(MODULE 8) INTRODUCTION TO ENGINEERING GEOLOGY, GEOLOGIC STRUCTURES, AND GEOLOGIC MAPS Flashcards
the science of rocks, minerals, soils, and surface water, including the study of their formation, structure, and behavior
geology
the branch of geology that deals with the application of geologic principles to engineering works
engineering geology
the work of this type of geologist includes mapping, describing and characterizing the rock at a construction site; assessing stability issues, such as landslides; and appraising local seismicity and earthquake potentials
engineering geologist
the branch of civil engineering that deals with soil, rock, and underground water, and their relation to the design, construction, and operation of engineering projects
geotechnical engineering
what are the phases of geotechnical engineers’ methodology?
1.
2.
3.
- design phase
- construction phase
- beyond the construction phase
for the design phase, geotechnical engineers begin by assessing the underground conditions and the engineering properties of the various strata. we call this process ___.
site exploration and characterization
what are the two steps of the design phase done by geotechnical engineers?
- geotechnical engineers begin by assessing the underground conditions and engineering properties of the various strata through site exploration and characterization.
- the next step is to perform engineering analyses based on the information gained from the first step, through tools known as soil mechanics and rock mechanics
the analytical tools used for doing the second step of the design phase are ___ and __.
soil mechanics and rock mechanics
the construction phase involves three steps:
1.
2.
3.
- examining the soil and rock conditions actually encountered and comparing that to what is anticipated in the design
- comparing the performance between the two
- providing quality control testing, especially in compacted fills and structural foundations
beyond the end of construction, two steps are followed:
1.
2.
- monitoring of long-term settlements
- development of remedial measures to address geotechnical problems
what are the differences between rock and soil?
1.
2.
3.
4.
5.
- rocks are generally cemented whereas soils are rarely cemented
- rocks usually have less pores than soils
- the effects of weathering on soils are more subtle and less variable than on rocks
- rocks are often discontinuous due to the presence of fractures whereas soil masses can be represented as continuous
- it is harder to identify the stress histories of rocks
the study of the configuration and orientation of rock formations
structural geology
structural geology is an important part of engineering geology because ___.
it gives us important insights on how a rock mass will behave
dynamically-produced patterns or arrangements of rock or sediment from, and give information about, forces within the earth
geologic structures
force per unit area
stress
the three basic types of stress are
1.
2.
3.
- compressive
- tensional, and
- shear
a change in size or shape, or both in response to stress
strain
geological structures are indicative of
1.
2.
3.
- the type of stress
- the rate of application of such stress
- physical properties of the rocks or sediments
this type of stress results in rocks being shortened or flattened
compressive stress
rocks that have undergone compressive stress are found along ___.
convergent plate boundaries
this type of stress results in a stretching or extension and breaking of material
tensional stress
rocks that have undergone tensional stress are found along ___.
divergent plate boundaries
because rocks are weak when pulled apart, ___ and ___ are common structures.
fractures and faults
when stresses act parallel to a plane, ___ is produced.
shear stress
a shear stress results in a ___ parallel to the direction of the stresses.
shear strain
how do rocks respond to stress?
rocks remain elastic (bounce back to its original form) at low pressures, but deforms permanently when exceeding its elastic limit.
ductile rocks deform through bending plastically whereas brittle rocks deform through fracturing.
rocks exposed to elevated pressure and temperature behave in a ___ manner, and undergo foliation.
ductile
ductile behavior results in rocks permanently deformed by ___.
folding or bending of rock layers
rocks exhibit ___ at or near earth’s surface, where temperatures and pressure are low.
brittle behavior
bends or wavelike features in layered rock
folds
the ___ divides a fold into two limbs.
axial plane
the subtle trace of an axial plane is called the ___ of the fold.
hinge line
upward-arching folds with the oldest rocks in the center of the fold
anticlines
downward-arching folds with the youngest rocks in the center of the fold
synclines
types of folds
1.
2.
3.
4.
5.
6.
7.
- plunging folds
- open folds
- isoclinal folds
- overturned folds
- recumbent folds
- structural domes
- structural basins
folds in which the hinge line is not horizontal
plunging folds
folds which have limbs that dip gently and the angle between the limbs is large
open folds
the more open the fold, the ___ it has been strained by shortening.
less
open folds are exposed to ___ stress levels.
lesser
folds which have parallel limbs; implies even larger shortening strain or shear strain; forms a hairpin shape
isoclinal folds
folds wherein the axial plane is inclined to an extent where fold limbs dip diagonally and parallel to each other
overturned fold
folds overturned to the point where the limbs are horizontal
recumbent folds
structures in which the beds dip away from a central point, with the oldest rocks lying at the center of the structure
structural domes
structural domes are also called ___.
doubly plunging anticlines
structures in which the bends dip toward the central points, with the youngest rocks lying at the center of the structure
structural basins
structural basins are also called ___.
doubly plunging anticlines
a fracture or crack in bedrock where essentially no displacement occurs
joint
where joints are oriented approximately parallel to one another
joint set
when counting joint sets, you could the count the number of ___ on the rock.
orientations
When we say fractures in rock, they are the sources of discontinuities, and that they have ___.
impurities
How do discontinuities contribute to mass wasting?
discontinuities can weaken when the fractures become looser, causing mass wasting.
fractures in bedrock along which movement has occured
faults
faults are considered ___ if movement has occurred along them within the last 11,000 years
active
types of faults
1.
2.
3.
- dip-slip faults
- strike-slip faults
- oblique-slip faults
faults wherein the movement is up or down parallel to the dip of the inclined fault surface
dip-slip faults
parts of dip-slip faults:
the side of the fault above the inclined fault surface is called the ___
hanging wall
parts of dip-slip faults:
the side below the fault is called the ___
footwall
types of dip-slip faults
1.
2.
3.
- normal faults
- reverse faults
- thrust fault
a ___ results in extension or lengthening of the crust
normal fault
fault blocks, bounded by normal faults, that drop down
graben
fault blocks, bounded by normal faults, that are uplifted
horsts
horizontal compressive stresses cause ___ which tend to shorten the crust.
reverse faults
a reverse fault in which the dip of the fault of the plane is at a low angle (30°) or even horizontal
thrust fault
faults which have movement that is horizontal and parallel to the strike of the fault plane
strike-slip faults
faults which have movement with both vertical and horizontal components
oblique-slip faults
a ___ shows the distribution of geologic features, including different kinds of rocks and faults
geologic map
the geology is represented by ___, ___, and ___ unique to geologic maps
colors, lines, and special symbols
geologic units are named and defined by the ___
geologists who made the geologic map
the most common division of time used is the period, represented through ___.
letter symbols
geologic period of 195 to 141 million years ago
jurassic
geologic period of 141 to 65 million years ago
cretaceous
geologic period of 65 to 2 million years ago
tertiary
geologic period of 2 million years ago to today
quartenary
letter symbols for
1. jurassic
2. cretaceous
3. tertiary
4. quaternary
- J
- K
- T
- Q
the place where two different geologic units are found next to each other is called a ___.
contact
contacts are represented in a geologic map through different kinds of ___
contact lines
the two main types of contacts shown on most geologic maps are ___ and ___.
depositional contacts and faults
lava from a volcano flows over the landscape. when the lava hardens into rock, the place where the lava-rock rests on the rocks underneath is a ___.
depositional contact
what is a depositional contact
the place where the hardening lava-rock rests on the rocks underneath
depositional contacts is shown on the geologic map as a ___
thin line
when different geologic units have been moved next to one another after they were formed, the contact is a ___.
fault contact
what is a fault contact?
a fault contact is when different geologic units move next to one another
fault contacts are shown on the map by a ___
thick line
geologic units can also be bent and warped by the same forces into rounded, wavelike shapes called ___
folds
a line that follows the crest or trough of the fold is called the ___.
fold axis
this is marked on a geologic map with a ___
line thicker than a depositional contact but thinner than a fault
all thickness of lines are also modified by being ___, ___, or ___.
solid, dashed, or dotted
the places where the line is precisely located are shown as ___
solid lines
places where the line is uncertain in location are shown as ___
dashed lines
the shorter the dash of a dashed line in a geologic map, ___
the more uncertain the location
the compass direction of a line followed by the intersection of an inclined plane with a horizontal plane
strike
the ___ shows that horizontal direction in the beds; the short line is called the ___ and shows which way the bed tilts; the number is called the ___ and shows how much the bed is tilted, in degrees, from flat.
- strike line
- dip line
- dip
