Patricia M. Gallagher

Influence of colloidal silica grout on liquefaction potential and cyclic undrained behavior of loose sand

Cyclic triaxial tests were performed to investigate the influence of colloidal silica grout on the deformation properties of saturated loose sand. Distinctly different deformation properties were observed between grouted and ungrouted samples. Untreated samples developed very little axial strain prior to the onset of liquefaction. However, once liquefaction was triggered, large strains occurred rapidly and the samples collapsed within a few additional loading cycles. In contrast, grouted sand samples experienced very little strain during cyclic loading. Additionally, the strain accumulated uniformly throughout loading rather than rapidly prior to collapse and the samples never collapsed. Cyclic triaxial tests were done on samples stabilized with colloidal silica at concentrations of 5, 10, 15, and 20%. In general, samples stabilized with higher concentrations of colloidal silica experienced very little strain during cyclic loading. Sands stabilized with lower concentrations tolerated cyclic loading well, but experienced slightly more strain. Thus, treatment with colloidal silica grout significantly increased the deformation resistance of loose sand to cyclic loading.

Colloidal silica transport through liquefiable porous media.

Mitigation of liquefaction potential in loose granular soil can theoretically be achieved through permeation and subsequent gelation of dilute colloidal silica stabilizer. However, practical application of this technique requires efficient and adequate delivery of the stabilizer to the liquefiable soil prior to gelation. The purpose of this research was to evaluate colloidal silica transport mechanisms and to determine if an adequate concentration can be delivered to a soil column prior to gelation. The laboratory work consisted of grouting 15 short (0.9 m) columns tests packed with Nevada No. 120, Ottawa 20/30, or graded silty sand to identify the variables that influence stabilizer transport through porous media. It was found that colloidal silica can be successfully delivered through 0.9-m columns packed with loose sand efficiently and in an adequate concentration to mitigate the liquefaction potential. Transport occurs primarily by advection with limited hydrodynamic dispersion, so Darcys law can be used to predict flow. The Kozeny-Carmen equation can be used to include the effect of increasing viscosity on transport by incorporating the power law mixing rule of Todd. The primary variables influencing stabilizer transport were found to be the viscosity of the colloidal silica stabilizer, the hydraulic gradient, and the hydraulic conductivity of the liquefiable soil.

Centrifuge Modeling for Liquefaction Mitigation Using Colloidal Silica Stabilizer

AbstractThis paper reports the results of two centrifuge tests that were conducted to evaluate the effectiveness of colloidal silica for liquefaction mitigation. Colloidal silica has been selected as a stabilizer material in soils because of its permanence and ability to increase the strength of soils over time. The centrifuge model geometry was selected to study the effects of lateral spreading in a 4.8-m-thick liquefiable layer overlain by a silty clay sloping toward a central channel. The centrifuge test evaluates the response of untreated loose sands versus loose sands treated with 9, 5, and 4% colloidal silica concentrations (by weight). The models were subjected to a series of peak horizontal base accelerations ranging from 0.007 up to 1.3g (prototype) with a testing centrifugal acceleration of 15g. The results show a reduction in both lateral spreading and settlement in colloidal silica–treated sands versus untreated sands. The shear modulus at low strains was determined from shear wave velocity me...

Physical and Numerical Model of Colloidal Silica Injection for Passive Site Stabilization

Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. This technology is based on the concept of slow injection of stabilizing materials at the edge of a site and delivery of the stabilizer to the target location by using the natural or augmented groundwater flow. In this research, a box model was used to investigate the ability to uniformly deliver colloidal silica stabilizer to loose sands using low-head injection and extraction wells. Five injection wells and two extraction wells were used to deliver stabilizer in a generally uniform pattern to the loose sand formation. Numerical modeling was used to identify the key parameters affecting stabilizer migration and to determine their effective values for the box experiment. In our modeling approach, the stabilizer is treated as a miscible fluid, the viscosity of which is a function of time and the concentration of stabilizer in the pore water. Inverse modeling techniques are employed to reproduce data from the laboratory experiment for the determination of soil and stabilizer properties. While the details of the stabilizer distribution were difficult to reproduce with the simplified conceptual model we used, the overall system behavior was well captured, providing confidence that numerical simulation is a useful tool for designing centrifuge model tests, pilot tests, and eventually field stabilizer-injection projects.

Estimating Materials Stocked by Land‐Use Type in Historic Urban Buildings Using Spatio‐Temporal Analytical Tools

The construction industry is an important contributor to urban economic development and consumes large volumes of building material that are stocked in cities over long periods. Those stocked spaces store valuable materials that may be available for recovery in the future. Thus quantifying the urban building stock is important for managing construction materials across the building life cycle. This article develops a new approach to urban building material stock analysis (MSA) using land-use heuristics. Our objective is to characterize buildings to understand materials stocked in place by: (1) developing, validating, and testing a new method for characterizing building stock by land-use type and (2) quantifying building stock and determining material fractions. We conduct a spatial MSA to quantify materials within a 2.6-square-kilometer section of Philadelphia from 2004 to 2012. Data were collected for buildings classified by land-use type from many sources to create maps of material stock and spatial material intensity. In the spatial MSA, the land-use type that returned the largest footprint (by percentage) and greatest (number) of buildings were civic/institutional (42%; 147) and residential (23%; 275), respectively. The model was validated for total floor space and the absolute overall error (n = 46; 20%) in 2004 and (n = 47; 24%) in 2012. Typically, commercial and residential land-use types returned the lowest overall error and weighted error. We present a promising alternative method for characterizing buildings in urban MSA that leverages multiple tools (geographical information systems [GIS], design codes, and building models) and test the method in historic Philadelphia. [ABSTRACT FROM AUTHOR]

Environmental Life Cycle Performance of Recycled Materials for Sustainable Slope Engineering

We evaluate the environmental life cycle performance of the use of recycled materials for sustainable slope engineering. Crushed glass dredged material (CG-DM) blends, (in proportions of 20/80, 50/50, and 80/20, with crushed glass reported first) for embankment fill material were compared to primary fill materials for six life cycle impact assessment (LCIA) metrics: cumulative energy demand, 100-year global warming potential (GWP), and air quality indicators nitrogen oxides (NOx), sulfur dioxides (SOx), carbon dioxide (CO 2 ) and particulate matter (PM). Results suggest that life cycle energy, GWP, CO 2 , and SOx decline with use of recycled materials for embankment fills; however, due to increased processing at the site for the CG-DM blends, particulate matter surpasses primary-fill embankments studied herein. With respect to NOx emissions, the primary fill embankment and the 80/20 CG-DM blend have about the same amount, followed by the 50/50 blend and the 20/80 blend, in descending value, respectively. Results from this work suggest that recycled content in fill materials is beneficial to reducing energy resource consumption, GWP, CO 2 , SOx and NOx (except for the 80/20 blend); however, there may be increased health risks due to increased emissions of criteria pollutant particulate matter. Overall, this study demonstrates the importance of quantifying the life cycle benefits of recycled and marginal materials as an important step towards understanding the environmental tradeoffs of their increased use in construction.

Dynamic Response of Compacted CG, DM, and CG-DM Blends

The cyclic behavior of 9.5 mm (3/8 in.) minus curbside-collected crushed glass (CG) blended with dredged material (DM), classified as an organic silt by the Unified Soil Classification System, was evaluated using a cyclic triaxial testing program. Tests were performed on 100% CG and 100% DM specimens, and 20/80, 40/60, 60/40, and 80/20 CG-DM blends (dry CG content is reported first). The specimens were compacted to a dry unit weight equivalent to 95% of the maximum dry density based on ASTM D1557. For each material, a minimum of three specimens was tested at cyclic stress ratios of 0.20, 0.35, and 0.45. The DM used in this study exhibited significant plasticity, which would be expected to display cyclic softening behavior according to liquefaction susceptibility criteria proposed by Boulanger and Idriss in 2006. However, the high density of the material resulted in transitional behavior between cyclic mobility and cyclic softening. These findings suggest that as long as the CG, DM, and CG-DM blends are compacted, they should not be susceptible to strength loss or large strain under cyclic loading.

Carbon Footprint of Tuttle Creek Dam Seismic Retrofit

Tuttle Creek Dam in Manhattan, Kansas was found to be seismically deficient. Cement-bentonite slurry walls were used to remediate the dam. We use the EFFC DFI Carbon Calculator to calculate the carbon footprint of the cement- bentonite slurry walls, as well as the carbon footprint of an alternative remediation option, stone columns. The cement-bentonite slurry walls resulted in a GWP 100 of 71,000 tonnes CO2 equivalent, while the stone columns resulted in a GWP 100 of 3,900 tonnes CO2 equivalent, a significant difference even when considering the uncertainties in life cycle modeling. The Carbon Calculator is a simple tool for quantifying the carbon footprint of different geotechnical engineering techniques.

Construction waste management decision making process: identification, framework and detailed urban C&D waste profile analysis

Construction and demolition (C&D) activities require large inputs of resources and also create large outputs of waste while generating significant revenue and employment within the urban economy. As an intricate and multi-domain segment of building end-of-life (EOL) management, construction managers and other stakeholders within the waste management industry greatly influence decisions on the fate of C&D waste materials - whether they are landfilled, reused, or recycled. C&D waste is not federally regulated in the United States and the responsibility for reporting and tracking waste lies within the state and/or local government jurisdiction. Since reporting is not regulated, there are potential discrepancies in reporting of the quantities of C&D waste that are generated, recycled and disposed in landfills, and in the reporting frequency. We conduct a C&D waste audit through use of a multi-year data archive comprised of completed C&D projects in the greater Philadelphia area. This audit establishes a discrete, private industry data set that is normally confidential and unpublished from a local C&D waste reclamation center. The research may enable the early identification of sustainable practices for the owners, reducing demolition and hauling costs, rather than leaving secondary scrap markets to define which materials they will accept. We posit that higher recycling rates will be found within the city of Philadelphia relative to suburban recycling rates in greater Philadelphia and neighboring states. These rates will be higher based on established local infrastructure and the emergence of recipient markets and partnerships with construction industry material manufacturers. This collection of data may inform the decision makers, advance recycling within the construction industry, and minimize impact on local landfills. Recycling activities are occurring in the Philadelphia region which may point toward market maturity and established infrastructure. The overall center diversion rates are consistent. The collected data could represent maturity over time and smaller secondary markets may continue to develop and may be supported by manufacturer recycling partnerships or local markets. Case study matches overall center performance which is on par with rates from developed countries.