A Lateral Stress Measuring Apparatus for Shear Strength Determination of Soft Clay Under Plane Strain Condition

Piyachat Chattonjai; Chonpisitt Yathuam

Authors

Piyachat Chattonjai Department Civil Engineering, Faculty of Engineering, Burapha University, Chonburi, Thailand
Chonpisitt Yathuam Department Civil Engineering, Faculty of Engineering, Burapha University, Chonburi, Thailand

Keywords:

Pressure Measurement, Air-Pressure Balance, Lateral Earth Pressure, Undrained Shear Strength, Plane Strain, Soft clay

Abstract

This research aimed to design and construct an artificial device for measuring the magnitude of lateral stress of Bangkok soft clay under plane strain condition. Lateral stress is of importance as it is not only used to calculate the coefficient of lateral earth pressure at rest at the end of primary consolidation, but is also used to create 3-D stress path when a soil sample is sheared. According to the principle of equilibrium, when the pressures on both sides of a diaphragm plate are equal, deformation would not occur. As a result, the magnitude of soil stress beside the diaphragm plate can be measured by knowing the magnitude of applied air pressure that turns the diaphragm plate back to its equilibrium condition. Strain gauges are typically installed on the diaphragm plate at particular positions to detect the equilibrium condition; signals from strain gauge circuit must not nevertheless exceed the tolerance value. A suitable magnitude of the injected air pressure is then controlled via an automatic closed-loop control system. However, such a system would require approximately 5-10 seconds to reach an equilibrium; this lengthy time period is not suitable for the measurement of instantaneous lateral stress during shearing of a soil sample. Therefore, in this research, a new approach to measure the lateral stress without reaching an equilibrium condition is proposed and was tested. According to the calibration and test results, the newly developed apparatus has sufficient linearity and accuracy for measuring the lateral total stress.

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