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

Jemal Jibril Muhammed,Stephen Ekwaro-Osire,Priyantha W Jayawickrama

doi:10.3390/geosciences10020042

Jemal Jibril Muhammed, Stephen Ekwaro-Osire + Show 1 more

Open Access

https://doi.org/10.3390/geosciences10020042

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Journal: Geosciences	Publication Date: Jan 23, 2020
Citations: 6	License type: CC BY 4.0

Affiliation: Jimma University, Texas Tech University

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.

Highlights

Infrastructure construction over soft soil deposits often involves pre-construction improvement of the soil to increase the strength and stiffness, so that anticipated risks of excessive post-construction settlement and associated instability can be minimized
The large degree of variability and uncertainty associated with the input soil parameters pose special challenges in obtaining reliable results from geotechnical analyses
Though the use of probabilistic methods did not avoid the need to conduct a high-quality laboratory and field tests, installing field monitoring systems, implementing proper model parameters, and constitutive models, it would provide the advantage of estimating uncertainties in a more understandable, reliable and practicable way

Summary

Introduction

Infrastructure construction over soft soil deposits often involves pre-construction improvement of the soil to increase the strength and stiffness, so that anticipated risks of excessive post-construction settlement and associated instability can be minimized. Among the available ground improvement methods for soft soils, the installation of prefabricated vertical drains (PVDs) accompanied by preloading is one of the most widely used and cost-effective stabilization techniques. A number of theoretical, analytical [1,2,3,4] and numerical models [5,6,7,8,9,10] are available for estimating ground movement parameters such as ultimate settlement, degree of consolidation, and excess pore water pressure. Alluvial deposits are formed over flood plain areas and along river terraces where the terrain is flat and drainage conditions are poor. These deposits are mainly formed in four different facies models [15]. Estuarine clays are coastal region formations with thick deposits that are characterized as very low overconsolidation ratio and preconsolidation pressure and large consolidation settlements [17]

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