Essays: Curing Method and Performance Evaluation of Sand Stabilized with Lignin and Enzyme-treated Lignin and Numerical Simulation for Drainage of Permeable Friction Course (PFC) Considering Surface Runoff and Seepage Flow




Zheng, Chao

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Series of laboratory tests were conducted on poorly graded sand to investigate the curing method, strength improvement and water resistance for alkali lignin before and after laccase enzyme treatment. The first part explored the preparing steps for enzyme-treated lignin and specimens stabilized by lignin or enzyme-treated lignin, determined the optimum curing methods and lignin dosage, which was used as reference for the following testing plan. Then the strength improvement of treated soil was evaluated under different contents of lignin and enzyme-treated lignin with or without lime. The performance on water resistance was also assessed for sand stabilized by lignin and enzyme-treated lignin with lime through water soaking test and dry-wet cycle test. The results of this study showed sand treated by lignin with lime has the feature of increased maximum dry unit weight with reduced optimum moisture content. Enzyme-treated lignin showed better strength improvement than untreated lignin when the lime was not used, and it made treated sand more ductile. Addition of lime provided more strength improvement on lignin treated sand than those stabilized by enzyme-treated lignin, while it decreased the ductility of treated sand. Water soaking tests showed that lime greatly improved the water stability of sand with lignin/enzyme-treated lignin, and enzyme-treated lignin showed better water resistance than raw lignin. Higher lignin and lime content offered more improvement on water resistance. The strength of lignin/enzyme-treated sand with lime was not able to fully recover but decreased with dry-wet cycles.

The fourth essay introduced a newly developed numerical model for drainage of PFC pavement under different rainfall events. The numerical model was composed by two-dimensional (2D) shallow water equation for surface runoff and the three-dimensional (3D) Richards equation for subsurface porous medium flow. The numerical model was first calibrated by the data from large-scale experimental tests. Then it was utilized to evaluate the water accumulation at the pavement during different rain intensities. The results indicated that PFC pavement was effective to remove surface water timely. Pavement slope and underdrain will be necessary to further facilitate water flow under extreme rainfall events.


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Civil and Environmental Engineering