Shear Strength Properties of Clean and Clay Infilled Rock Joints: An analysis of the impact of moisture content under CNL conditions

Downing, Elizabeth (2022) Shear Strength Properties of Clean and Clay Infilled Rock Joints: An analysis of the impact of moisture content under CNL conditions. [USQ Project]

Text (Project)

Download (5MB) | Preview


The aim of this project is to quantitatively analyse the effects of clay infill moisture content and infill layer thickness on the shear strength characteristics of clean and infilled rock joints being subjected to Constant Normal Loading (CNL) boundary conditions. Understanding the failure mechanisms and conditions of slope stability is key to both safety and economic considerations in geotechnical engineering. Rock joints are common geological features with the potential to decrease the shear capacity of the rock material and affect the stability of slopes on small and large scales. While significant research has been performed previously with consideration to critical conditions (full saturation of infill), there has been relatively little consideration to infill material with a moisture content below full saturation. In areas of high risk, such as Asia and South America, a high factor of safety needs to be implemented. However, in areas of lower risk the factor of safety might be able to be decreased (potentially minimizing construction and maintenance costs).

This project consists of six main phases: extensive literature review, procurement of materials and organization of laboratory facilities, modelling (and printing) of three-dimensional moulds and concrete casting, testing of samples, data analysis and modelling, and final dissertation report as outlined in Table 2.

Rock-like samples will be constructed using three-dimensional printed moulds and concrete. The scope of this project is limited to one clay soil type with various moisture contents and applied normal stress (100 to 700 kPa) subject to CNL boundary conditions, with the potential for further research using a wider variety of conditions. The expected outcomes for this project were decreased shear strength as infill thickness and moisture content increase, the shear strength of the clean rock joint to be greater than that of an infilled rock joint, and sufficient and conclusive data that can contribute to the development of a new slope stability model in relation to rock joints. Testing was conducted in accordance with AS1289 to ensure the validity of the results and minimize human factor errors, and graphical data analysis was be conducted using Microsoft Excel. The testing and data analysis in this project, and future research, has the potential to establish a new slope stability model for use in industry.

Actual outcomes (as outlined in Chapter 5) include: higher shear strength of clean rock joints in comparison to clay infilled joints, when the infill thickness was less than the asperity height the asperity profile of the artificial rock joint controlled the behaviour of the sample, at higher thicknesses (infill thickness equal to or greater than asperity height) the infill material predominantly controlled the behaviour of the joint, and that as the moisture content increased the magnitude of the converging trend remained largely unaffected. The key finding of this project is that as the moisture content increased, ii the rate of convergence of the shear stress, normal stress and normal displacement trends increased at lower applied normal loading conditions. However, due to the limiting loading of 2200 N of the direct shear apparatus used the data at higher applied normal loadings is generally inconclusive. Due to limited data set at higher applied normal stresses, further research should investigate the impact of variable moisture conditions on the shear strength properties of clay infilled rock joints by narrowing the scope to include more moisture content conditions tested at relatively low applied normal stresses (up to 300 kPa). In addition, testing under CNS conditions should be investigated to determine the behaviour on deeper rock joints.

Statistics for USQ ePrint 51878
Statistics for this ePrint Item
Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Supervisors: Mirzaghorbanali, Ali
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 19 Jun 2023 04:48
Last Modified: 20 Jun 2023 01:12
Uncontrolled Keywords: clay infill moisture content; shear strength; Constant Normal Loading (CNL)

Actions (login required)

View Item Archive Repository Staff Only