Technology News

No. 467 November 1997

U.S. Department of Health and Human Services

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Wood Crib Performance Model

Objective

To provide an engineering solution to wood crib design and

deployment strategies that will ensure safety for underground

coal mine workers. This is accomplished by preserving

necessary ground control requirements while minimizing

support costs or by developing new support strategies to enhance

ground support in difficult conditions. A secondary objective is

to be able to quantify wood crib support performance to define

support requirements for alternative support systems. These

objectives have been achieved through a simple-to-use computer

program called the wood crib performance model (wcpm).

Background

Wood cribs are the most widely used support in

underground coal mines and provide critical roof support in

many applications. Optimal use of these timber supports has

been overlooked in the past due in part to the low cost of wood,

which allowed highly conservative support strategies. With the

increasing cost of wood and greater dependency on wood cribs

for support in applications such as longwall tailgate and bleeder

entries (figure 1), more efficient use of wood crib supports is

required.

Approach

The WCPM is unique in that it was developed through fullscale testing of wood crib supports in the unique mine roof

simulator load frame at the National Institute for Occupational

Safety and Health’s Pittsburgh Research Laboratory. Several

hundred full-scale tests were conducted to evaluate the design

parameters associated with various wood crib constructions.

The performance of wood cribs is determined by not only the

type of wood used in the crib construction, but also how the crib

is built. Therefore, full-scale testing is required to develop a

realistic model that accurately predicts wood crib performance.

Using the WCPM

The interactive computer program is currently written in

MicroSoft QuickBASIC and is very easy to use. Simply install

the computer disk into the drive and type "woodcrib" to execute

the program. A general description of the program is

described, followed by a main menu that allows to user to select

from five subprograms:

• WCPM: This program computes crib load as a function

of displacement of the support structure induced by roof and

floor convergence. The program will provide the user with

recommendations to improve the current crib construction.

• MINLOAD: This program helps the user to define

support requirements based on designated mine conditions.

• CRIBOPT: This program optimizes wood crib design by

determining whether to use a 4- or 9-point crib and how big the

timbers should be to provide the required support capacity and

crib stability.

• PLACOPT: This program determines the optimum crib

spacing for a specified crib design and required support

capacity per foot of mine entry.

• SYSOPT: This program evaluates the material handling

requirements and cost of the current support design in

conjunction with the support capacity and allows comparison of

up to three alternative support systems.
Figure 1.—Installation of cribs in a longwall tailgate entry. (Photo by Frank E. Chase, NIOSH

Pittsburgh Research Laboratory.)

For More Information

To obtain the WCPM computer program or to receive a copy

of a report detailing full-scale test results and mathematical

derivation of the WCPM, contact Thomas M. Barczak, NIOSH

Pittsburgh Research Laboratory, Cochrans Mill Rd., P.O. Box

18070, Pittsburgh, PA 15236-0070, phone: (412) 892-6557, fax: (412)

892-6891, e-mail: thb0@cdc.gov

Mention of any company name or product does not constitute

endorsement by the National Institute for Occupational Safety and

Health.

To receive additional information about mining issues or

other occupational safety and health problems, call 1-800-

35-NIOSH (1-800-356-4674), or visit the NIOSH Home

Page on the World Wide Web at http://www.cdc.gov/niosh/

homepage.html

As of October 1996, the safety and health research functions

of the former U.S. Bureau of Mines are located in the

National Institute for Occupational Safety and Health

(NIOSH).