G MS THESIS_final version_Maxim Prokudin.pdf - Digital Repository ...

135Having a limited amount of experience at this stage of the testing, the process of collectingstress-settlement data had to inevitably undergo trial and error. Therefore, the piers that weresubjected to stress-settlement evaluation were tested and loaded to a different top of the pierlevels of displacement. As a consequence, the comparison between stiffness values of thepiers compacted via different tamper heads could only be made at the level of 2 mm ofdisplacement.As it can be observed from Figure 57, some of the tamper heads did not show consistency inamount of relative aggregate pier stiffening for short 305 mm and long 610 mm piers, as inthe case with cone beveled head. Other beveled heads such as flat shape tamper have shownmore consistent results, where the least amount of aggregate stiffening was produced.Moreover, the flat head compacted aggregate piers were observed to have reduction instiffness below the undisturbed stiffness level of unreinforced matrix soil. This effect can beattributed to the loose state of the last compacted aggregate pier lift that had a tendency toundergo additional amount of compression under imposed loading. For the consecutive teststages the loose portion of the last aggregate lift was cleaned out and the concrete cap waspoured to provide full contact load transfer to the top of the pier.Overall, the obtained results were discovered to have a relatively small variation, however byobserving higher stiffness for the short 305 mm aggregate pier compacted via cone tamperhead a slight sign for a potential for better performance was noted. Moreover, theconventional aggregate pier truncated cone tamper head has also indicated ability to betterstiffen the piers. Therefore, additional testing was required to confirm the hypothesis, wheresofter soil conditions were to be utilized in order to favor aggregate pier bulging. As aconsequence, construction of aggregate piers during the latter stages of testing was partiallytargeted towards evaluation of relative amount of stiffness provided by cone and truncatedcone tamper heads.As it can be recalled, the aggregate piers constructed during the phase where single piers ofvarious compositions were utilized, the installation was performed using the truncated cone