CVEN30010 Geotechnical Modelling and Design (2022)
Lab Practical Instructions and Assignment Briefs
1. Introduction
The Lab Practical session is designed to facilitate the understanding of the
fundamental concepts of water flow in soils, which include the seepage phenomenon
and quicksand condition. A Cussons Technology permeability apparatus is to be
used in the experiment, as shown in Fig. 1. The experiment is to be conducted in
Francis Lab of Melbourne School of Engineering, located at mezzanine level, Block
D, Building 176.
Fig. 1 Test apparatus from Cussons Technology
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2. Experimental apparatus
As can be seen from the detailed components shown in Fig. 2, the apparatus consists
of a glazed aluminum tank supported on a steel frame, which is designed to contain
the permeable medium (e.g., sand). The front, back and sides of the tank are made
of clear toughened glass (giving scratch-free visibility without the risk of abrasion
of the inner surfaces).
Fig. 2 Components of the permeability apparatus
Fourteen piezometers are connected to the base of the tank with flexible tubes. The
spacing of piezometers is 120 mm as shown in Fig. 3. The left and right sides of the
tank accommodate seven piezometers each, to read the water head. These
piezometers are provided to allow measurement of head at various points along the
permeability tank.
Two removable end baffles are installed in the tank to retain the soil in the middle
part. Two header compartments are thus formed between the baffles and the two
ends of the tank. In the figure, the left compartment is the inlet, whereas the right is
the outlet. The water height in the testing tank can be adjusted and maintained using
the inlet and outlet header compartments.
A water sump tank equipped with a variable speed centrifugal pump acts as a source
of water supply. The water is circulated through the tank via header compartments
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at each end of the tank. Weir tanks piezometer is provided to measure the discharge
rate from the outlet head compartment located at the right-hand side of the tank.
Fig. 3 Schematic of the setup (for illustration purpose and not in scale)
3. Experimental setup
A sheet pile is fitted in the tank (which seals against the front and back walls of the
tank). Two tests were conducted, namely a seepage flow test with constant head
difference and a quick sand test with varying head difference. The first test is
designed to help you understand the concepts of flow nets through tracing the
seepage path and verify the theoretical formula based on Darcy’s Law. The second
is to observe quicksand (piping/ boiling) phenomenon, which helps you understand
the concepts of critical gradient and effective stress principle.
4. Experimental procedure
4.1 Test 1: Seepage flow experiment
(1) Start the circulation pump and adjust the speed to achieve a level of 450 mm in
the left-hand header compartment (inlet) with a steady but small flow in to the
overflow pipe. Adjust the height of the overflow to maintain a water level of
300 mm in the right header compartment (outlet).
(2) Maintain the constant head difference between the two sides of the sheet pile
as shown in Fig. 3.
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(3) Measure the dimensions of the tank, the hydraulic heads and sand level based
on a datum (e.g., the base of the sand). Record the hydraulic head at each
piezometer.
(4) Inject a shot of red dye into the sand away from the glass (approximately in the
middle) on the upstream side and observe where and how the dye reappears.
Please assess the type of the flow (laminar or turbulent) and give explanations
in your report.
(5) Inject a shot of blue dye on the upstream side against the glass. Make sure the
tip of the injection syringe is positioned just below the sand surface. Trace the
path of the flow line by marking the dye’s movement on the glass until the dye
reaches the ground surface on the downstream side.
(6) Repeat the above step at different spots on the upstream side to trace the flow
lines on the glass. Observe the change in velocity of the flow as it travels. Please
explain in your report how and why the velocity changes when the flow gets
closer to the sheet pile or leaves away from the pile. Did you observe the flow
lines intersecting each other? Please give your explanations.
(7) Measure the discharge rate at the water outlet using a beaker (i.e. measuring
cylinder) and a timer. Please convert this flow rate into litres per minute per
metre width of the tank.
In addition, the flow rate q can be calculated by using the following empirical
equation provided by the apparatus manufacturer:
= 0.001269?2.353/
where the flow rate q is in the unit of L/min and h is the head in the unit of mm
which can be obtained from the weir tank piezometer. Please calculate the flow
rate based on this empirical equation and convert this flow rate into litres per
minute per metre width of the tank.
(8) In your report, please sketch a flow net to represent the seepage flow in the
sand. Please draw it on the graph paper (with squares) provided in Appendix C.
Make sure the horizontal and vertical dimensions of your sketch are in same
scale. The photo of the experimental flow lines needs to be included for
comparison in your report.
(9) From your sketch of flow net, please calculate the discharge (litres per minute
per metre width of the flow net model) and compare your theoretical
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calculations with test results in step (7). The permeability coefficient of the sand
can be estimated from the Hazen’s Equation, k = 10 d2 , where k is in units of
mm/sec, and d10 is in units of mm (d10 can be estimated based on a particle size
distribution curve). Please find the particle size distribution in Appendix A.
(10) Based on your sketched flow net, please calculate the hydraulic head at each
piezometer. Compare the calculated results with the measured ones in step (3).
The numbering orders of piezometers in your report need to be consistent with
the experimental setup. Additionally, you are required to calculate the
theoretical hydraulic head at the positions marked with black dots (see
Appendix B) based on the flow net in step (8).
(11) Please analyse the discrepancies between the calculated results and test results
mentioned in step (9) and (10). Please give at least 3 reasons to explain it.
4.2 Test 2: Quicksand experiment
(1) The setup of this experiment is similar as that described in Section 4.1 except that
the sheet pile has a shallower embedment (to facilitate the occurrence of
quicksand).
(2) Instead of maintaining a constant head, gradually increase the hydraulic head
difference between the two sides of the test tank, until a quicksand phenomenon
occurs.
(3) Explain the phenomenon by referring to the change in effective stress in the soil
where quicksand occurs. Please give at least 3 methods to control seepage and
avoid the occurrence of quicksand.
5. GeoStudio modelling
You are required to model the experiment in 4.1 using the SEEP/W software and
compare the model outputs with your hand calculations and the experimental results.
Please include sufficient evidence (i.e. geometry, material, boundary conditions and
results) from the SEEP/W outputs such as screenshots of the results to support your
interpretation and analysis.
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6. Report requirement
Lab Practical Report will be assessed individually. Students are required to prepare
the report based on your own experimental data. For students attending the
practical remotely (i.e. online session P6), your experimental data will be provided
separately.
1. Your report should cover all the tasks above.
2. Your report should contain cover, content, seepage flow experiment,
quicksand experiment and SEEP/W modelling. There is no need to repeat the
experimental setup and procedures.
3. Page limit: 6 pages, single spacing, size 12 font. Page limit includes
everything in your report. If your report is beyond the 6-page limit, only the
first 6 pages will be marked.
4. If you have any question, please post it on the Discussion board under the
section of “Discussions on Lab practical”. Remember all technical questions
must be asked on the Discussion board and will not be answered when sent to
personal emails.
5. For Lab Practical related non-technical issues, you can contact Zeliang Li
(zeliangl@student.unimelb.edu.au). Please include ‘CVEN30010’ in the
subject line in your email and remember emailing is for personal issue only.
6. A one-hour online consultation session is scheduled on 4:00 pm Monday in
Week 8 (12th September). Please see Canvas->Zoom for further information
on the meeting.
The due date for submission of the laboratory report is 11:59 pm on Sunday 18
September 2022. Your report should be submitted electronically via the submission
link in Canvas, which will be opened and announced in Week 7. Submissions
through email will NOT be accepted. Please note late submissions incur penalty of
20% per day.
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Appendix A: Sieve analysis result
Table 1 Sieve analysis result