School of Civil Engineering

Projects in geotechnical engineering

RESEARCH TOPIC 1 – Shotcrete

Project 1/1 – Tensile strength of Shotcrete

Supervisor: Dr Jurij Karlovšek (j.karlovsek@uq.edu.au), A/Prof Harry Asche (Aurecon) and Mr Zhongyu Xu

A significant proportion of total annual shotcrete volume used in Australia goes into the construction of underground lining support. Unplanned cracking of lining is serviceability related problem that continues to occur in a large number of structural elements. The aim of the present investigation is to establish a relationship between the restrained shrinkage behaviour of shotcrete ring specimens and shrinkage in tunnelling lining construction. This information will be used in design to estimate associate shrinkage-induced movement and minimise incidence of uncontrolled shotcrete lining cracking.

 

Project 1/2 – Shotcrete Round Determinate Panel testing

Supervisor: Dr Jurij Karlovšek (j.karlovsek@uq.edu.au), A/Prof Harry Asche (Aurecon) and Mr Zhongyu Xu

Maximum permissible crack widths are an important issue for many Fibre Reinforced Shotcrete (FRS) tunnel linings due to the influence cracks have on post-crack strength, durability, and water ingress. Round Determine Panel (RDP) testing will be conducted for Quality Control in accordance with ASTM C1550 and correlated with other standard concrete tests. There are manifested regulations about (a) fibre dosage, aspect ratio and tensile strength; and (b) cement and grading of the shotcrete mix that will be investigated in this research.

 

RESEARCH TOPIC 2 – Tunnel excavation and rock mass

Project 2/1 – Testing and defining brittle failure damage thresholds using acoustic emissions - Hawkesbury Sandstone

Supervisor: Dr Jurij Karlovšek (j.karlovsek@uq.edu.au), Thomas Roper (LandLease) and John Sutton (Golder Associates)

Intact rock damage detection, using acoustic emission events counts during UCS testing, has been successfully used to define behaviour thresholds in hard, massive, non-porous rocks (Crack Initiation, CI, and Crack Damage, CD). This sample scale behaviour correlates well to macro, tunnel scale spalling observations as discussed by Cai and Kaiser, 2014.

This progressive brittle failure is now being applied to Sydney’s Hawkesbury sandstone, a medium strength sandstone, in current tunnelling projects (Oliveira and Deiderichs, 2017, McQueen et al, 2017 and Tepevac et al, 2017). Very little testing AE testing has been carried out on Hawkesbury Sandstone therefore the variability of sample scale behaviour is not well understood.

Scope of Works:

  1. Undertake a review of the brittle failure in antistrophic geology and the use of AE testing during UCS tests
  2. Formulate a testing and plan and conduct AE during UCS testing on samples of Hawkesbury Sandstone
  3. Analyse the results and compare them to traditional CI/CD behaviour of hard rock
  4. Discuss the appropriateness of applying the brittle failure model to Hawkesbury Sandstone

 

Project 2/2 – Risk of unexpected ground conditions

Supervisor: Dr Jurij Karlovšek (j.karlovsek@uq.edu.au) and Thomas Roper (LandLease)

On design and construction tunnelling projects, the contractor accepts the risk of unexpected ground conditions. Ground conditions are often the primary factor in tunnelling rates and therefore the financial success of the project. If during the tender phase the geotechnical conditions are poorly predicted, and more challenging geology is encountered, the delivery of the project can be delayed at the contractor’s financial detriment. For contractors there is not enough time to carry out a comprehensive site investigation in the period prior to tender. This makes it very difficult for the contractor to include an accurate price for controlling the conditions that it might encounter. Review the practices and effectiveness of ground investigation and rock mass classification to predict tunnelling rates and ground support requirements. The project will:

  1. Review the effectiveness of borehole data in predicting tunnelling ground conditions.
  2. Review the predicted ground conditions from a construction site compared to the actual encountered conditions.
  3. Develop an empirically derived (Or the means to) risk assessment tool to consider forecasted vs actual ground conditions for tunnel projects in Sydney.