1
25-078
Retrospective Analysis of Solvay Chemicals #5 Shaft
William G Pariseau
University of Utah, Salt Lake City, Utah
INTRODUCTION
Solvay Chemicals Company mines trona in south-central
Wyoming and has done so for many years. The mine is one
of several in a mid-continent sedimentary basin that hosts
the largest trona resource in the world. Trona is an evapo-
rite, a sesquicarbonate that occurs in several seams of vary-
ing thicknesses and depths. Trona is processed into soda ash
which has a number of industrial uses in the manufacture
of glass, detergent, paper and chemicals. Figure 1 shows the
location of the Solvay Mine.
A ventilation shaft was recently excavated at Solvay
Chemical Company’s mine in the trona patch. In fact, a
22 ft (6.7 m) diameter shaft (inside diameter) was bored
upwards from the 1500 ft (457 m) level to the surface.
The first bored section was 26 ft (7.9 m) in diameter that
allowed for a 2 ft (0.6 m) thick concrete liner. This sec-
tion began at a depth of approximately 1500 ft (457 m).
A second bored section was 24 ft, (7.3 m) in diameter that
allowed for a 1 ft (0.3 m) thick concrete liner. This section
began at a depth of approximately 750 ft (229 m). This
shaft is the #5 Shaft. Figure 2 shows the cutter head used to
excavate the shaft.
PROBLEM DEFINITION
The immediate problem is to compute stress changes
induced by excavation of the shaft, given the pre-excavation
stress. Stress changes are then added to the pre-excavation
stress and are used to compute the final stresses about the
shaft. Final stresses, in turn, are, used to compute element
safety factors defined as a ratio of element strength to stress
using appropriate three-dimensional measures of each.
Elements in the elastic domain and elements that have
reached the elastic limit are clearly defined in the distribu-
tion of element safety factors. Displacements and strains are
also computed in the process of analysis using the versatile
finite element method. In this regard, an elastic-perfectly
plastic material model is used. Neither strain hardening
nor softening occur with deformation beyond the elastic
limit as illustrated in Figure 3. To be sure, strata may be
Figure 1. Map showing the location of the Solvay Chemicals and other trona mines in
southwest Wyoming north and south of I-80, courtesy of the Wyoming Mining Association
website
25-078
Retrospective Analysis of Solvay Chemicals #5 Shaft
William G Pariseau
University of Utah, Salt Lake City, Utah
INTRODUCTION
Solvay Chemicals Company mines trona in south-central
Wyoming and has done so for many years. The mine is one
of several in a mid-continent sedimentary basin that hosts
the largest trona resource in the world. Trona is an evapo-
rite, a sesquicarbonate that occurs in several seams of vary-
ing thicknesses and depths. Trona is processed into soda ash
which has a number of industrial uses in the manufacture
of glass, detergent, paper and chemicals. Figure 1 shows the
location of the Solvay Mine.
A ventilation shaft was recently excavated at Solvay
Chemical Company’s mine in the trona patch. In fact, a
22 ft (6.7 m) diameter shaft (inside diameter) was bored
upwards from the 1500 ft (457 m) level to the surface.
The first bored section was 26 ft (7.9 m) in diameter that
allowed for a 2 ft (0.6 m) thick concrete liner. This sec-
tion began at a depth of approximately 1500 ft (457 m).
A second bored section was 24 ft, (7.3 m) in diameter that
allowed for a 1 ft (0.3 m) thick concrete liner. This section
began at a depth of approximately 750 ft (229 m). This
shaft is the #5 Shaft. Figure 2 shows the cutter head used to
excavate the shaft.
PROBLEM DEFINITION
The immediate problem is to compute stress changes
induced by excavation of the shaft, given the pre-excavation
stress. Stress changes are then added to the pre-excavation
stress and are used to compute the final stresses about the
shaft. Final stresses, in turn, are, used to compute element
safety factors defined as a ratio of element strength to stress
using appropriate three-dimensional measures of each.
Elements in the elastic domain and elements that have
reached the elastic limit are clearly defined in the distribu-
tion of element safety factors. Displacements and strains are
also computed in the process of analysis using the versatile
finite element method. In this regard, an elastic-perfectly
plastic material model is used. Neither strain hardening
nor softening occur with deformation beyond the elastic
limit as illustrated in Figure 3. To be sure, strata may be
Figure 1. Map showing the location of the Solvay Chemicals and other trona mines in
southwest Wyoming north and south of I-80, courtesy of the Wyoming Mining Association
website