Influencing Soil Suction-Water Content Relationship

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A Study on Measuring Methodologies and Critical Parameters Influencing Soil Suction-Water Content Relationship

Thesis

submitted in partial fulfillment of the requirements

of the degree of

DOCTOR OF PHILOSOPHY

V my 9^

Malaya Chetia

Roll No. 07610404

Department of Civil Engineering Indian Institute of Technology Guwahati

Guwahati=781039, India February 2012

Abstract-TH1845_07610404

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Influence of Salt and Additives on Suction-Water

Content Relationship

8.1 General

8.2 Soil suction measurements in salt laden soils

8.3 Soil suction measurements in soil mixed with fly ash

8.4 Soil suction measurements in soil mixed with fertilizer 8.5 Summary

Appraisal on the Role of SWR in Unsaturated Soil

Hydraulic Conductivity Estimation

9.1 General

9.2 Estimation of unsaturated soil hydraulic conductivity

function from SWRs

9.2.1 Unsaturated soil hydraulic conductivity of non-plastic soils

9.2.1.1 Using continuous drying and spot SWRs of non-plastic

soils

9.2.1.2 Using continuous drying and wetting SWRs of non-plastic

soils

9.2.2 Unsaturated soil hydraulic conductivity of plastic soils 9.2.2.1 Using continuous and spot SWRs of plastic soils

9.3 Summary

Conclusions

uture Scope of Research

References

of Publications

Abstract

The knowledge of unsaturated soil behavior is indispensable for many of the field situations such as compacted pavements, swelling clays, slopes, embankments, shallow waste disposal facilities etc. One of the important attributes of unsaturated soil is the negative pore water pressure or soil suction existing in it. The study of unsaturated soil behavior is dependent on the basic relationship between soil suction and water content (either, gravimetric or volumetric) or soil saturation. Such a relationship, in general, is termed as suction-water content relationship (SWR) or specifically soil-water characteristic curve (SWCC). Last few decades have witnessed a tremendous development in soil suction measurement methodologies, which are based on different measuring principles. There is a possibility that the inherent features and measuring procedures of these methodologies may influence the uniqueness of SWR/ SWCC. Apart from the measuring methodologies, there are physical, chemical and mechanical parameters of soil influencing the SWR. Reviewed literature indicates some contrasting observations and anomalies related to unsaturated soil characterization, which needs to be understood in detail.

A systematic experimental work has been conducted in this study to evaluate the influence of suction measuring methodologies, different procedures adopted, and critical soil parameters affecting the uniqueness of SWR. The implication of non-uniqueness of SWR on unsaturated soil behavior is investigated by taking unsaturated soil hydraulic conductivity as an example. For this purpose, the unsaturated soil hydraulic conductivity estimated by using different measured SWRs for a particular soil has been compared and evaluated. Another important issue related to the implementation of unsaturated soil mechanics into routine geotechnical engineering practice is the excessive costs, time and complexities associated with the measurement of high soil suction. To take this into account, the present study attempts to investigate the possibility of standardizing a cost- effective, less time consuming and simple methodology for measuring high range of soil suction greater than 1000 kPa. Moreover, most of the reported studies discuss about

drying SWCC due to the simplicity of its measurement. But it must be noted that wetting

SWCC is also equally important for situations like seepage through unsaturated soil.

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However, it is challenging to experimentally obtain the wetting SWCC. A simple column set up has been used in this study to determine the wetting SWCC.

Key words; unsaturated soil, suction, suction-water content relationship, measurement methodology, parameter, unique, unsaturated hydraulic conductivity.

List of Figures

Caption

Idealized soil-water characteristic curves and its details

Idealized bimodal soil-water characteristic curve and its details Details of the T5 tensiometer

Details of the MPS-1

Details of the EQ2 equitensiometer

Diagrammatic representation of the test set up EC-TE probe used for 6 measurement

EC-5 probe used for 0 measurement

Gradational characteristics of non-plastic soils used in the study Gradational characteristics of the plastic soils used in the study Compaction characteristics of FA

Compaction characteristics of plastic soils Details of the test set up used in the study

HygroClip S (ROTRONIC AG, Grindelstrasse 6) relative humidity sensor used in this study

Variation of relative humidity of saturated salt solutions with

time at 25 °C

Comparison of measured RH with standard RH of saturated salt solutions at 25 °C

Total soil suction measurement using RHS

Influence of aging on total suction measurements using RHS Suction measurements in RS, FS, FC and ES using FPM

Comparison of suction measurements using relative humidity sensor and filter paper method

Variation of soil suction and volumetric water content with time for continuous measurement of SA

Variation of soil suction and volumetric water content with time for continuous measurement of BS

Variation of soil suction and volumetric water content with time for continuous measurement of FA

Drying SWCC for the soil SA corresponding to different

compaction states

Drying SWCC for the soil BS corresponding to different

compaction states

Continuous drying SWR for FA samples corresponding to

different compaction states

SWR in terms of w and 0 obtained from spot measurements for

SA

BS

FA