The essay presents a sample paper for SPT29 Geotechnics and Soil Mechanics including Assignment 1 and 2. Sample papers are donitated to Archive Homework when there is a breach of contract based on our copyrights policies (i.e. failed to pay for the services offered)
SPT29 Assignment 1
An understanding
of the mechanical behavior of soils and rocks is critical in order to design
and construct any geotechnical application. Considering that the life of any
structure depends on soil for foundation in one way or another, understanding
its properties is of equal importance before geotechnical applications. Samples
of soils from the boreholes are taken regularly during the ground investigation
to establish the specific soil properties that is suitable for geotechnical
design (Batog & Stilger-Szydło, 2019). The soil samples collected during
ground investigation are taken to the labs for geotechnical testing to
determine whether its properties will support the intended geotechnical
application (Li et al., 2018).
As a results, the
paper will present a report that will analyze soil properties determined by geotechnical
procedures during ground investigation. The report will focus on describing the
importance of soil mechanics when designing the embankments, bridge and road
foundations by evaluating how the soil samples are compacted and the main
reason behind the technic. It will also present a proposal for conducting a
geotechnical procedures to analyze the soil properties for a project of
constructing a new highway and bridge to connect the site to the Sha Tsui peninsula.
Based on the survey data from the soil sampling and testing, the calculations
to determine the suitable soil properties for the project will also be considered.
The results will be used to address the identified geotechnical weaknesses and
problems
LO1: Reviewing the rock types, formation, and uses within
civil engineering
There are three main types of rocks which include
igneous, sedimentary, and metamorphic. Any rock can transform into any other
rock by passing through processes such as crystallization, metamorphism,
erosion, and sedimentation which creates the rock cycle as shown by Figure 1 below (Geoguide 3, 2017). The paper will present a report based
on survey and soil sampling for a proposed construction project. The proposal
is for a large infrastructure project, in an area of mixed geological
conditions. The project will include significant earth working for highway
construction, and the construction of bridges supported on pile foundations.
The land across which the project covers, is undulating with significant rises
and falls over the alignment of the main highway corridor. The site
investigation and soil sampling were undertaken by a different firm
Figure 1: The Rock Cycle.
Formation
of Igneous Rocks
The igneous rocks are formed when the magma cools and
solidifies through crystallization to form a mixture of minerals. They can be
divided into intrusive which are formed by the cool magma within the magma
chambers underground and extrusive rocks which are formed at the ground surface
from fissures or eruptions. While extrusive rocks are formed at the ground
surface from fissures or eruptions, intrusive rocks are formed by the cooling
of magma within the magma chambers underground. Depending on the amount of SiO2
content in the rocks, the igneous rocks can be classified as either acidic or
basic.
The classification of igneous rocks can be conducted
visually because it is usually based on the sizes and colors of their
particles. Igneous rocks are known to have crystalline structures such as granite
which is formed by slow cooling of magma. However, other classes of ingenious
rocks do not have a crystalline structure for natural glass and tuff, which is
formed by the cementation of volcanic ashes. Igneous rocks are considered
resilient to Weathering and susceptibility which affects the discontinuity
nature of rock mass. Moreover, igneous rocks are considered to be generally
strong and resistant to weathering which often starts within the faults and
rock joints. Faults and rock joints can be formed within the weak spots during
the cooling of molten rock which results in the weak spots where water can
penetrate through to cause weathering. The rocks can also be weathered by wind
and temperature actions. The key examples of igneous rocks include Granite,
basalt, and gabbro
Formation
of Sedimentary Rocks
In contrast to metamorphic and igneous rocks, which are
formed deep within the Earth, Sedimentary rocks are formed on or near the
Earth’s surface. Sedimentary rocks are formed by sediments which are generally
through the process of cementation and compaction such as sandstone and
siltstone. The rocks can also be formed as a result of biological processes
such as coal, Chert, and limestone. Sedimentary rocks can also be formed by
precipitation of solutions such as gypsum and halite. Their classification can
done based on the size of their gains which are formed through the
sedimentation of clay, sand, silt, biological matter, or chemical matters. The
process can also result in the formation of a layered structure. Under the view
of a microscope, the layered structure formed by sedimentary rocks is different
from igneous rocks which give crystalline structure
Figure 2:
formation of sedimentary rocks
The key geological processes that lead to the formation of
sedimentary rocks include weathering, erosion, lithification, precipitation,
and dissolution. Erosion and weathering transform stones and even mountains
into sediments such as sand and mud as show by Figure 2 above. The erosion and weathering can result from the
effects of wind and rain on the rocks which slowly break down large rocks into
smaller ones. The cementing material often performs chemical action with rain,
which is slightly acidic, and causes enlargement of the weak spots which
disintegrates the sedimentary rocks. Dissolution is a form of chemical
weathering where slightly acidic water slowly wears away stone. The process
relies on the weak spots that are located within the cementing materials which
contributes to the process considering that the cementation process is not
perfect.
Sedimentary rocks are generally weaker as they are often
formed by cementation between materials such as pre-existing rocks, sand, silt,
or pieces of once-living organisms. The type of rocks can also be weathered by
natural actions from wind and temperature. Given the weak nature of the rocks,
they are much more susceptible to weathering. However, their weathering
resistance depends on the weathering resistance of its constituent material and
the durability of the cementing materials. Therefore
Formation
of Metamorphic rocks
Metamorphic rocks are formed when rocks are subjected to
high pressure, heat, hot mineral-rich fluids, or a combination of the factors.
Extreme heat and pressure are responsible for changing the nature of the
pre-existing rocks to form metamorphic rocks. High-temperature reactions may
take place without melting. Their texture would also change by the
recrystallization process and their mineral formations can also change due to
the ingress of hot fluids. The three types of metamorphic rocks include contact
metamorphism which is formed when magma comes in contact with an already
existing body of rock, and regional, and dynamic metamorphism.
The classification of the metamorphic rocks is based on
their texture, mainly foliations. And may be also accompanied by mineral
contents. Metamorphic rocks tend to have bands that can contain minerals,
crystal structures, and some traces of fossils in cases where the pressure was
not applied too hard. As metamorphic rocks have changed their nature due to
high temperature and pressure, weathering has little effect on the
discontinuity nature of rock mass. Metamorphic rock is generally found near
tectonic plates where the plates come together or converge. Due to differences
in temperature, and pressure, their properties cannot be easily predicted by
their parent rocks. However, the rocks can also be weathered by wind and
temperature actions.
LO2 Exploring and classifying soils to current codes of
practice
The methods used today in site investigation include
drilling, sampling, or testing the soil or rock directly, using equipment such
as boreholes, cones, probes, or test pits. The current technological
advancements have also made it possible to utilize non-intrusive methods in
site investigation which include the use of remote sensing techniques to
measure the properties of the subsurface remotely. According to Geoguide 3
(2017), soil and rocks can be classified into grades which range from grade 1
to grade 6.
Grade I entails the types of rocks that a ringing sound
when struck by a geological hammer with no visible sign of decomposition or
discoloration. Grade 2 entails the rocks that also not be easily broken by a
geological hammer. a ringing sound is produced but the color of fresh rock is
retained when it is struck with a hummer but stained near the joint surface.
Grade 3 contains the type of rocks that are easily broken by geological hammer
but cannot be broken by hand. When struck with a geological hammer, a dull sound
is produced leaving it completely stained. Grade 4 contains the types of
materials that cannot satiate when submerged in water but can be broken into
smaller particles by hand. Grade 5 contains the particles that preserve the
original rock texture and can be crumbled by hand into grains. Lastly, Grade 6
includes the weak particles, and their original rock texture is destroyed.
The site investigation is initiated with a desk
study which studies the geological map, finding relevant geological data that
can be useful. The data can be derived from places such as the geological
library for nearby boreholes, and aerial photos showing the previous
developments and instability. A site visit and investigation are then performed
to give a general impression of the site and its geological features. After
completion, drill holes, trial pits or stripping would be performed to verify
the sub-surface geology. In the drill holes and trial pits, rock and soil
samples can be collected from samples, coring, and block samples. The rock is
classified by Grades I to IV and soil is generally classified as clay, silt,
sand, gravel, cobble, and boulders with a size of 200mm respectively. The soil
classification is done by sieving and sedimentation. It would also be
classified based on its minerals
SPT29 Assignment 2
Soil properties determined by
geotechnical procedures
Soil testing is a
process used in geotechnical procedures to which entails performing relatively
straightforward tests to determine the type of the soil and identify its basic
properties. The tests are used to identify the strength of the soil and
determine if it can physically support the weight of the geotechnical
structure. For retaining walls, the tests are used to check if the wall will
support the pressures placed on the back of it by the soil and the geotechnical
structure
Determining the
properties of a soil during ground investigation is also for important to identify
the compressibility of the soil. The approach checks whether the structure will
have a firm foundation to settle into the soil over time (Caicedo, 2021).
Besides, the studies have demonstrated that the determining the soul properties
is important during when a geotechnical structure
is to be constructed on slopes (Li et al., 2018).It is used to ensure the soil
mass will not “slip” and collapse. Thus, the tests procedures for the common
tests will be discussed below:
(i)
water
content
Water content is
also referred to as moisture content is used to express the amount of water in
a soil.
The test utilizes
the formula: w = 
The results are
reported as a percentage where w < 10, to one decimal place and w > 10,
to nearest whole number.
For example. We
can use the the fomula to solve the following example from the studies:
|
Soil
Sample |
Mass |
|
water content tin of
mass |
19.52 g |
|
combined mass of the
soil and the tin |
48.27 g |
|
After oven drying the
soil and the tin |
42.31 g |
|
water content |
? |
To determine the
water content of the soil we can use: w = mass of water mass of dry soil =
= 0.262 = 26%
(ii)
liquid
and plastic limit
Liquid limit is
the water content at which the soil sample can no longer flows like a liquid
while the plastic limit is the moisture content at the soil particles cannot be
remolded without cracking. The approach utilize the plasticity index is the
range of water content within which a soil is plastic where finer soil samples
demonstrates high plasticity index.
|
Liquid limit test |
||||
|
Date of test: 18 July
2021 |
||||
|
Location: Borehole 2 |
Depth: 4.0 m |
|||
|
Test No |
1 |
2 |
3 |
4 |
|
Cone penetration
reading (mm) |
17.5 |
18.9 |
21.3 |
22.9 |
|
Average penetration
(mm) |
17.6 |
19.4 |
21.3 |
22.45 |
|
Container number: |
1 |
2 |
3 |
4 |
|
Mass of wet soil +
container (g) |
37.71 |
38.85 |
32.04 |
38.22 |
|
Mass of dry soil +
container (g) |
27.2 |
27.99 |
22.99 |
26.74 |
|
Mass of container (g) |
7.03 |
7.04 |
7.1 |
7.02 |
|
Water content (%) |
30.68 |
31.81 |
24.94 |
31.2 |
Liquid
limit =30%
The plastic limit
of a soil sample from a given site can be measured using the formula:
Plasticity index = Liquid limit – Plastic limit
The liquidity
index tests makes it easier to compare the plasticity of a sample soil with its
natural water content. When plotted against the liquid limit on the plasticity
chart the plasticity index enables the classification of cohesive soils.
For example, the
formula can be used to calculate the void ratio and the degree of saturation
where a soil sample of total volume 200 ml contains 25 ml air and 30 ml water..
𝒆 = 
=
=0.38
Sr=
(iii)
California
bearing ratio
The laboratory California
bearing ratio tests are conducted by formulating a sample of soil in a tubular
steel ampule and then forcing a cylindrical steel nozzle with a nominal diameter,
into the soil sample at a precise rate to determine the force required to penetrate
through the soil sample. For instance,
the California bearing ratio can be measured by applying weight to a small diffusion
piston at a rate of 1.3 mm (0.05″) per minute as shown by the sketch below. The
results shows that the total weight was logged at penetrations stretching from
0.64 mm (0.025 in.) up to 7.62 mm (0.300 in.)
Figure
1: Sketch of CBR
Proposal to address identified
geotechnical weaknesses and problems
Natural soil
comprises a mass of solid particles separated by spaces or voids which are
sometimes filled with water and some with air. The project of constructing a
new highway and bridge connecting the site to the Sha Tsui peninsula will
require efficient approach for conducting geotechnical procedures to analyze
the soil properties. Considering the current state of the soil from the site,
the approach should aim to address geotechnical problems related to
embankments, bridge and road foundations before the construction.
|
Natural water content test |
|
|
Date of test: 18 July
2021 |
|
|
Location: Borehole 1 |
Depth: 3.5 m |
|
Mass of wet soil +
container (g) |
374.3 |
|
Mass of dry soil +
container (g) |
348.5 |
|
Mass of container (g) |
256.5 |
|
Water content (%) |
117.8 |
According to Batog
and Stilger, (2019) research, the primary geotechnical issues that impact
embankment performance for a site for constructing a new highway and a bright are
overall stability, compressibility and strength of the soil. Thus, the report
proposes leveling the land to strengthen the soil for highway construction to
as the first step to ensure the pavement layers can be supported.
Figure2:
boreholes from the site
The site presents the
geotechnical problems occurring in the interaction area between road
embankments and the bridge structures in case a subsoil characterized by
complex geological and engineering conditions .The next step can include cut
and fill where rock or soil cut to reduce the land level, is reused on the site
as fill to construct embankments to raise the ground level. The method will
allow the vertical alignment of the highway to be constant and strong rather
than undulating
Figure
3: Cut and Fill
Geotechnical
engineering for bridge building faces unique challenges due to bridges being
constructed over waterways. Compaction of soils can also be useful to minimize
the volume change produced by input of work by impact, vibration by eliminating
the air or water spaces between the soils. Foundations for bridges differ from
those for buildings, and scouring during hurricanes or storms can carry away
sediments, undermining the bridge and leading to failure. Given that the high
rates of water concentration from results from the data corrected from borehole
1 and 2, the project should consider the compaction. The key objective of compaction is to minimize
the volume of the soil by eliminating the spacing between the particle which
will give the soil increased strength and decreased compressibility
Conclusion
The report has
analyzed how the soil properties are determined during geotechnical procedures
when conducting a ground investigation. It has described the importance of soil
mechanics on the design of embankments, bridge and road foundations by
describing how soils are compacted and explaining why soils are compacted. It
has also presented a proposal for conducting a geotechnical procedures to
analyze the soil properties for a project of constructing a new highway and
bridge connecting the site to the Sha Tsui peninsula. Based on the survey data,
soil sampling and testing, the results from borehole 1 and 2 were used to determine
the required soil properties for the project have been included to address the
identified geotechnical weaknesses and problems
References
Batog, A., &
Stilger-Szydło, E. (2019). Geotechnical problems of the foundation of road
embankments by the bridge structures. Studia Geotechnica et Mechanica, 41(4),
272–281. https://doi.org/10.2478/sgem-2019-0036
Caicedo, B. (2021).
Unsaturated soil mechanics applied to road materials. Geotechnics of Roads,
65–111. https://doi.org/10.1201/9780429025921-2
GEO, G. (2017). 3—Guide to
Rock and Soil Descriptions. Geotechnical Engineering Office, Civil Engineering
Department, The Government of the Hong Kong Special Administrative Region.
Li, P., Song, E., &
Zheng, T. (2018). Initial sinking method for large open caisson in a highway
bridge project. Springer Series in Geomechanics and Geoengineering,
1692–1696. https://doi.org/10.1007/978-3-319-97115-5_172
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