Search

This article describes the approach, methods, and findings of a quantitative analysis of the seismic vulnerability in low-to-moderate seismic hazard regions of the Central and Eastern United States for system-wide assessment of typical multiple span bridges built in the 1950s through the 1960s. There is no national database on the status of seismic vulnerability of bridges, and thus no means to estimate the system-wide damage and retrofit costs for bridges. The study involved 380 nonlinear analyses using actual time-history records matched to four representative low-to-medium hazard target spectra corresponding with peak ground accelerations from approximately 0.06 to 0.3 g. Ground motions were obtained from soft and stiff site seismic classification locations and applied to models of four typical multiple-girder with concrete bent bridges. Multiple-girder bridges are the largest single category, comprising 55% of all multiple span bridges in the United States. Aging and deterioration effects were accounted for using reduced cross-sections representing fully spalled conditions and compared with pristine condition results. The research results indicate that there is an overall low likelihood of significant seismic damage to these typical bridges in such regions, with the caveat that certain bridge features such as more extensive deterioration, large skews, and varied bent heights require bridge-specific analysis. The analysis also excludes potential damage resulting from liquefaction, flow-spreading, or abutment slumping due to weak foundation or abutment soils.

Stress–time avalanches of recycled polyethylene terephthalate (PET) fiber–reinforced concrete during flexure were investigated based on high temporal resolution signals in this study. Stres...

Engineering and engineers are considered central to maintaining global competitiveness and the workforce needs of any nation. Media shapes public opinion, and the image of a profession can ...

Excessive streambank erosion is a significant source of fine sediments and associated nutrients in many river systems as well as poses risk to infrastructure. Geomorphic change detection using high-resolution topographic data is a useful method for monitoring the extent of bank erosion along river corridors. Recent advances in an unmanned aircraft system (UAS) and structure from motion (SfM) photogrammetry techniques allow acquisition of high-resolution topographic data, which are the methods used in this study. To evaluate the effectiveness of UAS-based photogrammetry for monitoring bank erosion, a fixed-wing UAS was deployed to survey 20 km of river corridors in central Vermont, in the northeastern United States multiple times over a two-year period. Digital elevation models (DEMs) and DEMs of difference allowed quantification of volumetric changes along selected portions of the survey area where notable erosion occurred. Results showed that UAS was capable of collecting high-quality topographic data at fine resolutions even along vegetated river corridors provided that the surveys were conducted in early spring, after snowmelt but prior to summer vegetation growth. Longer term estimates of streambank movements using the UAS showed good comparison to previously collected airborne lidar surveys and allowed reliable quantification of significant geomorphic changes along rivers.

Analyses of landslides, slopes and embankments often require reliable drained residual shear strength estimates for cohesive deposits involving pre-existing shear surfaces. Laboratory tests to measure residual shear strength can be costly and time consuming. Therefore, empirical correlations based on more readily available index properties such as liquid limit and clay-size fraction appear as an attractive alternative in practice. This paper presents residual strength and index properties for 25 natural samples, predominantly claystone and siltstone, collected from a single geologic setting over an approximately 0·25 km2 site. The data show substantial variability in residual strength against any single index parameter considered in a site-specific correlation. Comparisons of these data, along with three additional data sets, generally indicated notable variability among data sets and relatively poor fit to published empirical correlations. Empirical correlations for residual strength may be useful in approximating the expected range of residual strength. However, given the significant variability in the data, both within and between data sets, empirical correlations should not entirely replace carefully performed site-specific laboratory tests measuring residual strength, when reliable values are required.

The motivation for this study is the damage caused to over 300 long-span bridges in Vermont in 2011 by Tropical Storm Irene, which is part of the Hurricane Irene system. This study of the ...

In this work, we studied stress variations occurring during flexure of early-age steel fiber reinforced concrete beams. By preparing beams with different fiber volume ratios, four-point bending tests were performed to evaluate the specimens at different loading rates. A new experimental system was created to collect the stress-time curves collected at 100 kHz sampling rate so that temporal profiles of stress drops were analyzed in high resolution. Meanwhile, stress drops were modeled as avalanches due to interactions between steel fibers and cement matrices during flexure. Good agreement on avalanche statistics and dynamics was obtained between measurements and the predicted power law exponents and scaling functions from the mean field model. The observations of different avalanche types also illustrated the essential failure features evolved during flexure of steel fiber reinforced beams.

The semi-empirical simplified procedure for liquefaction triggering of level-ground is largely based on correlating post-earthquake field observations such as presence/absence of sand boils to field measurements such as penetration resistance or shear wave velocity (Vs). These correlations could be interpreted in such a way that for a given penetration resistance or Vs, the cyclic resistance ratio (CRR) increases as fines content increases. However, some studies have indicated that this interpretation may not be correct, particularly for soils containing non-plastic fines. An experimental research program involving cyclic triaxial tests was undertaken to investigate cyclic resistance of F-75 sand with varying amounts of non-plastic fines (Sil-Co-Sil 125). Bender elements were incorporated in the triaxial cell to facilitate Vs measurements. Other similar data sets found in the literature were used to supplement the laboratory data and evaluate the overall trends implied by the Vs-based field CRR curves. The comparison suggests that the laboratory data are generally consistent with the trends embedded in the field curves, with boundary curves shifting slightly to the left with increasing fines content.

Applications, such as the long term in-situ monitoring of geotechnical structures and of agricultural soils, motivate the use of wireless sensors that are of a passive design. However, the effectiveness of such passive devices will be dependent on the power received via a forward interrogation link and the power returned to a data collector via a reverse link. For these applications, link losses will be determined by the transmission medium, i.e., soil. This paper presents a pathloss study of microwave attenuation versus soil type and moisture. Then, we present results for a passive frequency doubling reflectenna (FDR), operating at 1.3 GHz for the forward link and 2.6 GHz for the reverse, buried at various depths in agricultural soil of different moistures. Results indicate that a FDR-based wireless sensors operating in this frequency range could be effectively embedded to a depth of 0.5 m or more, significantly deeper than reported for other passive technologies.

Given the variable biogeochemical, physical, and hydrological processes driving fluvial sediment and nutrient export, the water science and management communities need data-driven methods to identify regions prone to production and transport under variable hydrometeorological conditions. We use Bayesian analysis to segment concentration-discharge linear regression models for total suspended solids (TSS) and particulate and dissolved phosphorus (PP, DP) using 22 years of monitoring data from 18 Lake Champlain watersheds. Bayesian inference was leveraged to estimate segmented regression model parameters and identify threshold position. The identified threshold positions demonstrated a considerable range below and above the median discharge—which has been used previously as the default breakpoint in segmented regression models to discern differences between pre and post-threshold export regimes. We then applied a Self-Organizing Map (SOM), which partitioned the watersheds into clusters of TSS, PP, and DP export regimes using watershed characteristics, as well as Bayesian regression intercepts and slopes. A SOM defined two clusters of high-flux basins, one where PP flux was predominantly episodic and hydrologically driven; and another in which the sediment and nutrient sourcing and mobilization were more bimodal, resulting from both hydrologic processes at post-threshold discharges and reactive processes (e.g., nutrient cycling or lateral/vertical exchanges of fine sediment) at prethreshold discharges. A separate DP SOM defined two high-flux clusters exhibiting a bimodal concentration-discharge response, but driven by differing land use. Our novel framework shows promise as a tool with broad management application that provides insights into landscape drivers of riverine solute and sediment export.

Given the limited resources available for managing erosion hazards and addressing water quality impairment along rivers, stakeholders engaged in water resource management would benefit from tools to identify those river reaches most prone to adjustment and which disproportionately load sediment to receiving waters. The extent and rate of vertical and lateral channel adjustments in response to natural and human disturbances vary considerably across space and time; and this complexity and nonlinearity introduce challenges for classification or modeling of river reaches using conventional statistical techniques. The Self-Organizing Map (SOM) is a data-driven computational tool with advantages for clustering or classifying multivariate observations and for exploratory data analysis and visualization of complex, nonlinear systems. We applied a SOM to cluster multivariate stream geomorphic assessment data into reach-scale sediment process domains for 193 river reaches in glacially-conditioned catchments of northeastern US using field- and GIS-derived hydraulic and geomorphic parameters. The reaches comprised a range of channel types from confined to unconfined, steep- to shallow-gradient, mid-to-high order, and bedrock to alluvial channels. Fifteen variables were identified that meaningfully separated reaches into seven sediment regimes, following a two-stage application of the SOM. A coarse-tune SOM identified sediment regime classes at the supply-limited and transport-limited extremes of a continuum, including bedrock channels and confined, steep-gradient reaches as well as braided, depositional channels at alluvial fan or delta settings. A second-stage, fine-tune SOM nuanced differences in sediment production and transport for unconfined reaches with varying degrees of floodplain disconnection resulting from natural or human stressors. This classification framework is transferable to other hydroclimatic regions, with consideration of additional or alternate independent variables unique to those regions, and can provide valuable insights for river management to promote flood resiliency, restore water quality and improve instream and riparian habitats.

This paper examines pressure-sinkage and shearing behavior via bevameter testing of a light-weight, granular simulant called Fillite in support of laboratory modeling of rover mobility in high-sinkage, high-slip environments typically found on Mars, the Moon, and other planetary bodies. Normal bevameter test results helped to determine parameters for the Bekker model, the New Model of Mobility (N2M) sinkage model, and the Bekker-Wong model. A case study used the Bekker-Wong model parameters to predict the possible sinkage of 84% into Fillite of a wheel on the Mars Spirit rover, a value within the observed sinkage of 50–90% of the wheel diameter of the Spirit rover on Mars. Shear bevameter testing of Fillite provided a second set of parameters to assess shear behavior, this time simulating the stresses and shear deformations imparted by rotating wheels. The results compared well to the estimated shear stresses and deformations of Martian soil caused by the wheels of the Spirit rover. When compared to other simulants (e.g. GRC-1), the results confirm that Fillite is possibly more suitable for high-sinkage and high-slip rover studies than other typical simulants derived from natural terrestrial soils and rocks.

The leading cause of bridge failure has often been identified as bridge scour, which is generally defined as the erosion or removal of streambed and/or bank material around bridge foundations due to flowing water. These scour critical bridges are particularly vulnerable during extreme flood events, and pose a major risk to human life, transportation infrastructure, and economic sustainability. Retrofitting the thousands of undersized and scour critical bridges to more rigorous standards is prohibitively expensive requiring effective yet economical countermeasures. This research tested the efficacy of using approach embankments as intentional sacrificial “fuses” to protect the bridge integrity and minimize damage during large flow events by allowing the streams to access their natural floodplain and reduce channel velocities. This countermeasure concept was evaluated using the Hydrologic Engineering Center’s River Analysis System models. Steady flow models were developed for three specific bridges on two river reaches. Streamflow return period estimators for both river reaches were developed using Bayesian analysis and available United States Geological Survey stream gauge data to evaluate sacrificial embankments under non-stationary climatic conditions. The use of sacrificial embankments was determined to be a cost-effective scour mitigation strategy for bridges with suboptimal hydraulic capacity and unknown or shallow foundations. Additional benefits of sacrificial embankments include reductions in upstream flood stage and velocity.

Structural alterations to bridges may result in unintended consequences up- or downstream, such as changes in discharge, velocity, stream power, and water levels. This work presents a framework and methodology to analyze interconnected bridge-stream interactions under flood conditions. Such analysis may help prioritize limited resources available for bridge and river rehabilitations, facilitate holistic design of bridges and better-informed cost/benefit analyses, and address stakeholder concerns raised in response to planned bridge and infrastructure alterations. A two-dimensional unsteady HEC-RAS hydraulic model of the Otter Creek between Rutland and Middlebury, VT is used to simulate the impact of individual structures on the bridge-stream network, as well as potential sensitivity to those impacts, during extreme flood events. The presence of a bridge and approach roadway may induce measurable changes in peak discharge throughout the entire 46 miles of modeled river. These may be by as much as 10% at adjacent structures, down to 1% at structures as far as six miles upstream and nine miles downstream. Depending on their characteristics, bridges and roadways may either attenuate or amplify peak flood flows up- and downstream, or have little to no effect at all, suggesting that there is no easily predictable impact, and that hydraulic modeling is necessary for such analysis on rivers. Alterations to structures that develop substantial backwaters may result in the most dramatic impacts to the network, which can be both positive and negative. Affected bridges may or may not be sensitive to these changes in discharge; structures that do not experience relief (e.g., roadway overtopping) may be most sensitive to any distant perturbations.

International audience; Turtle shells comprising of cortical and trabecular bones exhibit intriguing mechanical properties. In this work, compression tests were performed using specimens made from the carapace of Kinixys erosa turtle. A combination of imaging techniques and mechanical testing were employed to examine the responses of hierarchical microstructures of turtle shell under compression. Finite element models produced from microCT-scanned microstructures and analytical foam structure models were then used to elucidate local responses of trabecular bones deformed under compression. The results reveal the contributions from micro-strut bending and stress concentrations to the fractural mechanisms of trabecular bone structures. The porous structures of turtle shells could be an excellent prototype for the bioinspired design of deformation-resistant structures.Statement of SignificanceIn this study, a combination of analytical, computational models and experiments is used to study the underlying mechanisms that contribute to the compressive deformation of a Kinixys erosa turtle shell between the nano-, micro- and macro-scales. The proposed work shows that the turtle shell structures can be analyzed as sandwich structures that have the capacity to concentrate deformation and stresses within the trabecular bones, which enables significant energy absorption during compressive deformation. Then, the trends in the deformation characteristics and the strengths of the trabecular bone segments are well predicted by the four-strut model, which captures the effects of variations in strut length, thickness and orientation that are related to microstructural uncertainties of the turtle shells. The above results also suggest that the model may be used to guide the bioinspired design of sandwich porous structures that mimic the properties of the cortical and trabecular bone segments of turtle shells under a range of loading conditions.

In this work, we studied stress variations of loading histories on polypropylene fiber reinforced concrete beams during flexure. A new experimental system was created to collect the stress-time curves at 100 kHz sampling rate to reveal temporal profiles of stress drops in high resolution. Concrete beams prepared at the early age of seven days with different fiber volume fractions were loaded at various rates during four-point bending tests. Stress drops induced by interactions between polypropylene fibers and cementitious matrices or matrix cracking were modeled as avalanches along the time history. We used the mean field model to predict statistics and dynamics of avalanches occurred inside polypropylene fiber reinforced concrete beams during flexure. Good agreement was obtained between measurements and predicted power law exponents and scaling functions from the mean field model. Two types of avalanches were observed for polypropylene fiber reinforced beams during flexure, i.e., small avalanches collapsed onto the scaling regime and large avalanches beyond the regime. Maximum stress drop rates of small avalanches were on the order of kPa/s, whereas maximum stress drop rates of large avalanches could reach the order of MPa/s. Observations of different avalanches revealed insights into the essential failure evolved during flexure concrete beams, i.e., small avalanches with limited plastic deformation and large avalanches with extended incubation periods. Findings from this study could help measure the evolved damage of concrete structural members under service loads, which provide valuable hints to improve the durability of reinforced concrete structures.

In this work, stress variations during flexure of early age basalt fiber reinforced concrete beams were studied using high resolution temporal measurements. An experimental system was created to collect stress-time curves at 100 kHz sampling rate so that temporal profiles of stress variations were analyzed in detail. Stress drops were modeled as avalanches resulting from interactions between basalt fibers and cementitious matrices. Four-point bending tests at different loading rates were conducted to investigate avalanches during flexure of beams with different fiber volume fractions. Good agreement was obtained between measured avalanche statistics or dynamics and predictions from the mean field model. Different types of avalanches were detected during the flexure of basal fiber reinforced concrete beams, including avalanches with limited size and durations collapsed onto the scaling regime in the logarithmic scale, avalanches with an incubation period before stress drops beyond the scaling regime and giant avalanches occurred at the fracture of bottom concrete. Observations of different avalanche types disclosed the critical failure evolution during flexure of basalt fiber reinforced beams, which could lead to the creation of durable ecofriendly fiber-reinforced concrete structures.

Characterization of surface gas permeability measurements on a variety of natural and engineered building materials using two relatively new, non-destructive surface permeameters is presented. Surface gas permeability measurements were consistent for both laboratory and field applications and correlated well with bulk gas permeability measurements. This research indicates that surface permeability measurements could provide reliable estimates of bulk gas permeability; and due to the non-destructive nature and relative sampling ease of both surface gas permeability tools, it is possible to quantify the range of the spatial autocorrelation, heterogeneity, and anisotropy in porous building materials and their degree of degradation from weathering.

Physical modeling experiments related to lunar in situ resource utilization activities use suitable soil simulants such as GRC-3. Only the index properties (e.g., specific gravity, particle...

In the past twenty years or so, numerous investigations on the centrifuge have been carried out to reproduce seismically induced liquefaction phenomena and to study their effects on the stability of such earth structures as homogeneous or stratified level ground, slopes, embankments, water front structures, sheet pile walls, buried structures, etc. In this paper, a review of some of these investigations is presented. A good centrifuge experiment is expected to produce repeatable, quantitative data. In seismic centrifuge experiments, close attention is required on such issues as generation of earthquake motions, simulation of boundary conditions, and scale effects such as particle size and the conflict in the time scaling for the coupled dynamic pore pressure generation and diffusive pore pressure dissipation phenomena. These and some other issues are also discussed in this paper, in the context of their effects on the study of liquefaction.

Nacre, a composite made from biogenic aragonite and proteins, exhibits excellent strength and toughness. Here, we show that nacreous sections can exhibit complete brittle fracture along the tablet interfaces at the proportional limit under pure shear stresses of torsion. We quantitatively separate the initial tablet sliding primarily resisted by nanoscale aragonite pillars from the following sliding resisted by various microscale toughening mechanisms. We postulate that the ductility of nacre can be limited by eliminating tablet interactions during crack propagations. Our findings should help pursuing further insights of layered materials by using torsion.

On August 28, 2011, Tropical Storm Irene hit the state of Vermont with a severity that deposited 100–200 mm (4–8 in.) of rain across the state and resulted in damage or failure of over 300 ...

For cast-in-place abutments and retaining walls, structural backfill is preferred to be free-draining, which generally implies less than 5% fines content. This fines content is expected to eliminate the need to design for hydrostatic pressures. The availability of high-quality structural backfill with naturally low fines content is declining. This situation warrants an evaluation of whether granular backfill materials with greater than 5% fines content could be successfully used in practice. Flexible wall, hydraulic conductivity tests on a granular structural backfill with 0%, 5%, 10%, 15%, 20%, and 25% nonplastic fines content were conducted at 41, 83, and 124 kPa (6, 12, and 18 psi) confining pressures followed by consolidated drained triaxial compression tests for obtaining associated drained shear strength parameters of these gradations. The 15.2-cm (6-in.) diameter specimens were prepared at optimum moisture content and 95% of maximum standard Proctor density. To enable a comparison with respect to modified Proctor maximum densities, modified Proctor tests were also performed for all base soil–fines content mixtures. The experimental results were compared with relevant studies found in the literature. This research indicates that a nonplastic fines content up to 10% may be justified in structural backfill specifications for retaining walls and abutments.

Knowledge of microscopic geomorphic structures is critical to understanding transport processes in porous building materials. X-ray scans were obtained of a variety of commonly used porous building materials to both qualitatively and quantitatively evaluate their pore structures. The specimens included natural materials (two sandstones and a limestone) and engineered materials (three types of concretes and a brick). Scanned images were processed to reconstruct the geomorphic structures of these materials. Random walk analyses were performed on the reconstructed pore structures to estimate macroscopic transport properties (including tortuosity, specific surface, and permeability). The effective porosity and permeability of these materials were also experimentally determined and compared to computed values. Calibration of the threshold pixel value used in the postprocessing of X-ray images against measured effective porosity appears to be a more appropriate method of selecting this value than the typical approach, which employs selection based solely on observed histograms. The resulting permeabilities computed by using a calibrated threshold pixel value compare better with the measured permeabilities. This study also demonstrates that the relatively homogeneous and heterogeneous pore structures associated with the natural and engineered building materials under investigation can be captured by X-ray tomography.

In a typical seismic dam safety evaluation, standard penetration, cone penetration, Becker penetration, or shear wave velocity ( V s ) tests are often first conducted near the toe of an earth dam to infer if any liquefiable soil exists in the foundation of the dam footprint. In current practice, a level-ground condition is commonly assumed when normalizing penetration resistance and V s , and may be assumed (particularly in preliminary assessments) in applying the cyclic stress method (with or without the K α correction) to evaluate liquefaction. However, the presence of an earth dam, or any other large embankment or structure, significantly alters the normal and shear stresses in the foundation. This paper identifies and quantifies potential errors in ignoring altered stresses near heavy structures, and presents a methodology to incorporate these effects within the framework of the simplified procedure. Specifically, the effects of these altered stresses (in comparison to the level-ground assumption with and without K α correction) on the: (1) normalization of field measurements such as penetration resistance and V s ; (2) cyclic stress ratio ( CSR ); (3) cyclic resistance ratio ( CRR ); and (4) factor of safety against liquefaction triggering ( FS liq ), are evaluated by considering static and dynamic analyses of a generic earthen embankment (60 m high) resting on a saturated, cohesionless foundation (30 m deep). Our analyses indicated that ignoring the presence of induced static shear stresses can result in potentially unconservative errors in overburden correction factors of 30% to 60% at shallow depth (although this error is greatly muted at depths exceeding about 15 m), while errors in CSR potentially can range from about 20% too conservative to 40% unconservative. Potential errors in CRR can approach 50% unconservative at shallow depths, but again, this error is muted at depths exceeding about 15 m. Combining these factors, potentially unconservative errors in computing FS liq could exceed 100% at shallow depths (less than 15 m to 20 m) while at greater depth (exceeding 20 m) errors approach 20% on the conservative side.

Earthbound testing of the mobility of lunar, Martian, and other extraterrestrial rovers benefits from the use of suitable soil simulants. To this end, a granular material called Fillite was selected as a simulant for modeling high-sinkage, high-slip situations that could be encountered by rovers, such as the one encountered by the Spirit rover on Mars. Fillite consists of alumino-silicate hollow microspheres harvested from the pulverized fuel ash of coal-fired power plants. It is available in large quantities at a reasonable cost and it is chemically inert. The focus of this paper is to summarize geotechnical characterization of Fillite, specifically the mechanical properties such as shear strength parameters, elastic modulus, Poisson’s ratio, and small-strain shear modulus. These measured properties are expected to enable analysis of rover mobility tests conducted in Fillite. The properties of Fillite are compared with the known and estimated properties of Martian and lunar regoliths as well as o...

Stakeholders are often required to make judgments and decisions about the tradeoffs between multiple competing objectives inherent in any engineering design. Design optimization can provide decision support for such situations, but often prescribes that only a single design solution be selected for a given set of preferences. The purpose of this study is to frame an objective function for assessing how the sensitivity of one objective relative to another varies in space and to demonstrate the method using a real site, with spatially-dependent floodplain access and bridge scour as the objective tradeoffs. Bridge scour is a widespread and expensive infrastructure problem, and the proposed methodology provides the ability to assess how the sensitivity of bridge scour to floodplain access varies at different locations in a river reach. The site chosen for demonstration purposes was the Lewis Creek in the vicinity of the Quinlan Covered Bridge in Charlotte, VT. Differential evolution (DE) was wrapped around an existing HEC-RAS model. The decision variables corresponded to floodplain access at locations up and downstream of the bridge; the objective function was constructed so that optimal solutions may be interpreted as relative salience of floodplain access to bridge scour. Multiple weightings of the objectives were used to verify that the rank-order of locations was robust. The optimal DE solutions for all weightings resulted in the same sensitivity ranking of locations, providing evidence that the analysis is not dependent on a particular choice of stakeholder objective weightings. For systems with spatially dependent variables that impact a constraint or objective of interest to stakeholders, a tool for identifying locations where that variable has a particularly strong or weak impact (e.g. where floodplain access is more or less important for bridge scour) has obvious advantages. This study demonstrates a method for conducting such a sensitivity analysis using a numerical optimization scheme. On the real test site, the sensitivity ranking was consistent across multiple stakeholder weightings, providing evidence that the technique is robust, and one that can be used at multiple stages of design. This work demonstrates the utility of a novel interpretation of optimization results in which locations are ranked according to the relative sensitivity of competing objectives.

Seismic design of geotechnical structures often requires estimates of how shearing resistance of liquefiable soil is reduced to its minimum value (residual strength, sr) as pore pressures build up and is subsequently regained as pore pressures dissipate. It was envisioned that the shear strength of liquefying sands could be measured in-flight in a seismic geotechnical centrifuge model by pulling thin coupons (plates) horizontally through the sand models before, during, and after shaking to simulate the large strains and strain rates associated with liquefaction flow failures. This paper presents the results of seismic centrifuge tests that were used to make such measurements. Companion ring shear (RS) tests also are described. Although centrifuge and RS residual strengths were generally similar and increased with relative density, the centrifuge sr and sr/σvo′ (sr divided by preshaking effective vertical stress) increased significantly with small changes in relative density, while the RS test sr a...

Pervious concrete pavement (PCP) is used because of its unique properties that allow water to infiltrate into the surface. The objectives of the study reported in this paper were to observe the performance of PCP in the field, determine the effectiveness of cleaning methods to restore infiltration rates, and compare field observations with laboratory results when possible. Two PCP sites in Vermont were monitored over a year through the measurement of infiltration rates at several locations. Facility-wide cleaning operations, such as street sweeping and vacuum-truck cleaning, were tested for their capability to restore infiltration rates. Spot-cleaning methods, such as hand vacuuming, pressure washing, and a combination of the two, were also tested. Infiltration rates decreased gradually during the monitoring period, with average reductions of 59% at the first facility and 26% at the second. Street sweeping and vacuum-truck cleaning restored infiltration rates by 21% and 30%, respectively, but could not restore severely clogged areas. Spot-cleaning methods increased infiltration rates by 85% after pressure washing, 10% after vacuuming, and 100% after pressure washing followed by vacuuming. Vacuum-truck cleaning was recommended. Either method, however, should be used for maintenance operations and should be started after construction. Spot-cleaning methods, with the exception of vacuuming, restored infiltration rates of severely clogged areas and were recommended for localized cleaning. Long-term monitoring compared reasonably well with that of earlier studies, whereas the results associated with cleaning were substantially lower than those found in the literature.

Many communities and nonprofit organizations in the United States grapple with the reuse of publicly owned buildings and infrastructure from the 19th and early 20th centuries that have become landmarks in their communities. Often these communities or organizations do not have adequate resources (technical expertise, funding) for even preliminary engineering services. Engineering programs at universities can assist these communities by providing engineering expertise through service-learning (SL) projects, at the same time providing engineering students exposure to the field of heritage preservation and to important preservation engineering issues. This article presents SL case studies at the University of Vermont (UVM) as examples of this type of collaboration. Benefits, challenges, and SL assessment results are included. For the past 4 years, as part of a National Science Foundation Department Level Reform (NSF DLR) grant, civil and environmental engineering students at UVM have worked on multiple SL pro...

A study evaluating the mechanical and hydraulic properties of several porous concrete pavement mix designs is presented. Objectives of the study were to examine various mix designs with constituents available in Vermont, evaluate compressive strength and hydraulic conductivity of laboratory and field-cured specimens, compare results with those found in the literature, and characterize the effects of specimen size on measured parameters. To evaluate the role of sample size on these testing procedures, experiments were performed on specimens of three diameters: 76.2 mm (3 in.), 101.6 mm (4 in.), and 152.4 mm (6 in.). Multiple specimens were tested for a particular size. A specimen size of 101.6 mm (4 in.) was found to be optimal for the experiments performed and is therefore recommended. The measured compressive strength and hydraulic conductivity for the various mix designs showed a clear linear dependence on sample density. Also, the measured values fall within the expected range obtained from a review of the literature. Parametric studies included effects of the water-to-cement ratio and admixtures. Generally, increased water content yielded a higher density, higher compressive strength, and reduced hydraulic conductivity. Admixtures such as a high-range water reducer and viscosity modifying admixture had insignificant effects on the compressive strength, hydraulic conductivity, and workability of the porous concrete mixes examined. Field cores displayed a much greater variability in hydraulic conductivity than that of laboratory-prepared specimens, largely because of differences in compaction effort that are inherent to porous concrete placement in the field.

Hands-on inquiry-based educational modules were designed for two undergraduate geotechnical engineering courses at the University of Vermont. The modules were designed to achieve three objectives: (1) meet the goals of our ongoing civil and environmental engineering curricular reform (e.g., inquiry-based experiential learning and civic engagement through service-learning); (2) reach higher levels of Bloom’s taxonomy in specific topical areas addressed by the modules; and (3) help achieve Accreditation Board for Engineering and Technology (ABET) outcomes for civil and environmental engineering programs. All four modules were conducted within team settings and required students to write formal technical papers or reports followed by presentations. An additional underlying objective was the development of students’ interpersonal and communication skills. The educational modules included: (1) Atterberg limits using Casagrande and fall cone devices; (2) physical, analytical, and numerical modelings of steady-s...