A New Index to Quantitatively Assess Clogging Potential Based on Mixing Test and Investigate Impacts of Different Beater Shapes to Mixing Test
Creators: Ma, Qiming
Publisher: name: University of Alberta Library
Year: 2024

<p>In the tunneling process, cohesive soil can readily adhere to tunneling equipment, potentially causing project delays and exceeding the budget. As a result, researchers have endeavored to establish indexes for evaluating the likelihood of soil clogging along the planned drilling route before commencing drilling operations. Various approaches and tests have been adopted to evaluate clogging potential, including analytical, semi-empirical, and physical simulation methods. The analytical approach entails shear tests to measure soil adhesion and cohesion, employing tests like shear box, plate shear, vane shear, and more. The difference between shear force and shear resistance was used as an indicator to assess the clogging potential. The semi-empirical approach utilizes universal classification diagrams based on Atterberg limit tests to categorize clogging potential which is commonly adopted. It was also considered that physical simulation methods, such as the cone pull-out test, can mimic the clogging process. Therefore, the corresponding measurements, e.g., torque force and soil weight on drilling machines were adopted to assess soil clogging. The dynamic and static lateral adhesion tests, as well as drilling tests, were also used to evaluate clogging through torque, sliding angles, and soil stickiness. However, penetration rate, drilling speed, soil properties are having an impact on clogging potential. None of the proposed indexes has taken these factors into consideration. Additionally, the tests to obtain most of the indies are complex and time-consuming. <br>
In this context, a newly dimensionless index, W/(Ac×dc×ρw), is proposed based on the mixing test, which is independent of drilling beater, drilling time, etc. In total, six groups of tests were conducted, and the changed parameters were beater size, beater shape, container size, soil content and water content. Since clogging potential should be independent of container size and soil weight, 2 groups of tests were conducted with soil mass varying from 0.5 kg to 2.0 kg and container size changing from 5L to 20L. The results indicated clogging potential only changes with consistency index. Changes in soil mass and container size have no effect on the soil clogging potential. <br>
Similarly, clogging potential relies on beater shape, beater size, soil content and water content of soil. Therefore, six groups of tests were conducted with bentonite content varying from 0% to 100%, and varied water content also three different shapes of beaters with varying surface area were used in the test. The results indicated that soil clogging potential increases as the bentonite content rises from 0% to 100%. The change of the water content is presented using the consistency index.  Soil clogging potential increases as the consistency index increases from 0, reaching its peak around 0.5, after which it gradually decreases as the consistency index approaches 1. Regarding the beater shape and sizes, it was observed that the soil clogging potential is higher when using beaters with smaller surface areas.<br>
Additionally, the clogging potential of the same soil was assessed using other indexes like stickiness ratio for comparison purposes which indicated that the newly developed index is more accurate and straightforward than the stickiness ratio. The change of soil mass, soil type, mixing time can be effectively studied using the newly developed index, W/(A<em>c*d</em>c*ρ_w), instead of the stickiness ratio. <br>
This research provided a dimensionless index and repeatable test for evaluation of clogging potential, which can advance the risk assessment prior to drilling work.</p>