1. Soil mould was assembled with rubber membrane lining inside of mould. 2. The mould was filled with soil so the approximate compacted height was equal to 1/6th the height of the mould (approx. 50mm). 3. Soil was compacted using hammer drill equipped with tamping attachment 4. Steps 2 and 3 were repeated 5 additional times until the mould was filled. 5. The mould was removed and the sample was placed into the testing apparatus. 6. Rubber membrane was secured using rubber rings placed at the top and bottom of the sample, ensuring contact with the sample did not occur. 7. Pressure cell was placed over sample and secured into place. 8. Sample was brought to cell pressure of 3 kPa. 9. Sample was conditioned for shakedown 10. Cyclic loading was applied to sample, with a loading duration of 0.1 second and a rest period of 0.9 seconds, displacements and forces during this loading were recorded using supplied software. 11. This loading was applied in groups of five with a 95 second rest period between sets of load application. A total of three sets of load applications were applied to the sample. 12. Steps 8 and 10 were repeated at cell pressures of 5, 10, 15 and 20 kPa. 13. At the end of testing soil samples from the top, middle and bottom of the sample were taken in order to determine moisture content.
Results:
Tabulated results can be seen in Table 2 in the Appendix, handwritten sample calculations to support tabular data are supplied in the appendix as well.
Graphs:
The relation of resilient modulus to deviatoric and bulk stresses can be seen in Figure 1 and Figure 2 in the Appendix.
Analysis:
Uzan Model -
Coefficients of the Uzan model were determined by using Excel Solver to minimize the sum of the squares of the errors between the experimental data collected in the laboratory and the results predicted by the Uzan model.
Mr=k1pAθpAk2σdpAk3 Equation 1 – Uzan Model
The constants of regression within Equation 1 as determined by use of Excel Solver can be seen in Table 1.
Table 1 - Regression Constants
As seen in Table 2 the Uzan model is reasonably accurate in predicting the Resilient Modulus of a soil, with an average error of approximately 5% when compared to the Resilient Modulus calculated using Equation 2. Mr=σcyclεr1000
Equation 2 - Resilient Modulus (MPa)
Moisture Content –
As the moisture content of a material increases past it’s optimum proctor moisture content, the resilient modulus of the material decreases. This is due to a reduction of internal friction in the sample. In fine grained materials such as sands the Mr of the material has a tendency to increase as the moisture content is increased from dry towards the optimum Proctor moisture content. In coarse grained materials the optimum moisture content is dry, so as moisture increases the resilient modulus has a tendency to decrease. The moisture content for the sample tested in laboratory is tabulated in Table 3.
Table 2 - Moisture Content of Experimental Sample
Repeatability -
The results of this test are quite repeatable, the trends found in the relation between Mr and bulk stress are identical throughout all materials.
Sources of Error –
The compactive effort during this lab is a source of error. The sample compaction was done using a handheld vibratory compactor, the level of compaction was determined by the feeling of the operator. This method of compaction is non-standardized and therefore may have led to uneven compaction in the aggregate layers which would affect the results of the test.
Table 3 - Table of Experimental Results
Figure 1 - Variation of Mr with Respect to Bulk Stress
Figure 1 - Variation of Mr with Respect to Bulk Stress
Figure 2 - Variation of Mr with Respect to Deviator Stress
Figure 2 - Variation of Mr with Respect to Deviator Stress
