Geotechnical and Geological Engineering

, Volume 25, Issue 2, pp 163–176 | Cite as

Settlement of compacted ash fills

Origianl Paper


The coal ash is a by-product of coal-fired thermal power station. It is extensively used as a geo-material for landfill. The compacted ash is used as a structural fill if it is properly characterized for load-bearing capacity and settlement. The main objective of the present work is to characterize ash material and to evaluate its settlement characteristics. The ash is normally compacted by vibration at or near optimum moisture for its performance as structural fill. The overt characteristics of ashes are viewed similar to cohesionless soils. However, the mass behavior may have differences due to the subtle influence of chemical and physical processes involved in its formation. The empirical and analytical methods predicting settlement of footing under static loading require direct or indirect measurement of density and stress state in the deposit. In the present work, experimental investigations for settlement prediction were carried out on compacted coal ash produced at Ropar thermal power station in India, which was conveniently classified as ASTM class F ash. The settlement was experimentally obtained for the rigid plates having least dimension more than 0.3 m on ashes compacted at varying degree of compaction. The predicted settlement based on the observed data of coal ash using conventional techniques for soils was found to be conservative. A relationship between settlement and foundation size is proposed at varying compaction to obtain the settlement of compacted ash. At a higher degree of compaction, the settlement of a foundation may not exceed the allowable settlements in the working stress range.


Coal ash Settlement behavior Degree of compaction Plate load test 

List of Notations

\(\gamma_{\rm d}^{\rm max}\)

Maximum dry unit weight (kN m−3) in Proctor compaction


Dry unit weight (kN m−3)

Bf, Bp

Width of footing and plate, respectively in meter


Degree of compaction, a ratio of γd and \(\gamma_{\rm d}^{\rm max}\), normally presented as percent.


Mean size (mm)


Minimum void ratio


Maximum void ratio

F1, F2, F4, F5

Ash sampled from various fields of electrostaticprecipitator


Optimum moisture content

PA1, PA2

Ash sampled from different locations of ash ponds

Sf, Sp

Settlement of footing and plate, respectively in mm


Settlement of plate in mm at a stress level (σ in kPa)


Settlement of footing in mm at 100 kPa


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  1. 1.Department of Civil EngineeringDelhi College of Engineering (Government of NCT of Delhi)DelhiIndia
  2. 2.Department of Civil EngineeringThapar Institute of Engineering & Tech.PatialaIndia

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