Performance-related properties of large particle sized tire-derived aggregate (TDA) for leachate collection and removal systems (LCRS)
Date
2020-11-04
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-2166-5111
Type
Thesis
Degree Level
Doctoral
Abstract
The compressive response of large particle sized TDA (>50 mm in size) to large applied loads, and the resulting effects on void ratio, vertical and horizontal hydraulic conductivity were studied to evaluate the use of the material in constructing the leachate collection and drainage layer of landfills. The applied loads studied ranged from 28 kPa to 375 kPa to simulate 2 m to 40 m of overlying waste over a landfill drainage layer. The performance of a drainage layer in a landfill depends on a high hydraulic conductivity to rapidly transmit leachate from the base of the landfill into collection and removal units to prevent excessive mounding of leachate on basal liner materials. It also depends on a high void volume to store inevitable biogeochemical clog material that will accumulate around the TDA particles as leachate flows through the drainage layer.
Given that TDA compresses under applied loads, unlike gravel – which is typically used in constructing the drainage layer of landfills, the hydraulic conductivity of TDA and void volume will change under applied loads with time. The individual and combined effects of immediate compression (the instantaneous response upon application of load) and creep (the time delayed compression following immediate compression) on void ratio under applied loads were studied. Study of biogeochemical clogging was outside the scope of work; however, parameters such as void volume under applied loads and specific surface area were measured. These can be used in the simulation and evaluation of biogeochemical clogging in future studies.
The inherent nature of TDA required innovative design of the laboratory testing equipment and iterative re-design and modification of the units and their components. The testing units had to be large to accommodate the testing of the large particle sized TDA, whilst minimizing the effects/inevitable artifacts of constrained large scale testing (such as sidewall friction). Despite all efforts to minimize sidewall friction loss, this was still highly prevalent during the testing, causing higher applied loads and compression in TDA sublayers closer to the applied loads and lower applied loads and compression in the sublayers farther away from the loads. Sidewall friction loss during compression testing was accounted for by determining the vertical distribution of applied loads and void ratio across the TDA thickness. In the evaluation of permeability and hydraulic conductivity, sidewall friction effects were removed from the data using some formulated analytical forms. High velocities and inertia effects were also accounted for in the analyses of the permeability and hydraulic conductivity data.
Laboratory testing was carried out using two main large sized, purpose built units – a one dimensional (1D) consolidometer (1.8 m high, 0.7 m diameter) and a two dimensional (2D) permeameter and consolidometer (1 m high, 1.2 m long, 0.6 m wide). The 1D cell was used to measure immediate compression and creep under applied loads. The 2D cell was used to measure vertical, horizontal air permeability, and hydraulic conductivity under sustained load; compression data was also collected from testing in the 2D cell. Eight compression/creep tests were completed in the 1D cell over a combined 705 days, individual duration ranged from 24 to 317 days. The duration of testing in the 2D cell was over 430 days (combined for all the tests), individual duration ranged from 112 to 316 days. Air permeability and hydraulic conductivity were evaluated from several dozens of tests completed at different flow rates and pressures.
The results from this study show that the void ratio of TDA can decrease to as low as 0.2 at applied loads of 224 kPa (20 m to 25 m of overlying waste on a landfill drainage layer). Nonetheless, the corresponding vertical and hydraulic conductivity values at a void ratio of 0.2 were both greater than 0.01 m/s. Projections of void ratio to higher applied loads up to 800 kPa (70 m – 85 m of overlying waste) showed a decrease to 0.01 and beyond that, void ratio was considerably less than 0.01. Corresponding vertical and horizontal hydraulic conductivity values at a void ratio of 0.01 were both higher than 0.001. These thus imply that void ratio alone is not sufficient for evaluating the performance of a TDA drainage layer, as even at considerably low void ratios, adequate flows can still be maintained in a TDA drainage layer. Many landfill regulations (for instance Standard for landfills in Alberta – used in Saskatchewan) stipulate a hydraulic conductivity of 0.0001 m/s. The measured and projected values (up to 800 kPa) meet and exceed the common stipulation for landfills, and are comparable to the typical range of values for gravel used in landfill leachate drainage layers. Given these results, large particle sized TDA can be considered adequate for use as drainage material in the leachate collection and removal systems of landfills.
The results from this research work were used in an existing analytical form for evaluating maximum leachate head in a drainage layer. The maximum leachate head values obtained from the analytical form were validated and corrected using finite element numerical modeling. The corrected values were presented in the form of design charts. The design charts and the results from this work were used to prepare a design guidance that may be used when constructing a landfill drainage layer with large particle sized TDA.
Description
Keywords
leachate collection and drainage layers, tire derived aggregate, landfill, scrap tires, immediate compression, vertical and horizontal hydraulic conductivity, creep, void ratio, specific surface, biogeochemical clogging
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Civil and Geological Engineering
Program
Civil Engineering