This thesis discusses the field testing of a newly-developed product, a geosynthetic capillary break (GCB). The GCB was developed for use in engineered soil covers when a cover incorporating a capillary break effect would be desirable, but the coarse-grained material (gravel or sand) is unavailable or uneconomical. Engineered soil covers aim to reduce the amount of acid generated from sulphide bearing waste by limiting the ingress of water and/or oxygen. The GCB is a geosynthetic system that is composed of a finely ground rock flour sandwiched between two nonwoven geotextiles and manufactured as a composite layer by needle punching in a process similar to the used for GCL (geosynthetic clay liner). The goal of the GCB is to recreate the capillary break that is achieved with soil layers using a geosynthetic product that is only a few centimetres thick and that can be rolled up and for transportation, The GCB concept has been demonstrated in a previous study (Park, 2005) based on laboratory column studies and computer modelling. The goal of this project was to determine the effectiveness of the GCB when applied at field scale. Four 25 square test plots were constructed at the tailings management area (TMA) of the HudBay Minerals Inc.(HudBay) mine site located near Flin Flon, MB. One plot contained 1 m of cover soil over top of the GCB (Plot A), one contained only 1 m of cover soil (Plot B), one contained 0.3 m of cover soil over top the GCB (Plot C), and one consisted of a conventional capillary break system with 1 m of cover soil over lying 0.2 m of sand. All of the plots, along with a control plot with no cover, were instrumented with water content sensors and gas sampling ports to monitor the movement of water and oxygen through the various covers. Matric suction sensors were also installed in Plots A and B to measure the water suction within the covers. A meteorological station was installed to gather climatic data which was used to develop a water balance for each of the plots. The plots were constructed and instrumented in the fall of 2005. Data was collected and analyzed until spring of 2007. Data from the water content sensors show that the GCB was effective in increasing the water content in the soil portion of the cover system. The suction sensors show that the suction across the GCB drops significantly (40 kPa versus less than 1 kPa) as compared to plots which contain no GCB. Data from the gas concentration sensors show that the plots containing capillary breaks reduce the oxygen flux into the tailings. The plots containing the GCB (Plots A and C) resulted in the lowest flux rates, followed by the sand capillary break (Plot D )and no capillary break (Plot B), respectively. This reduction in oxygen flux will reduce the amount of acid generated from waste, as oxygen is required for the creation of acid mine drainage. Overall the study demonstrated that at field scale that the GCB is effective in limiting the ingress of water and oxygen into the tailings under the observed conditions and the manufactured GCB is comparable to the performance of the previous hand constructed column tests.

One of the major issues in the successful decommissioning of any waste disposal system is to mitigate the spread of contaminants into the surrounding environment. In many instances this is achieved by reducing amounts of net percolation and/or oxygen diffusion into the underlying waste. An engineered cover system incorporating a capillary break is a common solution to this problem. However, traditional soil capillary breaks can often be impractical for large facilities where desirable construction materials are not readily available. The primary objective of this research is to show the initial steps in the development of a new type of geosynthetic product, namely a geosynthetic capillary break (GCB). This new product, composed of a nonwoven geotextile coupled with a fine-grained rock flour, will function similar to, and has the possibility of replacing traditional, soil capillary breaks in many applications. The specific objectives of this research are to: i) determine the pertinent material parameters of the materials used to evaluate the GCB; ii) examine one-dimensional column testing of a typical engineered soil cover system incorporating the GCB; and iii) model the cover systems to better understand current performance and predict long-term performance of the GCB. The GCB was evaluated based on the objectives outlined above. The material characterization consisted of the selection of suitable materials for the GCB, as well as the determination of their unsaturated properties. The results indicate that a geotextile-rock flour combination will develop a capillary break within an engineered cover. The one-dimensional column tests evaluated four cover systems. Soil thicknesses of 30 and 60 cm were utilized, with one column of each cover thickness incorporating the GCB. The columns were tested under both high evaporative fluxes and high infiltration rates over the course of 111 days. The measured results show that there is less moisture movement in columns that incorporate the GCB. A coupled soil-atmospheric finite element model was then used to develop a predictive model for the cover systems. The model was calibrated to the measured results from the column testing to ensure consistency. The parameters obtained from this model were used to evaluate an engineered cover system incorporating the GCB for a minesite in Flin Flon, MB. The results from the predictive modeling show that moisture infiltration is reduced approximately 80% when comparing columns with the same cover thickness. Oxygen diffusion is also reduced by 20 to 25% with the inclusion of the GCB.

One of the major issues in the successful decommissioning of any waste disposal system is to mitigate the spread of contaminants into the surrounding environment. In many instances this is achieved by reducing amounts of net percolation and/or oxygen diffusion into the underlying waste. An engineered cover system incorporating a capillary break is a common solution to this problem. However, traditional soil capillary breaks can often be impractical for large facilities where desirable construction materials are not readily available. The primary objective of this research is to show the initial steps in the development of a new type of geosynthetic product, namely a geosynthetic capillary break (GCB). This new product, composed of a nonwoven geotextile coupled with a fine-grained rock flour, will function similar to, and has the possibility of replacing traditional, soil capillary breaks in many applications. The specific objectives of this research are to: i) determine the pertinent material parameters of the materials used to evaluate the GCB; ii) examine one-dimensional column testing of a typical engineered soil cover system incorporating the GCB; and iii) model the cover systems to better understand current performance and predict long-term performance of the GCB. The GCB was evaluated based on the objectives outlined above. The material characterization consisted of the selection of suitable materials for the GCB, as well as the determination of their unsaturated properties. The results indicate that a geotextile-rock flour combination will develop a capillary break within an engineered cover. The one-dimensional column tests evaluated four cover systems. Soil thicknesses of 30 and 60 cm were utilized, with one column of each cover thickness incorporating the GCB. The columns were tested under both high evaporative fluxes and high infiltration rates over the course of 111 days. The measured results show that there is less moisture movement in columns that incorporate the GCB. A coupled soil-atmospheric finite element model was then used to develop a predictive model for the cover systems. The model was calibrated to the measured results from the column testing to ensure consistency. The parameters obtained from this model were used to evaluate an engineered cover system incorporating the GCB for a minesite in Flin Flon, MB. The results from the predictive modeling show that moisture infiltration is reduced approximately 80% when comparing columns with the same cover thickness. Oxygen diffusion is also reduced by 20 to 25% with the inclusion of the GCB.

This thesis discusses the field testing of a newly-developed product, a geosynthetic capillary break (GCB). The GCB was developed for use in engineered soil covers when a cover incorporating a capillary break effect would be desirable, but the coarse-grained material (gravel or sand) is unavailable or uneconomical. Engineered soil covers aim to reduce the amount of acid generated from sulphide bearing waste by limiting the ingress of water and/or oxygen. The GCB is a geosynthetic system that is composed of a finely ground rock flour sandwiched between two nonwoven geotextiles and manufactured as a composite layer by needle punching in a process similar to the used for GCL (geosynthetic clay liner). The goal of the GCB is to recreate the capillary break that is achieved with soil layers using a geosynthetic product that is only a few centimetres thick and that can be rolled up and for transportation, The GCB concept has been demonstrated in a previous study (Park, 2005) based on laboratory column studies and computer modelling. The goal of this project was to determine the effectiveness of the GCB when applied at field scale. Four 25 square test plots were constructed at the tailings management area (TMA) of the HudBay Minerals Inc.(HudBay) mine site located near Flin Flon, MB. One plot contained 1 m of cover soil over top of the GCB (Plot A), one contained only 1 m of cover soil (Plot B), one contained 0.3 m of cover soil over top the GCB (Plot C), and one consisted of a conventional capillary break system with 1 m of cover soil over lying 0.2 m of sand. All of the plots, along with a control plot with no cover, were instrumented with water content sensors and gas sampling ports to monitor the movement of water and oxygen through the various covers. Matric suction sensors were also installed in Plots A and B to measure the water suction within the covers. A meteorological station was installed to gather climatic data which was used to develop a water balance for each of the plots. The plots were constructed and instrumented in the fall of 2005. Data was collected and analyzed until spring of 2007. Data from the water content sensors show that the GCB was effective in increasing the water content in the soil portion of the cover system. The suction sensors show that the suction across the GCB drops significantly (40 kPa versus less than 1 kPa) as compared to plots which contain no GCB. Data from the gas concentration sensors show that the plots containing capillary breaks reduce the oxygen flux into the tailings. The plots containing the GCB (Plots A and C) resulted in the lowest flux rates, followed by the sand capillary break (Plot D )and no capillary break (Plot B), respectively. This reduction in oxygen flux will reduce the amount of acid generated from waste, as oxygen is required for the creation of acid mine drainage. Overall the study demonstrated that at field scale that the GCB is effective in limiting the ingress of water and oxygen into the tailings under the observed conditions and the manufactured GCB is comparable to the performance of the previous hand constructed column tests.