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

70The horizontal axis on both charts represents the time scale and is expressed in units ofseconds. Therefore, from the data charts it can be observed that the loading was performed inincremental sequence. As the time-load chart shows, the duration of the load maintained ateach load increment was limited to approximately 15 minutes. The reason behind applyingthe load for a certain time of duration is for the deflection measurement to reach themaximum magnitude while undergoing creep under load.While the load would peak out at the initial phase of each load increment, the load wouldcontinue dropping in exponential fashion until an asymptote is reached. Therefore, a certainload was applied to the pier until the change in rate of deflection was less than 0.25 mm perhour or 0.0635 mm per each 15 minutes.Maximum load applied to the aggregate piers was 150 percent of the maximum design stress(assumed at 70MPa), however the controlling parameter was the amount of settlement beingproduced. In some cases, the maximum stress imposed on the pier exceeded 150 percent toachieve the total 12 mm amount of displacement. For the purpose of generating stressdisplacementplots the average value of peak and end loads was used for each interval.Consequently, the incremental loading levels were different for different groups of piers,while the majority of aggregate piers were loaded at 9, 17, 33, 50, 67, 83, 100, 117, 133, 150percent of maximum design stress (assumed at 70MPa). It is also important to note that theload on the aggregate piers at 117 percent level required special treatment, where longer loadincrement of 60 minutes was imposed. Therefore, the load was adjusted to the desired 117percent for total number of four times. The unloading phase was also performed where loadwas reduced to the design stress levels of 100, 66, 33 percent of the design stress.Group and Individual Pier LayoutThe second stage of this research study, the individual piers of various length andcomposition were built. A total number of 20 piers were evenly spaced within the available