Methodology
Overview
The aim of this project is to quantify the improvement in cyclic resistance of sand after laponite permeation. To obtain this information the shear strength of sand subjected to cyclic loading will be measured before and after permeation with laponite solution using a triaxial testing unit in the laboratory. The rheological properties of the laponite solution will also need to be investigated to find the optimum concentration of solution to use for permeation.
Prior to experiment
The following objectives will have to be satisfied before testing can begin:
Laboratory Experiments
Step 1:
-It is this high viscosity that helps increase the soil’s resistance to cyclic loading as particle contact forces are increased.
-From previous research by (Mollamahmutoglu and Yilmaz, 2010) on a similar nanoparticles we know that the viscosity-time relationship for different concentrations of laponite will be similar to that shown in figure 2 below.
-The optimum solution will be one with a sufficient gel time to allow permeation into the soil, whilst it is a low viscous solution, but still with a high viscosity after gelation.
Overview
The aim of this project is to quantify the improvement in cyclic resistance of sand after laponite permeation. To obtain this information the shear strength of sand subjected to cyclic loading will be measured before and after permeation with laponite solution using a triaxial testing unit in the laboratory. The rheological properties of the laponite solution will also need to be investigated to find the optimum concentration of solution to use for permeation.
Prior to experiment
The following objectives will have to be satisfied before testing can begin:
- Research and review current literature on the subject
- Order laponite and silica (sand) from external companies
- Learn how to operate the equipment in the laboratory and develop a relevant reproducible procedure
- Book laboratory equipment and time slots
Laboratory Experiments
Step 1:
- Use a rheometer (figure 1 below) to characterise the rheological properties of different concentrations of laponite/ water solution.
-It is this high viscosity that helps increase the soil’s resistance to cyclic loading as particle contact forces are increased.
-From previous research by (Mollamahmutoglu and Yilmaz, 2010) on a similar nanoparticles we know that the viscosity-time relationship for different concentrations of laponite will be similar to that shown in figure 2 below.
-The optimum solution will be one with a sufficient gel time to allow permeation into the soil, whilst it is a low viscous solution, but still with a high viscosity after gelation.
Figure 1: Advanced Rheometer 2000 equipement that will be used Figure 2: Illustration of the change of viscosity and gel time with laponite concentration
Step 2:
-To do this a measurement of the shear strength of the soil, subjected to monotonic loading, before and after permeation with laponite will be taken
-Different concentrations of laponite solution and initial confining pressures will be evaluated to increase reliability of the results
Step 3:
-Comparing the results of the samples with and without laponite, will help establish the gain in cyclic resistance
-Both tests will be conducted at the same frequency of loading, trying to mimic the frequency of an earthquake scenario as best as possible
-The same cyclic stress ratio (CSR), which is defined as the ratio of maximum cyclic shear stress to initial effective confining stress, will also be applied
-Several tests at various CSR’s will be conducted to increase the reliability of the findings
-Different concentrations of laponite and initial confining pressures will be also be evaluated
A full risk assesment is avaliable here.
After testing
Step 2:
- Carry out monotonic loading triaxial tests on sand sample with and without a laponite solution added.
-To do this a measurement of the shear strength of the soil, subjected to monotonic loading, before and after permeation with laponite will be taken
-Different concentrations of laponite solution and initial confining pressures will be evaluated to increase reliability of the results
Step 3:
- Carry out cyclic loading triaxial tests on sand samples with and without laponite solution added.
-Comparing the results of the samples with and without laponite, will help establish the gain in cyclic resistance
-Both tests will be conducted at the same frequency of loading, trying to mimic the frequency of an earthquake scenario as best as possible
-The same cyclic stress ratio (CSR), which is defined as the ratio of maximum cyclic shear stress to initial effective confining stress, will also be applied
-Several tests at various CSR’s will be conducted to increase the reliability of the findings
-Different concentrations of laponite and initial confining pressures will be also be evaluated
A full risk assesment is avaliable here.
After testing
- Analysis and evaluation of the results to quantify the increase in resistance of the sand to cyclic loading
References
Mollamahmutoglu, M. & Yilmaz, Y., 2010. Pre- and post-cyclic loading strengths of silica grouted sand. Geotechnical Engineering, Issue GE6, pp. 343-348.
Figures courtesy of:
Figure 1: www.ales.ualberta.ca/lipid/FacilitiesandEquipment/AdvancedRheometerAR2000.aspx
Figure 2: Graham Scobie