Engineering Geology Multiple Choice Questions on “Occurrence of Joints”.
1. Tensile stresses in igneous rocks are developed during ___________
a) Cooling
b) Crystallisation
c) Cooling and crystallisation
d) Molten state
Answer: c
Clarification: The igneous rocks are formed by cooling and crystallisation of hot molten material called magma or lava. As such, in most cases they show joint systems related to the tensile stresses developing during the process of cooling and crystallisation.
2. The type of regular joint not belonging to igneous rocks is?
a) Sheet jointing
b) Box jointing
c) Mural jointing
d) Columnar jointing
Answer: b
Clarification: The three regular or systematic types of joints observed in igneous rocks are: sheet joints, mural joints and columnar joints.
3. Which jointing gives layered sedimentary structure appearance?
a) Sheet jointing
b) Mural jointing
c) Box jointing
d) Columnar jointing
Answer: a
Clarification: In granites and other related igneous rocks, a horizontal set of joints often divides the rock mass in such a way as to give it an appearance of a layered sedimentary structure, called in this case as a sheeting structure.
4. Sheet joints are caused not due to ___________
a) Consequence of loading
b) Weathering
c) Removal of overlying rock mass
d) Consequence of unloading
Answer: a
Clarification: Sheet joints are sometimes caused due to weathering and removal of overlying rock masses, which cause expansion of the underlying igneous and other rocks as a consequence of unloading.
5. The geometrical distribution where rock mass is divided into cubes is ___________
a) Sheet jointing
b) Mural jointing
c) Columnar jointing
d) Radial jointing
Answer: b
Clarification: Mural jointing is a sort of geometrical distribution of joints dividing the rock mass into cubical blocks or murals and hence the name.
6. Types of joint found in volcanic igneous rocks are?
a) Sheet joints
b) Mural joints
c) Columnar joints
d) Radial joints
Answer: c
Clarification: Columnar joints are typical of volcanic igneous rocks although they may also be observed in other rocks.
7. Columnar joints are also called ___________
a) Radial joints
b) Pyramid joints
c) Prismatic joints
d) Box joints
Answer: c
Clarification: Columnar joints are also called as prismatic joints. The joints divide the rock mass into polygonal blocks each block being bounded by three to eight sides.
8. How are the main joints aligned to the cooling surface?
a) Perpendicular
b) Parallel
c) At 45°
d) At 30°
Answer: a
Clarification: Normally, the main joints are vertical or perpendicular to the cooling surface and may extend to varying depths ranging a few centimetres to many metres.
9. How and what are the polygonal cracks related to?
a) Directly related to compressive forces
b) Directly related to tensile forces
c) Inversely related to tensile forces
d) Directly related to shearing forces
Answer: b
Clarification: The polygonal cracks are thought to be directly related to the tensile forces developed during cooling (accompanied by contraction) of hot molten material (lava).
10. The contraction is equally developed in all directions in which kind of mass?
a) Non-homogenous
b) Isotropic
c) Anisotropic
d) Homogenous
Answer: d
Clarification: In a homogenous mass undergoing uniform cooling throughout the surface, contraction is equally developed in all directions.
11. At what angle do the fractures appear to the lines of tensile stresses?
a) 180°
b) 90°
c) 45°
d) 60°
Answer: b
Clarification: When the strength of the rock is overcome, fractures appear at right angles to the lines of tensile forces.
12. In sedimentary rocks, joints are genetically related to those forces that have caused the major structural deformation.
a) True
b) False
Answer: a
Clarification: Since sedimentary rocks are often folded and faulted, the joints in them are genetically related to those forces that have caused the major structural deformations.
13. Joints in metamorphic rocks are due to ___________
a) Indirect stresses
b) Local stresses
c) Regional stresses
d) Local and regional stresses
Answer: d
Clarification: The metamorphic rocks types are heavily jointed in many cases, the joints being of irregular or non-systematic types. These joints are often the result of local and regional stresses acting on rocks as a source of metamorphism.
14. In mural jointing, one set is horizontal and two sets are vertical.
a) True
b) False
Answer: a
Clarification: In granitic and other rock masses, there may occur three sets of joints in such a way that one set is horizontal and the other two sets are vertical, all the three sets being mutually perpendicular to each other.