Development of wireless sensor network using Bluetooth Low Energy (BLE) for construction noise monitoring

In this paper the development of a Wireless Sensor Network (WSN) for construction noise identification and sound locating is investigated using the novel application of Bluetooth Low Energy (BLE). Three WSNs using different system-on-chip (SoC) devices and networking protocols have been prototyped using a Raspberry Pi as the gateway in the network. The functionality of the system has been demonstrated with data logging experiments and comparisons has been made between the different WSN systems developed to identify the relative advantages of BLE. Experiments using the WSN for vehicle noise identification and sound location have further demonstrated the potential of the system. This paper demonstrates the versatility of a BLE WSNs and the low power consumption that is achievable with BLE devices for noise detection applications

Modeling the performance of distributed fiber optical sensor based on spontaneous Brillouin scattering

An optical model to simulate the distributed fiber optical sensor based on spontaneous Brillouin spectrum is derived. The reliability of this model is validated with experimental measurements. Using this analytical expression, parametric studies are conducted to investigate impacts of key factors including fiber loss, signal to noise ratio, bandwidth and scanning step on the optical fiber sensor measurement error. The simulation results exhibit good agreement with previous published calculation results. Applying this novel model into the data interpretation, measurement error of distributed fiber optical sensor based on spontaneous Brillouin scattering can be better controlled

Modelling tertiary creep in geomaterials using a continuum damage mechanics approach.

Tertiary creep is often observed in soft rocks and it represents a problem in a mining environment. Tertiary creep behaviour appears due to progressive micro cracking of the material and would result in a loss of strength and stiffness, which may eventually lead to failure and a complete loss of load carrying capability of the material. In this paper, the authors combined the continuum damage mechanics within the framework of hyperplasticity, thus encompassing viscoplasticity and damage within a single theory. The authors present a family of models which obeys the laws of thermodynamics. The entire constitutive behaviour is derived from two scalar potentials; a free energy potential which provides the elasticity law, and a dissipation potential which provides the yield function, the direction of plastic flow and the evolution of a damage variable. No additional assumptions are required. These new models require only few parameters which have physical meanings and are capable of capturing tertiary creep observed in soft rocks

Distributed Fiber Optics Strain Measurements for Monitoring Geotechnical Structures

Recent advances in strain measurement using optical fibers provide new opportunities for monitoring the performance of geotechnical structures during and after construction. Brillouin optical time-domain reflectometry (BOTDR) is an innovative technique that allows measurement of full strain profiles using standard optical fibers. In this paper, two case studies illustrating the application of the distributed optical fiber strain sensors are presented. One is monitoring of an old masonry tunnel when a new tunnel was constructed nearby and the other is monitoring the behavior of secant piled walls for basement construction. Both sites are located in London. The advantages and limitations of this new sensor technology for monitoring geotechnical structures are discussed

Simulation of BOTDA and Rayleigh COTDR systems to study the impact of noise on dynamic sensing

This is the author acepted manuscript. It is currently under an indefinite embargo pending publication of the final version.Dynamic distributed sensing of strain and temperature is the key for real-time structural health monitoring (SHM) across a wide range of geo-engineering challenges, for which Brillouin Optical Time Domain Analysis (BOTDA) and Rayleigh Coherent Optical Time Domain Reflectometry (COTDR) are promising candidates. A noise model with specific parametric simulation of the two systems has been developed. Noise in both laser(s) and detector is independently simulated to identify the key noise sources. In this simulation, although averaging can significantly enhance the signal-to-noise ratio (SNR) in the two systems, it is a barrier to dynamic sensing due to its time-consuming accumulation procedure. The sequence of averaging in the signal processing workflow can vary the SNR for the two systems. The system components should be optimized to reduce the averaging times to achieve the required system specifications, especially the dynamic sensing performance.This project was carried out under the UCL-Cambridge Centre for Doctoral Training in Photonic Systems Development, with funding from EPSRC (EP/G037256/1) gratefully acknowledged. The funding from Cambridge Centre for Smart Infrastructure and Construction is acknowledged

Micro-scale visualization of Microbial-Induced Calcium Carbonate Precipitation (MICP) processes

Microbial-Induced Calcium Carbonate (CaCO₃ ) Precipitation (MICP) has been explored for its potential engineering applications such as soil stabilization, but our understanding of the fundamental MICP processes at the microscale is limited. In this study, real-time in situ micro-scale experiments were conducted using glass slides and microfluidic chips (synthetic porous media which simulate soil matrices to model the conditions similar to actual MICP treatments) to visualize the CaCO₃ precipitation process. The results of this study show that irregularly-shaped CaCO₃ precipitates initially emerged on bacterial aggregates and subsequently dissolved with time as regularly-shaped CaCO₃ crystals started growing; less stable and smaller CaCO₃ crystals may dissolve at the expense of growth of more stable and larger CaCO₃ crystals. The time-dependent phase transformation of CaCO₃ precipitates makes the size of the crystals formed during MICP highly dependent on the time interval between cementation solution injections during a staged injection procedure. When the injection interval was 3-5 hours, a larger number of crystals (200-1000 per 10⁶ μm³) with smaller sizes (5-10 μm) was produced. When the injection interval was longer (23-25 hours), the crystals were larger (10-80 μm) and fewer in number (5-20 per 10⁶ μm³). The direct observation of MICP processes in this study improves the understanding of MICP fundamentals and the effect of MICP processes on the properties of CaCO₃ crystals formed after MICP treatment. These observations will therefore be useful for designing future MICP treatment protocols which improve the properties and sustainability of MICP-treated samples

The use of distributed fibre-optic strain data to develop finite element models for foundation piles

Distributed fibre-optic strain sensing using BOTDR or BOTDA is an instrumentation technique that offers a spatially-continuous data. This is superior to more conventional discrete point-based sensors which provided limited monitoring information at pre-specified location points. The availability of a distributed strain regime offers a number of advantages when it comes to studying soil-structure interaction problems such as foundation piles. Distributed strain profiles from foundation piles are useful in understanding the actual behaviour of these structures and can provide important information to develop relevant computational finite element models. Axial pile strains can be integrated to obtain absolute pile displacements or can be differentiated to get pile shaft friction values. This paper describes the use of BOTDR/A in monitoring axially-loaded foundation piles and presents recent case studies in London. It also proposes an approach to develop finite-element load-transfer models for future analysis and design of foundation piles

Multi-frequency Operation of a MEMS Vibration Energy Harvester by Accessing Five Orders of Parametric Resonance

The mechanical amplification effect of parametric resonance has the potential to outperform direct resonance by over an order of magnitude in terms of power output. However, the excitation must first overcome the damping-dependent initiation threshold amplitude prior to accessing this more profitable region. In addition to activating the principal (1st order) parametric resonance at twice the natural frequency ω0, higher orders of parametric resonance may be accessed when the excitation frequency is in the vicinity of 2ω0/n for integer n. Together with the passive design approaches previously developed to reduce the initiation threshold to access the principal parametric resonance, vacuum packaging (< 10 torr) is employed to further reduce the threshold and unveil the higher orders. A vacuum packaged MEMS electrostatic harvester (0.278 mm3) exhibited 4 and 5 parametric resonance peaks at room pressure and vacuum respectively when scanned up to 10 g. At 5.1 ms−2, a peak power output of 20.8 nW and 166 nW is recorded for direct and principal parametric resonance respectively at atmospheric pressure; while a peak power output of 60.9 nW and 324 nW is observed for the respective resonant peaks in vacuum. Additionally, unlike direct resonance, the operational frequency bandwidth of parametric resonance broadens with lower damping