Development of Some Novel Suction-Based Correlations for Swell Behavior of Expansive Soils

Swelling and shrinkage are the two distinctive characteristics of expansive soils, and due to this behavior, these soils are considered a natural hazard for infrastructure. Many structures in different regions have been impaired due to the swell/shrink behavior of the expansive soil. Most of the severe distress is impeded because of the inherent suction (negative pore water pressure) present in expansive soils. Both suction and swelling parameters are greatly affected by the surrounding moisture content. Due to this feature of expansive soil, geotechnical engineers are interested in utilizing the suction-based correlations for the assessment of unsaturated expansive soils. The current investigation was carried out to develop novel correlations incorporating lab testing and field instrumentation. To fulfill the objectives, eight sites of the local expansive soil in Pakistan were selected for samples collection and field testing. Conventional odometer testing was conducted to measure the swell pressure (Sp) and swell potential (S) of the fabricated/remolded specimens. Gypsum block (G-block) sensors were additionally utilized for estimating the matric suction in the field. To expand the database, the previously published data of the same nature was also incorporated. Based on the results, the power form of the novel correlations (suction-based) is highly significant for estimating (Sp), while for swell potential, the logarithmic correlation with R2 = 0.6551 is more significant than other forms of correlations. The proposed suction-based correlation can be equally utilized for the estimation of field suction as well as for swell behavior of expansive soil having a plasticity index (PI) ≥ 22%.

Development of a Virtual Flowmeter as an Enhanced Alternative for Field Production Monitoring

Flowrate is a valuable information for the oil and gas industry. High accuracy on flowrate estimation enhances production operations to control and manage the production. Recognized as a cost-efficient solution, the VFM (virtual flowmeter) is a mathematical-based technology designed to estimate the flowrates using available field instrumentation. The VFM approach developed in this work combines black-box simulations with mixed-integer linear programming (MILP) problem to obtain the flowrates dismissing the tuning process. The methodology included a set of multiphase flow correlations, and the MILP was developed to estimate the flowrate and designate the best fit model. We evaluated the proposed VFM against 649 well test data. The methodology presented 4.1% average percentage error (APE) for percentile 25% and 13.5% APE for percentile 50%. We developed a VFM technology to be used in scenarios with a lack of data, and we believe that our tuning-free method can contribute to the future of VFM technologies.

Near-Field and Far-Field Sampling of Aerosol Plumes to Evaluate Particulate Emission Rates From a Falling Particle Receiver During On-Sun Testing

High-temperature falling particle receivers are being investigated for next-generation concentrating solar power applications. Small sand-like particles are released into an open-cavity receiver and are irradiated by concentrated sunlight from a field of heliostats. The particles are heated to temperatures over 700 °C and can be stored to produce heat for electricity generation or industrial applications when needed. As the particles fall through the receiver, particles and particulate fragments in the form of aerosolized dust can be emitted from the aperture, which can lower thermal efficiency, increase costs of particle replacement, and pose a particulate matter (PM) inhalation risk. This paper describes sampling methods that were deployed during on-sun tests to record near-field (several meters) and far-field (tens to hundreds of meters) concentrations of aerosol particles within emitted plumes. The objective was to quantify the particulate emission rates and loss from the falling particle receiver in relation to OSHA and EPA National Ambient Air Quality Standards (NAAQS). Near-field instrumentation placed on the platform in proximity to the receiver aperture included several real-time aerosol size distribution and concentration measurement techniques, including a TSI Aerodynamic Particle Sizers (APS), TSI DustTraks, Handix Portable Optical Particle Spectrometers (POPS), Alphasense Optical Particle Counters (OPC), TSI Condensation Particle Counters (CPC), Cascade Particle Impactors, 3D-printed prototype tipping buckets, and meteorological instrumentation. Far-field particle sampling techniques utilized multiple tethered balloons located upwind and downwind of the particle receiver to measure the advected plume concentrations using a suite of airborne aerosol and meteorological instruments including POPS, CPCs, OPCs and cascade impactors. The combined aerosol size distribution for all these instruments spanned particle sizes from 0.02 μm – 500 μm. Results showed a strong influence of wind direction on particle emissions and concentration, with preliminary results showing representative concentrations below both the OSHA and NAAQS standards.

Soil-structure interaction analysis in reinforced concrete structures on footing foundation

Soil-structure interaction (SSI) evaluates how soil or rock deformability imposes on the structure a different load path in a hypothesis of fixed supports, altering the loads acting on the structural elements and the ground. This paper discusses the results of the SSI effects in two buildings with a reinforced concrete structure and shallow foundations in a rock mass. The settlements were monitored by field instrumentation in five stages of their construction, making it possible to estimate through interpolation curves the settlements values of some points. The numerical modeling and structural analysis of the buildings were obtained for two different cases of soil-structure interaction. The structure was considered having fixed supports (non-displaceable) and displaceable supports (with stiffness spring coefficients K). The results reveals the occurrence of SSI effects, with a load redistribution between the columns that occurred differently for the different construction stages. Structural modeling proved to be quite representative, pointing to higher vertical load values than the average values present in building edge zones, which contradicts the conventional idea that central columns are more loaded than the edge columns. The soil-structure interaction analyses resulted in different behaviors regarding both towers; pointing out that low settlements and building symmetry in plan minimize the effects of interaction, with no tendency of load redistribution between columns as the structure rigidity increases, as construction development.

A Validated Train-Track-Bridge Model with Nonlinear Support Conditions at Bridge Approaches

A bridge approach, an essential component connecting a relatively rigid bridge and a more flexible track on subgrade soil, is one of the most common types of track transition zones. The tracks on a bridge deck often undergo significantly lower deformations under loading compared to the approach tracks. Even though there have been numerous efforts to understand and remediate performance deficiencies emerging from the differences in stiffness between the bridge deck and the approach, issues such as differential settlement and unsupported hanging crossties often exist. It is often difficult and expensive to try different combinations of mitigation methods in the field. Therefore, computational modeling becomes of vital importance to study dynamic responses of railroad bridge approaches. In this study, field instrumentation data were collected from the track substructure of US Amtrak’s Northeast Corridor railroad track bridge approaches. After analyses and model implementation of such comprehensive field data, an advanced train-track-bridge model is introduced and validated in this paper. Nonlinear relative displacements under varying contact forces observed between crosstie and ballast are adequately considered in the dynamic track model. The validated model is then used to simulate an Amtrak passenger train entering an open deck bridge to generate typical track transient responses and better understand dynamic behavior trends in bridge approaches. The simulated results show that near bridge location experiences much larger transient deformations, impact forces, vibration velocities and vibration accelerations. The validated track model is an analysis tool to evaluate transient responses at bridge approaches with nonlinear support; it is intended to eventually aid in developing improved track design and maintenance practices.

Estimation of unsaturated flow parameters and hysteresis curve from field instrumentation

The negative pore water pressure or soil suction has significant effect on the performance of geotechnical infrastructures (e.g., slope, pavement, embankment etc.). The unsaturated behavior of soil is not static, rather offers variation in response to climatic loading. The objective of the study was to evaluate field-based techniques of SWCC construction in terms of capturing these variation as compared to laboratory methods and predictive models. The field assessment could allow the quantification of hysteresis effect on the SWCC. Instrumentation data from one Texas, USA highway was used in this study. Soil Water Characteristic Curves (SWCCs) were regenerated utilizing co-located moisture and suction data from the field. Laboratory and field measured SWCCs from the instrumented site were fitted by van Genuchten model. Previously developed predicted models were also utilized to evaluate the SWCC parameters. Based on the evapotranspiration and rainfall amounts, distinct drying and wetting cycles were recorded. Though hourly data was collected in this study, average daily values were used for the analysis. Unsaturated flow parameters (α, n, m) were determined from both laboratory testing and field moisture-suction data along with the predictive models. Clear differences were observed between the values obtained from predictive models and field generated SWCC. The outcome from this study revealed that field reconstructed SWCCs can be used to simulate higher precision in numerical modeling in numerous geotechnical applications.

Estimation of percolation of water balance cover using field scale unsaturated soil parameter

Water balance covers for landfill closure are used as a barrier which act with the natural processes to reduce percolation. The ideal performance of water balance cover is characterized by the minimal quantity of percolation. The rate of percolation of water balance cover largely depends on unsaturated soil behavior. In this study, percolation was evaluated through unsaturated soil parameters of six instrumented lysimeters. The field instrumentation included moisture sensors, tensiometers, rain gauge, dosing siphon, and pressure transducer. Soil water storage (SWS) capacity (SA) was quantified from the soil water characteristic curves (SWCC) which were developed based on laboratory experiments and field instrumentation data. Required SWS (SR) was also measured from the field monitoring results. Based on analysis, the relative storage ratio (SR/SA) was observed to be greater than unity (1) in most of the cases, indicating potential percolation. The SR/SA was also found competent to identify the lysimeter with higher quantity of percolations. The estimated percolation from the laboratory experimented and field generated SWCCs fairly resembled with the actual field measured percolation. The analyzed results also developed a framework to estimate the thickness of the cover storage layer required to manage percolation for the specific region of the study area.