Time-dependent behaviour of micro-tunneling construction in Queenston shale

The Queenston shale among other shales from southern Ontario exhibits time-dependent deformation behaviour. This behaviour is manifested in the form of volume increase which can cause damages to the hosted underground structures. The time-dependent deformation of rocks can cause cracks in the springline of tunnels, wall inward movement, roof spalling and floor heave, which requires costly remedial measures. The expansion of the existing infrastructures in southern Ontario requires construction techniques, such as micro-tunneling to build new tunnels and pipelines under the existing structures with minimal impact to these structures and to the environment. However, adopting this technique in swelling rocks, such as the Queenston shale requires an evaluation of its feasibility and functionality prior to its application. Accordingly, a comprehensive study that included experimental and numerical investigations was conducted to evaluate the impact of lubricant fluids used in micro-tunneling applications on their time dependent behaviour. The experimental program evaluated the impact of water, bentonite and polymer solutions on the Queenston shale through: i) investigating the influence of lubricant fluids on the time-dependent deformation behaviour of the Queenston shale through performing free swell, semi-confined, and null swell tests on Queenston shale in these fluids, ii) investigating the impact of lubricant fluids on the strength of the Queenston shale utilizing the Brazilian, direct tension, unconfined compression, and triaxial compression tests, before and after soaking in lubricant fluids, and iii) investigating the depth of penetration of lubricant fluids and water into the Queenston shale. It was revealed that the impact of polymer solution was significant in reducing the time-dependent deformation of the Queenston shale compared to bentonite solution and water. The strength of the Queenston shale was remarkably decreased after their continuous exposure to water and lubricant fluids with minimal impact caused by polymer solution. The penetration of lubricant fluids was found smaller compared to water, and a relation was derived to compute the penetration depth of each fluid in Queenston shale with time. The numerical investigation comprised finite element parametric analyses using the derived tests results along with time-dependent deformation model employing computer program PLAXIS 2D. Different pipe diameter, pipe depth, in-situ stress ratio, and waiting time before final grouting were used in the analyses. Accordingly, micro-tunneling was found to be workable and feasible technique to construct tunnels and pipelines in the Queenston shale of southern Ontario. Recommendations to use the appropriate strength of the make concrete; waiting time and the most suitable depth for micro-tunneling applications are given. The results are envisioned to aid in determining whether or not micro-tunneling technique is a feasible construction technique for pipelines / tunnels in Queenston shale of southern Ontario

Numerical modeling of time-dependent deformation and induced stresses in concrete pipes constructed in Queenston shale using micro-tunneling technique

Effects of time-dependent deformation (TDD) on a tunnel constructed using the micro-tunneling technique in Queenston shale (QS) are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids (LFs) used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio (Ko), and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining. The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling. Keywords: Numerical model, Micro-tunneling, Queenston shale (QS), Lubricant fluids (LFs

The Influence of Water and Lubricant Fluids on The Peak Strength of Queenston Shale from Southern Ontario

The strength of Milton Queenston Shale (MQS) before and after soaking in water and lubricant fluids (LFs) was examined. The investigated LFs (i.e. bentonite and polymer solutions) are utilized in micro-tunnelling technique (MTT) to facilitate the installation of tunnel/pipe sections. To investigate the relevant mechanical properties of MQS under different wetting conditions, a series of laboratory tests including Brazilian split, uniaxial compression, and triaxial compression were carried out. These tests were performed on vertically and horizontally cored specimens with respect to the rock bedding. Fresh specimens (i.e. intact), and specimens soaked for 100 days in LFs and in water were examined. The 100 days period was selected as it may reasonably represents the construction period where some swelling of the Queenston Shale can occur. It was revealed that the strength of MQS substantially decreased after soaking. With greater impact in vertical direction, both water and bentonite solution caused similar decrease in MQS strength of 23-70 %, while polymer solution caused a smaller decrease of 10-57 %. Accordingly, strength envelopes of MQS were established for vertical and horizontal directions before and after soaking.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

The Influence of Lubricant Fluids on Swelling Behaviour of Queenston Shale In Southern Ontario

The feasibility of micro-tunnelling technique to install pipelines through Queenston Shale of Southern Ontario is being investigated. In micro-tunnelling technique, lubricant fluids, such as bentonite slurry and polymer solution are used to facilitate excavation during the installation of the pipeline sections. In this regard, a comprehensive testing program was performed to investigate the time-dependent deformation behaviour of Queenston Shale considering lubricant fluids used in construction. The free swell test, semi-confined swell test, and the null swell test were utilized to perform this study. The results of 144 tests are presented and the variation of swelling characteristics of Queenston Shale in lubricant fluids and in water is briefly discussed. The swelling model suggested by Lo and Hefny (1996) was adopted to develop the swelling envelopes of Queenston Shale in lubricant fluids and water in both horizontal and vertical directions with respect to the rock bedding. In comparison to swelling in fresh water, the study revealed that the polymers solution has substantially reduced the swelling of Queenston Shale in all directions, while the bentonite solution was less efficient in reducing the swelling of Niagara Queenston Shale, and has a slight negative influence on the swelling (i.e. increased swelling) of Milton Queenston Shale.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author