Collapse compression upon wetting an unsaturated and recycled inert fill

Abstract

Expansive and collapsible soils are a major concern for geotechnical engineers. These soils may lead to costly geological hazards due to change in volume and settlement in response to wetting. Upon inundation, collapsible soils experience sudden increase or decrease in volume whilst subjected to an applied constant stress. Geotechnical engineers have long investigated the mechanical behaviour of compacted unsaturated soil, via both theoretical and experimental considerations. Research focused on past experimental work, portraits the use of the oedometer test when investigating fine grained soil samples. However, this study focuses on soil with larger particle, which precludes the use of the typical oedometer test used in past research for fine grained soil. As a result, volume change was examined with the use of a large scale oedometer test, designed from first principles. Specific loading and unloading sequences were utilized to represent typical field conditions that the man-made fill materials, locally known as ‘Type 1’ may experience. Past experimental research highlights that upon inundation, soil samples with the lowest initial moisture content are more prone to collapse when compared to other soil samples with higher initial moisture content whilst having the sample applied stress. Therefore, different initial conditions related to moisture content and compaction were applied to represent the in-situ soil. Three samples at varying initial moisture content and subjected to respective compaction effort were applied to simulate effects of excess or lack of water added to the soil and to the level of over or under compaction applied. Experimental results show that, volumetric deformation exists in Type 1 fill material and the degree of expansion and/or contraction depends on the initial water saturation. Through this research the transition from dilation to contraction was also observed. In addition, this research also notes that maximum collapse in Type 1 fill material exists at the lowest initial moisture content and its respective level of compaction. Improved methods of testing and interpretation are further discussed in this research.