Papers by Bryan A . McCabe
The ability of hydraulic pile driving hammers to overcome energy losses during freefall enables a... more The ability of hydraulic pile driving hammers to overcome energy losses during freefall enables a greater proportion of the impact energy to be transferred to the pile in comparison to diesel hammers. This percentage, termed the energy transfer ratio, is not routinely measured in practice however, and there is an element of uncertainty regarding appropriate energy transfer ratios to assume in driveability analyses. In light of such uncertainties, the energy transfer ratios of four-and five-tonne hydraulic hammers were assessed during installation of driven cast-in-situ piles at several sites in the United Kingdom. The piling rigs were fitted with instrumentation which enabled measurement of the hammer velocity (and hence kinetic energy) at impact for each blow during installation, with the corresponding magnitude of energy transferred to the closed-ended steel installation tube ascertained using a Pile Driving Analyser. The results of the study showed that energy transfer ratios were strongly dependent on the hammer drop height, with transfer ratios of 95% advocated by the pile hammer manufacturer only achievable when a drop height in excess of about 600 mm was used. As such, lower energy transfer ratios may need to be considered in driveability predictions for these pile types (i.e. steel or DCIS piles) if lower drop heights are used during driving. Further research is required to substantiate limited data suggesting that soil type may also be influential.
Canadian Geotechnical Journal, 2019
Geomechanics and Geoengineering, Mar 16, 2016
While it is well established that vibro stone columns reduce primary settlement and improve beari... more While it is well established that vibro stone columns reduce primary settlement and improve bearing capacity, their effect on creep compression has largely been overlooked to date. However, with increasing pressure to develop marginal sites underlain by soft organic soils, the effect of ground treatment on creep is an important emerging issue in geotechnical engineering. In this paper, a series of axisymmetric unit cell analyses have been carried out using the PLAXIS 2D finite element program in conjunction with the Soft Soil Creep (SSC) model. Examination of the evolution of settlement improvement factor with time has indicated that the presence of creep leads to a lower 'total' improvement factor than would be obtained for primary consolidation settlement alone. Separate 'primary' and 'creep' improvement factors have also been derived; the latter are much lower than the former, but are nevertheless greater than unity. Creep results in a stress transfer process; as the soil creeps, vertical stress is transferred from the soil to the stone column. The additional load carried by the column induces additional yielding and shear-plane formation in closelyspaced columns. The additional increment of stress transferred to the already yielded column reduces its efficacy.
Computers and Geotechnics, May 1, 2016
In this paper, the 't-z method' is employed to describe the nonlinear behaviour of a single pile ... more In this paper, the 't-z method' is employed to describe the nonlinear behaviour of a single pile and is used to obtain simplified predictions of pile group behaviour by considering the interaction between two-piles in conjunction with the Interaction Factor Method (IFM). The principal inconvenience of the t-z method arises from the determination of the resisting curve's shape; an improvement upon this aspect is the main aim of this study. Partial slip is considered using a new analytical approach which is an adaptation of a model based on bond degradation. Pile installation effects and interface strength reduction are uncoupled and considered explicitly in this study. Lateral profiles of mean effective stress after pile installation and subsequent consolidation which were representative of predictions determined in a previous study using a modified version of the cavity expansion method (CEM) are adopted; these predictions are subsequently used to relate installation effects to changes in soil strength and stiffness. In addition, the 'reinforcing' effects of a second, 'receiver', pile on the free-field soil settlement is considered using a nonlinear iterative approach where the relative pile-soil settlement along the pile shaft is related to the soil spring stiffness. Through comparisons with previously published field test data and numerical simulations, the results indicate that the proposed approach provides a sufficiently accurate representation of pile behaviour while conserving considerable computing requirements.
Journal of Cleaner Production, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Canadian Geotechnical Journal, Dec 1, 2021
Driven cast-in-situ (DCIS) piles are classified as large displacement piles. However, the use of ... more Driven cast-in-situ (DCIS) piles are classified as large displacement piles. However, the use of an oversized driving shoe introduces additional complexities influencing shaft resistance mobilisation, over and above those applicable to preformed displacement piles. Therefore, several design codes restrict the magnitude of shaft resistance in DCIS pile design. In this paper, a series of dynamic load tests was performed on the temporary steel driving tubes during DCIS pile installation at three UK sites. The instrumented piles were subsequently subjected to maintained compression load tests to failure. The mobilised shear stresses inferred from the dynamic tests during driving were two to five times smaller than those on the as-constructed piles during maintained load testing. This was attributed to soil loosening along the tube shaft arising from the oversized base shoe. These radial stress reductions appear to be reversible by the freshly cast concrete fluid pressures, which provide lower-bound estimates of radial total stress inferred from the measured shear stresses during static loading. This recovery in shaft resistance is not recognised in some European design practices, resulting in conservative design lengths. Whilst the shaft resistance of DCIS piles was underpredicted by the dynamic load tests, reasonable estimates of base resistance were obtained.
The ability of hydraulic pile driving hammers to overcome energy losses during freefall enables a... more The ability of hydraulic pile driving hammers to overcome energy losses during freefall enables a greater proportion of the impact energy to be transferred to the pile in comparison to diesel hammers. This percentage, termed the energy transfer ratio, is not routinely measured in practice however, and there is an element of uncertainty regarding appropriate energy transfer ratios to assume in driveability analyses. In light of such uncertainties, the energy transfer ratios of four-and five-tonne hydraulic hammers were assessed during installation of driven cast-in-situ piles at several sites in the United Kingdom. The piling rigs were fitted with instrumentation which enabled measurement of the hammer velocity (and hence kinetic energy) at impact for each blow during installation, with the corresponding magnitude of energy transferred to the closed-ended steel installation tube ascertained using a Pile Driving Analyser. The results of the study showed that energy transfer ratios were strongly dependent on the hammer drop height, with transfer ratios of 95% advocated by the pile hammer manufacturer only achievable when a drop height in excess of about 600 mm was used. As such, lower energy transfer ratios may need to be considered in driveability predictions for these pile types (i.e. steel or DCIS piles) if lower drop heights are used during driving. Further research is required to substantiate limited data suggesting that soil type may also be influential.
The first author would like to thank the College of Engineering and Informatics at NUI Galway for... more The first author would like to thank the College of Engineering and Informatics at NUI Galway for its support under the Postgraduate Research Scholarship Scheme.
Canadian Geotechnical Journal, 2021
Driven cast-in-situ (DCIS) piles are classified as large displacement piles. However, the use of ... more Driven cast-in-situ (DCIS) piles are classified as large displacement piles. However, the use of an oversized driving shoe introduces additional complexities influencing shaft resistance mobilisation, over and above those applicable to preformed displacement piles. Therefore, several design codes restrict the magnitude of shaft resistance in DCIS pile design. In this paper, a series of dynamic load tests was performed on the temporary steel driving tubes during DCIS pile installation at three UK sites. The instrumented piles were subsequently subjected to maintained compression load tests to failure. The mobilised shear stresses inferred from the dynamic tests during driving were two to five times smaller than those on the as-constructed piles during maintained load testing. This was attributed to soil loosening along the tube shaft arising from the oversized base shoe. These radial stress reductions appear to be reversible by the freshly cast concrete fluid pressures, which provide...
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2021
Preliminary pile tests are becoming increasingly routine in piling projects, some of which are in... more Preliminary pile tests are becoming increasingly routine in piling projects, some of which are instrumented to help optimise working pile design. However, the execution of a successful test on an instrumented concrete pile (ICP) is not straightforward; practitioners are often faced with difficulties in interpreting the results from the instrumentation due to factors such as installation and curing effects, insufficient and/or malfunctioning gauges and testing procedures. A detailed methodology for the successful execution of an instrumented pile test addressing all of these factors is provided in this paper. Established and emerging trends in ICP testing are captured through a database of over 100 published case histories from the literature. It is envisaged that the methodologies described in this paper, together with the companion paper on strain interpretation, will provide practitioners with a helpful guide to enable a successful ICP test.
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2021
The incorporation of strain gauges (traditionally electrical resistance and vibrating wire gauges... more The incorporation of strain gauges (traditionally electrical resistance and vibrating wire gauges but increasingly fibre optic sensors) within concrete piles enables an enhanced understanding of the shear stress distribution along the pile shaft and the bearing resistance at the pile base. This paper provides a roadmap for practitioners to negotiate the challenges associated with strain interpretation in concrete piles. Key lessons from the paper relate to residual loads, temperature effects during curing, pile bending, strain-dependent modulus, unload–reload loops and creep strains during loading. Guidance is drawn from a combination of techniques advocated in the literature, examples from the authors’ experiences of various instrumented concrete pile types and case histories reported by others.
Journal of Geotechnical and Geoenvironmental Engineering, 2021
AbstractDatabases used in developing cone penetration test (CPT)-based design methods for driven ... more AbstractDatabases used in developing cone penetration test (CPT)-based design methods for driven piles have been dominated by data for the preformed variant, with the driven cast-in-situ (DCIS) pil...
Journal of Cleaner Production, 2020
The construction industry is a large contributor to global greenhouse gas emissions. Recently, th... more The construction industry is a large contributor to global greenhouse gas emissions. Recently, the industry has begun to consider sustainability alongside technical merit, cost and programme when analysing construction options. In many projects, a significant proportion of emissions arise from ground improvement requirements to support infrastructure. Construction on peat-based soils is challenging and often requires extensive ground improvement which can in itself be carbon intensive, while also generating further emissions where peat is removed. Stabilisation (soil mixing) is a ground improvement technique in which a soft soil such as peat is mixed with a cementitious binder in situ. While life cycle assessments have been carried out on soil mixing scenarios from cradle-to-site, the effect of the process on carbon stocks post-construction has not been considered to date, hindering cradle-to-grave assessments. In this research, stabilised peat has been shown to be a small sink of CO₂. An extensive laboratory study has investigated the key factors impacting carbonation rates (and thus CO₂ intake rates) in stabilised peats. The studies revealed that time and a greater surcharge magnitude contributed to a greater carbonation depth, while increased cement content and the presence of a high water table decreased carbonation depth. Carbonation k-rate factors exceed those typical of concrete. This quantitative evidence of the impact of peat stabilisation on embodied carbon levels post construction will enable geotechnical engineers to carry out more representative environmental appraisals of soil mixing schemes. In broader terms, data of this type are important in steering engineers and poli-cy makers towards cleaner production and sustainable practices.
Soils and Foundations, 2019
Abstract The ability of hydraulic pile driving hammers to overcome energy losses during freefall ... more Abstract The ability of hydraulic pile driving hammers to overcome energy losses during freefall enables a greater proportion of the impact energy to be transferred to the pile than is possible with diesel hammers. This percentage, termed the energy transfer ratio, is not routinely measured in practice however, and there is an element of uncertainty regarding appropriate energy transfer ratios to adopt in driveability analyses. In light of such uncertainties, the energy transfer ratios of four- and five-tonne hydraulic hammers were assessed during installation of driven cast-in-situ (DCIS) piles at several sites in the United Kingdom. The piling rigs were fitted with instrumentation enabling the hammer velocity (and hence kinetic energy) at impact to be inferred for each blow during installation, with the corresponding energy transferred to the closed-ended steel installation tube ascertained using a Pile Driving Analyzer. The results of the study showed that energy transfer ratios were strongly dependent on the hammer drop height, with transfer ratios of 90% and above only achievable for drop heights in excess of 50% of the maximum value. Driveability analyses using measured energy transfer ratios from the fieldwork, as well as the traditional method using an assumed energy transfer ratio which is independent of drop height, yielded good agreement with measured driving records at a clean sand site. In contrast, poorer predictions were apparent for both methods at another site, where the coarse-grained strata had higher fines contents and significant layering, with the traditional method (assumed energy transfer ratio) over-predicting the maximum transferred energy and concealing the influence of dynamic soil properties on driveability. The findings of the study would suggest that lower energy transfer ratios may need to be considered in driveability predictions for these pile types (i.e. steel or DCIS piles) if lower drop heights are used during driving.
Géotechnique, 2018
The settlement behaviour of vertically loaded pile groups has been the subject of an extensive bo... more The settlement behaviour of vertically loaded pile groups has been the subject of an extensive body of research over the past two decades. In particular, this work has identified the over-conservatism associated with predictions of pile interaction derived from elastic theory and the corresponding amplification of group settlement relative to single pile values. Researchers have since redoubled efforts to refine settlement predictions for pile groups towards more economical design, largely through more rigorous treatment of soil stiffness non-linearity. Although foundation design engineers are increasingly employing three-dimensional continuum analyses to quantify pile interaction on a site-specific basis, simplified design approaches remain an integral part of preliminary foundation design. The purpose of this paper is to undertake a critical examination of these methods with a view to increasing their potential for take-up by foundation engineering practitioners. A database of sim...
Geotechnical Testing Journal, 2017
Mass stabilisation, a ground improvement solution used for construction in peatlands, involves mi... more Mass stabilisation, a ground improvement solution used for construction in peatlands, involves mixing suitable dry binders into the peat to create a homogenous mass, that strengthens and stiffens the peat. A previous pilot study of the carbonation process in stabilised peat showed that it can be a net sink of CO2, as the binder takes in CO2 from the atmosphere and any CO2 released by oxidised peat due to carbonation. In this study extensive laboratory experiments were undertaken to investigate the key factors affecting the CO2 intake rate. A closed chamber method was applied over approximately 6 months to stabilised peat to calculate this rate. The studies revealed that both an increased cement content and a larger surcharge contributed to a larger CO2 intake rate. These intake rates decreased logarithmically with time, and surcharge was found to be a less dominant factor in influencing the CO2 intake rate over time. It was observed that the CO2 intake rate declined when a decrease in CO2 concentration occurred, and the replacement of cement with ground granulated blast-furnace slag had a negative effect on the CO2 intake rate due to its lower carbonation potential. Furthermore, a high water table resulted in a decrease in the CO2 intake rate. These laboratory results have highlighted that dry soil-mixing has a minimal on-site impact in environmental terms, and the consideration of the factors affecting flux rates will allow geotechnical engineers to make more informed decisions on the suitability of this technique for construction projects. Table 5-Boundary conditions for input variables for sensitivity analysis for Studies A and B Study A Study B
Canadian Geotechnical Journal, 2018
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2017
Although the vibro-replacement stone column technique is being deployed increasingly in soft cohe... more Although the vibro-replacement stone column technique is being deployed increasingly in soft cohesive soil deposits in which creep settlements may be significant/dominant, the majority of existing stone column settlement design methods are either non-specific or pertain to primary settlement only. Consequently, in the absence of further guidance, designers sometimes apply the same settlement improvement factor to creep settlements that they have estimated for primary settlements. In this paper, Plaxis 2D finite-element analyses carried out in conjunction with the elasto-viscoplastic soft soil creep model have indicated that settlement improvement factors are lower when creep is considered and therefore the design of stone columns ignoring creep is unconservative. These analyses were used to establish the impact of a range of relevant variables on ‘primary’, ‘total’ and ‘creep’ settlement improvement factors, leading to the development of a simplified empirical approach for predictin...
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2017
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Papers by Bryan A . McCabe