Geotechnical Evaluations of a Tailings Dam for Use by a Molybdenum and Copper Mine Project in Southern Idaho

A proposed mining project in Boise County, Idaho for the extraction of copper, molybdenum, and silver deposits, required investigations into a possible tailings dam construction that will be built using the processed material from the mine. The mine is located southwest of Lowman Idaho, northeast of Pioneerville Idaho, and directly north of Jackson Peak Mountain. The total area for the proposed project is approximately 12 square kilometers and the estimated material to be excavated is about 1.99 billion cubic meters (BCM) (USDA 2013). Typical investigations into the construction of a tailings dam consist of identifying the types of ore contained within the mine, identifying a suitable location for the dam based on topography, and conducting an analysis of the geotechnical aspects of constructing the dam. In this project, construction of the tailings dam will adequately model a cut and fill operation where the excavated waste material will be used to construct the tailings dam. Construction of the tailings dam will happen in stages, with a starter dam followed by successive additions to accommodate the need for reservoir capacity. Several aspects such as excavation depth, the types of excavated soil and rock, the ore processing methods, and mechanical properties of the waste material, have been considered for properly conducting an analysis of the tailings dam. Also, aspects including the slope stability of the tailings dam, seepage velocities through the tailings dam, and slope stability after a seismic event have also be studied. This paper discusses the geotechnical aspects of the tailings dam construction including the stability of the dam under both hydrological and seismic conditions

A Practical Framework to Assess the Sustainability and Resiliency of Civil Infrastructure

Research within civil engineering is focusing on newer ideas and philosophies such as sustainability and resiliency (S&R). This is evident in the development of frameworks for assessing the sustainability or the resiliency of civil infrastructures. Several frameworks have been developed by researchers to quantify the S&R of civil infrastructures. It is evident that the S&R are not mutually exclusive, and it is important to assess these aspects at the same time and that frameworks are able to accommodate simultaneous assessments. While there are other frameworks that follow a unified approach to S&R assessments, they do not account for the risk of the hazard as part of the framework. In the proposed framework, an attempt was made to include the risk of the hazard as part of the assessment to gain a realistic perspective of the hazard impact. This paper presents explicit steps to use the framework, along with an example of using the framework in assessing an earthen dam subjected to two types of hazards, earthquakes and floods. The novel aspects of this framework revolve around the simplicity and flexibility of the framework. Major input parameters are user-defined, which allows for a wide range of variables to be considered when determining the overall quality of the infrastructure

Evaluating the Effectiveness of Soil-Native Bacteria in Precipitating Calcite to Stabilize Expansive Soils

The use of chemical additives to stabilize expansive soils is a common practice. However, the environmental concerns associated with the greenhouse gas generation during the production of these chemicals have launched engineers in search of sustainable stabilization alternatives. Microbial induced calcite precipitation (MICP) is a bio-cementation technique that could be a potential solution to this problem. Typically, MICP is achieved via bio-augmentation; however, bio-stimulation was argued to be a more realistic alternative due to its field implementation potential. Hence, in this research study, two expansive soils with varying plasticity characteristics were examined to understand the potential of MICP in treating expansive soils. These two soils were subjected to MICP treatments using enrichment and cementation solutions. The treatment effectiveness was studied via response measures such as Atterberg limits, unconfined compressive strengths, one-dimensional swell test, and calcium carbonate precipitation. The results indicate that MICP has potential in stabilizing expansive soils and further research is warranted to explore this idea

Evaluating the Applicability of Biostimulated Calcium Carbonate Precipitation to Stabilize Clayey Soils

Clayey soils with medium to high plasticity are prevalent in several parts of the world, causing billions of dollars in damage annually to various civil infrastructures. Several ground-improvement techniques can be employed to counteract this issue. However, these methods are impractical in certain situations and unsustainable in others due to their economic and environmental impacts. Microbial-induced calcite precipitation (MICP) could provide a more sustainable alternative. Researchers have successfully used MICP to alter specific geotechnical properties of sands and silts. This research investigates the applicability of MICP via biostimulation to treat clayey soils with low to high plasticity. The goal is to determine the viability of this technique to alter the engineering behavior of clayey soils, especially given the low permeability of these soils. For this purpose, four soils were selected from four different locations in Idaho and Montana. The soils were selected such that their plasticity varied from low to high to study the effect of plasticity index on the effectiveness of MICP treatments. In addition to the four soils, three additional artificial mixes were studied to study the effect of clay content on MICP effectiveness. Both macroscale and microscale studies were conducted on untreated and biostimulated soils to observe strength gain, swelling reduction, and calcium carbonate precipitation. The results show that MICP via biostimulation would be a promising method to treat problematic clayey soils

Addressing Clay Mineralogy Effects on Performance of Chemically Stabilized Expansive Soils Subjected to Seasonal Wetting and Drying

Premature failures in chemically stabilized expansive soils cause millions of dollars in maintenance and repair costs. One of the reasons for these failures is the inability of existing stabilization design guidelines to consider the complex interactions between clay minerals and the stabilizers. It is vital to understand these complex interactions, as they are responsible for the strength improvement and swell/shrink reduction in these soils, in turn affecting the overall health of the infrastructure. Hence, this research study examined the longevity of chemically stabilized expansive soils subjected to wetting/drying conditions with a major focus on clay mineralogy. Eight different natural soils with varying clay mineralogy were subjected to wetting/drying durability studies after stabilizing with chemical additives including quicklime and cement. Performance indicators such as volumetric strain and Unconfined compressive strength trends were monitored at regular intervals during the wetting/drying process. It was observed that clayey soils dominant in the mineral Montmorillonite were susceptible to premature failures. It was also noted that soils dominant in other clay minerals exhibited early failures at lower additive contents. Also, an attempt was made for the first time to address the field implications of the laboratory studies by developing a correlation that predicts service life in the field based on clay mineralogy and stabilizer dosage

Studying the Relationship Between Indigenous Microbial Communities, Urease Activity, and Calcite Precipitation in Artificial Mixes of Clay and Sand

Microbial-induced calcium carbonate precipitation (MICP) is evolving as a new method of improving the mechanical properties of soil. This environmentally friendly technique is a bio-geo-chemical process where microbes play a key role in increasing soil strength through precipitating calcium carbonate. Past studies at Boise State University have indicated that MICP via bio-stimulation could be a viable alternative for expansive clayey soil treatments. However, these studies raised a new question about the relationship between soil composition, urease activity, and calcite precipitation. To answer this question, batch studies were conducted using autoclaved-sterilized sand mixed with different percentages of non-sterile natural clay and tested for urease activity. Moreover, to investigate the difference in urease activity between sand and clay bacterial communities, experiments were repeated on samples with different amounts of non-sterile sand and autoclaved-sterilized clay. MICP-treated clay/sand mixes were then evaluated for calcite precipitation. Our results showed that soil mixes with higher clay content have more urease activity and higher levels of calcite precipitation for both sand-autoclaved and clay-autoclaved soil mixes. Test results indicate that urease activity could potentially be used as an indicator of MICP performance in different soil compositions

Work in Progress: Integrating Computational Thinking in STEM Education Through a Project-Based Learning Approach

This work in progress describes the design of a project-based, STEM +C (Computing) curriculum for 4th to 6th grade students in an afterschool setting, which is part of a large NSF-funded STEM+C project. The paper reports the preliminary outcome of the implementation of the first two STEM+C projects that focuses on student attitudes toward STEM and the computational thinking revealed during students’ scientific inquiry and problem solving processes

Senior Civil Engineering Students’ Views on Sustainability and Resiliency

In recent years, civil engineering education and workforce development have evolved to include a greater emphasis on sustainability and resiliency. Sustainability balances economic, ecological, and societal needs by being responsive to community impact, human health, and the environment. Resilient infrastructure lasts, retaining functional and structural capacity and supporting interconnected transportation, energy, water, and social systems after a distress event. While many undergraduate civil engineering programs address sustainability, it tends to be limited to individual courses, and resiliency concepts are rarely incorporated. To address these shortcomings, we are incorporating sustainability and resiliency conceptual threads and activities throughout our curriculum, from our first-year engineering course through senior design. To understand the effectiveness of this initiative, at the beginning of this project we conducted interviews with senior civil engineering students to collect baseline data on our current students’ views and understanding of sustainability and responsibility. Thematic analysis of these interviews suggests that there is significant variability in students’ understanding of sustainability, with some students recognizing that sustainability involves tradeoffs between economic, environmental, and societal needs, while others tended to conflate sustainability with environmentalism. While students reported encountering sustainability in a portion of their undergraduate courses, they generally did not learn about how sustainability related to much of their technical coursework such as structures, soils, or transportation. Most current students have little conceptual understanding of resiliency which is not surprising given that it is not addressed in any substantial way in our current curriculum. This provides clear evidence of the need for greater exposure to both sustainability and resiliency and understanding the relationship between these practices as part of the undergraduate civil engineering curriculum. By incorporating sustainability and resiliency throughout the undergraduate civil engineering curriculum, students will be better prepared to address these topics as part of their senior design projects, and in their future careers

Evaluating Shallow Mixing Protocols as Application Methods for Microbial Induced Calcite Precipitation Targeting Expansive Soil Treatment

Expansive soils, also known as swell-shrink soils, undergo substantial volumetric changes due to moisture fluctuations from seasonal variations. These volumetric changes cause millions of dollars in damages annually. Microbial Induced Calcite Precipitation (MICP) is a promising soil improvement technique, which uses urease producing bacteria to precipitate calcium carbonate. In this study, a stabilization alternative for expansive soils was studied using MICP. Specifically, indigenous bacteria were stimulated by mixing enrichment and cementation solutions with expansive natural soils to precipitate calcium carbonate and make soil stronger and less expansive. This study examined three expansive soils with varying plasticity and mineralogical characteristics. Two protocols for shallow mixing were studied. In Protocol-1, soil samples were mixed with enrichment solutions at optimum moisture content and allowed to mellow for 1, 2, 3, and 4 days. In Protocol-2, soil samples were mixed with enrichment solutions at moisture content corresponding to 95% of maximum dry unit weight on the wet-side of a standard Proctor curve. Moisture was allowed to escape from the mix during the mellowing period under both protocols. Following the mellowing periods, the lost moisture is replaced with cementation solution to reach optimum moisture content, and the soil sample was compacted to its maximum dry unit weight. Unconfined compression strength test was used to evaluate the strength improvements due to treatments. The treatment effectiveness was also evaluated with measurements of calcium carbonate precipitation. The results show promise for this method as an alternative to current shallow stabilization methods. An increase in mellowing period for low and medium plastic soils was determined to be beneficial. The current results also showed that the presence of higher amounts of enrichment solution and addition of less cementation solution is not advantageous for this procedure based on the performance of Protocol-2

Closure to the Discussion of “Long-term Performance of a Highway Embankment Build with Lightweight Aggregates”

The authors thank Dr. Diyaljee for his interest on the subject and providing assessments based on the two research articles (Saride et al. 2010 and Puppala et al. 2017). Authors appreciate the comprehensive analysis done in the discussion. Following the comments noted in the discussion, we would like to provide our explanations on the discussion