Estimation of unsaturated flow parameters and hysteresis curve from field instrumentation

Asif Ahmed,Md Sahadat Hossain,Md Jobair Bin Alam,Pratibha Pandey,T.M.P De Campos,G.F.N Gitirana,F.A.M Marinho,M.M.A Mascarenha

doi:10.1051/matecconf/202133701008

Abstract

Abstract: The negative pore water pressure or soil suction has significant effect on the performance of geotechnical infrastructures (e.g., slope, pavement, embankment etc.). The unsaturated behavior of soil is not static, rather offers variation in response to climatic loading. The objective of the study was to evaluate field-based techniques of SWCC construction in terms of capturing these variation as compared to laboratory methods and predictive models. The field assessment could allow the quantification of hysteresis effect on the SWCC. Instrumentation data from one Texas, USA highway was used in this study. Soil Water Characteristic Curves (SWCCs) were regenerated utilizing co-located moisture and suction data from the field. Laboratory and field measured SWCCs from the instrumented site were fitted by van Genuchten model. Previously developed predicted models were also utilized to evaluate the SWCC parameters. Based on the evapotranspiration and rainfall amounts, distinct drying and wetting cycles were recorded. Though hourly data was collected in this study, average daily values were used for the analysis. Unsaturated flow parameters (α, n, m) were determined from both laboratory testing and field moisture-suction data along with the predictive models. Clear differences were observed between the values obtained from predictive models and field generated SWCC. The outcome from this study revealed that field reconstructed SWCCs can be used to simulate higher precision in numerical modeling in numerous geotechnical applications.

Highlights

The soil which supports transportation infrastructures is unsaturated in most of the cases (Gupta et al 2007 [1])
The flow rate depends on the induced negative pore water pressure or matric suction which alters with the change in soil moisture
Soil water characteristic curve (SWCC), an important relation in the field of unsaturated soil mechanics describes a correlation between matric suction and moisture content within the soil mass (Fredlund & Rahardjo 1993 [3]; Lu & Likos 2004 [5]; Lu et al 2010 [6])

Summary

Introduction

The soil which supports transportation infrastructures is unsaturated in most of the cases (Gupta et al 2007 [1]). The soil in unsaturated conditions is frequently subjected to change in stress state due to transient wetting and drying climatic conditions (Fredlund & Rahardjo 1993 [3]; Rahardjo et al 2019 [4]), the impact of which is reflected on the performance of structures over time. The flow rate depends on the induced negative pore water pressure or matric suction which alters with the change in soil moisture. Soil water characteristic curve (SWCC), an important relation in the field of unsaturated soil mechanics describes a correlation between matric suction and moisture content within the soil mass (Fredlund & Rahardjo 1993 [3]; Lu & Likos 2004 [5]; Lu et al 2010 [6]). Accurate measurement of SWCC is generally required; it is often rather estimated through mathematical functions which could lead to weak interpretation of soil behavior

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