Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering (PhD)

Administrative Home Department

Department of Civil and Environmental Engineering

Advisor 1

Stanley J Vitton

Committee Member 1

Thomas Oommen

Committee Member 2

Zhen Liu

Committee Member 3

Snehamoy Chatterjee

Abstract

The abandoned Domtar Mine in Grand Rapids, MI underlies Interstate I-196. The mine operated for over 140 years, mining a 30-meter-deep, four-meter thick gypsum seam. In 2000, the mine was abandoned with the removal of the mine’s dewatering pumps allowing groundwater to flood the mine. The initial flooding resulted in saturating the mine pillars along with some amount of pillar dissolution. Overtime, gypsum dissolution would cease as the water becomes saturated with the gypsum dissolution products. The mine, however, is located adjacent to the Grand River and has groundwater moving through the mine resulting in the potential for continuing dissolution. The stability of the mine relies on the support pillars, which are being reduced in size due to the dissolution. In this research, we analyzed the long term stability of the Mine’s pillars. Samples from a quarry that mined the same gypsum seam were obtained. The moisture content of gypsum specimens was measured. The drying temperature according to ASTM standard, however, should not exceed 60 °C since heating can result in the transformation of gypsum to hemihydrate. The research investigated the temperature at which this transformation occurred using a helium pycnometer and determined that 80 °C can be used for gypsum’s moisture content measurements. The saturation process of specimens for mechanical testing was also investigated, concluding a saturated gypsum-water solution is required to minimize dissolution when saturating process. The dissolution rate of gypsum in both stagnant and flowing water was experimentally investigated, confirming the dissolution of pillars is a first-order kinetics reaction. The normalized dissolution coefficient for stagnant water was measured at 1.6×10-3 (cm/s) following a power law for flowing water. A simple analytical model was developed to predict the change of specimen’s diameter by time due to dissolution. A finite volume model was developed in FLAC3D to model the strength reduction of specimens due to both saturation and dissolution. The model was used to estimate the long-term stability of pillars in Domtar Mine. Finally, combining the analytical model and the numerical simulations, the time to failure of a pillar was estimated under different groundwater flow rates.

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