Effects of Microbially Induced Carbonate Precipitation on Diffuse Double Layer and Particle Fabric of Oil Sands Fine Tailings

Microbially induced carbonate precipitation (MICP) is a sustainable biological process that catalyzes carbonate mineral precipitation within geomaterials. This study evaluates the performance and mechanisms of the MICP treatment for flocculating the oil sands fine tailings (FT). Column tests showed that the untreated FT did not decant during the 31 days. However, the MICP technique shortened the dewatering process. To elucidate the mechanisms of the MICP-induced flocculation of the FT, the diffuse double layer (DDL) thickness and microstructure of the specimens were evaluated. Three chemical equilibrium scenarios that gradually considered the MICP-biochemical reactions were explored to analyze the change of the DDL thickness. The results showed that increasing of ionic strength by urea hydrolysis decreased the DDL thickness. The fabric observation indicated that the specimens with the most calcium carbonate precipitation had the densest fabric. In summary, the MICP technique densified the fabric of FT via ureolysis process and precipitating minerals.

Semi-quantitative seismic risk screening tool for existing buildings in Canada

The National Research Council Canada (NRC) recently developed a semi-quantitative seismic risk screening tool (SQST) for existing buildings in Canada. The SQST aims to supersede the Manual for Screening of Buildings for Seismic Investigation developed by NRC in the early 1990s. The SQST consists of three key components: (1) a structural scoring system that quantitatively assesses the structural seismic risk based on probability of collapse; (2) a non-structural component scoring system that qualitatively assesses the seismic risk of non-structural components based on seismic demand; and (3) a ranking procedure that prioritizes potentially hazardous buildings for seismic evaluations and possible upgrading. The SQST intends to inexpensively identify and exempt buildings with acceptable life safety risk and optimize the allocation of resources to assess the seismic risk of portfolios of buildings. Seismic screening with the SQST can be completed with either paper-based screening forms or a web-based application. The applicability of the SQST is demonstrated by conducting a pilot study for 33 existing buildings across Canada.

Climate Change Impact and Adaptation for Highway Asphalt Pavements: A Literature Review

For the past few decades, researchers all over the world have agreed that the service life of civil infrastructure is significantly affected by climate change. Pavement is one of these significant infrastructures that can be easily affected by climate change. However, it is well known that predicting climate change is highly complex and dynamic. Hence, a review has been done on available climate change models and the uncertainties involved in climate change prediction. This review addresses various important questions such as (1) What is climate change? (2) How to use climate change models? (3) Uncertainties involved in using climate change models. (4) How does climate change impacts the pavement infrastructure? (5) What are the adaptation and mitigation strategies available? and (6) How do economic costs and emissions change due to climate change? This review is useful to understand climate change and its implications on pavement infrastructure.

Influence of Headwater Reservoirs on Climate Change Impacts and Flood Frequency in the Kabul River Basin

While climate change impacts vary globally, for the Kabul River Basin (KRB), concerns are primarily associated with frequent flooding. This research describes the influence of headwater reservoirs on projections of climate change impacts and flood frequency, and how the riparian countries can benefit from storing of floodwaters for use during dry seasons. Six climate change scenarios and two Representative Concentration Pathways (RCPs) are used in three periods of a quarter-century each. The Soil and Water Assessment Tool (SWAT) is used to assess how the proposed reservoirs will reduce flooding by ~38% during the wet season, reduce the flood frequency from five to 25 years return period, and increase low flows by ~110% during the dry season, which reflect an ~17.5% reduction in the glacier-covered area by the end of the century. The risks and benefits of reservoirs are highlighted in light of the developmental goals of Afghanistan and Pakistan.

Coupling Impacts of Spray and Rainfall on Road Visibility and Vehicle Speeds: A Simulation-based Analysis

Impaired visibility resulting from rainfall contributes greatly to the occurrence of traffic accidents. This study presents a numerical simulation approach to analyze the extent to which the coupling of spray and raindrops reduces visibility and thus proposes safe speeds against inadequate visibility. The spray-raindrop coupling particles were modeled by considering the real highway design parameters and rainfall conditions. The road visibility was estimated through simulating the multiple scattering process of taillights in the spray-rain medium, and the maximum safe speed against inadequate visibility was then derived by comparing the visibility with the required stopping sight distance. Results show that: 1) either a high speed of the front truck or a thick water-film results in a significant reduction in road visibility and the maximum safe speed of the ego vehicle, 2) front vehicle speed plays a more important role in visibility reduction than the water-film thickness does.

Exploring Implicit Relationships between Pavement Surface Friction and Vehicle Crash Severity Using Interpretable Extreme Gradient Boosting Method

Pavement friction has been identified as crucial in traffic safety. Since the Highway Safety Manual prediction algorithm is often based on crash frequency, the crash severity distribution might be assumed unchanged before and after the countermeasure. However, pavement surface treatments can improve the friction to different levels, by which crash severity outcomes may vary greatly. To explore the implicit effects of pavement friction on vehicle crash severity, this paper first validates the extreme gradient boosting model performance and then the Shapley additive explanations interaction values are employed to interpret individual features and the nonlinear interactions among predictors. Under various scenarios, the XGBoost output probability is utilized to convert into dynamic crash severity distributions. Results also indicate that friction becomes more significant when the friction number is less than 38, and immediate corrective actions are needed when the friction number is below 20.

Assessment of Sediment Arsenic and Iron Occurrence and Leaching Potential in a Potable Water Treatment Wastewater Stabilization Pond System

Wastewater stabilization ponds (WSPs) are commonly used to reduce wastewater metal(loid) concentrations from drinking water treatment plants (DWTPs) through sedimentation. However, this results in increased sediment concentrations that can be released back into the overlying water. Thus, our goal was to evaluate the WSP metal(loid)s occurrence and leaching potential. Currently, a Saskatchewan based DWTP’s WSP system was investigated given historically elevated effluent As and Fe concentrations. The WSP consists of five ponds that were sampled on six occasions in 2019 and 2020. In addition, sediments were used in laboratory-based experiments to determine their leaching potential. Overall, the sediments were found to contain elevated concentrations of As and Fe with 25 to 400 and 10,000 to 45,000 mg/kg, respectively. Leaching experiments indicated that the pond sediments could potentially release As and Fe with log Kd values ranging from 2.21 to 4.31 L/kg, while Fe ranged from 3.32 to 5.53 L/kg.

Response analysis of subgrade soils using signal phase shift obtained from laboratory lightweight deflectometer tests

Over the past decades, the use of fast and reliable measurement techniques of soil mechanical properties has gained popularity. The lightweight deflectometer (LWD) is among the tools developed that can allow one to determine the elastic modulus of soil. Viscosity response components in pavement or soil typically induce phase shifts between stress and strain peaks, which can be translated to phase angle. Subgrade soil may exhibit varying response types depending on its nature and characteristics. Using large laboratory subgrade samples, an experiment was designed to measure the elastic modulus and phase angle with an LWD in different stress and humidity conditions. A model associating the elastic modulus inferred from LWD tests with parameters describing stress, water content and soil properties was proposed. This model is fundamentally inferred from the relationship between elastic modulus and phase shift, and was used to assess the relative contribution of varying conditions on soil stiffness.

Experimental Investigation of 900 Intake Flow Patterns with and without Submerged Vanes under Sediment Feeding Conditions

In this study, two experiments were conducted in a 90⁰ water intake to study 3D flow patterns and sediment distribution using submerged vanes under sediment feeding and live-bed conditions. One column three vanes were installed at a 20⁰ angle maintaining for a water discharge ratio of q_r ~ 0.1. Three-dimensional mean and turbulent velocity components of flow in 90⁰ channel intake were measured by Acoustic Doppler Velocimetry (ADV). Flow characteristics of the intake structure area with no vanes are compared with those condition. Results showed that three vanes with single column reduced the amount of sediment by 20% in the intake diversion. In the downstream corner of the intake, high velocities were measured where scouring occurred. The vanes affected the intensity of secondary flow, turbulence energy, flow separation, and moved sediment deposition downstream of the main channel.