ASBOG- engineering geology

Strain

An alteration in the shape or volume of a soil related to stress. It is calculated as the ratio of the new shape compared to the original shape

Effective Stress

The total amount of stress placed on a soil minus the pore-water pressure

Normal Stress

The component of total stress that acts perpendicular to the plane.

Shear stress

The component of total stress that acts parallel to any point in question.

Dilatancy

Tendency of a material to increase in volume when subjected to a shape change. Assume a closed-packed structure from an open-packed structure

Quick Condition

Tendency of some soils that lack cohesion to allow water to flow rapidly between grains and to liquefy the material. Soil does NOT possess significant bearing capacity

Elastic Modulus

Measure stiffness in a material (bulk, shear, Young's(Elastic))

Triaxial Test

Test for mechanical properties of deformable solids.

Direct Shear test

Measure shear strength when sample is surrounded withstand subjected to mechanical stresses.

Unconfined compressive strength test

Similar to triaxial but without external confining pressure.

Consistency

General amount of cohesion in soil particles

Critical void ratio

Void ratio of soil that stays the same even during shearing events.

Mohr circle

Graph showing stresses that act on a single point on a plane. The x-axis - normal stress. Y-axis - shear stress

Seepage

The flow of a fluid through soil pores

Proctor test

4-inch diameter; three lifts; 25 blows by 5.5 lb hammer; falling 12-inches

Modified proctor test

five lifts; 10lb hammer; 18-inches

Differentiate between the three different types of modulus: bulk
(incompressibility) modulus, shear (rigidity) modulus, Young's
(elasticity) modulus.

There are three different kinds of modulus, or ways to measure the stiffness of the material:

• bulk modulus (K; otherwise known as incompressibility modulus): a measure of a substance's resistance to uniform compression. It is defined as the pressure increase needed to affect a given relative decrease in volume

• shear modulus (G; also known as rigidity modulus): refers to the deformation of a solid when exposed to a force parallel to one of its surfaces as its opposite face is exposed to an opposing force. This will cause an object that is shaped like a rectangular prism to be deform into a parallelpiped

• Young's modulus (E; also known as the modulus of elasticity): a measure of the stiffness of a given material. Defined as the ratio, for small strains, of the rate of change of stress with strain

Compare and contrast the equations used to determine percentages
or ratios relevant to soil phase relationships such as: water content,
porosity, void ratio, bulk density, unit weight, and degree of
saturation.

Water content, porosity, and degree of saturation are typically
expressed as a percentage. The equations for water content are: w
= WwiWs * 100% (weight of water I weight of solids) and w = MwiMs
* 100% (mass of water I mass of solids). The equation for porosity
is: n = Vv/V * 100% (total volume of void spaces I total volume).
The equation for degree of saturation is: SR = VwiVv * 100%
(volume of water I volume of voids). Void ratio, bulk density, and
unit weight are ratios not expressed as a percentage. The equation
for void ratio is: e = Vv/Vs (volume of voids I volume of solids). The
equation for bulk density is: p = M/V (total mass I total volume).
The equation for unit weight is: y = W/V (total weight I total
volume, usually in poundslft3
).

Discuss the three phases of matter found in partially saturated soils
and how they contribute to volume and weight relationships.

Partially-saturated soils will contain matter in the solid, gas, and
liquid phases. The volume of a partially-saturated soil can be
calculated with the equation: V = V.+Vw+Vs, in which Va is the
volume of air, Vw is the volume of water, and Vs is the volume of
solids. When soil water content is reduced below saturation the
interface between air and water within pores are curved because of
surface tension. As the water content is reduced, drainage occurs
from progressively smaller openings, and the interface radius
decreases. On occasion, it will be necessary to simply calculate the
volume of air and water, which is expressed as Vv. It can be
assumed that the gaseous constituents of a partially-saturated soil
do not have any weight.

Discuss the ways density is tested, and explain why these are
examined.

Density is a property of particulate materials defined as the mass of
the particles of a given volume divided by the volume that they
occupy. There are a number of different techniques to test for
density in soils. The Proctor Compaction Test and the similar
Modified Proctor Compaction Test are utilized to ascertain the
maximum achievable density of soils. The Proctor Compaction Test
(ASTM 0698) uses a 4-inch diameter mold holding 113oth of a cubic
foot of soil. The soil is compacted in three separate lifts using 25
blows by a 5.5 lb hammer falling 12 inches. This delivers an
effective compactive effort of approximately 12,400 ft-lblft3 . The
Modified Proctor Compaction Test (ASTM 01557) utilizes the same
mold as the Proctor Compaction test, but differs in the use of a 10
lb. hammer falling through 18 inches with 25 blows on each of five
lifts. This achieves an effective compactive effort approaching
56,000 ft-lblft 3 . There is also a test (ASTM 04253) which uses a
vibrating table using standard vibrations for a standard time to
densify the soil.

Relate the following quantities, calculated in investigations of soil
phase relationships: weight of solids, dry density, unit weight of dry
soil, porosity and void ratio.

Soil is usually composed of three phases: solid, liquid, and gas.
Mechanical properties of soil directly depend on the way these
phases interact with each other and with applied potentials. The
following equations all have the same denominator and are used to
calculate the above mentioned properties (w is the percentage of
water content). The equation for the weight of solids is: WS = WI
(1 + w), in which W is total weight. The equation for dry density is:
Pd = pI (1 + w), in which p is bulk density, calculated as mass
divided by volume. The equation for unit weight of dry soil is: yd =
y 1 (1 + w), in which y is unit weight. The equation for porosity is: n
= e 1 (1+e), in which e is void ratio. Finally, the equation for void
ratio is: e = n 1 (1-n), in which n is porosity.

Discuss the common groupings used when discussing Atterberg
limits.

The Atterberg limits are a measure of the nature of a fine-grained
soil. Soil occurs in four physical states, depending on water content:
solid, semi-solid, plastic and liquid. In each state the consistency
and behavior of a soil is different and thus so are its engineering
properties. The following terms relate to the designation of
Atterberg limits:
• Atterberg limits: the boundaries between the four levels of
soil consistency including plastic, semi solid, liquid, and
solid
• A-line: the division mark between clay and silt on the
Atterberg plasticity chart
• plastic limit: lower boundary of plasticity, upper boundary
of semisolid
• liquid limit: upper limit of plastic state, lower limit of liquid
state
• plasticity index: range in water content between liquid and
plastic boundaries
• U-line: mark dividing the upper limit of plasticity from the
lower limit of liquidity

Review the general procedure for compaction testing of soil, and
discuss how the resulting data is interpreted.

Compaction is the process of increasing the bulk density of a soil or
aggregate by driving out air. For any soil the density obtained
through compaction depends on the moisture content. At very high
moisture contents, the maximum density is achieved when the soil is
compacted to saturation with most or all of the air being driven out.
At low moisture contents, the soil particles interfere with each other
and the addition of some moisture will allow for a greater bulk
densities. Peak density occurs at the point at which this effect
begins to be counteracted by the saturation of the soil. The
procedures for compaction testing include: The Proctor Test, which
uses a 4-inch diameter mold holding 1l30th of a cubic foot of soil
that is compacted in three separate lifts of soil using 25 blows by a
5.5 lb hammer falling 12 inches; and the Modified Proctor Test,
which uses the same mold, but uses a 10 lb. hammer falling through
18 inches, with 25 blows on each of five lifts.

Provide a description for each Unified Soil Classification System
(USCS) subdivision of coarse-grained soils.

Under the Unified Soil Classification System (USCS) .coarse grained
soils will have more than 50% of total material retained on a No.200
(0.075 mm) sieve. The two subdivisions of coarse grained soils are:
gravel, with a requirement that greater than 50% of coarse fraction
be retained on No.4 (4.75 mm) sieve; and sand, required to have
50% of its coarse fraction pass a No.4 sieve. Gravel can consist of
clean gravel up to gravel with greater than 12% fines. The group
divisions of gravel are: well graded gravel, fine to coarse gravel,
poorly graded gravel, silty gravel, and clayey gravel. Sand can
consist of clean sand up to sand with greater than 12% fines. Sand
group subdivisions are: well graded sand, fine to coarse sand, poorly
graded sand, silty sand, and clayey sand

Discuss the general divisions found in the Unified Soil Classification
System and provide the abbreviations associated with them.

The Unified Soil Classification System (USCS) is a soil classification
system used in the engineering and geology disciplines to describe
the texture and grain size of a soil. The classification system can be
applied to most soils and unconsolidated materials, and is
represented by a two-letter symbol. The first letter in the
classification system describes the grain size of the particles in the
soil or aggregate as follows: (G) gravel, (S) sand, (M) silt, (C) clay,
(0) organic. The second letter designation describes particle size
and grading, (P) poorly graded (uniform particle size), and (W) well
graded (diverse particle size), or (H) high plasticity, and (L) low
plasticity. Soils can be classified into fairly small groups based on
this two-letter system.

Discuss the sieve characteristics of coarse-grained soils.

Under the Unified Soil Classification System (USCS) coarse grained
soils will have more than 50% of total material retained on a No.200
(0.075 mm) sieve. The two subdivisions of coarse grained soils are:
gravel, with a requirement that greater than 50% of coarse fraction
be retained on No.4 (4.75 mm) sieve; and sand, required to have
50% of its coarse fraction pass a No.4 sieve. Gravel can consist of
clean gravel up to gravel with greater than 12% fines. The group
divisions of gravel are: well graded gravel, fine to coarse gravel,
poorly graded gravel, silty gravel, and clayey gravel. Sand can
consist of clean sand up to sand with greater than 12% fines. Sand
group subdivisions are: well graded sand, fine to coarse sand, poorly
graded sand, silty sand, and clayey sand.

Provide descriptions for each Unified Soil Classification System
subdivision of fine-grained soils and highly organic soils, and include
their dry strength, dilatancy, and toughness characteristics.

Fine grained soils will have more than 50% of their content pass
through a No.200 sieve. The subdivisions are: silt and clay with a
liquid limit less than 50; and silt and clay with a liquid limit ;::: 50.
Both are further subdivided in organic and inorganic components.
Inorganic silts and fine sands will have a very small dry strength, no
toughness, and either a quick or slow dilatancy. Inorganic clay has
a low to medium plasticity and will have a medium to high dry
strength, a moderate amount of toughness, and little if any
dilatancy. Organic silts and organic silt-clays with a low plasticity
will have a slight to medium dry strength, slight toughness, and a
slow dilatancy. Inorganic silts and fine sandy or silty soils will have
a low level of toughness, a slight dry strength, and a slow dilatancy.
Inorganic clays with a high level of plasticity will have a high dry
strength, a high degree of toughness, and no dilatancy.

Discuss how sands and gravels are classified as well sorted or poorly
graded in the Unified Soil Classification System (USCS).

Sand and gravel are classified as coarse grained soils under the
USCS. Coarse grained soils will have more than 50% of total
material retained on a No.200 (0.075 mm) sieve. The two
subdivisions of coarse grained soils are: gravel, with a requirement
that greater than 50% ofcoarse fraction be retained on No.4 (4.75
mm) sieve; and sand, required to have 50% of its coarse fraction
pass a No.4 sieve. Gravel can consist of clean gravel up to gravel
with greater than 12% fines. The group divisions of gravel are: well
graded gravel, fine to coarse gravel, poorly graded gravel, silty
gravel, and clayey gravel. Sand can consist of clean sand up to sand
with greater than 12% fines. Sand group subdivisions are: well
graded sand, fine to coarse sand, poorly graded sand, silty sand,
and clayey sand.

Compare and contrast the Unified Soil Classification System (USCS)
and the Modified Wentworth (MW) scale.

Particle size, also called grain size, refers to the diameter of
individual grains of sediment, or the particles in clastic rocks. There
are two different scales used to classify the grain size of soils: the
Unified Soil Classification System (USCS), and the Modified
Wentworth (MW) scale. The uses scale is typically used for soils,
while the MW scale is more commonly used for rocks. In the
Modified Wentworth scale size ranges define limits of classes that
are given names. The classes: coarse, medium, and fine, are
augmented by the qualifying term "very" for further distinction.
The use of this scale relies on observation, rather than the sieve
analysis used in the uses scale. The uses system relies more on
specifications based on sieve analyses. The classification system
can be applied to most soils and unconsolidated materials, and is
represented by a two-letter symbol

Describe the three tests used to determine dry strength, dilatancy,
and toughness of soil samples.

There are three tests performed to determine the basic
characteristics of a soil sample:
• In the toughness test, the sample is rolled into a cylinder
about an eighth of an inch in diameter. The sample is then
·folded and re-rolled again. This process is repeated several
times. When the plastic limit of the sample has been
reached, it will become rigid and lose plasticity.
• In the dilatancy test, the sample is made slightly moist and
is shaken latterly in the hand. If water beads up on the
surface of the sample, it is considered dilatant.
• In a dry strength test, the soil is moistened until it has a
consistency similar to putty. The sample is then dried out
and broken. A soil with a high degree of plasticity will also
have a high degree of dry strength.

Discuss how fine-grained soils are classified in the Unified Soil
Classification System (USCS).

Under the Unified Soil Classification System (USCS), fine grained
soils are required to have more than 50% of their content pass
through a No.200 sieve. The subdivisions are: silt and clay with a
liquid limit less than 50; and silt and clay with a liquid limit ;::: 50.
Both are further subdivided in organic and inorganic components.
Inorganic silts and fine sands will have a very small dry strength, no
toughness, and either a quick or slow dilatancy. Inorganic clay has
a low to medium plasticity and will have a medium to high dry
strength, a moderate amount of toughness, and little if any
dilatancy. Organic silts and organic silt-clays with a low plasticity
will have a slight to medium dry strength, slight toughness, and a
slow dilatancy. Inorganic silts and fine sandy or silty soils will have
a low level of toughness, a slight dry strength, and a slow dilatancy.
Inorganic clays with a high level of plasticity will have a high dry
strength, a high degree of toughness, and no dilatancy

Discuss what stress is and how it is commonly expressed in a
drawing.

Stress is a measure of force per unit area within a body. It is a
body's internal distribution of force per area that reacts to external
applied loads. Stress is often broken down into its shear and normal
components as these have unique physical significance. In short,
stress is to force as strain is to elongation. When discussing soils,
stress is defined as the amount of force that needs to be applied per
unit area in order to cause a certain amount of deformation. A
normal or compressive stress is considered positive when it points in
the direction of the object; a parallel or shear stress is considered
positive when it tends to place the object in a counterclockwise
rotation. When drawn, stresses are divided into three vectors, one
for each of the three dimensions.

Discuss how organic soils and boundary soils are classified in the
Unified Soil Classification System (USCS).

In the Unified Soil Classification System (USCS), highly organic soils
are labeled Pt (peat). There are organic subdivisions in the silt and
clay divisions, both those with high and low liquid limit. Organic
soils are those that have an organic content above 18%. If the
organic content is between 18 and 36%, the soil is most likely an
organic clay or an organic silt. If the sample has an organic content
between 36% and 90%, it is classified either as peaty. A boundary
soil is one that has characteristics of two different soil types.
Boundary soils will typically have a liquid limit value close to 50 so
that they straddle the dividing line between the two subdivisions of
silt and clay.

Discuss how a Mohr circle is used to evaluate stresses acting on an
object.

Coulomb's hypothesis determines the combination of both shear and
normal stress required to cause the fracture of a material. Mohr's
circle is used to determine which principal stresses that will produce
this combination of shear and normal stress, and the angle of the
plane in which this will occur. Normal stresses are plotted on the xaxis
while shear stresses are plotted on the y-axis. The center point
of the circle is the normal stress, and the radius is the maximum
shear stress. A Mohr circle is formed by drawing a diagram of the
object and all the stresses that are acting upon it. The diameter of
the Mohr circle is determined by the maximum and minimum
principal stresses. Any plane that is drawn through the object in
question will lie in some relation to the major principal plan; the
angle of relation is called the Mohr circle plot. The Mohr's circle is
used to find the planes of maximum normal and shear stresses, as
well as the stresses on known weak planes.

Differentiate between effective stress and total vertical stress,
referring to where they occur and how they are calculated

The concept of effective stress is one of the most important
contributions to soil mechanics. It is a measure of the stress on the
soil skeleton (the collection of particles in contact with each other),
and determines the ability of soil to resist shear stress. Effective
stress (a ') on a plane within a soil mass is the difference between
total stress (a) and pore water pressure (u). The total stress a is
equal to the overburden pressure or stress, which is made up of the
weight of soil vertically above the plane, together with any forces
acting on the soil surface (e.g. the weight of a structure). Thee
equation used to calculate total vertical stress is: which z is the depth, and y is the total unit weight of soil.

Discuss the elastic properties that an object may have, and how
they are measured.

And elastic material is one that changes shape in response to any
stress, but immediately reverts back to its original shape when the
stress ends. The relationship between stress and strain can be
quantified with Poisson's ratio, Young's modulus, the shear or
rigidity modulus, or the bulk or incompressibility ratio. Poisson's
ratio is the comparison of the change in length divided by the
change in diameter. Young's modulus is calculated as normal stress
divided by axial strain in cases where the stress-strain ratio is
constant. The bulk or incompressibility modulus is calculated as
hydrostatic pressure divided by volumetric strain, and is used in
cases where pressure is uniform on the object in all directions. Bulk
modulus is the inverse of compressibility, and shear modulus is
calculated as shear stress divided by shear strain.

Describe the three types of strain that a material can experience
based on different types of shear.

In any branch of science dealing with materials and their behavior,
strain is the geometrical expression of deformation caused by the
action of stress on a physical body. When an object is subjected to
pure shear stress, this is known as volumetric strain. Volumetric
strain is quantified as the ratio of the change in volume to the
original volume. Shear strain, on the other hand, is the result of
either simple or simple rotational shear. Sheer strain is calculated
as the maximum displacement divided by either the tangent of the
angle of displacement or the link between the bottom and top planes
of the object. Axial strain, otherwise known as normal strain, is a
compressive force that acts along one axis of the object. It is
calculated as the ratio of the change in length divided by original
length.
Shear

Explain what the Mohr-coulomb failure envelope is, and how it can
be determined for soil samples.

The Mohr-Coulomb theory is used in soil engineering to define shear
strengths of soils at different effective stresses. Coulomb's friction
hypothesis describes and determines the combination of both shear
and normal stress that will cause a material to fracture. A soil
failure envelope, also known as a strength envelope, is an indication
of the maximum amount of shear stress that a soil can withstand
before fracturing. This level can be determined by plotting the
experimental results of a strength test on a Mohr plot axis. Failure
envelope can be calculated with the following equation:
s = c + cr n tan

Discuss what shear strength of soils is, and how it can be measured
and quantified.

Shear strength describes the maximum physical ability of a soil to
deform before a point of significant plastic deformation or yielding
occurs due to an applied shear stress. Two theories are commonly
used to estimate the shear strength of a soil depending on the rate
of shearing as a frame of reference. The Tresca theory applies to
short term loading and is also referred to as the undrained strength
or the total stress condition. The Mohr-Coulomb theory applies to
long term loading of soil and is known as drained strength or the
effective stress condition. In modern soil mechanics, including
building design for earthquake protection, the above mentioned
classical techniques are frequently superseded by critical state
theory. The factors controlling shear strength in soils are: soil
composition, state (or void ratio), structure, and loading conditions.
Shear strength is determined and quantified through the following
tests: cone penetration test, direct shear test (ASTM 03080), triaxial
shear test, and the unconfined compression test (ASTM 02166).

Describe how the shear strength of cohesive and mixed soils can be
determined, and what the shear strength is affected by.

Shear strength in soils describes the maximum deflection point at
which significant plastic deformation or yielding will occur due to an
applied shear stress. There is no definitive "shear strength" of a soil
as it depends on a number of factors affecting the soil at any given
time and on the frame of reference, in particular the rate at which
the shearing occurs. The factors which influence shear strength in a
soil are: soil composition, state (void ratio), structure, and loading
conditions. Shear strength is determined and quantified through the
following tests: cone penetration test, direct shear test (ASTM
03080), triaxial shear test, and the unconfined compression test
(ASTM 02166). In a mixed soil, the behavior will most closely
resemble that of the dominant component.

Explain how cohesion less soils or soils with apparent cohesion
behave in direct shear tests, and why this occurs.

Cohesion is the component of shear strength of a soil that is
independent of interparticle friction. In soils, true cohesion is
caused by electrostatic forces, cementing, or through cohesion by
contained plant roots. Apparent cohesion is caused by capillary
pressure and pore pressure. Depending on the initial void ratio of a
soil, the material can respond to loading by either strain-softening or
strain-hardening. Strain-softened soils may be triggered to collapse
if the static shear stress is greater than the ultimate or steady-state
shear strength of the soil. In this case, liquefaction occurs. Soil
liquefaction describes the behavior of loose saturated cohesionless
soils which go from a solid state to having the consistency of a
heavy liquid as a consequence of increasing porewater pressures

Describe how the shear strength of cohesive and mixed soils can be
determined, and what the shear strength is affected by.

Shear strength in soils describes the maximum deflection point at
which significant plastic deformation or yielding will occur due to an
applied shear stress. There is no definitive "shear strength" of a soil
as it depends on a number of factors affecting the soil at any given
time and on the frame of reference, in particular the rate at which
the shearing occurs. The factors which influence shear strength in a
soil are: soil composition, state (void ratio), structure, and loading
conditions. Shear strength is determined and quantified through the
following tests: cone penetration test, direct shear test (ASTM
03080), triaxial shear test, and the unconfined compression test
(ASTM 02166). In a mixed soil, the behavior will most closely
resemble that of the dominant component.

Discuss the types of landslides that may occur, including falls,
topples, spreads, and flows.

When describing landslides, geologists typically used a system of
two-word descriptors: the first describing the material that is fallen,
and the second describing the movement that has occurred. A
landslide may contain a number of different materials ranging from
soil to rock. A fall is defined as the relatively free falling or
precipitous movement of a newly detached segment of bedrock
(usually massive, homogeneous, or jointed) of any size from a cliff
or other very steep slope; it is the fastest form of mass movement
and is most frequent in mountain areas and during spring when
there is repeated freezing and thawing of water in cracks in the rock.
A topple is a an overturning slope movement, with a turning point
below the center of gravity of the falling unit. A spread is a simple
dry landslide. A flow is defined as a mass movement of
unconsolidated material that exhibits a continuity of motion and a
plastic or semifluid behavior resembling that of a viscous fluid.
Water is usually required for most types of flow movement.

Compare the types of downward movements that may occur in
geology: settlement, differential settlement, hydrocompaction,
subsidence, soil creep, triggered creep.

There are six kinds of downward movement that may occur in
geology:
settlement: natural compaction or re-compaction in disturbed
sediments
differential settlement: general downward movement or subsidence
that occurs in differing areas of a structure at differing rates
hydrocompaction: the collapse or densification of soil due to the
effects of saturation or wetting
subsidence: the sudden sinking or gradual downward settling of the
Earth's surface with little or no horizontal motion. The movement is
not restricted in magnitude or area involved. Subsidence may be
caused by natural geologic processes, such as solution, thawing,
compaction, slow crustal warping, or withdrawal of fluid lava from
beneath a solid crust; or by human activity, such as subsurface
mining or the pumping of oil or groundwater
soil creep: the gradual, steady downhill movement of soil and loose
rock material on a slope that may be very gentle but is usually steep
triggered creep: any slow movement downhill that occurs as a result
of an externally applied force. For example, an earthquake

Describe the elements of a landslide investigation, and tell what it is
used for.

A geologist will perform a landslide investigation in order to
determine whether a landslide is likely to occur in some location
where a structure is to be placed. A landslide investigation has a
number of steps. The first step in performing such an investigation
is to assemble historical information on the natural and human
history of the region. The following sources are useful for acquiring
this information: municipal files, notes from other geological
projects, aerial photos, reports, and maps. A full investigation of the
subsurface conditions, including topography, drainage, geological
structure and weathering, and faults, should be performed before
any construction is initiated. In general, all the data should be
aimed at locating any weak regions in the location.

Discuss what causes landslides, and group causative factors
according to type.

The term landslide covers a wide variety of mass-movement and
other gravity-driven downslope transport processes involving the
movement of soil and rock material en masse. Typically displaced
material in landslides will move over a relatively confined zone or
surface. Wide ranging slope angles and diversity of geologic
materials of varying properties that affect resistance to shear, result
in a great range of landslide morphologies, slide rates, and sizes.
Landsliding is often preceded and followed by perceptible creep
along the surface of sliding and/or within the slide mass itself.
Terminology used to classify and describe landslide types generally
includes the landform or material involved, as well as the process
responsible for it. Some examples are: rockfall, translational slide,
block glide, avalanche, mudflow, liquefaction slide, and slump.

Review the general strategies used to help prevent landslides.

There are a few basic ways to mitigate the possibility of landslide.
Extremely steep grades can be minimized by recontouring and
moving material from the crown to toe area, thus reducing the
chance of a landslide. Decreasing saturation and pore-pressure of
soils by diverting surface water or adding dewatering wells,
horizontal drains, or trenches, can minimize the risk of landslide.
Monitor wells and piezometers can be installed to monitor interior
dynamic of potential slide areas and to alert for potential landslide
events. Architecturally, buttresses and retaining walls can be put in
to stabilize unsteady slopes. Rocks that are considered to be
unstable may be shored up with rock bolts, and soil can be hardened
through thermic treatment or grouting.

Explain what landslide stability analysis methods involve, and what
their function is.

As part of a landslide investigation, a landslide and stability analysis
will be performed in order to calculate what is known as the factor of
safety (F). The factor of safety is simply the ratio of the forces that
will resist a landslide divided by the forces that will promote a
landslide. The factor of safety (F) is the likelihood of a landslide
occurring in a particular area. In order to perform this analysis, a
geologist will need to have an equilibrium slope analysis, a measure
of the sheer strength of local soil, and the general idea of the
orientation and angle of internal friction of the subsurface materials.
In many cases, it will be possible to perform a landslide stability
analysis by using a general slope stability chart.

Review the factors that contribute to subsidence.

Subsidence is the sudden sinking or gradual downward settling of
the Earth's surface with little or no horizontal motion. The
movement is not restricted in rate, magnitude, or area involved.
Subsidence is many times caused by the activity of humans.
Human-caused subsidence can be related to subsurface mining, oil
extraction, or the pumping of groundwater. Underground and nearsurface
coal mining is especially susceptible to subsidence as the
sedimentary host rocks are seldom competent. Hard-rock mining
related subsidence can be severe near stoped areas or buried
shafts/adits. Removal of large amounts of oil or gas from a section
can cause subsidence. Occasionally urban or suburban planners are
challenged by subsidence from abandoned mines. Subsidence may
also be caused by natural geologic processes, such as solution,
thawing, compaction, slow crustal warping, or withdrawal of fluid
lava from beneath a solid crust.
The following

Discuss how the steepness of a slope can be expressed.

There are a few different ways to express the steepness of a slope.
The most common way to express slope is as the ratio between the
horizontal and vertical. It is commonly expressed, for example, as
three-to-one (3:1), or two-to-one (2:1), with the vertical component
of slope as one. Another way to express slope is as a grade, or as a
ratio between vertical and horizontal slope; this is typically
expressed as a percentage. The third and final way to express slope
is to consider the angle of the slope as compared to the horizontal
as measured with a slopemeter. The slope angle is calculated by
considering the arctangent of the vertical extent divided by the
horizontal extent.

Discuss what causes expansive soils, and how they can be identified
and mitigated.

Expansive soils, referred to as swelling soils, are those that assume
a general volume increase when subjected to moisture. Swelling
soils always contain clay minerals that readily attract and absorb
water. Another type of swelling material is known as swelling
bedrock, containing rock called claystone. When water is absorbed
these clays or bedrock experience a large increase in internal
pressure or an expansion of volume. In many cases, expansive
soils are buried under a layer of topsoil or dense vegetation and
cannot be identified at the surface. Test holes can be drilled by
geotechnical and civil engineering firms or by some construction
companies to collect samples. After the samples are taken, they are
sent to a laboratory where the swelling potential is determined. In
areas where there is a high concentration of swelling soils,
laboratory analysis of the soil is required by law. Mitigation of
expansive soils involves dewatering foundations in existing and
designed structures.

Define the following terms relating to different types of ground
materials: flowing ground, raveling ground, running ground,
squeezing ground, swelling ground.

The following terms relate to the different types of ground materials:
• flowing ground: liquefied soil that is emplaced or propelled
by seepage into a tunnel or excavation due to a lack of soil
cohesion or adequate sealing
raveling ground: rock that breaks into small round pieces
when being drilled that tends to cave into the hole when
the drill string is pulled. Rock or soil that forms
agglomerated particles that bind a drill string by becoming
wedged between the drill rod and the borehole
running ground: soil that is cohesionless. May be
semiplastic or plastic and is typically seen in wet clays.
These soils readily deform under pressure and squeezing
into openings and crevices. These soils may enter a mine
tunnel once the roof and wall supports have been removed
• squeezing ground: any soil or rock that after entering a
mine excavation or tunnel which is seen to maintain a
constant volume
swelling ground: any rock or soil which undergoes a volume
increase after excavation. Typical of many clay-rich soils or
formations

Discuss how the following parts of a tunnel relate to the ground surface: shaft, adit, stope, raise, drift, winze, crown, invert.

The following parts of a tunnel all relate to the ground surface:
• shaft: A vertical excavation, driven from the surface, that is
typically of limited area compared to its depth.
• adit: a horizontal or nearly horizontal tunnel constructed
into a hillside, typically at a level below a known ore body
or coal seam, for accessing working or for dewatering of a
mine.
• stope: any excavation in a mine designed for removing ore.
Shape and size are determined by, and are directly related
to, the physical dimensions or shape of the orebody
• raise: a vertical opening in a mine driven upward from a
tunnel level to
connect with the level above. Typically does not connect to
the surface
• drift: an entry constructed into the slope of a hill that is
usually driven horizontally into an ore body or coal seam
• winze: a vertical shaft connecting two underground levels in
a mine. Does not reach to the surface
• crown: the curved roof of a tunnel excavation
• invert: the floor or bottom of a closed water conduit, aqueduct, tunnel, or drain

Discuss how the rock quality designation is defined, and compare
the information provided by the RQD with the information provided
with the Terzaghi number.

The designation of rock quality, known by the initials RQD, is
performed by analyzing the rock core. In order to be suitable for
analysis, the rock core must be at least 2 inches in diameter. RQD
is the total length of all pieces of core that are twice the diameter of
the core divided by the total length of the core; this value is
expressed in terms of a percentage. A rock in good condition has an
RQD of between 75 and 90%. A rock in fair condition has a RQD of
between 30 and 75%. A rock in poor condition has a RQD between
25 and 30%. Another way of designating rock quality is with
Terzaghi numbers, which place a rock on a scale of one to nine: nine
is a swelling rock, and one is a hard rock.

Review the principles used when siting tunnels, including things that should be avoided, and how the area should be characterized.

A tunnel should be oriented such that it cuts across geology and
intercepts desired zones of interest. Rock competence and ground
stability at the portal site and available space for tailings are of
concern. In general, areas with high groundwater and weak
subsurface formations should not be tunnel sites. If at all possible,
a tunnel should not cross a large fault or void in the subsurface
unless it is a targeted zone such as a vein or ore body. Pretunneling
core drilling data will assist in layout of planned tunnels.
Tunnel siting should maximize efficiency of access to underground
target, environmental concerns, and storage and site plan issues. A
major concern in tunnel siting is avalanche danger. Tunnels must be
sites out of direct and recurrent avalanche zones.

Describe the general structure of a dam.

Dams are walls to hold back water. They are typically secured at
either side by an abutment. The main part of the dam will be
constructed of some impervious material, with pervious areas on
either side of the dam's core. The water in the reservoir being held
back by the dam will be able to penetrate the pervious areas
upstream. Below the dam, a cutoff trench will be dug that prevents
seepage from emerging from the reservoir. In order to prevent the
dam from leaking, the phreatic line must curve down and away from
the reservoir heights on the upstream side, in the direction of the
dams based on the downstream side. Water pressure relief can be
furnished by blanket and toe drains at the base of the pervious zone,
as well as by further relief wells beyond the toe drain.

Compare and contrast conventional tunneling and boring or continuous excavation methods of tunneling.

Conventional methods of tunneling involve drilling and blasting.
After each shot, the broken rock (muck) at the face must be
removed and any timbering completed before the next shot can be
drilled. These methods are preferred for hardrock mining. After the
tunnel has been established structures like arches and rock bolts
must be created to maintain the tunnel structure. In continuous
mining a machine cuts or rips coal from the face and loads it onto
conveyors or into shuttle cars in a continuous operation. This
eliminates the drilling and shooting operations of conventional
mining. Continuous mining provides a continuous flow of ore and
eliminates the need for multiple heading in conventional technique
to achieve the same. This method is more applicable to coal mining.

Review the main types of dams that are built in the United States.

Large dam in the USA are typically masonry arch dams. In the arch
dam, stability is obtained by a combination of arch shape and
gravity action. The large dams such as Hoover Dam are concrete
gravity arch dams. Gravity dams are designed to ensure that their
stabilities are secured by size and shape. This guarantees that they
will resist overturning, sliding and crushing at the toe. Embankment
dams are made from compacted earth, and have three main types,
rock-fill, earth-fill, and asphalt-concrete core dams. Embankment
dams rely on their weight to hold back the force of water. A
cofferdam is commonly made of wood, concrete, or steel sheeting,
and is a (usually temporary) barrier constructed to exclude water
from an area that is normally submerged.

Discuss the major' geologic considerations that must be dealt with to
site a dam, and how a proper geologic investigation would be conducted to build one.

Building a dam to hold back a water reservoir is an enormous
engineering endeavor. A river diversion is typically required
involving coffer dams and construction site de-watering before
construction of the dam can begin, a major project in itself. Rock
scaling and wall preparation must be performed upon the canyon
walls where the dam is located. Beforehand, geologists spend many
hours analyzing aerial photographs, geologic maps,
photogrammetric data, core drill data and logs, and results of
engineering tests on the rocks hosting the dam site. Test would
include shearing and compression tests on rock near the dam and
fracture and detailed structural analyses of rocks in and around the
dam site. Any dam investigation must contain a very detailed and
specific earthquake and prior tectonic evaluation of the dam site and
environs.

Discuss how flow nets can be used to help design a dam.

A flow net is a graphical representation of two-dimensional steadystate
groundwater flow through aquifer. Construction of a flownet is
often used for solving groundwater flow problems where the
geometry makes analytical solutions impractical. , These diagrams
are often used in the design of dams, to determine where water
pressure will tend to accumulate. On such a diagram, the maximum
equipotential line will be the horizontal line at the base, while the
minimum equipotential line will be the horizontal line at the base of
the downstream area. Flow lines will then be drawn to show the
possible paths of water beneath the structure. The shortest flow line
will be the curve that joins the intersection of the dam and the
upstream ground with the intersection of the dam and the
downstream ground; the line drawn along the impervious boundary
beneath the ground at the base of the dam will be the longest flow
line.

Discuss the major causes of dam failures, and which types of dams are most likely to fail.

The main causes of dam failure are: spillway design error; geological
instability caused by changes to water levels during filling or poor
surveying; poor maintenance of outlet pipes; extreme rainfall; and
human or computer design error. Dam failures are generally
catastrophic if the structure is breached or significantly damaged.
Routine monitoring of seepage from drains in, and around, larger
dams is necessary to anticipate any problems and permit remedial
action to be taken before structural failure occurs. Most dams
include a mechanism that permits the reservoir to be lowered in the
event of such problems. Embankment dams are probably the most
susceptible to failure as they are generally constructed of
unconsolidated or grouted material. Concrete gravity arch dams are
less prone to catastrophic failure due to their concrete construction.

Review some of the techniques used when grouting dams.

Grout is a thinly-mixed slurry of cement, or a mixture of cement,
sand, and water that is commonly forced into boreholes or rock
fractures to prevent ground water from seeping into an excavation.
In dam construction, grout can be used to prevent seepage and to
enhance stability of the overall dam. It should be applied after the
site has been excavated but before dam construction begins. Often
times, engineers will use so-called grout blankets, which are broad
expanses of relatively thin grout, in order to limit permeability on
the upstream side of the dam. In order to increase the strength of
surrounding rocks, engineers might use off pattern grouting
techniques, which involve forcing grout into specially arrayed
boreholes.

Describe some of the uses of grout, and how it should be mixed correctly.

Grout is a mixture of cement and fine sand that is commonly forced
or pumped into boreholes to prevent ground water seepage from
flowing into an excavation or underground working. Grouting is
utilized to seal crevices in a dam foundation, or to consolidate and
cement together rock fragments in a brecciated or fragmented
formation. Grout is often used to stabilize abandoned mine related
subsidence hazards in areas of near-surface mining. Pressure
grouting is used to re-densify vuggy ground and to re-level
structures damaged by subsidence or settling. Grout is typically
prepared with very high slumps and most often does not contain a
coarse aggregate faction. It is usually a combination of cement,
sand, fly ash, and water. Some grout is prepared so as to be nonshrinking
in order to insure competent seals.

Bulk modulus (K)

otherwise known as incompressibility modulus. a measure of a substance's resistance to uniform compression. It is defined as the pressure increase needed to affect a given relative decrease in volume

Shear modulus (G)

also known as rigidity modulus: refers to the deformation of a solid when exposed to a force parallel to one of its surfaces as its opposite face is exposed to an opposing force. This will cause an object that is shaped like a rectangular prism to be deform into a parallelpiped

Young’s modulus (E)

also known as the modulus of elasticity: a measure of the stiffness of a given material. Defined as the ratio, for small strains, of the rate of change of stress with strain

Dilatancy (soils)

the tendency of a material to increase in volume when subjected to a shape change. Also refers to material which can assume a close-packed structure from a openpacked structure

dry strength (soils)

the resistance that a dry soil possesses to being crushed. A soil that is composed of clays and gravels will have relatively high dry strength

quick condition (soils)

the tendency of some soils that lack cohesion to allow water to flow rapidly between grains and to liquefy the material. Such a soil does not possess significant bearing capacity.

Bearing capacity

the ability of soils to support the loads imposed by buildings or structures

Well-graded soil

soil or unconsolidated sediment consisting of particles of several different sizes and having a uniform or equal distribution of particles from coarse to fine. A graded sand or sandstone containing coarse, medium, and fine particle sizes is an example

effective size

corresponds with the weight percentage of material equal to a certain size amount. Measures the distribution of grain sizes; for example, a grain with an effective size of D3o would be finer than 70% of the other grains in the sample

gap-graded soil

any soil that is missing distinct particle size ranges

coefficient of curvature (Cc)

a measure of the curve on a grain size distribution plot

coefficient of uniformity (Cu)

a measure of the degree to which grain sizes are uniform. Found by determining the ratio of particle sizes

bearing capacity

the maximum load per unit area that a particular soil can be subjected to before it collapses. Bearing capacity is the ability of soils to support the loads imposed by buildings or structures

consistency

the general amount of cohesion in soil particles

critical void ratio

the void ratio of soil that stays the same even during shearing events

Mohr circle

a graph showing all of the individual stresses that act on a single point on a plane. The x-axis will indicate normal stress, while the y-axis will indicate shear stress

Mohr-Coulomb equation

calculates the amount of shear stress that causes a material to fracture

liquefaction

Soils that transform from the solid state to a consistency of a heavy liquid as a consequence of increasing porewater pressure. Liquefaction is caused by the tendency of a soil to decrease in volume when subjected to cyclic undrained loading

optimum moisture content

the level of moisture required to reach the maximum dry density level of the soil. At this point any further addition of moisture increases the density of the soil

piping

erosion by percolating water in a layer of subsoil which results in caving and in the formation of narrow conduits, tunnels, or pipes through which soluble or granular soil material is removed. An example is the movement of material from the permeable foundation of a dam or levee by the flow or seepage of water along underground passages

seepage

the flow of a fluid through soil pores

Atterberg limits

the boundaries between the four levels of soil consistency including plastic, semi solid, liquid, and solid

A-line

the division mark between clay and silt on the Atterberg plasticity chart

plastic limit

lower boundary of plasticity, upper boundary of semisolid

liquid limit

upper limit of plastic state, lower limit of liquid state

plasticity index

range in water content between liquid and plastic boundaries

U-line

mark dividing the upper limit of plasticity from the lower limit of liquidity

G (USCS first letter)

gravel

S

sand

M (USCS first letter)

silt

C (USCS first letter)

clay

O (USCS first letter)

organic

P (USCS second letter)

poorly graded (uniform particle size), and (W) well graded (diverse particle size), or (H) high plasticity, and (L) low plasticity. Soils can be classified into fairly small groups based on this two-letter system.

W

well graded (diverse particle size)

H (USCS second letter)

high plasticity

L (USCS second letter)

low plasticity

fall

the free falling or precipitous movement of a detached segment of bedrock of any size from a cliff or other very steep outcrop or slope