Exercise Figure 8.1 20 ft 220 ft -200 ft- 8.1). The concrete has a unit weight of 2.4 Mg/m³ (150 lb/ft³). The height of the dam is 67.1 m (220 ft), the crest is 6.1 m (20 ft) wide, and the base is 61 m (200 ft) wide. Note: 1 ft = 0.3048 m. a. What is the average pressure exerted on the rock foundation in MPa (lb/ft2)? What is the maximum pressure? Explain. b. Refer to the different sedimentary rocks listed in Table 8.1. Using average compressive strength and shear strength values for these sedimentary rocks compare them to the average pressure calculated in part (a). Are any so low to be of concern? Explain. c. Assume that the pressure from the weight of the dam is dissipated within 30.3 m (100 ft) below the rock surface and the full pressure acts over this distance. How much settlement will occur in the center of the dam because of the gravity force for the different sedimentary rocks listed in Table 8.1 (use average values)? Ind
Exercise Figure 8.1 20 ft 220 ft -200 ft- 8.1). The concrete has a unit weight of 2.4 Mg/m³ (150 lb/ft³). The height of the dam is 67.1 m (220 ft), the crest is 6.1 m (20 ft) wide, and the base is 61 m (200 ft) wide. Note: 1 ft = 0.3048 m. a. What is the average pressure exerted on the rock foundation in MPa (lb/ft2)? What is the maximum pressure? Explain. b. Refer to the different sedimentary rocks listed in Table 8.1. Using average compressive strength and shear strength values for these sedimentary rocks compare them to the average pressure calculated in part (a). Are any so low to be of concern? Explain. c. Assume that the pressure from the weight of the dam is dissipated within 30.3 m (100 ft) below the rock surface and the full pressure acts over this distance. How much settlement will occur in the center of the dam because of the gravity force for the different sedimentary rocks listed in Table 8.1 (use average values)? Ind
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
Related questions
Question
100%
8.1
![20 ft
220 ft
-200 ft-
Exercise Figure 8.1
8.1). The concrete has a unit weight of 2.4 Mg/m³
(150 lb/ft³). The height of the dam is 67.1 m (220 ft),
the crest is 6.1 m (20 ft) wide, and the base is 61 m
(200 ft) wide. Note: 1 ft = 0.3048 m.
a. What is the average pressure exerted on the rock
foundation in MPa (lb/ft2)? What is the maximum
pressure? Explain.
b. Refer to the different sedimentary rocks listed in
Table 8.1. Using average compressive strength and
shear strength values for these sedimentary rocks
compare them to the average pressure calculated in
part (a). Are any so low to be of concern? Explain.
c. Assume that the pressure from the weight of the
dam is dissipated within 30.3 m (100 ft) below the
rock surface and the full pressure acts over this
distance. How much settlement will occur in the
center of the dam because of the gravity force for
the different sedimentary rocks listed in Table 8.1
(use average values)?
7. Excavation for a gravity dam foundation revealed a
unit of poorly cemented sandstone 30.3 m (100 ft)
wide (plan view) within a massive dolomite sequence.
The dolomite has an E value of 5.5 x 104 MPa
(8 x 106 psi) and the sandstone has an E value of
6.9 x 10³ MPa (1 x 106 psi).
a. What would be the concern if both rocks were
loaded equally by the gravity dam? What would be
the effect on the dam?
b. How could this problem be alleviated? Consider
both replacement and strengthening possibilities.
8. A 333.3-m (1100-ft) long, horseshoe-shaped tunnel
is to be driven through massive granite with a unit
weight of 2.72 Mg/m³ (170 lb/ft3). The tunnel is 9.1 m
(30 ft) high and 9.1 m (30 ft) wide in cross section
(Exercise Figure 8.2). The maximum rock cover above
the tunnel in the middle of the mountain is 366.5 m
(1200 ft). Note: 1 ft = 0.3048 m.
15 ft
-30 ft-
Exercise Figure 8.2
a. What is the total overburden stress at the midway
point in the tunnel in MPa (psi and psf)?
b. Because of arching effects that transfer load around
the tunnel opening, the roof or crown of the tunnel
does not commonly support the full overburden
stress, but instead is typically much less. If the
roof stress was found to be 0.12 MPa (2500 psf),
how many meters (feet) of rock above the tunnel
does this represent? How do you suppose this load
would be supported in the tunnel?
ant to s
c. If the tunnel excavation was completed in 80 work-
ing days with two shifts per day, how many lineal
meters (feet) of tunnel were excavated per day?
How many meters (feet) per shift? What was the
average volume of rock removed per day, per shift?
(Hint: Calculate the area of the cross section.)
As
d. The tunnel project was bid at $1,878,000. What
would be the cost per lineal foot of the tunnel?
Right
abutment
9. An arch dam transfers much of the water load onto
the abutments (the rock mass on the sides of the
dam) (see Exercise Figure 8.3 for a plan view). The E
value for the concrete is 4.14 x 104 MPa (6 x 106 psi).
Exercise Figure 8.3
a. What would occur if the abutments were shale
with an E of 2.07 x 104 (3 x 106 psi)?
b. What if the abutments were diabase with an E of
9.66 x 104 MPa (14 x 106 psi)? Which of the two
rocks would be preferred, the shale or the diabase?
Explain why.
Upstream
Downstream
/Left
abutment](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F8ea503b5-9839-4a05-b482-50f8a035eb54%2Fe1de3522-ee10-4e0d-be31-a0051940d578%2Faf0b8jq_processed.jpeg&w=3840&q=75)
Transcribed Image Text:20 ft
220 ft
-200 ft-
Exercise Figure 8.1
8.1). The concrete has a unit weight of 2.4 Mg/m³
(150 lb/ft³). The height of the dam is 67.1 m (220 ft),
the crest is 6.1 m (20 ft) wide, and the base is 61 m
(200 ft) wide. Note: 1 ft = 0.3048 m.
a. What is the average pressure exerted on the rock
foundation in MPa (lb/ft2)? What is the maximum
pressure? Explain.
b. Refer to the different sedimentary rocks listed in
Table 8.1. Using average compressive strength and
shear strength values for these sedimentary rocks
compare them to the average pressure calculated in
part (a). Are any so low to be of concern? Explain.
c. Assume that the pressure from the weight of the
dam is dissipated within 30.3 m (100 ft) below the
rock surface and the full pressure acts over this
distance. How much settlement will occur in the
center of the dam because of the gravity force for
the different sedimentary rocks listed in Table 8.1
(use average values)?
7. Excavation for a gravity dam foundation revealed a
unit of poorly cemented sandstone 30.3 m (100 ft)
wide (plan view) within a massive dolomite sequence.
The dolomite has an E value of 5.5 x 104 MPa
(8 x 106 psi) and the sandstone has an E value of
6.9 x 10³ MPa (1 x 106 psi).
a. What would be the concern if both rocks were
loaded equally by the gravity dam? What would be
the effect on the dam?
b. How could this problem be alleviated? Consider
both replacement and strengthening possibilities.
8. A 333.3-m (1100-ft) long, horseshoe-shaped tunnel
is to be driven through massive granite with a unit
weight of 2.72 Mg/m³ (170 lb/ft3). The tunnel is 9.1 m
(30 ft) high and 9.1 m (30 ft) wide in cross section
(Exercise Figure 8.2). The maximum rock cover above
the tunnel in the middle of the mountain is 366.5 m
(1200 ft). Note: 1 ft = 0.3048 m.
15 ft
-30 ft-
Exercise Figure 8.2
a. What is the total overburden stress at the midway
point in the tunnel in MPa (psi and psf)?
b. Because of arching effects that transfer load around
the tunnel opening, the roof or crown of the tunnel
does not commonly support the full overburden
stress, but instead is typically much less. If the
roof stress was found to be 0.12 MPa (2500 psf),
how many meters (feet) of rock above the tunnel
does this represent? How do you suppose this load
would be supported in the tunnel?
ant to s
c. If the tunnel excavation was completed in 80 work-
ing days with two shifts per day, how many lineal
meters (feet) of tunnel were excavated per day?
How many meters (feet) per shift? What was the
average volume of rock removed per day, per shift?
(Hint: Calculate the area of the cross section.)
As
d. The tunnel project was bid at $1,878,000. What
would be the cost per lineal foot of the tunnel?
Right
abutment
9. An arch dam transfers much of the water load onto
the abutments (the rock mass on the sides of the
dam) (see Exercise Figure 8.3 for a plan view). The E
value for the concrete is 4.14 x 104 MPa (6 x 106 psi).
Exercise Figure 8.3
a. What would occur if the abutments were shale
with an E of 2.07 x 104 (3 x 106 psi)?
b. What if the abutments were diabase with an E of
9.66 x 104 MPa (14 x 106 psi)? Which of the two
rocks would be preferred, the shale or the diabase?
Explain why.
Upstream
Downstream
/Left
abutment
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