Laserfiche WebLink
2. Verification of colluvium modulus and shear strength properties from inclinometer <br />measurements <br />3. Assessment of the stability of the waste rock pile <br />2.2.4 Fall 2013 Drilling and Laboratory Testing <br />Eight soil borings were performed in late September and early October 2013 to better ascertain the <br />colluvium thickness and to collect samples for laboratory testing. Another objective of this exercise <br />was to determine if the geotechnical characteristics, especially the drained shear strength, of the <br />colluvium changes laterally or with depth in the area that will be underneath the proposed refuse fill. <br />A laboratory test that can be used effectively to screen for potentially weak clays in terms of drained <br />shear strength is the Atterberg limits test, which provides an indication of the material's plasticity. <br />The liquid limit resulting from this test has a strong correlation to drained residual shear strength and <br />a good but less reliable correlation to the fully softened shear strength. In general, higher liquid limits <br />lead to lower drained shear strength envelopes. Table 2 shows the borings, locations, and results of <br />the colluvium liquid limit testing for the Fall 2013 drilling program in addition to the original drilling <br />work in 2009. <br />Figures 2-1 and 2-2, respectively, depict the average and maximum liquid limit values as a function <br />of borehole location. It can be seen from these figures that very little spatial variability in terms of <br />soil plasticity is present in the colluvium. It was previously thought that the characteristics of the <br />colluvium could vary with location, and possibly improve in higher elevations within the draw. <br />Based on the amount of data collected to date, it is concluded that the colluvium can be treated as <br />having generally the same plasticity characteristics throughout. However, the presence of an Upper <br />Colluvium exhibiting weaker and lower stiffness characteristics compared to a Lower Colluvium <br />exhibiting stronger and higher stiffness is considered valid as discussed in subsequent sections. It <br />should be noted that the Upper Colluvium is assumed to exhibit its residual shear strength while the <br />Lower Colluvium is assumed to mobilize the fully softened shear strength. Because there was no <br />distinct trend with depth in each borehole in terms of liquid limit, the reason for the difference in the <br />shear strengths for each material apparently is the level of shear straining occurring in each soil <br />stratum, not the plasticity characteristics. <br />10 <br />P:\Mpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />