Uncertainty Analysis in Prediction of Settlements for Spatial Prefabricated Vertical Drains Improved Soft Soil Sites

Abstract

This paper presents the quantification of uncertainties in the prediction of settlements of embankments built on prefabricated vertical drains (PVDs) improved soft soil deposits based on data collected from two well-documented projects, located in Karakore, Ethiopia, and Ballina, Australia. For this purpose, settlement prediction biases and settlement distributions were statistically computed based on analyses conducted on two Class A and Class C numerical predictions made using PLAXIS 2D finite element modelling. From the results of prediction bias, Class C predictions agreed well with the field measured settlements at both sites. In Class C predictions, the computed settlements were biased to the measured values. For Class A predictions, the calculated settlement values were in the range of mean and mean minus 3SD (standard deviations) for Karakore clay, and they were within mean and mean minus 2SD limit for the Ballina soil. The contributing factors to the settlement uncertainties of the Karakore site may include variability within the soil profile of the alluvial deposit, particularly the presence of interbedded granular layer within the soft layers, and the high embankment fills, and the limited number of samples available for laboratory testing. At the Ballina test embankment site, the uncertainties may have been associated with the presence of transitional layers at the bottom of estuarine clay and sensitivity of soft soil to sample disturbances and limitations in representing all the site conditions.

Settlement Forecast of Marine Soft Soil Ground Improved with Prefabricated Vertical Drain-Assisted Staged Riprap Filling

“…The above methods are widely and successfully used in settlement predictions and forecasts for various types of soils in different engineering projects, such as in soft soils improved with vacuum-prefabricated vertical drain [37], foundation pit of artificial fill and silty clay layers [16], subgrade filled with construction and demolition waste [10], metro shield tunnel in saturated sand [38], and the full load-settlement curve of a strip footing [39]. Although the prediction or forecast accuracy has been significantly improved, there are still errors between the predicted and observed magnitudes of settlements [40], which may be due to the application limitation and different suitability of each prediction or forecast method for varied situations and time periods. Consequently, it is particularly important to select the appropriate and reliable method according to the different soil properties and project characteristics.…”

Uncertainty Quantification for Fatigue Life of Offshore Wind Turbine Structure

“…Whilst Fatigue damage calculations involve several parameters, and also several combinations of environmental conditions to account for realistic operation scenarios, it is also paramount to account for the uncertainty in the models and parameters to ensure a service life of at least 20 years [4,6]. Albeit accounting for the variability of certain parameters, such as wind speed and wave height, is a common practice in the industry, other parameters are normally considered as constants, even though data has suggested that they may vary significantly [7,8]. Therefore, it is necessary to analyze the importance of those variables in terms of the structural response and reliability of the OWT.…”