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RMC711S - Rock Mechanics - 1st OPP - june 2023 |
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nAmlBIA UnlVERSITY
OF SCIEnCE Ano TECHOOLOGY
·FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
DEPARTMENT OF CIVL, MINING AND PROCESS ENGINEERING
QUALIFICATION: BACHELORS OF ENGINEERING IN MINING ENGINEERING
QUALIFICATION CODE: 08BMEG LEVEL: 7
COURSE CODE: RMC711S
COURSE NAME: ROCK MECHANICS
SESSION: JUNE 2023
PAPER: THEORY
DURATION: 2.5 HOURS
MARKS:80
FIRST OPPORTUNITY QUESTION PAPER
EXAMINER(S) Mallikarjun Rao Pillalamarry
MODERATOR: Prof. Mapani Benjamin
INSTRUCTIONS
I. Answer all questions.
2. Read all the questions carefully before answering.
3. Marks for each question are indicated at the end of each question.
4. Please ensure that your writing is legible, neat and presentable.
PERMISSIBLE MATERIALS
1. Examination paper.
2. Graph Papers
3. Mathematical Instruments
THIS QUESTION PAPER CONSISTS OF 3 PAGES (Including this front page)
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Instructions: Answer all questions.
Time allowed: 2.5 hours
Question I An opening is made to access the orebody in an underground mine. The opening was (20)
intersected by a fracture as shown in Figure. In order to assess the stability of the opening
the stresses acting parallel and perpendicular to the fracture must be known. State of stress
near the fracture (A) is given in the Figure. Determine following quantities.
a) Shear stress acting parallel to the fracture.
b) Normal stress acting perpendicular to the fracture.
c) Draw the state of stress element along the discontinuities.
d) Determine principal stresses and major principal direction with respect to the
fracture.
ISMPa
y
'-----------+
I 6MPa
State of Stress
X
IOMPa
Fracture "'-
•A
40°
Mine Opening
Figure I
Question 2 A series oftriaxial stresses test of shale reveals the following results. Determine
(20)
Test No
I
2
3
4
Confining Pressure
(MPa)
2
4
6
8
Failure Stress
(MPa)
45
56
63
75
a) Mohr Coulomb failure envelope
b) Uniaxial compressive strength of shale
c) Tensile strength of shale
d) If the state of stress at a point is expressed as CT3 = 1.5 MPa and cr1 = 55 MPa,
determine whether the point is safe
Question 3 Briefly describe measurement of Rock Quality Designation (RQD) with the help of figures. (20)
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Question 4
a) Briefly discuss the in-situ stress measurement with hydraulic fracturing method.
( I 0)
b) The stress in a granitic rockmass has been measured by the hydraulic fracturing technique. (IO)
Two tests are conducted in a vertical borehole. One test at a depth of 800 m and the other
test at a depth of 1200 m. The results are as follows:
Depth (m)
800
1200
Breakdown Pressure (Ps)
(MPa)
14
24.5
Shut-in Pressure (P,)
(MPa)
7.0
19.0
Given the tensile strength of the rock is IO MPa, estimate and list the values of major,
intennediate and minor principal stresses at two depths. Average unit weight of the rock.mass
is 26 kN/m 3•
ADDITIONAL INFORMATION
RMC711S June/July Exam
Plane Stresses
Nonna] stresses
= + ± ± (Jxx <Jyy)
<Jn (
2
((Jxx - <Jyy) cos 28 Tyx sin 28
2
Shear Stress
Principal stress direction
T
=-
(Jxx - <Jyy)
(2
sin 28
+ Tyx
cos 28
Direction of maximum shear stress
Mohr Coulomb Failure Criteria
(Jl
=
2c
cos
(1)+ <J3 (1 + sin
1- sin(/)
0)
In-situ stresses measurement using hydraulic fracturing
Major horizontal stress (<YH)= 3ah-Ps+a1
2