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SAB 2712 SKAA 2712 1 FINAL EXAMINATION SEMESTER I, SESSION COURSE CODE : SAB 2712 SKAA 2712 COURSE : ENGINEERING GEOLOGY AND ROCK MECHANICS PROGRAMME : SAW SKAW DURATION : 2 HOURS DATE : JANUARY 2016 INSTRUCTION TO CANDIDATES: 1. ANSWERS ALL QUESTIONS IN SECTION A AND SECTION B 2. USE SEPARATE ANSWE...

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SAB 2712 / SKAA 2712 1

FINAL EXAMINATION SEMESTER I, SESSION 2015/2016 COURSE CODE

:

SAB 2712 / SKAA 2712

COURSE

:

ENGINEERING GEOLOGY AND ROCK MECHANICS

PROGRAMME

:

SAW / SKAW

DURATION

:

2 HOURS

DATE

:

JANUARY 2016

INSTRUCTION TO CANDIDATES: 1.

ANSWERS ALL QUESTIONS IN SECTION A AND SECTION B

2.

USE SEPARATE ANSWER BOOKLET FOR EACH SECTION

WARNING! Students caught copying/cheating during the examination will be liable for disciplinary actions and the faculty may recommend the student to be expelled from the study.

This examination question consists of ( 7 ) printed pages only.

SAB 2712 / SKAA 2712 2

SECTION A: GEOLOGY Q1.

Dynamism of the earth can be explained by the theory of plate tectonics. Based on the statement, answer the following questions a)

What are the major ideas of the theory of plate tectonics? (5 marks)

b)

Discuss the existence of volcanoes using the theory of plate tectonics (5 marks)

c)

Applying the same theory, explain how tsunami is generated? (5 marks)

Q2.

Rocks can be classified into three groups which are igneous, sedimentary and metamorphic rocks. a)

What criteria are used to classify the igneous rocks in terms of its mass and material characteristics? (6 marks)

b)

Discuss the characteristics of the depositional environment that influence the properties of sedimentary rocks? (5 marks)

c)

How is foliation produced in a metamorphic rock? (2 marks)

d)

Q3.

Discuss some of the engineering problems associated with metamorphic rocks? (6 marks)

Weathering is a natural process in altering and causing decay in rock mass. Various construction issues caused by weathering effects can be predicted based on different rock types.



a)

Discuss typical issues on the state of weathering in interbedded sandstone and shale rock masses. (5 marks)

b)

Evaluate the characteristics of residual soil produced from sandstone and shale bedrock. (4 marks)

c)

What would be the possible issues to be considered when undertaking foundation works ininterbedded sandstone and shale bedrock? (7 marks)

SAB 2712 / SKAA 2712 3

SECTION B: ROCK MECHANICS

Q4.

Most laboratory tests data (e.g. UCS from UCT) represent material properties of rock and therefore cannot be used directly in design of an engineering structure associated with in situ rock mass. Certain factors (e.g. FOS) need to be imposed on this data so that it can represent the mass properties of the in situ rock body more appropriately. a)

For highly jointed rocks, explain why their material properties are different from its mass properties? (2 marks)

b)

For the rock properties listed in Table 2 below, indicate whether it is mass or material property? (5 marks) Table 1

c)

No

Properties

1

Joints spacing

2

RQD

3

Poisson’s ratio

4

Tensile strength

5

Thickness of bedding planes

Mass OR Material property

Data obtained from uniaxial compression test (UCT) on a core sample is listed in Table 2. Based on the given data (without plotting the stress-strain graph), name and calculate four (4) rock properties for this sample? (8 marks)

SAB 2712 / SKAA 2712 4

Table 2

Q5.

Stress (MPa)

Vertical strain (%)

Horizontal strain (%)

0.0

0.000

0.000

1.4

0.001

0.000

7.5

0.011

-0.001

18.4

0.029

-0.004

32.0

0.054

-0.008

40.0

0.066

-0.010

48.5

0.081

-0.013

56.5

0.096

-0.016

65.0

0.113

-0.019

71.5

0.128

-0.022

Rock Quality Designation (RQD) is the most basic parameter used to describe the discontinuous nature of in situ rock masses. In the absence of core samples obtained from borehole drilling, the RQD can also be estimated indirectly. Answer the following questions: a)

Name two indirect method that can be used to calculate the RQD (2 marks)

b)

Based on the data listed in Table 3, calculate the RQD value (%) for this rock mass? (4 marks)

c)

As seen in Table 3, explain why propagation velocity of primary wave in the in situ rock mass (VF) is always lower than in the rock sample (VL)? (2 marks)

d)

Based on Figure 1, calculate the RQD value (%) for the same rock mass? (Given RQD = 115 – 3.3 Jv) (7 marks)

SAB 2712 / SKAA 2712 5

Table 3 Panel / core sample

Average primary wave velocity m/s VF

VL

Panel A / Core sample A

2000

2040

Panel B / Core sample B

1980

2020

200 160 200

300

500

90

750 430

280

FIGURE 1

90

SAB 2712 / SKAA 2712 6

Q6.

A tunnel has been proposed in a granite rock mass. For the associated calculations on stresses the rock mass is assumed to be intact and continuous (no weakness planes are present in the granite). The rock properties, tunnel depth and other related parameters are listed in Table 4. Answer the following questions: Table 4 Item/parameters

Value/equations

Depth of tunnel below ground surface, h

570 m

Unit weight of granite, γ

26 kN/m3

Poisson’s ratio of granite, υ

0.25

Vertical or overburden stress, σv (MPa)

γ×h

Horizontal stress, σh (MPa)

[υ/(1 −υ)] ×σv

Average UCS of granite rock samples from lab tests

120 MPa

a)

Based on the depth of the tunnel calculate the expected vertical stress (in MPa) acting on the tunnel? (2 mark)

b)

Besides the vertical stress, horizontal stress also occurs in the granite rock mass at 570 m depth. Calculate this horizontal stress? (2 marks)

c)

Compare the value between the σv and σh, named of the rock constant that leads to the formation of this horizontal stress? (2 marks)

d)

It is a grave mistake to assume the rock mass is continuous and free from discontinuities. If the in situ granite mass is highly jointed and discontinuous what would you expect the UCS value of the in situ granite, with reference to the UCS value shown in Table 4? Explain why you would expect such as a value? (5 marks)

e)

Figure 2 shows a rectangular shape tunnel excavated in a stratified rock. The thickness of the beddings above the tunnel roof is also indicated in the figure. State one reason why there will be ‘bed separation’ occurring in the tunnel roof? (2 marks)

f)

Recommend one type of rock reinforcement method to reduce separation between bed h1 and h2? Describe how this method is effective to minimise bed separation. (3 marks)

SAB 2712 / SKAA 2712 7

g)

The weight of bed h per m length of the tunnel is equivalent to 2000 kN, and the tensile strength of 20 mm φ rock bolt is 150 kN. Based purely on this information, calculate the number of bolt required to avoid bed separation from occurring if sagging of the h is expected to occur at 200 m length of the tunnel (take FOS = 1.2 for effective suspension effect of the rock bolts)? (4 marks)

h2=2.4m Beddedstrata h1 =1.2m

Rectangular‐ shapedtunnel

w=12m

FIGURE 2...