Kenichi Soga

Factors Affecting Efficiency of Microbially Induced Calcite Precipitation

AbstractMicrobially induced carbonate precipitation (MICP) using ureolytic bacteria shows promise in the field of geotechnical engineering for several different applications, such as ground improvement and groundwater control. This study examined optimal use and efficient control of Sporosarcina pasteurii to induce the precipitation of CaCO3 in open environments. Laboratory tests were conducted to investigate the effect of changing treatment factors, such as chemical concentrations, retention times, and effective input rates (mol/L/h) on chemical efficiency. Chemical efficiency was measured based on weight measurements of CaCO3 precipitation compared with the amount of chemical reactants injected to samples. Based on the experimental results, the optimal time required for the precipitation process to take place in porous media for a specific range of bacterial optical density was determined. Results show that, below a certain urea and CaCl2 input rate (0.042  mol/L/h) and for a bacterial optical density (...

Effects of source zone heterogeneity on surfactant-enhanced NAPL dissolution and resulting remediation end-points

The effectiveness of removal of nonaqueous phase liquids (NAPLs) from the entrapment source zone of the subsurface has been limited by soil heterogeneity and the inability to locate all entrapped sources. The goal of this study was to demonstrate the uncertainty of degree of source removal associated with aquifer heterogeneity. In this demonstration, source zone NAPL removal using surfactant-enhanced dissolution was considered. Model components that simulate the processes of natural dissolution in aqueous phase and surfactant-enhanced dissolution were incorporated into an existing code of contaminant transport. The dissolution modules of the simulator used previously developed Gilland-Sherwood type phenomenological models of NAPL dissolution to estimate mass transfer coefficients that are upscaleable to multidimensional flow conditions found at field sites. The model was used to simulate the mass removal from 10 NAPL entrapment zone configurations based on previously conducted two-dimensional tank experiments. These entrapment zones represent the NAPL distribution in spatially correlated random fields of aquifer hydraulic conductivity. The numerical simulations representing two-dimensional conditions show that effectiveness of mass removal depends on the aquifer heterogeneity that controls the NAPL entrapment and delivery of the surfactant to the locations of entrapped NAPLs. Flow bypassing resulting from heterogeneity and the reduction of relative permeability due to NAPL entrapment reduces the delivery efficiency of the surfactant, thus prolonging the remediation time to achieve desired end-point NAPL saturations and downstream dissolved concentrations. In some extreme cases, the injected surfactant completely bypassed the NAPL source zones. It was also found that mass depletion rates for different NAPL source configurations vary significantly. The study shows that heterogeneity result in uncertainties in the mass removal and achievable end-points that are directly related to dissolved contaminant plume development downstream of the NAPL entrapment zone.

Smart bridges, smart tunnels: Transforming wireless sensor networks from research prototypes into robust engineering infrastructure

We instrumented large civil engineering infrastructure items, such as bridges and tunnels, with sensors that monitor their operational performance and deterioration. In so doing we discovered that commercial offerings of wireless sensor networks (WSNs) are still geared towards research prototypes and are currently not yet mature for deployment in practical scenarios. We distill the experience gained during this 3-year interdisciplinary project into specific advice for researchers and developers. We discuss problems and solutions in a variety of areas including sensor hardware, radio propagation, node deployment, system security and data visualization. We also point out the problems that are still open and that the community needs to address to enable widespread adoption of WSNs outside the research lab.

Soil engineering in vivo: harnessing natural biogeochemical systems for sustainable, multi-functional engineering solutions

Carbon sequestration, infrastructure rehabilitation, brownfields clean-up, hazardous waste disposal, water resources protection and global warming—these twenty-first century challenges can neither be solved by the high-energy consumptive practices that hallmark industry today, nor by minor tweaking or optimization of these processes. A more radical, holistic approach is required to develop the sustainable solutions society needs. Most of the above challenges occur within, are supported on, are enabled by or grown from soil. Soil, contrary to conventional civil engineering thought, is a living system host to multiple simultaneous processes. It is proposed herein that ‘soil engineering in vivo’, wherein the natural capacity of soil as a living ecosystem is used to provide multiple solutions simultaneously, may provide new, innovative, sustainable solutions to some of these great challenges of the twenty-first century. This requires a multi-disciplinary perspective that embraces the science of biology, chemistry and physics and applies this knowledge to provide multi-functional civil and environmental engineering designs for the soil environment. For example, can native soil bacterial species moderate the carbonate cycle in soils to simultaneously solidify liquefiable soil, immobilize reactive heavy metals and sequester carbon—effectively providing civil engineering functionality while clarifying the ground water and removing carbon from the atmosphere? Exploration of these ideas has begun in earnest in recent years. This paper explores the potential, challenges and opportunities of this new field, and highlights one biogeochemical function of soil that has shown promise and is developing rapidly as a new technology. The example is used to propose a generalized approach in which the potential of this new field can be fully realized.

Multispectral image analysis method to determine dynamic fluid saturation distribution in two-dimensional three-fluid phase flow laboratory experiments

The need for measuring dynamic fluid saturation distribution in multi-dimensional three-fluid phase flow experiments is hampered by lack of appropriate techniques to monitor full field transient flow phenomena. There is no conventional technique able to measure dynamic three-fluid phase saturation at several array points of the flow field at the same time. A multispectral image analysis technique was developed to determine dynamic NAPL, water and air saturation distribution in two-dimensional three-fluid phase laboratory experiments. Using a digital near-infrared camera, images of sand samples with various degrees of NAPL, water and air saturation were taken, under constant lighting conditions and within three narrow spectral bands of the visible and near-infrared spectrum. It was shown that the optical density defined for the reflected luminous intensity was a linear function of the NAPL and the water saturation for each spectral band and for any two and three-fluid phase systems. This allowed the definition of dimensionless lump reflection coefficients for the NAPL and the water phase within each spectral band. Consequently, at any given time, two images taken within two different spectral bands provided two linear equations which could be solved for the water and the NAPL saturation. The method was applied to two-dimensional three-phase flow experiments, which were conducted to investigate the migration and the distribution of LNAPL in the vadose zone. The method was used to obtain continuous, quantitative and dynamic full field mapping of the NAPL saturation as well as the variation of the water and the air saturation during NAPL flow. The method provides a non-destructive and non-intrusive tool for studying multiphase flow for which rapid changes in fluid saturation in the entire flow domain is difficult to measure using conventional techniques.

Performance monitoring of a secant piled wall using distributed fiber optic strain sensing

An optical fiber strain-sensing technique, on the basis of Brillouin optical time domain reflectometry (BOTDR), was used to monitor the performance of a secant pile wall subjected to multiple props during construction of an adjacent basement in London. Details of the installation of sensors and data processing are described. Distributed strain profiles were obtained by deriving strain measurements from optical fibers installed on opposite sides of the pile to allow monitoring of both axial and lateral movements along the pile. Methods for analyzing the thermal strain and temperature compensation are also presented. Measurements obtained from the BOTDR were found to be in good agreement with inclinometer data from the adjacent piles. The relative merits of the two different techniques are discussed.

Monitoring Twin Tunnel Interaction Using Distributed Optical Fiber Strain Measurements

In this field trial, a new monitoring technique using distributed strain sensing known as Brillouin optical time-domain reflectometry (BOTDR) was introduced to monitor the behavior of bolted-concrete linings of a recently completed tunnel when a second bored tunnel was constructed side by side at a distance less than one tunnel diameter apart. This was done by measuring circumferential strains in 12 rings using optical fiber that was installed using the point-fixing method. The strain distributions around the circumference of the rings show a generally similar profile. Maximum compressive strains measured below the tunnel springline nearest to the excavated tunnel were larger than the maximum tensile strains measured at the tunnel crown, distorting the circular tunnel into an oval/ellipsoid that was about symmetrical to the horizontal axis. Several methods were introduced to compare strain measurements made by BOTDR and diameter changes recorded by tape extensometer. This involves the use of a symmetrical tunnel distortion model and the basic differential equation for a circular arch. The calculated results showed some degree of similarity between the two methods. The analysis highlighted the importance of measuring the axial strain in the tunnel ring and subtracting the axial strain component to calculate the actual deflection of the lining as a result of bending.

Material Point Method for Coupled Hydromechanical Problems

This paper describes a new formulation of the material point method (MPM) for solving coupled hydromechanical problems of fluid-saturated soil subjected to large deformation. A soil-pore fluid coupled MPM algorithm based on Biots mixture theory is proposed for solving hydromechanical interaction problems that include changes in water table location with time. The accuracy of the proposed method is examined by comparing the results of the simulation of a one-dimensional consolidation test with the corresponding analytical solution. A sensitivity analysis of the MPM parameters used in the proposed method is carried out for examining the effect of the number of particles per mesh and mesh size on solution accuracy. For demonstrating the capability of the proposed method, a physical model experiment of a large-scale levee failure by seepage is simulated. The behavior of the levee model with time-dependent changes in water table matches well to the experimental observations. The mechanisms of seepage-induced failure are discussed by examining the pore-water pressures, as well as the effective stresses computed from the simulations.

Relay node placement for Wireless Sensor Networks deployed in tunnels

Node placement plays a significant role in the effective and successful deployment of Wireless Sensor Networks (WSNs), i.e., meeting design goals such as cost effectiveness, coverage, connectivity, lifetime and data latency. In this paper, we propose a new strategy to assist in the placement of Relay Nodes (RNs) for a WSN monitoring underground tunnel infrastructure. By applying for the first time an accurate empirical mean path loss propagation model along with a well fitted fading distribution model specifically defined for the tunnel environment, we address the RN placement problem with guaranteed levels of radio link performance. The simulation results show that the choice of appropriate path loss model and fading distribution model for a typical environment is vital in the determination of the number and the positions of RNs. Furthermore, we adapt a two-tier clustering multi-hop framework in which the first tier of the RN placement is modelled as the minimum set cover problem, and the second tier placement is solved using the search-and-find algorithm. The implementation of the proposed scheme is evaluated by simulation, and it lays the foundations for further work in WSN planning for underground tunnel applications.

Theoretical Study on Pile Length Optimization of Pile Groups and Piled Rafts

Pile groups are frequently designed with equal or similar pile lengths. However, the significant interaction effects among equal-length piles imply that this may not be the optimized configuration. This paper presents the optimization analyses of piled rafts and freestanding pile groups, where pile lengths are varied across the group to optimize the overall foundation performance. The results of the analyses are applicable in cases where the piles derive a majority of the capacity from the frictional resistance. It is demonstrated that, with the same amount of total pile material, an optimized pile length configuration can both increase the overall stiffness of the foundation and reduce the differential settlements that may cause distortion and cracking of the superstructure. The benefits of the optimization can be translated to economic and environmental savings as less material is required to attain the required level of foundation performances. The reliability of the optimization benefits in relation to construction-induced variability is also discussed.