Forward modelling and inversion of streaming potential for the interpretation of hydraulic conditions from self-potential data

The self-potential method responds to the electrokinetic phenomenon of streaming potential and has been applied in hydrogeologic and engineering investigations to aid in the evaluation of subsurface hydraulic conditions. Of specific interest is the application of the method to embankment dam seepage monitoring and detection. This demands a quantitative interpretation of seepage conditions from the geophysical data. To enable the study of variably saturated flow problems of complicated geometry, a three-dimensional finite volume algorithm is developed to evaluate the self-potential distribution resulting from subsurface fluid flow. The algorithm explicitly calculates the distribution of streaming current sources and solves for the self-potential given a model of hydraulic head and prescribed distributions of the streaming current cross-coupling conductivity and electrical resistivity. A new laboratory apparatus is developed to measure the streaming potential coupling coefficient and resistivity in unconsolidated soil samples. Measuring both of these parameters on the same sample under the same conditions enables us to properly characterize the streaming current cross-coupling conductivity coefficient. I present the results of a laboratory investigation to study the influence of soil and fluid parameters on the cross-coupling coefficient, and characterize this property for representative well-graded embankment soils. The streaming potential signals associated with preferential seepage through the core of a synthetic embankment dam model are studied using the forward modelling algorithm and measured electrical properties to assess the sensitivity of the self-potential method in detecting internal erosion. Maximum self-potential anomalies are shown to be linked to large localized hydraulic gradients that develop in response to piping, prior to any detectable increase in seepage flow through the dam. A linear inversion algorithm is developed to evaluate the three-dimensional distribution of hydraulic head from self-potential data, given a known distribution of the cross-coupling coefficient and electrical resistivity. The inverse problem is solved by minimizing an objective function, which consists of a data misfit that accounts for measurement error and a model objective function that incorporates a priori information. The algorithm is suitable for saturated flow problems or where the position of the phreatic surface is known.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

Response of the self-potential method to changing seepage conditions in embankment dams

Internal erosion is of great concern to owners and operators of earthfill dams worldwide. The migration of fine-grained soil particles from the dam core in the direction of seepage leads to the development of preferential zones of increased fluid flow, which can compromise the structural stability of the embankment. Standard dam safety monitoring techniques provide sparse sampling of subsurface hydraulic conditions and may not be sufficient to effectively detect the onset of internal erosion. Consequently, there is a clear need for a comprehensive monitoring tool that is sensitive to changing seepage conditions. The self-potential (SP) method is a non-invasive geophysical technique that responds directly to seepage through the phenomenon of streaming potential: the voltage gradient induced by the flow of water through a porous medium. However, current standard methods of SP data interpretation do not provide information about soil properties and seepage flow rates required by geotechnical engineers to assess dam performance. A three-dimensional numerical modelling tool is presented for predicting the SP response to fluid flow based on a comprehensive seepage analysis. Both the hydraulic regime and the resultant electrical potential distribution are calculated based on the distribution of hydraulic and electrical properties within the subsurface. Effective characterization of these parameters is fundamental in achieving an accurate numerical solution. An examination of the influence of internal erosion on hydraulic conductivity, cross-coupling conductivity and electrical conductivity is achieved through theoretical analyses based on published parametric data. The numerical procedure is validated against a theoretical closed-form solution, and is further verified through a comparison with measured values in a controlled physical model of an embankment dam. The capacity for threedimensional analysis and interpretation of the SP response to seepage is illustrated through preliminary models of a zoned embankment dam located in British Columbia.Applied Science, Faculty ofCivil Engineering, Department ofGraduat

Tobacco Outlet Density and Demographics at the Tract Level of Analysis in New Jersey: A Statewide Analysis

Aim: Geographic relationships between tobacco outlet density and demographics were examined at the tract level in New Jersey, a Northeastern US state. Method: Data for 1938 residential census tracts were analyzed. The 2000 TIGER/Line files were used to geocode addresses of licensed tobacco-selling retail outlets. Median income, percent African-American residents, and percent Hispanic residents were based on year 2000 census data. Address matching with ArcGIS® resulted in successful geocoding of 13,984 (93.1%) outlets. Findings: Results showed that outlet density was significantly related with demographics. Tracts with greater density of tobacco outlets tended to have lower median household income and higher percentages of African-American or Hispanic residents. Cluster analysis of tracts resulted in a three-cluster solution, identifying high, medium and low areas of disparity. The high disparity area was characterized by tracts with the highest tobacco outlet density, the highest percentages of African-American and Hispanic residents, the lowest percentage of white residents, and the lowest median income. Further analysis showed that while there were significant associations between tobacco outlet density and all three demographic variables across the state, such associations varied in each of the three clusters. Conclusions: Results may be used to inform strategic planning and policy decisions on a statewide basis

Triathlon training for women breast cancer survivors: feasibility and initial efficacy

Exercise can improve quality of life (QOL) in breast cancer survivors. In contrast to many group or home-based exercise programs, little is known about the effectiveness of goal-oriented recreational activities. PURPOSE: The purpose of this study was to evaluate a clinically overseen team triathlon training program on improving physiological and psychosocial health-related measures in female breast cancer survivors. METHODS: Twenty-three participants (age = 48 (8), BMI = 25 (1), mean (SE)) were recruited from a 14-week sprint triathlon (800-m swim, 20-km bike, 5-km run) team training program for women breast cancer survivors (4 (3) years post-surgery, chemo-, or radiation-therapy). Training included two supervised group and three home-based individual sessions per week. Pre- and post-training outcomes included isokinetic knee extensor strength (60, 180, and 300° s(-1)), 6-min walk test (6MWT), maximal oxygen uptake (VO2 max), QOL (Functional Assessment of Cancer Therapy -Breast (FACT-B)), and barriers to exercise. Outcomes were also obtained 6 months post except for VO2 max. Significance was set at p \u3c 0.05. RESULTS: Data are mean (SD) from 21 complete data sets. Knee extensor peak torque significantly improved only at 300° s(-1) (pre 40.3(8.5) ftlb; post 45.2(8.4); p = 0.001). 6MWT significantly improved (pre 632.8(62.1) m; post 657.4(53.2); p = 0.014) as did VO2 max (pre 31.3(5.8) ml kg(-1) min(-1); post 35.9(5.8); p \u3c 0.001). FACT-B also improved (pre 114(12); post 122(13); p = 0.004), including the FACT-G total score, social well-being, and breast cancer subscales while barriers to exercise decreased (pre 54(12); post 36(9); p \u3c 0.001). Strength, 6MWT, and barriers to exercise remained improved after 6 months. CONCLUSIONS: Team triathlon training in breast cancer survivors can increase aerobic capacity and improve QOL which may contribute to healthier lifestyles in breast cancer survivors