Geotextiles are often incorporated in engineered structures—including landfill liners and covers, earthen dams, retaining walls, and roads—to perform the separation, filtration, and/or drainage functions. Under unsaturated conditions typical of such structures, a capillary break may form at the interface between soil and geotextile. If the break is unplanned, the resulting build-up of moisture may be detrimental to the structure. Conversely, properly designed geotextile capillary barriers have the potential for many positive applications. Design information, including a complete framework for analysis and an accepted laboratory characterization approach, is lacking. The primary objectives of this study were to investigate geotextile capillary barrier performance with a simple laboratory model and propose a framework for complete analysis of a geotextile capillary barrier life cycle. Soil columns were designed to allow the formation and breakthrough of a geotextile capillary barrier to be observed. Materials used in the columns were obtained from a capillary barrier system currently under construction at the Rocky Mountain Arsenal in Denver, CO. Hydraulic characterization of the soil and geotextile were performed in the lab. Eleven column tests were completed for this study—soil compaction and applied flow rate were varied to investigate their effect on capillary barrier response. Analysis was approached within a proposed framework covering each stage of a capillary barrier life cycle. While there was considerable scatter in the test results, important insight was gained. The geotextile capillary barrier performed consistently. Conditions near the interface at breakthrough were similar between tests, regardless of soil compaction or applied flow rate, and were predicted adequately with the laboratory characterization. Storage capacity of the capillary barrier decreased with increasing relative compaction. A framework for analysis, from which the entire capillary barrier response may be modeled, was developed. Application of this model allowed for identification of weaknesses and recommendations for future work. / text

Understanding the deformation mechanisms of soils and geosynthetics in response to the formation of a void below a geosynthetic-reinforced soil is crucial to provide efficient designs of geosynthetic-reinforced soil systems such as embankments and landfill liners. Centrifuge modelling of the soil and geosynthetic behaviour was conducted using a trapdoor to simulate the formation of a void in a controlled environment at realistic stress levels. A plane-strain model allowed visual observations of the deformation mechanisms using Particle Image Velocimetry. Granular soils and model clay liners were tested, as would be relevant to embankments and landfills respectively. These soils were tested with and without the reinforcement to evaluate the benefit provided by the geosynthetic. Detailed analysis of the centrifuge test results showed that arching significantly reduces the stress at the base of the soil when a void forms; this mechanism is due to stress redistributions and not the formation of a physical arch. A new method to reliably predict this reduction was provided by calculating the coefficient of lateral stress on the failure plane based on the observations of a continuous convex arc of major principal strains above the void, and the assumption that this is indicative of the stress behaviour. The observed results were also used to address the limitations in the current design methods related to the fill behaviour. Expansion in the soil was confined to a parabolic zone above the void estimated from the soil dilatancy, rather than a single, unique coefficient of expansion in the deforming soil. The zone of subsidence was characterised by the combination of a vertical prism and funnel to the surface, with the surface settlement profile better described by a Gaussian distribution rather than the parabolic profile used previously. An adaptation to the design methods for use with compacted clay liners was proposed by considering the clay as a beam with the maximum strain related to curvature and not elongation, and calculating the applied stress on the geosynthetic ignoring the clay arching. Analysis and interpretation of the centrifuge tests has thus given new insight into the soil and geosynthetic behaviour based on visual observations relevant to how these systems deform in practice. This has allowed the recommendation of more efficient design procedures and consequently will facilitate better predictions of geosynthetic-reinforced soil behaviour above voids.

Geosynthetic reinforced soil (GRS) walls involve the use of geosynthetic reinforcement (polymer material) within the retained backfill, forming a reinforced soil block where transmission of overturning and sliding forces on the wall to the backfill occurs. Key advantages of GRS systems include the reduced need for large foundations, cost reduction (up to 50%), lower environmental costs, faster construction and significantly improved seismic performance as observed in previous earthquakes. Design methods in New Zealand have not been well established and as a result, GRS structures do not have a uniform level of seismic and static resistance; hence involve different risks of failure. Further research is required to better understand the seismic behaviour of GRS structures to advance design practices. The experimental study of this research involved a series of twelve 1-g shake table tests on reduced-scale (1:5) GRS wall models using the University of Canterbury shake-table. The seismic excitation of the models was unidirectional sinusoidal input motion with a predominant frequency of 5Hz and 10s duration. Seismic excitation of the model commenced at an acceleration amplitude level of 0.1g and was incrementally increased by 0.1g in subsequent excitation levels up to failure (excessive displacement of the wall panel). The wall models were 900mm high with a full-height rigid facing panel and five layers of Microgird reinforcement (reinforcement spacing of 150mm). The wall panel toe was founded on a rigid foundation and was free to slide. The backfill deposit was constructed from dry Albany sand to a backfill relative density, Dr = 85% or 50% through model vibration. The influence of GRS wall parameters such as reinforcement length and layout, backfill density and application of a 3kPa surcharge on the backfill surface was investigated in the testing sequence. Through extensive instrumentation of the wall models, the wall facing displacements, backfill accelerations, earth pressures and reinforcement loads were recorded at the varying levels of model excitation. Additionally, backfill deformation was also measured through high-speed imaging and Geotechnical Particle Image Velocimetry (GeoPIV) analysis. The GeoPIV analysis enabled the identification of the evolution of shear strains and volumetric strains within the backfill at low strain levels before failure of the wall thus allowing interpretations to be made regarding the strain development and shear band progression within the retained backfill. Rotation about the wall toe was the predominant failure mechanism in all excitation level with sliding only significant in the last two excitation levels, resulting in a bi-linear displacement acceleration curve. An increase in acceleration amplification with increasing excitation was observed with amplification factors of up to 1.5 recorded. Maximum seismic and static horizontal earth pressures were recorded at failure and were recorded at the wall toe. The highest reinforcement load was recorded at the lowest (deepest in the backfill) reinforcement layer with a decrease in peak load observed at failure, possibly due to pullout failure of the reinforcement layer. Conversely, peak reinforcement load was recorded at failure for the top reinforcement layer. The staggered reinforcement models exhibited greater wall stability than the uniform reinforcement models of L/H=0.75. However, similar critical accelerations were determined for the two wall models due to the coarseness of excitation level increments of 0.1g. The extended top reinforcements were found to restrict the rotational component of displacement and prevented the development of a preliminary shear band at the middle reinforcement layer, contributing positively to wall stability. Lower acceleration amplification factors were determined for the longer uniform reinforcement length models due to reduced model deformation. A greater distribution of reinforcement load towards the top two extended reinforcement layers was also observed in the staggered wall models. An increase in model backfill density was observed to result in greater wall stability than an increase in uniform reinforcement length. Greater acceleration amplification was observed in looser backfill models due to their lower model stiffness. Due to greater confinement of the reinforcement layers, greater reinforcement loads were developed in higher density wall models with less wall movement required to engage the reinforcement layers and mobilise their resistance. The application of surcharge on the backfill was observed to initially increase the wall stability due to greater normal stresses within the backfill but at greater excitation levels, the surcharge contribution to wall destabilising inertial forces outweighs its contribution to wall stability. As a result, no clear influence of surcharge on the critical acceleration of the wall models was observed. Lower acceleration amplification factors were observed for the surcharged models as the surcharge acts as a damper during excitation. The application of the surcharge also increases the magnitude of reinforcement load developed due to greater confinement and increased wall destabilising forces. The rotation of the wall panel resulted in the progressive development of shears surface with depth that extended from the backfill surface to the ends of the reinforcement (edge of the reinforced soil block). The resultant failure plane would have extended from the backfill surface to the lowest reinforcement layer before developing at the toe of the wall, forming a two-wedge failure mechanism. This is confirmed by development of failure planes at the lowest reinforcement layer (deepest with the backfill) and at the wall toe observed at the critical acceleration level. Key observations of the effect of different wall parameters from the GeoPIV results are found to be in good agreement with conclusions developed from the other forms of instrumentation. Further research is required to achieve the goal of developing seismic guidelines for GRS walls in geotechnical structures in New Zealand. This includes developing and testing wall models with a different facing type (segmental or wrap-around facing), load cell instrumentation of all reinforcement layers, dynamic loading on the wall panel and the use of local soils as the backfill material. Lastly, the limitations of the experimental procedure and wall models should be understood.

Asphalt pavements often experience premature distresses caused by extreme environmental condition of both high and low temperatures. By maintaining a stable temperature a potentially longer lasting pavement is achievable. Laboratory tests and a field study were conducted on Hot Mix Asphalt pavements using a Geosynthetic Reinforced Chip Seal (GRCS); the temperature data from the two tests were compared for the GRCS’s effectiveness in reducing the pavement high temperatures. It was found that using a GRCS with an asphalt saturated geosynthetic layer and a chip seal with high reflectivity aggregates is an effective way to reduce high temperatures at different depths in the pavements. Field studies showed a temperature reduction of 9.2OC at the original surface and 10.3OC at 12.5 mm below the original surface, for an air temperature of 49OC.

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.

The physical response of composite landfill liners consisting of a geomembrane on top of a geosynthetic clay liner (GCL) are examined under simulated landfill conditions. The deformation and strains of a 1.5-mm-thick high-density polyethylene geomembrane and thickness and hydraulic performance of a nominally 7-mm-thick GCL are quantified when the composite liner was buried beneath 50 mm coarse gravel, at applied pressures up to 1000 kPa, with a firm sand foundation layer, and with and without a wrinkle in the geomembrane. At an applied pressure of 250 kPa, with either no protection or conventional thick nonwoven needle-punched geotextile protection layers, the tensile strains in the geomembrane exceeded a 3% allowable limit and the GCL was reduced in thickness to as little as 2.2 mm from extrusion of bentonite beneath a gravel particle. Whereas a 150-mm-thick sand protection layer limited strains in the geomembrane to 0.1% and prevented extrusion in the GCL so that deformation was from bentonite consolidation and not from extrusion. A GCL with a thickness of less than 3 mm from extrusion was shown to be susceptible to failure from internal erosion of bentonite in the GCL at hydraulic head differences across the GCL between 1-10 m. Conversely with the sand protection layer, the GCL could withstand a head difference of greater than 100 m without any evidence of internal erosion. Further, the permittivity of an extruded 3.5-mm-thick GCL was found to be 4.5 times larger than a 7-mm-thick GCL that did not experience extrusion. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2008-09-05 10:47:21.783

This research evaluated the use of geosynthetic clay liners (GCLs) as a potential barrier material to the migration of metals that are leached from mine waste. This thesis consists of two parts. In the first part, micro analytical methods including µXRD with synchrotron-generated µXRF elemental mapping and synchrotron-based µXRD (S-µXRD) were used to characterize the GCL bentonite and distinguish how mechanisms of metal attenuation could be identified. These analytical methods were of particular use for the clay material as they offer non-destructive, in situ investigation of various soil characteristics with microspatial resolution. The combination of the analytical methods allowed for identification of minerals such as gypsum and pyrite, not accessible by conventional methods. In particular, distinguishing accessory crystalline phases present in the “starting material” bentonite from those formed as a result of interaction with metal-bearing leachates is critical, as the development of metal-attenuating crystalline phases can have a significant long-term impact on metal mobility. In the second part of the thesis, the migration behaviour of metals (As, Al, Cd, Cu, Fe, Mn, Ni, Sr, and Zn) was investigated by means of diffusion tests and permeation experiments using four metal-containing waters: acidic rock drainage (ARD), lime-treated ARD, water from gold mine tailings, and landfill leachate with metal loading. Effective diffusion coefficients of the metals were calculated by modelling laboratory diffusion and sorption data. Water pre-hydrated GCLs were permeated with 15-21 pore volumes (PVs) of solution and their interaction with these solutions was examined in terms of both the hydraulic conductivity and the change in the geochemical characteristics of the permeant over time. The greatest increase in hydraulic conductivity occurred for the acidic rock drainage, where it increased from 1.6x10-11 m/s to 1.3x10-10 m/s following 21 PVs of permeation; still a very low value when compared to regulatory standards for clay barrier materials. Observed delayed breakthrough curves were indicative of the GCL’s strong attenuation capacity for a number of metals. An understanding of mechanisms of metal retention at both the micro and macro-scale levels will facilitate effective pollution prevention using GCLs. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2009-04-26 18:46:23.02