Amperage and Treatment Time Monitoring to Evaluate Stone Column Effectiveness

Abstract

During stone column installation for the seismic retrofit of the Mormon Island Auxiliary Dam, several important parameters of the construction process were continuously monitored using a data acquisition system. This system provided data on operating amperage, stone volume, and treatment time as a function of probe depth. In this study, treatment time and amperage values were analyzed in detail. In addition, equations combining amperage and time were developed to define the amount of energy applied to the soil during remediation. Applied energy, as measured by treatment time and amperage, was then compared to (N1)60 values from Becker penetration tests. This test was selected as the evaluation tool because of the presence of gravel and cobbles. Analysis of the data suggests that the maximum amperage at a given depth can be used to separate layers with high and low fines contents. In general, the maximum amperage was more a function of soil type than of treatment time. For soils with high fines content, the maximum amperage was consistently low relative to soils with low fines content and did not increase significantly with continued vibration. Comparisons between the applied energy and the posttreatment Becker penetration tests results showed that slight improvement is possible in soils with higher fines contents. However, increasing the vibration time in these soils did not increase the (N1)60 values. Therefore, additional time beyond that required to install the column was not useful. For soils with low fines contents, the posttreatment (N1)60 value did tend to increase with additional applied vibration energy, but the scatter in the results was substantial.