proposal:Soil elastic modulus measurement using triaxial test

| April 25, 2015

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REPORT TITLE: Soil elastic modulus measurement using triaxial test.(the soil is sandy loamy soil)

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This first project proposal is a report that defines the initial aims, scope and resource requirements for the project.Students will need to demonstrate a clear understanding of key literature that supports the need for the project, as well as detailing the specific aims and scope to be addressed. While a full methodology may have not been designed at this stage, students should understand what methods or techniques are likely to be used and demonstrate that they are achievable in the timeframes of the project using appropriate project planning tools. Students should also have discussed any training, consumable/materials ordering, and equipment access requirements with appropriate technical officers.

 SEV362 Triaxial Practical
Page 1 of 3
SEV362 ‐ Practical 2:
Triaxial Consolidated Undrained Testing, using Kaolin Clay
In this Practical you will learn how to do the following:
 Familiarise yourself with the Test Equipment
 Prepare a Kaolin Clay sample
 Install the sample and setup the test criteria using GDS Software.
 Collect data output from test
Introduction
In a conventional triaxial compression test, a cylindrical core sample is loaded axially to failure, at constant confining
pressure. Conceptually, the peak value of the axial stress is taken as the confined compressive strength of the
sample. In addition to axial stress, axial and radial strains may be monitored during this test, to determine basic
elastic constants (Young’s Modulus, E, and Poisson’s ratio, ν).
If triaxial testing is performed at several confining pressures, and preferably if unconfined compression and tensile
test data are available, a representative failure locus can be constructed. The selected confining pressures for triaxial
testing are generally spread over a range from very low to beyond the maximum anticipated in‐situ effective stress
conditions.
Why is Triaxial Compression Testing Performed?
 To provide data points for determining a failure locus (i.e. Mohr envelope).
 For parameters needed in constitutive modelling for numerical stability calculations.
 As a component in wellbore stability, sand production and subsidence calculations.
 To provide parameters for hydraulic fracturing design.
 Obtain strength parameters for design.
Methodology
This prac is set up in four parts:
1. Kaolin Clay Sample Preparation
Equipment:
 De‐aired water.
 Sample split mould.
 Glass Plate.
 Spatula.
 Tamping Rod.
 Scales to 1g.
 Mixing bowl.
 Petroleum Jelly.
 Scissors.
 Measuring cup.
Method
 Line the split mould sparingly with Petroleum Jelly
 In mixing bowl, thoroughly combine 300g dry Kaolin Clay powder and 115g de‐aired water into a consistent mix.
Cover with dampened towel and allow sample to sit for at least 1 hour to even out the moisture content.
 Fill the split mould with clay taking care not to include any trapped air pockets. Small amounts of clay pressed
down with a suitable implement or thumb is a good approach.
 Level off the ends using a flat edge scraper.
 Carefully remove the moulded clay from the mould.
 Place sample into the vacuum desiccator at 500 mmHg until ready to install into frame.
SEV362 Triaxial Practical
Page 2 of 3
2. Load Frame Setup.
Pressure Controllers Preparation
 Fill controllers with de‐aired water and purge any air from controllers.
 Purge Pore pressure and pedestal using back pressure controller line.
 Purge Top cap using back pressure controller and leave the line connected.
Sample Installation
 Cover the base of pedestal with a film of de‐aired water
 Take a de‐aired saturated porous disk and slide it onto the pedestal without trapping any air.
 Place a de‐aired saturated filter paper disk onto the porous disk.
 Place the pre‐prepared specimen onto the porous disk without delay.
 Place a second de‐aired saturated filter paper disk onto the sample.
 Place de‐aired saturated porous disks onto the filter paper.
 Place the rubber membrane into the vacuum tube and apply vacuum making sure membrane is not twisted.
 Place the membrane over the sample then release the suction so that the membrane clings to the sample at the
correct height.
 Unroll the lower end of the membrane over the base pedestal and seal it in place with an O‐ring using the Oring
stretcher.
 Place a second O‐ring onto the stretcher and slide stretcher with O‐ring over the sample.
 Flush the top‐cap and feed line to purge any air before fitting it onto the porous disk.
 Slide top cap into place inside the membrane.
 Slide stretcher up past the top cap leaving O‐ring in place to create a seal.
 Check visually that the sample axis is vertical and that the membrane and O‐rings are all correctly fitted.
Cell assembly
 Ensure Load cell is locked in fully ‘up’ position using the Yellow locking bar.
 Ensure load frame cross member is raised enough to allow cell installation.
 Carefully install cell into frame over specimen (Ask for assistance with lifting).
 Check that the specimen has not been damaged before locking the cell into place and redo sample if damaged.
 Lower load cell onto specimen top cap, raise by 1‐2mm and lock off the load cell.
 Removed air bleed screw from top of cell.
 Fill cell with tap water via cell pressure inlet (slowly).
 Replace air bleed screw into top of cell.
 Connect cell pressure line.
 Open the cell pressure and back pressure taps.
 Zero the cell and back pressure controllers via key pads soft‐set.
 Add 20kpa to cell pressure via cell pressure key pad, crack the back pressure valve to allow any surplus pressure
to escape from within the sample, then retighten the nut.
 Lock transducer into place ensuring that needle just makes contact with cell top.
SEV362 Triaxial Practical
Page 3 of 3
3. Sat/Con Program Parameters.
Stage 1, Saturation Stage
 Using the software SatCon Module, BS1337CU, create a Saturation ramp using values of 260kPa (Cell), 240kPa
(Back), over a period of 6 hours. Monitor the B value via the software.
Stage 2, B‐Check
 Using the software SatCon Module, create a B‐check.
Test Criteria:
 Increase Cell pressure +20kPa, to 280kPa.
 Stop the test if B is equal to or greater than 0.95 as sample is considered saturated.
 Run for 60 minutes.
 If B‐check criteria are not met after 60 min then repeat stage 1 with higher values.
Stage 3, Consolidation
 Using the software SatCon Module, create a consolidation stage.
Test Criteria:
 Target Pressures set at, Cell 300kPa, and Back 150kPa.
 Stop test if no volume change over a period of 5minutes is detected.
 Run for 13 hours (780min).
4. Shear Test (CU)
Hardware setup.
 Unlock the Yellow load cell shaft support.
 Lower the crosshead and dock the load cell onto top cap. Use the load cell readout as guide.
 Close the back pressure valve.
Program Parameters
 Using the Standard Triaxial Module, create a CU Shear test with the following test Criteria.
 Target Cell pressure 300kPa (producing an effective stress of 300 ‐ 150 = 150kPa)
 Loading velocity 2mm/min
 Zero the displacement transducer via software.
 Continue the test until test failure criteria is achieved: Terminate the test at maximum axial strain of 25%
(25mm in this case for 100mm high specimen).
 Save all data after completion of shear test.
 Open the back pressure and cell pressure valves at cell entry points manually.
 Set the cell pressure and back pressure to 0 kpa via the controller keypads.
 Close the cell pressure valve.
 Drain and disassemble the cell.
 Remove the sample and examine.
In order to determine ‘Mohr Circles & Failure Envelope’ a minimum of two additional shear tests should also be
carried out with cell pressures of 350kPa (effective stress = 200kPa) and 400kPa (effective stress = 250kPa). Data
from two prior tests will be supplied to students.

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Analysis of a System,
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