Characterization of Addis Ababa Expansive Soil Using Unsaturated Soil Properties
No Thumbnail Available
Date
2024-04
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Proper characterization of expansive soils is critical in geotechnical engineering practice for proper design. However, a limited researches were done on unsaturated expansive soil properties in Addis Ababa. The availability of soil suction profiles from in situ and laboratory measurements is currently limited. This research aims to enhance geotechnical site assessments in Addis Ababa’s expansive soil regions through combined laboratory testing and long-term field monitoring of unsaturated soil properties. To properly characterize the unsaturated properties of expansive soil laboratory pressure plate analyses were performed on twelve undisturbed soil samples to develop soil-water characteristic curves (SWCC) with two categories four of them from under roadway and eight from excavations for a building purpose with a varying depth and locations coupling with shrinkage curves (SC). The SWCCs were determined using a pressure plate apparatus with a suction range of 0 to 1300kPa. The laboratory-measured data points were then curve-fitted by using the Fredlund and Xing (1994) model. The SC was also determined to evaluate the change in volume of the different soil samples. Experimental results reveal Air Entry Value acquired through consideration of volume change with Degree of Saturation Soil-Water Characteristic Curve (S-SWCC) is higher in magnitude than gravimetric water content soil water characteristic curve (w-SWCC) and a volume change of 74.15-79.8 for soil samples from under roadway and 83.1% - 98.1% for soil samples sampled from excavations for building construction is quantified through void ratio characteristic curves. Concurrent field monitoring was conducted to capture seasonal matric suction profiles in Addis Ababa using a digital tensiometer and Diviner 2000 probes to directly measure matric suction profiles and volumetric water content. This study implemented direct long-term monitoring of matric suction in situ at multiple depths (140cm,160cm, and 190cm) using digital tensiometer equipment. And coupled with volumetric water content measurements gathered using Diviner 2000 sensors. Integrating the tensiometer data and diviner 2000 from June to October, the soil suction profile with depth and time is shown. Seasonal matric suction measurements from the field showed that temporal pattern of fluctuation with depth. The magnitude of matric suction values ranges from 23 to 83kPa based on the depth of the soil for a volumetric water content ranging from 12-53%. Matric suction profile with depth is found increasing with a magnitude of difference varying based on the soils volumetric water content for the depth of investigation.
Description
Keywords
Air Entry Value, Matric Suction, Shrinkage curve, Soil-water characteristic curve