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Module 1: Suction Measurement and Control

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Hydraulic Conductivity Functions (HCF) - Concept As the water content of soil increases, the hydraulic conductivity increases. The Hydraulic Conductivity Function and Soil-Water Characteristic Curve are two important constitutive relationships required in determining the flow behaviour of unsaturated soils. Hydraulic conductivity depends on the type of soil. It's not a state variable, but a material constant. Suction Measurement/Control Techniques The techniques in estimating or controlling the suction of soil are: Hanging Column Technique, Tesiometer, Axis Translation Technique, Osmotic Technique, Dew Point Potentiometer, Vapour Equilibrium Technique, Contact Filter Paper Technique and Non-Contact Filter Paper Technique. The Hanging Column Technique contains a soil column that is connected to a water reservoir. Volumetric Water Content (VWC) sensors are placed are different levels of the soil column to measure volumetric water content. The VWC sensors are connected to a data logger. This technique is purely a laboratory technique The Tensiometer has a sensing probe that is connected to the water-filled body tube. This water-filled body tube is connected to a pressure gauge which measures the negative water pressure in the tube. The tensiometer can be used in both the laboratory and field. The Axis Translation Technique is a laboratory technique. It involves increasing air pressure to a certain value and maintaining the water pressure at atmospheric pressure. Then, the required suction value could be maintained. Dew-Point Potentiometer: The technique is useful for measuring the suction of soil rather than controlling. This setup consists of a sample holder, where the soil sample is placed. In this technique, total suction can be estimated from the dew point temperature and relative humidity of the pore spacer of the soil. This is useful for estimating the suction at a high suction range. The Vapour Equilibrium Technique is useful for controlling the suction at a high suction range. Contact and Non-Contact Filter Paper Technique: The contact filter paper technique estimates the matric suction while the non-contact filter paper technique estimates the total suction of soil. The various suction measuring/controlling techniques have different suction ranges and types of suction they can measure/control.