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INNOVATION IN CIVIL AND STRUCTURAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping
Pavement Instrumentation Systems in Expansive Soils to Evaluate the Effectiveness of Stabilizers
A.J. Puppala and N. Intharasombat
Department of Civil and Environmental Engineering, The University of Texas at Arlington, Arlington, Texas, United States of America
A.J. Puppala, N. Intharasombat, "Pavement Instrumentation Systems in Expansive Soils to Evaluate the Effectiveness of Stabilizers", in B.H.V. Topping, (Editor), "Innovation in Civil and Structural Engineering Computing", Saxe-Coburg Publications, Stirlingshire, UK, Chapter 9, pp 187-207, 2005. doi:10.4203/csets.13.9
Keywords: pavements, expansive soil, shrink and swell, instrumentation, moisture sensor, pressure cell, strain gauge, calibration.
This paper describes applications of field instrumentation to evaluate two types of expansive soil treatments: one for controlling subsoil moisture fluctuations and the other for enhancing subsoil strength and volume change, or shrink-swell characteristics. Stabilizers evaluated in these soil treatments include biostabilizers, such as a biosolids compost and a dairy manure compost, and chemical admixtures such as sulphate-resistant cement, ground granulated blast furnace slag, quick lime, Class F fly ash and polypropylene fibers.
Laboratory studies conducted on stabilizer treated subsoils showed considerable enhancement of soil properties under controlled laboratory conditions. However, these may not be duplicated in real field conditions, where continuous moisture and temperature fluctuations due to seasonal changes may impede the chemical reactions expected in the stabilized soils. Therefore, field studies with continuous monitoring are currently being conducted and a few salient findings from the analysis of monitored data are presented in this paper.
In the first instrumentation case study, two types of solid waste composts, a biosolids compost and dairy manure compost were evaluated for biostabilization of expansive soils . Field instrumentation with embedded moisture probes showed moderate moisture encapsulation with the preservation of natural moisture when the biosolids compost was used for soil amendment. Soils underneath the dairy manure compost experienced considerable moisture fluctuations, resulting in surface elevation changes. Also, the erosion of the shoulder subsoil surface was minimal when the biosolids compost was used for soil amendment.
In the second case study, both pressure and strain transducers were installed at various interfaces between different chemically-treated subsoils and untreated expansive subsoils. The chemical treatment sections were stabilized with sulphate-resistant cement, ground granulated blast furnace slag (GGBFS), cement - fly ash and lime - fibers. All four treatment methods provided similar strains and pressures as well as expected soil property enhancements. When compared individually, cement and GGBFS treated sections did undergo lower compressive strains than the rest of the test sections. This explains the cementing nature of these materials, which resulted in considerable enhancement of soil strength properties. Dynamic cone penetration tests conducted on the treated soil sections showed considerable strength improvements in cement treated sections, which offered significant resistance to the dynamic cone device. Since the monitoring period is rather short, final evaluations of stabilizations are not made.
Nevertheless, both case studies reveal the potential of field instrumentation to provide better assessment of stabilizer treatments of expansive subsoils in enhancing soil properties of real field conditions. Such assessments, along with laboratory screening studies, will lead to new treatment methods that could reduce pavement distress and constant maintenance problems.
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