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(K_o), 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.

A Compilation of the Geo-Mechanical Properties of Rocks in Southern Ontario and the Neighbouring Regions

The available measurements of the geo-mechanical properties of rocks in Southern Ontario and the neighbouring regions (New York, Ohio, Michigan, Indiana, Illinois, Wisconsin, and Minnesota) are summarized and presented. These measurements were compiled from available published data in the relevant literature and also from data that were collected from major underground projects in these regions. The compiled data are presented in three categories: measured in-situ stresses in different rock formations;calculated strength, stiffness and deformation including time-dependent deformation properties;and the measured dynamic properties of intact rock specimens from different rock formations in Southern Ontario and the neighbouring regions. The data presented in this paper can be used as a resource for preliminary evaluation of the geomechanical properties of the rocks in these regions. The presented geo-mechanical properties were generally obtained from in-situ measurements and from laboratory tests that were conducted on intact rock specimens from freshly excavated rock samples. Moreover, the time-dependent deformation properties of rocks in these regions were obtained from laboratory tests that were performed on intact rock specimens submerged in water. However, the influence of drilling fluids such as bentonite slurry and synthetic polymers solution, on the geo-mechanical properties of rocks is not evident and needs to be investigated.

Wetting effects and strength degradation of swelling shale evaluated from multistage triaxial test

The multistage triaxial compression test was mainly utilized in this research to investigate the degradation in the strength of swelling shale under different wetting conditions.Shale samples were tested in four different conditions:(1)under their natural moisture content denoted as intact,and after soaking in,(2)water,(3)polymer solution,and(4)bentonite solution,separately.The experimental results showed that a considerable decrease in the shale’s strength was noted after soaking in water and the lubricant fluids(LFs).The polymer solution caused the least decrease in the strength compared to other fluids.Strength envelopes of the tested shale were constructed for intact and soaked states.These envelopes showed fair agreement between the single stage and the multistage triaxial compression test results,indicating suitability of the multistage triaxial compression test for the tested swelling shale.