510460929 GEOL1501 Final Exam
pdf
keyboard_arrow_up
School
The University of Sydney *
*We aren’t endorsed by this school
Course
1501
Subject
Geology
Date
Jan 9, 2024
Type
Pages
16
Uploaded by EarlMoon5843
SID:510460929
GEOL1501 Engineering Geology 1
A1 Plate Tectonic Settings, ‘Geological Hazards’ and Recurrence Intervals
The “Plate Tectonics” concept enables geologists to explain the major natural earth hazards that
occur in both ‘Plate Boundary Settings’ and ‘Intraplate Settings’.
a) Outline the main differences in earthquake frequency and seismic hazard between a ‘Plate
Boundary Setting’ e.g. New Zealand and an ‘Intraplate Setting’ e.g. Australia.
-
Intraplate settings experience less frequent earthquakes alongside lower magnitude earthquakes as
opposed to plate boundary settings. Earthquakes occur due to a slippage between tectonic plates
which induces a strong release in energy in the subsurface. Since earthquakes occur mostly at
plate boundaries, this means that the magnitude will be higher at this setting as it is closer to the
focus/epicenter of where the earthquake occurred, thus inducing a higher potential seismic
hazard. For countries within the intraplate settings, earthquakes occur due to the release of
stresses within the plates, due to the interaction with its neighbouring plate. This release of energy
is generally lower in magnitude, and is considered rare in comparison. The highest readings
which occurred in Chile, Southern Alaska, North-Sumatra, and Japan are countries which exist in
the plate boundary setting, all experiencing magnitudes of 9.1 and up, producing catastrophic
damages and high death tolls.
b) Indicate how our knowledge about Plate Tectonic Settings assists disaster management
authorities make planning decisions about a particular area’s seismic hazard.
-
Our knowledge of plate tectonic settings has given us an understanding of where earthquakes are
most likely to occur and the magnitudes which particular areas can experience. With the
understanding of the seismic hazards, authorities have a better understanding of what construction
techniques must be used to ensure the durability of structures, and construct buildings which can
withstand high magnitude earthquakes. Areas in which structures will be built on must be
properly examined to ensure that structures are built on strong consolidated bedrocks. Authorities
such as the California Earthquake Authority have devised a handbook to educate residents on
how to prepare for these seismic hazards and how they can implement fixes and reinforcement to
their homes in order to withstand upcoming earthquakes. These handbooks give instructions on
what construction materials should be used, information about the importance of strong
foundational rock, and the design principles which ensure safety. Authorities also educate
residents on what they should do during the event of an earthquake to ensure their individual
safety.
c) Identify two other, non-seismic, Geological or Natural Earth Hazards that can occur in both a
‘Plate Boundary’ and ‘Intraplate’ settings and suggest probable recurrence intervals for these two
non-seismic hazards.
-
Volcanic eruptions and cyclones/hurricane/typhoons are two natural earth hazards generated in
both plate boundary and intraplate settings. The recurrence intervals for volcanic eruptions
drastically vary in time. As volume and plume height of volcanic eruptions increases, so too does
the recurrence intervals of the eruptions. Non-explosive volcanoes with plume heights of less than
100m and volume of 1000s m3 will experience daily recurrence, whereas a mega-colossal
volcanic eruption with plume heights reaching greater than 25km and a volume of 1000s Km3
will occur every 10’000’s years The increase in silica content of the volcano, leads to an increase
in recurrence intervals.
-
Cyclones/hurricanes/typhoons are large tropical storms which form around warm tropical oceans.
Around 85 tropical storms are formed, with around 45 becoming cyclones/hurricane/typhoons,
around the world globally. These large tropical storms are named differently depending on which
part of the world it is occurring in.
(
https://public.wmo.int/en/our-mandate/focus-areas/natural-hazards-and-disaster-risk-reduction/tr
opical-cyclones
).
A2 Weathering Processes and The Built Environment
Certain rock types are particularly affected by weathering processes.
a) Name two rock-types that can be severely affected by dissolution.
-
Halites (Rock Salts) and Calcites (Limestone, marbles) are susceptible to dissolution in which the
minerals dissolve through acidic rain.
b) Provide a real-world example where buildings have been seriously damaged or destroyed due to
weathering by dissolution.
-
Florida is notorious for sinkholes which are caused due to dissolution. A known example is the
sinkhole which led to the collapse of a villa at Summer Bay Resort, FL. Florida is characterised
by limestone which is vulnerable and is susceptible to the process of dissolution. In Summer,
Florida experiences extreme weather conditions such as high amounts of rainfall. The sinkhole in
Summer Bay Resort, and many of the sinkholes in Florida are caused by this heavy rainfall
which contains weak acids. The rain combines with atmospheric carbon dioxide which forms
carbonic acid. The acid percolates through the soils and penetrates the limestone joints, forming
calcium bicarbonate, a soluble which gradually weathers the limestone. This in turn leads to a
collapse of limestone caves underneath the built structure and the formation of deep sinkholes
beneath structures. The sinkhole was around 12m to 15m in diameter which led to a collapse of
around 30 percent of the three storey building (BusinessInsider, 2013,
https://www.businessinsider.com/sinkhole-at-summer-bay-resort-in-florida-2013-8?r=AU&IR=T)
c) Suggest a strategy for managing, avoiding or minimising damage to structures located in areas
where dissolution of rock is problematic.
-
A standard site model is a visual tool which can be used to determine and predict the subsurface
geology of certain areas, this can be used to identify any potential issues which may occur when
partaking in construction on the site. With this information, adequate construction techniques can
be implemented to reduce the risks of sinkholes and other damages due to dissolution or rocks in
the subsurface. In order to avoid damages to structures, adequate site investigation must take
place in order to determine if the planned construction site is able to withstand the effects of
gradual dissolution. Site investigation can determine the rocks which are present in the area, and
thus laboratory testing and examination of the site and its rocks can minimise the risk of potential
damages to erected structures. The identification of which sites are in the Karst regions, regions
that are soluble, is vital in determining areas to avoid when constructing structures. To minimise
damage to the structure, the burning of coal should be reduced to a minimum, as burning of coal
generates large amounts of sulfur dioxide which combines with the rain to create sulfuric acid.
This sulfuric acid will lead to the breakdown of limestone and gypsum present in the areas, thus
leading to the formation of sinkholes. It will not only affect the rocks in the subsurface, but it will
also weather and damage any buildings and monuments that have been constructed with
limestones and marbles. The use of impermeable concrete solution in foundations can help avoid
or minimise the damage to sinkholes. If the correct concrete solution is used, it can withstand any
acidic rain and thus negate the chances of sinkholes forming beneath the surface of the structures.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
B1 Site Investigation Tools and Interpretation
A major, four-lane highway is required to cross an 1800-metre-wide, river valley. The river channel
is located in the middle of the valley and is five metres deep and three hundred metres wide.
This river floods regularly every summer during the wet season and submerges all of the valley’s
1800 metre wide, flat floodplain to a depth of 2 metres.
Hydrological assessments of the 1/50 and 1/100 year flood suggest that these larger floods will
submerge the valley to depths of 7 metres for the 1/50 year flood and 10 metres for the 1/100 year
flood.
The log shown on the next page is typical of all of the logs collected every 50 metres along the
highway route. The investigation tool refused at the base of the log and subsequent investigations
identified fresh, unweathered granite at 23 metres depth.
a) Name the site investigation tool that was used to acquire the sounding log shown in the image
provided on the next page.
-
The Cone Penetration Test
b) Describe the conditions that this tool is used to investigate and how the information is used to
assist in making construction decisions.
-
The conditions for the cone penetration test is to determine in a cheap and quick manner, the
stratigraphy of a subsurface and the engineering properties of the materials present in the
subsurface. The cone penetration test is a useful tool in investigating soils and rock that are at
depths of greater than 30 meters beneath the surface. A conical tip is hydraulically pressed into
the surface at a constant rate of 2 cm per second in which it descends into the subsurface while
measuring the forces and resistances experienced by the cone tip and the sleeve. These values are
used to determine the subsurface material behaviour, in which cone resistance (qt), sleeve
resistance (fs), friction ration (Rf) are measured. These can give a solid understanding of the
subsurface in which a potential structure may be constructed. Through CPT construction
decisions can be undertaken after determining whether the subsurface can adequately support the
loads which will be imposed onto it via the structure. If the CPT finds that the subsurface is too
weak, a potential disaster can be avoided by deciding to construct elsewhere.
c) Name and briefly describe the characteristics of the materials present between 4m and 8m depth
below the surface.
-
Materials present between 4m to 8m depth include:
●
Organic Soils - peat/turf (0 - 2 m)
-
Sleeve friction ~ 0.01 - 0.02 MPa
-
Pore pressure ~ 0
-
Cone Resistance ~ 0 - 2 MPa
-
Friction Ratio 0 - 2 %
●
Sand (2-8 m)
-
Sleeve friction ~ 0.02 - 0.06 MPa
-
Pore pressure ~ 0
-
Cone Resistance ~ 2 - 19 MPa
-
Friction Ratio ~ 0.1 - 0.9 %
Organic soils have low cone resistance and high friction ratios
Sands have intermediate to high cone resistance, and low to intermediate friction ratios.
d) Name and briefly describe the characteristics of the material present between 18m and 20m
depth below the surface.
-
Materials present between 18m to 20m depth include:
●
Clay
-
Sleeve friction ~ 0.04 - 0.02 MPa
-
Pore pressure ~ 0.1 - 0.9 MPa
-
Cone Resistance ~ 1 MPa
-
Friction Ratio 0.3 - 2 MPa
Clay has intermediate trending towards high cone resistance, and intermediate to high friction ratio.
e) Develop a construction solution that responds to the geotechnical and geological issues presented
by the local conditions in the project area that will enable the proposed freeway to function
properly and enable traffic flow during the 1/100 year flood event.
-
Since the 1/100 year flood event brings about a flood that reaches 10 meters high, it is vital that
the highway is constructed well above this level. With the newly found fresh granite, it can be
used as a foundation as granite is considered a strong material for structures. A use of pile
foundation can penetrate through the unconsolidated rock and soil and create a solid foundation
using the granite layer. With the pile penetrating down to the fresh granite, construction of the
highway can be adequately adjusted in height so that the flood will never impede on the highway.
Since the granite is strong, it can allow for a taller structure in which the highway will be
unaffected by the 1/100 year flood and the 1/50 flood. The granite occurs at least every 50 m of
the highway route, making it the perfect use for a foundational rock, in which the piles can be
erected upon.
B3
Dams and Geology
Identify the common factors shared between the Grand Teton and St Francis Dam Disasters. Both
of these events were discussed in lectures as they provide excellent examples of why it is important
to properly understand the geology and landscape history of a dam site and the potential for the
geology of a dam site to contribute to disasters that have catastrophic impacts on the downstream
communities. In your answers you should
a) Describe the sequence of events that occurred during both the Grand Teton and St Francis Dam
disasters;
-
The St Francis Dam abutments had been experiencing seepage through the foundation of the dam
alongside differential settlement in the foundation led to cracking of the dam and its rollover and
collapse. The failure led to the demise of approximately 431 people, and this disaster was
attributed to an array of human failures and extreme poor engineering judgement of William
Mulholland, the chief engineer of the dam. The differential settlement occurred due to the present
conglomerates and schists on the site which are characterised by different strengths which led to
the cracking and destabilisation of the dam. The engineers neglected the notion of saturation of
these materials which would have initiated the differential settlement.
-
The Grand Teton collapse of 1976 occurred due to joint fracturing within the rhyolite bedrock
foundation on which the dam was constructed. This joint fracturing meant that water would flow
easily through the rock mass below the dam and thus into the core of the dam where there internal
erosion and piping occurred. Alongside this was that the permeable solution which formed the
core of the dam, was a granular non-cohesive fine-grained silt which was easily eroded once the
water penetrated the joint fractures in the rock mass. This loose material was easily eroded by the
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
water. The collapse led to the demise of 11 people, and a substantial cost in damages reaching
$400 million.
b) Identify the common factors that contributed to the two disasters
-
The common factors which contributed to both disasters is the neglect of the geological
compositions present in the construction of the dams. St Francis Dam had neglected the presence
of the conglomerates and the schists which led to differential settlement, while Grand Teton
neglected the constituents which were used to construct the dam, using an easily soluble material
in the presence of water. In both cases, there was a high level of geotechnical neglect from the
engineers which led to catastrophic damages and the loss of life. Had proper construction taken
place, with adequate geotechnical practices, the disasters could have been avoided. In both case
studies, water had dissolved the materials on which the structure required in order to be stable and
retain its strength. With the presence of soluble materials in both dams, the water was the biggest
factor in the destruction of the dams.
c) Identify at least one strategy that might have prevented both of these two disasters (ie. at least
one strategy for the Grand Teton Disaster and at least one strategy for the St Francis Disaster.
-
For St. Francis Dam sheet piling would have been effective in potentially preventing the
occurrence of differential settlement. Sheet piling could have been used while the dam was
excavated for its conglomerates and schists and finding better foundational rocks, or developing a
solid foundation instead of relying on the conglomerates and schists present. Site investigation
would have helped prevent the differential settlement as there would have been a stronger
understanding of the geotechnical issues that were to arise, had they continued to build on the
problematic rock foundations.
-
For the Grand Teton Dam, the use of dense, low porosity materials in the construction of the dam
would have been critical in this particular case. As the materials used in the dam were highly
soluble, the material was easily eroded, which would not occur if proper material were used. With
low porosity materials, this means that there is less chance of water penetrating the materials.
Developing a solid low-porosity foundation could also be a useful strategy. The water which
penetrated the rhyolite bedrock joints was the passage in which the core of the dam was
penetrated. If the foundation of the dam was constructed with low porosity materials, then there
would be less risk of water penetrating the core of the dam.
You are advised to include one or more labelled sketches in your answer.
Map One – Karstens Hill (12 marks)
a) Identify the location of the angular unconformity in the Karstens Hill area by highlighting it or
outlining it on the geological map. Make sure you trace the entire length of the unconformity.
b) Justify your answer to part (a).
-
An angular unconformity on a geological map is characterised as a horizontal boundary that cuts
across multiple other outcrop boundaries. The lowest horizontal plane in the stacked sequence of
rocks is known as the angular unconformity. The angular unconformity in the geographical map
shows the deposited horizontal layering of ignimbrite which has deposited above the older
outcrop. The contour lines of the ignimbrite shows that the deposited layers are horizontal and are
on top of the older outcrops which dip at an angle of 74º, creating the angular unconformity with
the horizontal bedding planes.
c) What is the spatial orientation of the Ignimbrite unit?
-
The spatial orientation of the Ignimbrite unit is horizontal bedding.
d) What is the spatial orientation of each of the three Dolerite units?
-
The spatial orientation of the three Dolerite units is vertical dipping.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
e) Draw a geological cross section along the line A-B shown on the geological map. Please use the
cross-section space provided on the next page.
f) List all the rock types and major geological surfaces present in the Karstens Hill area in order
from the oldest to youngest. Note that you should include the Angular Unconformity and the
Present-Day Land-surface in this list.
1.
Muscovite Phyllite
2.
Purple Slate
3.
Chlorite Phyllite
4.
Hornfels
5.
Granite
6.
Angular Unconformity
7.
Ignimbrite
8.
Dolerite
9.
Basalt
10. Sandstone
11. Present-Day Land-surface
Map Two – Dylans Bluff (8 marks)
g) Draw a Geological Section for the Dylans Bluff Geological Map along the True Dip Direction of
the Fault along a line that will enable the ‘Dip Slip Displacement’ on the Fault to be determined.
h) What is the amount (distance in metres) of the horizontal displacement on the fault in the Dylans
Bluff map area?
-
275.05 m
i) Explain how you determined the amount of horizontal displacement on the fault in the Dylans
Bluff area and give a more conventional name for this measurement.
-
I determined the amount of horizontal displacement by first determining the value of the throw,
and then using SOHCAHTOA, using the angle of 35º and the properties of a right angle, to
determine the amount of heave (horizontal displacement)
j) What is the amount of the vertical displacement (i.e., the throw) on the fault in the Dylans Bluff
map area?
-
180 m
k) Explain how you determined the amount of vertical displacement on the Dylans Bluff Fault.
-
Using the geological cross section that I drew, I determined the height of sandstone between two
separate horizontal beds. I found that the bed to the East of the fault had a sandstone layer
beginning at approximately 839 m above sea level, whereas the sandstone layer to the West of the
fault began at approximately 659 m above sea level. Vertical displacement, or throw, can be
determined as the difference between the separate layers as this can be seen as the vertical
displacement which has occurred.
l) Determine the amount of ‘Dip Slip’ on the Dylans Bluff Fault.
-
Using right angle properties and pythagoras, the dip slip on Dylans Bluff fault was 328.71 m
m) What is the Net Slip on the Fault? (Show your working or otherwise explain how you
determined the Net Slip on the Fault)
-
Measuring the strike slip by using a ruler on the geological map, the strike slip is 550 m, using
pythagoras and the dip slip found previously, I solved for net slip which equals 640.74 m
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Task/Question One – Geological Cross-Sections (15 marks)
Use the map and core-logs to generate X-X’ and Y-Y’ geological cross-sections for the Jefferson
Centre Site. They should show appropriate and relevant geological information. You should also
generate at least one additional geological cross-section of this site (in a location of your choice) to
aid you in the development of your “Geological Site Model” and your recognition of the potential
problems that the geology of this site may present for the construction of the Jefferson Centre.
Task/Question Two – Interpretation and Advice (25 marks) There are many potential problems that
might affect this construction project. You are required to identify and deal with the problems that
you consider to be the most important. You should consider the short-term issues that will be
encountered during the excavation and construction as well as the long-term geological issues that
may affect the building during its 100-year-long ‘working-life’.
-
During excavation short term issues that will arise are potential leakages that will fill the
excavation site due to the nearby Jefferson Bay. This will cause excavation sites to fill up and will
lengthen construction time as the site must be properly drained before construction of the
Jefferson Centre begins. Proper drainage systems must be installed and it must be ensured that
there is no leakage into the excavation site. During excavation, there will be a lot of
unconsolidated sediments that the excavation crew will run into. These unconsolidated sediments
must be removed and excavated and proper foundational rock must be found as these
unconsolidated sediments are susceptible to dissolution through water. The breaking down of
these rocks and elements will lead to differential settlement with present chlorite schists. Another
problem during excavation is the compressive strength differences of these chlorite schists
between weathered and fresh samples. If the building is erected on top of two varying weathered
rock beds, then it will surely lead to differential settlement and cause cracking to occur in the
building in the future. Open joints means that the rock material is more porous than other rocks in
the site. In the chlorite schists, its joints are filled with clay, which further reinforces the notion of
dissolution of the clays. The chlorite schists in the site seem to be hazardous and should be
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
carefully examined before deciding on whether the construction should occur on it. During
construction it is imperative that the construction is planned ahead of time. If the timeline of
construction is not planned properly, the construction can be abruptly halted or delayed due to
strong and heavy rainfall. During the 100 year lifetime of the Jefferson Centre, the building will
be expected to experience a M7 earthquake within the next 70 years and an M8 earthquake in 600
years. The M7 earthquake can cause significant damage to the structure and must be accounted
for in order to prevent as much damage as possible. Another natural hazard which recurs
frequently are the tropical storms and major cyclones which are expected to occur every five
years. These cyclones however do not typically exceed rainfall of 300 mm per 24 hour period.
There are no guides or local precedents for designing and building the foundations or how to
complete a safe basement excavation for the Jefferson Site. This can be a key problem in the
construction of the building. Without proper guidance, there are likely to be mistakes and errors
which occur due to the undiscovered problems. If there is no guidance in the foundational works,
the whole building could collapse, as foundation is quintessential in the strength and stability of
every structure. The most important problem which must be addressed is the M7 earthquake
which occurs every 90 years. While the earthquake's recurrence frequency is almost a century, it
is still important to prepare for any catastrophic damages that may occur. The next most important
issue is the chlorite schists which are present in the site. These chlorite schists have seemed to
pose threats to the foundation of the structure from problems such as differential settlement, and
dissolution which can lead to potential sinkholes. It is vital that chlorite schists are carefully
examined and tested to ensure that the bearing capacity is adequate, and that it will be able to
withstand the rain and water from upcoming storms and rainfall. The final issue which should be
deemed pivotal is the notion that there is no guidance nor local precedents on how to properly
excavate the basement. If basement excavations are not properly handled, it could lead to
potential defects in the structure . The building must be level and proper guidance is essential in
ensuring the safety of all stakeholders in the building. To prevent and minimise the damage of the
M7 earthquakes, buildings must be properly built and designed so that harmonic frequencies do
not lead to the collapse of the building. The building must be built on hard consolidated rock
which can minimise the vibrations due to the earthquakes. If the building designs are strong, then
the earthquakes will pose minimal threat to the building. If the building were to collapse, there
would be many casualties as the tower would seemingly be tall. In order to account for the
schists, proper excavations must take place or excessive CPT must take place to determine the
strength of the present schist. Soldier pile walls can be used where grounds are being excavated
and tested to prevent any collapse of outer walls. A professional in excavation must be hired in
order to excavate the necessary basement structures. An architect and civil engineer is vital in the
foundational guidance in which the engineer and architect will be able to formulate strong and
load bearing foundations which can last throughout the working life of the building.