.

Permanent, pumpable, blast-proofventilation sealMinova, in cooperation with Marshall Miller & Associates, a

leading engineering consulting rm with over 35 years

experience in the mineral resource industry, has developed

the Tekseal® ventilation seal system, an MSHA-approved

permanent, pumpable, blast-proof ventilation seal system for

use in underground mines. The Tekseal pumpable seal

process is, and continues to be, a safe and easy system for

installing permanent underground ventilation seals.

The design is based on balancing the load applied to theface of the seal from a blast or underground explosion against

the resistance to shearing at the Tekseal and the surrounding

strata interface. The applicable design of the system is dened

under the parallel plug bulkhead formula identied by the

US Bureau of Mines IC 9020, “Design of bulkheads for

controlling water in underground mines”.1

The formula is an accepted design criteria by MSHA

technical support for the design of plug-type seals in

underground mines. The formula is modied to include a

dynamic load factor (DLF) to address the additional dynamic

loading imposed by an explosion or blast underground on

the face of the ventilation seal and to include a design factor

of safety for assumptions made in the design process

regarding actual conditions. The dynamic load factor was

determined from the maximum response of elastic,

one-degree-of freedom for rectangular load, based on design

criteria identied by the Department of the Army

Technical Manual 5-1300, “Structures to resist the effects of

accidental explosions”.2

The following plug bulkhead design formula was used to

compute the thickness of the ventilation seal by balancing the

dynamic load on the face of the ventilation seal versus theshearing forces along the perimeter of the seal:

L = P x W x H x Fs x DLF ÷ (2 x (W + H) x f shear)

In which:

L = the resultant adjusted thickness of the plug (ft).

P = the assumed blast pressure (50 or 120 psi).

W = the entry width after loose strata has been removed (ft).

H = the entry height after loose strata has been removed (ft).

Fs = the static factor of safety (1.5).

DLF = the dynamic load factor (2.0).

f shear = calculated laboratory shear strength for Tekseal (72 psi).The Tekseal ventilation seal system is a simple, innovative

and cost effective permanent seal system for the underground

mining industry. Formwork for the Tekseal “plug” may be

constructed by one of three following options:

 l Timber crib or posts, boards and brattice cloth. l Concrete blocks. l Prefabricated steel panels.

The Tekseal material forms a low density foam

(0.6 – 0.8 SG) when combined with a controlled amount of

air and water from a specially-designed Tekplacer pump

unit. The 400 psi compressive strength mixture begins to gel

in minutes, forming a non-toxic, non-combustible

ventilation seal. The lower causticity of the material enablessafer handling compared to other standard cement

products.

Advantages of the Tekseal ventilation seal system include:

 l Acid mine water resistance: determined as a result ofmonths of MSHA testing in pH 3 water.

 l Simplicity: easy to install; eliminates requirements forhitching into roof, ribs and floor.

 l Proven: thousands of installations have beenconstructed in the US alone.

 l Ease of use: ideal for areas difficult to reach and/or inneed of major rehabilitation for conventional seals.

 l Labour savings: requires minimal man hours. l Safety: reduces exposure time in hazardous areas and

handling of heavy material.

Formwork construction of the seal.

Brattice curtain.

Reprinted from June 2011  |  World Coal | 

8/18/2019 Airtight.pdf

4/4

 l

Yield: yields with ground pressure before brittlefailure, a substantial improvement over conventionalseals.

 l Reduced cure times: by controlled increases inthe material density, cure times to the requiredcompressive strength can be attained in as low asthree days.

 l MSHA approval: the seals are approved for variousentry dimensions for both Mainline and Gob seals at50 and 120 psi dynamic blast pressures.

Installation guidelinesThe installation guidelines for the Tekseal ventilation seal

area are very simple. The preparation, construction andpumping steps are as follows:

 l A professional engineer approves and certifies theseal location.

 l The ventilation seal plan is submitted and approved by MSHA.

 l The seal location must be at least 10 ft from thecorner of the underground pillar. (Approval for5 – 10 ft offsets may be submitted for approval toMSHA with additional pillar support).

 l The roof, ribs and floor must be cleaned and scaled tocompetent strata. All loose material must be removed

from within the seal location and for a distance of 3 fton each side of the seal. Rock dust should be removedfrom the strata within the seal area.

 l Supplemental roof support must be installed bycribbing or equivalent on both the outby and inbysides of the seal.

l The seal area must be free of debris, oil, standing orrunning water and unsound material.

l Each pair of formwork is constructed of wood and brattice cloth, 6 in. solid blocks or prefabricatedsteel panels. The minimum thickness of the seal is based on the maximum height and width once theseal area is prepped. The thickness is defined on theappropriate design table for the respective materialused for the forms.

l A nonmetallic water drainage trap and valve isinstalled in the lowest elevation seal(s) of the set.A low weir catchment, no more than 12 in. high, isconstructed across the entry inby the seal.

 l Each seal shall have one nonmetallic gas samplingtube extended into the next connecting crosscut inbythe seals.

 l At least three pressurisation fill pipes with shut offare installed in each seal. If a seal’s thickness exceeds10 ft, than six fill pipes are installed. A bleeder pipemay be used to confirm filling if any roof voids exist.

 l  An approved polyurethane foam pack may be usedaround the perimeter to minimise leakage duringmaterial pressurisation.

 l The Minova Tekplacer pump is calibrated before thefilling of the seals to insure the Tekseal material isproportionally correct.

 l A minimum of nine Tekseal samples are takenfrom each seal, stored at the ventilation seal for

the specified cure time, and then crushed to verifythe required minimum average 400 psi unconfinedcompressive strength.

ConclusionThe construction of underground ventilation seals has

successfully evolved, from a barrier that was originally

constructed from material that was deemed suitable to the

present day ventilation seal that is structurally engineered and

designed to withstand explosion overpressures of

50 and 120 psi. The new design criteria and innovative

materials of these ventilation seals have increased the safety of

the underground workers and the efciency of the mining

operations.As a result of the Minova and Marshall Miller & Associates

accepted plug design analysis for a ventilation seal, the

Tekseal ventilation seal system can be used in a wide variety

of geological conditions. This versatility, combined with the

many advantages of the system, has made the Minova

ventilation seal a proven and widely accepted ventilation seal

for use in underground mining operations.

References1. CHEKAN, G.J., “Design of bulkheads for controlling water in

underground mines,” US Bureau of Mines IC 9020 (1985).

2. US Department of the Army Technical Manual 5-1300 waswritten in 1969 and revised in 1990. It has since beensuperseded by the Department of Defense UFC 3-340-02 (2008).

Typical Tekplacer pump and water heater.

Finished seal.

  |  World Coal |Reprinted from  Jun e 2011