Lab 3 Triaxial Loading Test
Summary
TLDRIn this lab, students perform triaxial measurements to determine the elastic properties of rocks. They apply axial stress and confining stress using fluid pressure, measuring the rock's response. The process involves preparing the sample, setting up the loading frame, fracturing the rock, and analyzing data to find stress-strain relationships, modulus of elasticity, and rock strength. The experiment aims to understand how confining pressure affects rock behavior.
Takeaways
- 🪨 The lab focuses on triaxial measurements to determine the elastic properties of rock under confined conditions.
- 📏 Similar to laboratory one, axial stress is applied, but the main difference is the use of a confining vessel filled with fluid.
- 💧 A fluid pump is used to apply confining pressure, with differential stress being the difference between axial and confining stresses.
- 🔧 The workflow involves measuring the sample, preparing the assembly, fracturing the rock, and analyzing the data.
- ⚙️ A membrane is used to isolate the sample from the confining fluid, and components like end caps, plastic o-rings, and vacuum grease are crucial for sealing.
- 🚰 Once the sample is prepared and placed in the vessel, air is removed from the system to ensure only water remains in the confining chamber.
- 🔍 The key measurements in the process include load and displacement, which help determine elastic properties and the point of rock fracture.
- 📉 The analysis focuses on converting force and displacement into stress and strain to calculate Young's modulus during loading and unloading.
- 📐 By performing several measurements, more circles can be combined to estimate the rock's cohesion and internal friction angle.
- 💥 The peak stress during fracture represents the maximum axial stress, and the angle at which the rock fractures can be predicted based on confining pressure.
Q & A
What is the main objective of Laboratory Number Three?
-The main objective of Laboratory Number Three is to perform triaxial measurements to determine the elastic properties of the rock.
How is the principle used in Laboratory Number Three similar to Laboratory One?
-The principle used in Laboratory Number Three is similar to Laboratory One in that both involve applying axial stress to a rock sample to induce deformation and fracturing.
What is the role of the confining stress in the triaxial measurements?
-In triaxial measurements, confining stress is applied through a fluid to the rock sample, influencing the actual stress and vertical strain experienced by the rock.
What is the differential stress and how does it relate to the axial stress and confining stress?
-Differential stress is the difference between the axial stress and the confining stress, which is a crucial parameter in analyzing the rock's behavior under stress.
What is the purpose of the fluid pump in the laboratory setup?
-The fluid pump is used to increase the confining pressure in the system by allowing the confining fluid to be pressurized.
What are the steps involved in measuring the rock sample in Laboratory Number Three?
-The steps include ensuring the sample is straight, measuring the diameter at different points, checking that the interfaces are parallel, and weighing the sample.
How is the rock sample prepared for the triaxial test?
-The sample is placed in a membrane within a vessel, with components such as end caps, o-rings, vacuum grease, and water added to isolate it from the confining fluid.
What is the significance of the bleed valve and pump valve during the setup?
-The bleed valve and pump valve are used to control the air pressure within the vessel, ensuring that air is displaced and the system is filled with water.
How is the confining pressure applied and monitored during the test?
-The confining pressure is applied by connecting the vessel to the pump and using it to increase pressure. It is monitored by observing the pressure readings on the console.
What is the purpose of the strain gauge in the laboratory setup?
-The strain gauge is used to measure the displacement of the rock sample during the test, which is crucial for determining the rock's elastic properties.
How is the data from the triaxial test analyzed to determine the rock's properties?
-The data from the test is analyzed by converting the measurements of force and displacement into stress and strain. This allows for the calculation of the rock's elastic modulus and peak strength at different confining pressures.
Outlines
🔬 Introduction to Laboratory 3: Rock Mechanics Testing
The script introduces Laboratory 3, which focuses on determining the elastic properties of rock through triaxial measurements. The lab employs a similar principle to Laboratory 1, where axial stress is applied to a rock sample to understand its deformation and fracturing. The key difference is the application of confining stress through fluid in a vessel, creating a scenario where both axial stress and confining stress are considered. The lab includes the use of a Floyd pump to increase confining pressure. The workflow involves measuring the sample, preparing the assembly, fracturing the rock, and analyzing data. Special attention is given to ensuring the sample's straightness and parallelism, and the sample's weight is also measured.
🛠 Setting Up the Triaxial Test Vessel
This section details the preparation of the triaxial test vessel for the rock sample. Components such as the vessel, membrane, end caps, o-rings, vacuum grease, and water as the confining fluid are assembled. The process involves applying vacuum grease to the vessel's inner walls, placing end caps, and using o-rings to isolate the sample from the confining fluid. The vessel is filled with water after ensuring that the pump and plate valves are closed. The setup is completed by sealing the vessel with metal and golden o-rings, and adjusting it with screws. The vessel is then placed in the loading frame, connected to a pump, and air is removed from the system.
📈 Operating the Loading Frame and Measuring Confining Pressure
The script describes the operation of the loading frame, focusing on the measurements of load and displacement. The setup involves ensuring the bleed valve is closed and the pump valve is open to connect the pump and vessel. The confining pressure is increased step by step, monitoring the pressure and force to ensure they correspond. The process includes setting a target pressure, such as 50 psi, and observing the system's response. Once the desired confining pressure is reached, a strain gauge is placed and secured. The system is leveled, and the sample, vessel, and strain gauge are checked for proper alignment before commencing measurements.
📊 Analyzing Rock Strength and Elastic Modulus
The final section outlines the analysis of the rock's strength and elastic modulus. The process involves increasing force until the rock fractures, indicated by a drop in force. Safety measures are emphasized, including reducing the confining pressure to zero and ensuring the axial load is near zero before disassembling the setup. The rock sample is then extracted, photographed, and its data file is retrieved for analysis. The analysis focuses on converting force and displacement measurements into stress and strain, calculating the rock's modulus during loading and unloading, and determining the rock's strength at specific confining pressures. Multiple measurements can be used to calculate an envelope that provides information on cohesion and the internal friction angle, which in turn helps determine the rock's fracturing angle.
Mindmap
Keywords
💡Confining Pressure
💡Axial Stress
💡Elastic Modulus
💡Triaxial Measurement
💡Differential Stress
💡Fracture
💡Strain Gauge
💡Loading Frame
💡Cohesion
💡Internal Friction Angle
Highlights
Introduction to laboratory three focusing on confined compression and elastic modulus determination using triaxial measurements.
Comparison with laboratory one, where unconfined compressive strength (UCS) was measured by applying axial stress.
The main difference in this lab is the use of a fluid vessel to apply confining stress on the rock sample.
The importance of differential stress, calculated as the difference between axial stress and confining stress, is highlighted.
Preparation of the rock sample for testing, including the use of a membrane and end caps to isolate the sample from the confining fluid.
Workflow of the experiment involves four steps: measuring the sample, preparing the assembly, fracturing the rock, and analyzing the data.
Key setup process includes ensuring the sample is straight, measuring the diameter at different points, and confirming the interfaces are parallel.
Vacuum grease and plastic o-rings are used to isolate the sample from the fluid and ensure proper sealing in the vessel.
The process of filling the vessel with water to remove air before applying pressure is explained in detail.
The lab uses a pump to apply confining pressure, and the importance of safety checks during this step is emphasized.
The operation of the loading frame involves moving the vessel up to apply stress, with adjustable speed settings for different stages of the test.
The confining pressure is gradually increased step by step until the desired value is reached.
Final measurements include load and displacement, and the procedure continues until the rock fractures.
After the rock fractures, the system must be safely depressurized before disassembling the vessel.
The analysis phase includes calculating Young's modulus, peak strength, and constructing Mohr circles to estimate cohesion and internal friction angle.
Transcripts
basic properties of the rock hey
everybody
welcome to laboratory number three
laboratory number three is confined
compression
and elastic modulus determination
in this laboratory we are going to
perform
triaxial measurements to undermine
elastic properties of the rock
the principle that we use in this
laboratory
is similar to the approach here that we
follow
for laboratory one when we are trying to
calculate ucs
so it means
that again we are going to apply
an axial stress to a rock
we are going to apply
stress deforming the rock
and fracturing the rock but the main
difference
now is that we are going to place our
sample
in a vessel with fluid and we are going
to
apply through a fluid a confining
stress over the sample
consequently we are going to have again
an actual stress and a vertical strain
and now our junk monologues and
our big stress are going to be function
not only on the properties but
also on the confining that we are
applying in the rock
another parameter that is going to be
useful in our analysis
is the differential stress which is the
difference
between the axial stress and the
confining stress
compared to laboratory one we are adding
one more component in our analysis which
is the floyd pump
here the we are going to have again
the sample where we are applying the
differential stress
and as i mentioned before we are going
to have uh
the sample submerged into a confining
vessel
in in this this confining vessel is
going to be connected
to a fluid pump and this fluid pump
is going to allow us to increase
the confining pressure in the system
and once we set up the confining
pressure
until till the value that we want we are
going to apply our differential stress
and perform our measurements
the workflow that we follow in the
laboratory
is similar as the workflow that we
follow for laboratories one
and two it's going to have again
step one where we measure the sample
step two when we prepare the assembly
and the sample
and we will where we set up our loading
frame
step three where we fracture the rock
and finally uh
step four where we analyze our data
when we measure the sample the step that
we follow
is exactly the same as the one that we
observe for laboratory one
we are going to control again that the
sample is
straight and we are going to control
that the sample
has nearly the same values at different
uh points of our measurement
the diameter is going to be the average
of these points
then through measuring the length at
different angles
we are going to control that the
interfaces are
parallel in the rock again we are going
to measure at different angles
and we are going to average our
measurements
finally we are going to weight the
sample that we have now we are going to
initiate the setup of our loading frame
so the first step in this setup
is just controlling through a level that
the
bottom and the top of the
loading frame are parallel one
to each other now it's time to prepare
the vessel
with our sample so
now we have to add several components to
prepare the vessel that we are going to
put in the loading frame
so the components that we are using are
the vessel the membrane that we are
going to put the sample to us
isolate it from the fluid and
the end caps the plastic o-rings
the vacuum grease the water which is
going to
work as our confining fluid
the meron metal and golden o-rings
just to isolate the
confining fluid from the outside and the
screws that we are going to use just to
adjust the
vessels so
our first step is first putting the
sample in the membrane
and we are going to put the sample in
the middle so we have
nearly one inch at each side
of the of the membrane
now what we do is we are going to put
every component
until the sample looks like this
and to achieve this first we are going
to put vacuum grease
in the inner walls this areas
now after we put the vacuum grease we
are going to place the end caps
the short end cap is going to be at the
bottom and the long
end cap is going to be at the top
finally we are going to increase the
ceiling by putting plastic o-rings
at each side of the sample
this way we are going to
isolate our sample from the confining
fluid
now we are going to take the vessel if
we take
a look inside the vessel what we are
observing is that we have
a small spot in here which is going to
be the end gap slot
we have to place our sample
in here and we are going to fill it with
water before doing that we have to check
that our pump
and plate valves that are to the side of
the vessel
are closed once we check that they are
closed
we can fill the vessel with water
along the inner thinner section that
we have in here so the way that
our vessel with our sample
membrane it looks it's going to be like
this
once we done this we can
close the vessel to do that
first we are going to take our metal
o-ring
in this mineral or ring we have to put
a vacuum grease
in the inner side on top
and on the bottom toward the
bottom of the metal ring once we do that
we have to place them
metal or ring after that
we have to place the golden o-ring we
can use the screws that women
that we see in here at the back
just to fix this golden old ring
once we do that what we are going to
obtain is the closed vessel
with our two
valves closed now we can put this vessel
in the loading frame once we put the
vessel in the loading frame we are going
to connect it
with the pump and we are going to take
out the air
that is still remaining in our vessel
to do this first we are going to
open both the bleed and the pump
bounce and we are going to start using
our pump
so first we are going to hit
our constant flow and our lining here is
going to change into cfa
we are going to place a and we are going
to
input that a flow rate of 10 milliliters
per minute and we are going to
click enter and
first before
before hitting run we are going to check
that we have a low pressure in here
and we start hitting run
and what we are doing is we are
filling with water from the pump to
displace the air
that we have in here so what we are
going to control is that the plane
valve is plenty with air
and once what that water star
coming out we can hit stop
if we see that this pressure in here
start increasing when we are doing this
we have to
to hit stop immediately just because of
safety once we
take out all the water and all of the
air
and see that the blade bulb is
it is just reducing water
and it means that our system is
closed and filled with water and now we
can
close the bleed vault
now we can start operating our
loading frame so just a preview from our
rotary 1
what we can see is that again
our two measurements that we are going
to be interested about
are going to be load load 1 and
displacement 2
and that by pressing up or down
we can move our frame
either up or down and that to change
the speed we are going to click speed
and with f2
f3 and f4 we are going to change the
speed as we are using
during the seating we are going to use
again 0.22 inch per minute
and during the displacement speed we are
going to use again 0.02
inch per minute
now
based on that we are going to move up
our frame until it touch
the upper part of the frame
we will realize that because
force in our board is going to
slightly increase again
once we do that we have to
set up the pressure that we are going to
use for the measurement
to do that the first step is just check
that our bleed valve
is closed and that our pump
valve is open so the
pump and the vessel are connected
now we are going to use a console
pressure increase which means that we
are going
to press constant pressure a and we are
going to set up
as objective pressure 50 psi
we are going to hit enter and run and
these values should increase
what we are going to observe are two
main things
first we have to observe that the
pressure in here
is going to increase up to 50 psi
and it shall remain at 50 psi
also what we have to check is that
the actual force that we are reading
in the in our loading frame is going to
increase as well this is because we are
applying sound confining on the sample
and this force is going to
be transmitted to the force that we are
applying
to a sample in here
so if if we see that
these two indicators then it means that
we are
good to go and we can continue
increasing the confining pressure to
that we are going to repeat
steps two and four reaching
step by step the pressure and not in a
single run
until we achieve our desired confining
pressure
once we are at the our desired confining
pressure
we have one last step to which is place
and hold the string gauge
this uh we will see that this is done
when we place our strangle gauge
and displacement should slightly
increase
a picture of how it should look like
is like this where we have our vessel
touching the upper part of our loading
frame
and the strain gauge also
place and fix at the top
now we have to do
just a double check that we already did
the leveling
we see the sample we prefer the vessel
and the strain gauge is placed
which means that we are ready to measure
the first step that we are going to do
is just
increasing our force so we are moving
up our vessel until our force
increases up to two thousand pounds
then we are going to decrease this value
to
[Music]
thousand fifteen thousand and
fifteen hundred uh pounds and then we
are going to increase
the stress until rock fracture
where we are going to observe a drop in
the force
once we observe this stroke we have to
stop
our measurement now again because of
safety
is very important to before
disassembling
we have to reduce the vessel confining
pressure to zero
and to release the pressure that we have
there
in the system also we have to double
check that
our axial load is nearly zero or
in the same range of values once we
do that then we can take out the vessel
and we can extract it disassemble and
clean it
and now we can recover and take the
picture of the sample
and extract the data file for analysis
the sample once we extract it it will
look
like this
now let's move to that analysis again
as we observe for lower router v1 we are
going to have two main measurements
force and displacement
from these measurements we are going to
measure the
jungle models and the peak strength
that we have for that specific confining
pressure
so again we are turning these parameters
of force and vertical displacement into
stress and strain
and based on the trajectory that with it
we can estimate uh junk money's
modulus loading and jump modulus
during unloading and based on the big
string
that we read we can
see how the the the strength
of the rock for that specific combining
question
if we perform the measurement for
uh say for several measurements
then we can obtain different
values and different
more circles combining all of them
we can calculate an envelope
which is going to tell us the cohesion
and the internal friction angle
and from that internal friction angle
actually we can calculate
which is this angle at the at which
the rock is being fractured
here what we can see is that actually
the peak stress
is going to be our sigma 1 and the
confining pressure is our
is going to be our sigma 3.
finally when we compare this data with
other data what we observe is that as we
mentioned before
this angle is in this point in here
is going to tell us the fractal angle
that we shall
expect based on the confining that we
are applying to a rock
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