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"Haigh, Stuart"
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Characterisation of CaCO3 phases during strain-specific ureolytic precipitation
Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, however, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation. We have studied microbial induced calcium carbonate (CaCO
3
) precipitation (MICP) in three ureolytic bacterial strains from the
Sporosarcina
family, including
S. newyorkensis
, a newly isolated microbe from the deep sea. We find that the interplay between structural water and strain-specific amino acid groups is fundamental to the stabilisation of vaterite and that, under the same conditions, different isolates yield distinctly different polymorphs. The latter is found to be associated with different urease activities and, consequently, precipitation kinetics, which change depending on pressure-temperature conditions. Further, CaCO
3
polymorph selection also depends on the coupled effect of chemical treatment and initial bacterial concentrations. Our findings provide new insights into strain-specific CaCO
3
polymorphic selection and stabilisation, and open up promising avenues for designing bio-reinforced geo-materials that capitalise on the different particle bond mechanical properties offered by different polymorphs.
Journal Article
Dynamic and monotonic response of Monopile Foundations for Offshore wind turbines using centrifuge testing
The seismic response of monopile foundations is a growing area of research as the offshore wind industry expands worldwide, including in earthquake prone regions of the world. This paper presents dynamic centrifuge tests aimed at investigating the dynamic response of monopiles in both dry and saturated sandy soils. The latter case includes soil liquefaction under strong input motions, with measured excess pore pressures indicating liquefaction. The natural frequency of the monopile-soil system is experimentally determined by measuring the response to a sine sweep motion. Strong earthquakes are then applied at this frequency and its harmonics. This paper discusses the response of the monopile in terms of the peak accelerations observed in the dry and saturated tests, as well as using response spectra and amplification ratios. The dynamic bending moments along the pile are also measured to infer the bending moment profile with depth. Finally, two identical monopiles are pushed-over in each of the centrifuge tests to establish the pre and post-earthquake monotonic response, including the lateral stiffness and capacity, which are compared for the dry model tests and the saturated case.
Journal Article
A novel measurement system for self-sensing graphite-cement composites
Carbon-based conductive fillers have been incorporated into cement matrix to develop smart self-sensing materials with piezoresistive properties. However, accurately measuring the sensing property of the cement composite without compromising its mechanical performance is not easy to achieve in practical engineering. Therefore, in this study, a novel experimental setup for measuring the self-sensing properties of conductive fillers embedded cementitious composites was developed. This multi-functional measurement system is able to measure specimens under compressive and flexural stress with different loading profiles, apply various loading rates, obtain the electrical properties, and measure the strain using both LVDT and Particle Image Velocimetry (PIV) or Digital Image Correlation (DIC) techniques with all the data synchronised to one file sharing the same time stamp controlled by Python codes. In this study, the piezoresistivity and the performance on damage detection of the cementitious composites with low graphite concentration (5%) in a bulk form were investigated through monotonic compressive and flexural tests. Experiment results include the specimens’ stress, strain and Fractional Change in Resistivity (FCR). Data analysis showed that the set-up and methodology developed in this study are effective to test self-sensing cementitious composites, and the graphite-cement composites used in this study have a stable piezoresistivity and able to detect damage upon failure.
Journal Article
Liquefaction analysis of soil plugs within large diameter monopiles using numerical modelling
Soil plug formation in open-ended piles due to pile driving is a widely studied phenomenon in onshore applications. The narrow diameters of traditional onshore piles ranging from 0.5 to 1.5 m facilitate plug generation during installation and transfer of enhanced confining stresses across the whole body of the soil plug. Offshore wind monopiles with larger diameters and smaller aspect ratios may not enhance confining stress within the soil plug as effectively as their onshore counterparts. Monopiles are currently the most widespread foundation in the offshore wind sector including in seismic areas. Earthquake shaking can lead to accumulation of excess pore pressure and subsequent liquefaction of the soil retained inside the plug. This research investigates the influence of monopile diameter and confining stress on the development of earthquake-induced excess pore pressure within the soil plug using fully coupled time domain Finite Element Analysis. The results presented in this paper reveal lower accumulation of earthquake-induced excess pore pressure in soil plugs subjected to confining stress. However, the influence of additional horizontal stress caused by monopile driving on the generation of excess pore pressure within the soil plug diminishes as the monopile diameter is progressively increased.
Journal Article
Re-evaluating the strength of pit-latrine faecal sludge from dynamic cone penetrometer test data
In 2017, 55% of the global population were without safely managed sanitation services. On-site sanitation solutions, such as pit latrines, provide the majority of sanitation coverage across developing countries. Appropriate technologies are required in order to safely empty these latrines without damage to people or the environment. The design of appropriate emptying technologies can be hampered by a lack of knowledge of the mechanical properties of the waste, such as its strength. This paper will develop a calibration for a dynamic cone penetrometer to give accurate measurements of faecal sludge strength against a standard scale, rendering existing data comparable. It will be shown that the maximum shear strengths of faecal sludge found in practice are substantially greater than those previously reported; some pit latrines contain faecal sludge with strength values of 5–20 kPa at the surface, and exceeding 80 kPa at depth
Journal Article
Measurement of the Poisson expansion effect on crack openings in self-sensing concrete
Concrete infrastructure tends to degrade with extended service life, but detecting deterioration with conventional inspection methods can be challenging. Existing approaches such as developing self-sensing concrete by adding electrically conductive fillers to the cement matrix often suffer from high costs and complex manufacturing processes for casting the concrete from fresh. This study looks beyond the commonly discussed resistance-based and capacitance-based self-sensing mechanisms in the elastic deformation regime of the concrete and investigates the changes in electrical conductivity due to micro-crack opening through Poisson expansion by utilising the measurement technique of drilling the concrete to insert conductive epoxy for electrode embedment to achieve intrinsic self-sensing on as-built regular concrete (i.e. without conductive fillers). Experimental results on existing plain concrete samples showed a good correlation between the compressive load and the fractional change in resistivity (FCR). Finite element analysis (FEA) was then used to further investigate the effect of changes in conductivity in the direction of loading and orthogonal directions on the measured electrical behaviour of the concrete. Results showed that the correlation between the FCR and the compressive load depends on the relationship between the load-parallel and -orthogonal gauge factors. Beyond a threshold level, the electrical signal picked up by the electrodes reflects the material’s behaviour in the direction orthogonal to the loading direction due to Poisson expansion. Further numerical simulation has suggested that to achieve a stable measurement, the electrodes’ penetration should equal the spacing.
Journal Article
Geographically distributed hybrid testing & collaboration between geotechnical centrifuge and structures laboratories
Distributed Hybrid Testing (DHT) is an experimental technique designed to capitalise on advances in modern networking infrastructure to overcome traditional laboratory capacity limitations. By coupling the heterogeneous test apparatus and computational resources of geographically distributed laboratories, DHT provides the means to take on complex, multi-disciplinary challenges with new forms of communication and collaboration. To introduce the opportunity and practicability afforded by DHT, here an exemplar multi-site test is addressed in which a dedicated fibre network and suite of custom software is used to connect the geotechnical centrifuge at the University of Cambridge with a variety of structural dynamics loading apparatus at the University of Oxford and the University of Bristol. While centrifuge time-scaling prevents real-time rates of loading in this test, such experiments may be used to gain valuable insights into physical phenomena, test procedure and accuracy. These and other related experiments have led to the development of the real-time DHT technique and the creation of a flexible framework that aims to facilitate future distributed tests within the UK and beyond. As a further example, a real-time DHT experiment between structural labs using this framework for testing across the Internet is also presented.
Journal Article
Design of pile foundations in liquefiable soils
Pile foundations are the most common form of deep foundations that are used both onshore and offshore to transfer large superstructural loads into competent soil strata. This book provides many case histories of failure of pile foundations due to earthquake loading and soil liquefaction. Based on the observed case histories, the possible mechanisms of failure of the pile foundations are postulated. The book also deals with the additional loading attracted by piles in liquefiable soils due to lateral spreading of sloping ground. Recent research at Cambridge forms the backbone of this book with the design methodologies being developed directly based on quantified centrifuge test results and numerical analysis.
eBook
Lateral Spreading of Sloping Ground
The following sections are included:
Liquefaction-induced Lateral Spreading
Introduction
Simple Methods to Estimate the Extent of Lateral Spreading
Effects of Lateral Spreading on Pile Foundations
Presence of nonliquefiable crust
Lateral pressures generated on piles and pile caps
Current codal provisions
Specifications for Highway Bridges (JRA, 2002)
Design Standard for Railway Facilities (RTRI 1999)
Recommendations for Design of Building Foundations (AIJ 2001)
Recent experimental data vs codal provisions
Recommendations on Estimation of Lateral Loads for Pile Design
Book Chapter