SAB 2712 SAM 3722

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SAB 2712/ SAM 3722

UTMUNIVERSITI TEKNOLOGI MALAYSIA

Faculty

of Civil Engineering

R E S E A R C H U N I V E R S I T Y

FINAL EXAMINATION

SEMESTER I, SESSION 2011/2012

COURSE CODE : SAB 2712/SAM 3722

COURSE : GEOLOGY AND ROCK MECHANICS

PROGRAMME : SAW

DURATION : 2 HOURS

DATE : JANUARY 2012

INSTRUCTION TO CANDIDATES:

1. ANSWER ALL QUESTIONS IN SECTION A AND SECTION B

2. PLEASE USE SEPARATE ANSWER SCRIPT FOR EACH SECTION

3. DETACH AND SUBMIT PAGE 10 TOGETHER WITH ANSWER SCRIPT

FOR SECTION B

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 paper consists of (10) printed pages only.

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SAB 2712/ SAM 3722

SECTION A: GEOLOGY

This section consists of 3 questions (Q1 to Q3). Answer all questions in this

section.

Ql. Rocks are formed from various processes such as sedimentation, cooling of

magma and metamorphism. As such, rocks are named according to their

origins and modes of their formations. Based on these statements, answer the

questions below.

a) Discuss in details the criteria used to name different types of igneous

rocks.

(6 marks)

b) Explain the methods used to identify the differences between igneous

and sedimentary rocks in the field.

(4 marks)

c) There are many factors affecting the strengths and properties of a rock

mass. Explain in details how these factors affect the stability of slope

excavated in metamorphic rock.

(10 marks)

(20 marks)

Q2. Recent earthquakes that hit eastern Turkey with a 7.2 magnitude measured by

the Richter scale proved the dynamics nature of the earth. Turkey is known to

be a country that lies on several active fault lines. As a future civil engineer,

knowledge on this major geohazard is essential in dealing with the occurrence

of such incidents.

a) Explain in details what a fault line is, and how fault lines can induce major earthquake.

(6 marks)

b) Recent events show that even non-earthquake prone areas were also hit

by such geological catastrophic. Explain why these phenomena could

take place.

(6 marks)

(12 marks)

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SAB 2712/ SAM 3722

Weathering profile are very much dependant on the types of parent rock and

climate.

a) Describe the typical characteristics of weathering profile and how they

are formed in:-

i) Bedded sedimentary area consisting of sandstone and shale

ii) Limestone area

(10 marks)

j

b) Discuss briefly the problems associated with pile foundation design in

the rock types mentioned in a(i) and a(ii) above.

(8 rriarks)

(18 marks)

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SAB 2712/SAM 3722 4

SECTION B: ROCK MECHANICS

This section consists of 4 questions (Q4 to Q7). Answer all questions.

Q4. Laboratory tests on rock samples form the most essential scope in rock

mechanics as they provide means to evaluate the rock properties and strengths.

Answer the following questions.

a) For Point-load index test, state one of its advantages

(2 marks)

b) For the rock properties listed in Table 1 on page 10, name the test used

to verify each rock property (please write your answer in the column

provided in Table 1).(4 marks)

c) Plot of vertical stress versus vertical strain from uniaxial compression

test (UCT) can be used to determine several important rock properties.

Besides Young’s modulus ( E), name 2 other rock properties that can be

determined from this plot.

(2 marks)

d) Stress (MPa) and strain (%) data from UCT on a rock sample is shown

Table 2. Plot the curve of stress versus strains for this sample. Based on

the curve, estimate the average Young’s modulus (E) at 50 % UCS

(4 marks)

(12 marks)

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Table 2 : Stress-strain data from UCT

Axial stress (MPa) Vertical strain (%)

0.0 0.000

1.4 0.001

7.5 0.011

18.4 0.029

32.0 0.054

40.0 0.066

48.5 0.081

56.5 0.096

65.0 0.113

71.5 0.128

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SAB 2712/ SAM 3722

Construction of an RC dam has been proposed on two rock masses; Rock

Mass A and Rock Mass B. To evaluate their joint characteristics and load

bearing capability, cores were obtained from these two rock masses. The

typical cores obtained from each rock mass are shown in Figure 1 (a) and (b),

and all measurements are in mm. (Note: Assume that upon completion, the RC

dam induces compressive load onto the in situ rock mass).

a) Calculate the RQD values for Rock Mass A and Rock Mass B.

(6 marks)

b) Characteristic of the joint system in Rock Mass B creates uncertainty

on its load bearing capacity. Explain why the characteristic of the joint

in Rock Mass B creates such uncertainty.

(4 marks)

c) State one main weakness of RQD method in assessing load bearing

capability of a rock mass.

(2 marks)

d) Besides using drilled core samples to obtain RQD, state another

method that can be used to estimate RQD of rock.

(2 marks) (14 marks)

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Figure 2 shows four (4) core samples tested for their uniaxial compressive

strength (UCS). Three of these cores exhibit existing weakness planes (cracks)

and orientation of these planes with respect to loading axis is shown as (b), (c)

and (d) in the figure. Answer the following questions:

a) Which two (2) samples will show almost similar UCS value? State

reasons for your answer.

(4 marks)

b) Between sample (b) and (c), which one will show a lower UCS?

(2 marks)

c) Among the four samples, which one will show the lowest UCS? State one reason for your answer.

(4 marks)

d) If these four (4) samples are tested for their tensile strength (by direct

pulling), which two (2) samples will display ZERO tensile strength?

(2 marks)

(12 marks)

I I i

t t t(a) <b) (c)

I

' N ' \

t(d)

Figure 2: Core samples under uniaxial compression

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Stability is one of the main concerns of any excavation (e.g. slope, tunnel and

cavern) created in a rock mass. The stability of the excavation is usually

affected by several factors like in situ strength of the rock mass, prevailing

discontinuities and weakening effect due to presence of water. As such, installation of rock stabilisation methods is inevitable. However, type of

effective method to be installed depends on factors that contribute to the

instability.

(a) Describe ‘Rock Reinforcement System’ and ‘Rock Support System'.

(4 marks)

(b) For the various modes of instability listed in Table 3 on page 9,

recommend a suitable method to reduce the effect that creates the instability (write your answer in the column provided in Table 3).

(4 marks)

(c)

(d)

Figure 3 shows 2 modes of instability in slope face excavated in

jointed rock mass; namely wedge and toppling failure (rock fall). State

one main difference between wedge and toppling failure.

(2 marks)

For the wedge failure in Figure 3 (a), give two (2) examples of

weakness plane that can create this type of instability.(2 marks)

(12 marks)

sj * \ -V'

Vftdgfc vfsilixfc.

(a)

Of VtsiC*

Tbpp1»>5 faiUJ*'’*.

(b)

Figure 3: Mode of instability in rock

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I

NOTE: Detach and submit this page (Table 1 and 3) together with your answer spript

of SECTION B

SAB 2712/ SAM 3722

Table 1: Rock properties and laboratory tests

Property of rock Name of laboratory test

Relative compactness of rock sample

based on P-wave velocity

Poisson’s ratio, ui

Resistance against slaking

(disintegration)

! j

Strength of rock under compressive load

!

Table 3: Modes of instability and stabilisation methods1

Factors leading to various modes of

instability in excavated structures

Recommended method of

stabilisation

Surface run off water that penetrates

into rock slope and creates high pore-

water pressure in its joints

j

i

Unstable rock block created by an

inclined fault that tend to slide towards

slope face

ii

i

i

Loosening of small key blocks (less than

0.2 m3) on slope face

Flexural failure due to presence of near

vertical joint set in slope

i

i

SAB 2712 SAM 3722

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