Cyclic jacking of piles in silt and sand

Jacked piles are becoming a valuable installation method due to the low noise and vibration involved in the installation procedure. Cyclic jacking may be used in an attempt to decrease the required installation force. Small scale models of jacked piles were tested in sand and silt in a 10 m beam centrifuge. Two different piles were tested: smooth and rough. Piles were driven in two ways with monotonic and cyclically jacked installations. The cyclically jacked installation involves displacement reversal at certain depth for a fixed number of cycles. The depth of reversal and amplitude of the cycle vary for different tests. Data show that the base resistance increases during cyclic jacking due to soil compaction at the pile toe. On the other hand, shaft load decreases with the number of cycles applied due to densification of soil next to the pile shaft. Cyclic jacking may be used in unplugged tubular piles to decrease the required installation load. © 2013 Taylor & Francis Group, London.

Management and Analysis of Unstructured Construction Data Types

Compared with structured data sources that are usually stored and analyzed in spreadsheets, relational databases, and single data tables, unstructured construction data sources such as text documents, site images, web pages, and project schedules have been less intensively studied due to additional challenges in data preparation, representation, and analysis. In this paper, our vision for data management and mining addressing such challenges are presented, together with related research results from previous work, as well as our recent developments of data mining on text-based, web-based, image-based, and network-based construction databases.

Uplift resistance of buried pipelines at low cover-diameter ratios

Reliable estimates for the maximum available uplift resistance from the backfill soil are essential to prevent upheaval buckling of buried pipelines. The current design code DNV RP F110 does not offer guidance on how to predict the uplift resistance when the cover:pipe diameter (H/D) ratio is less than 2. Hence the current industry practice is to discount the shear contribution from uplift resitance for design scenarios with H/D ratios less than 1. The necessity of this extra conservatism is assessed through a series of full-scale and centrifuge tests, 21 in total, at the Schofield Centre, University of Cambridge. Backfill types include saturated loose sand, saturated dense sand and dry gravel. Data revealed that the Vertical Slip Surface Model remains applicable for design scenarios in loose sand, dense sand and gravel with H/D ratios less than 1, and that there is no evidence that the contribution from shear should be ignored at these low H/D ratios. For uplift events in gravel, the shear component seems reliable if the cover is more than 1-2 times the average particle size (D50), and more research effort is currenty being carried out to verify this conclusion. Strain analysis from the Particle Image Velocimetry (PIV) technique proves that the Vertical Slip Surface Model is a good representation of the true uplift deformation mechanism in loose sand at H/D ratios between 0.5 and 3.5. At very low H/D ratios (H/D < 0.5), the deformation mechanism is more wedge-like, but the increased contribution from soil weight is likely to be compensated by the reduced shear contributions. Hence the design equation based on the Vertical Slip Surface Model still produces good estimates for the maximum available uplift resistance. The evolution of shear strain field from PIV analysis provides useful insight into how uplift resistance is mobilized as the uplift event progresses. Copyright 2010, Offshore Technology Conference.

Sustainable binders for soil stabilisation

Portland cement is the most commonly and widely used binder in ground improvement soil stabilisation applications. However, many changes are now affecting the selection and application of stabilisation additives. These include the significant environmental impacts of Portland cement, increased use of industrial by-products and their variability, increased range of application of binders and the development of alternative cements and novel additives with enhanced environmental and technical performance. This paper presents results from a number of research projects on the application of a number of Portland cement-blended binders, which offer sustainability advantages over Portland cement alone, in soil stabilisation. The blend materials included ground granulated blastfurnace slag, pulverised fuel ash, cement kiln dust, zeolite and reactive magnesia and stabilised soils, ranging from sand and gravel to clay, and were assessed based on their mechanical performance and durability. The results are presented in terms of strength and durability enhancements offered by those blended binders.

Soil conditioning under London

The CTRL Contract 220 covered 7.5km twin-bore tunnels excavated between late 2002 and early 2004 from Stratford Box to St Pancras station in Central London. To ensure efficient machine operation as well as the transport and disposal of soil, soil conditioning treatments were applied. Specifically, the foam injection ratio (FIR) and the polymer injection ratio (PIR) (injected volume of foam and polymer solution expressed as a percentage of the excavated soil volume) were employed. It was found that carefully selected soil conditioning allowed chamber pressures of 200kPa or more to be accurately controlled in the stiff London Clay and to an extent, in the very stiff clays of the Lambeth Group. Average FIRs of 50% and PIRs of 7 and 9% were used in the Thanet Sand and in the Lambeth Group Clays. In contrast, much lower quantities of foam were used in the London Clay.

Mechanism of pile group settlement in liquefiable soils

This paper examines the settlement of instrumented 2 × 2 model pile groups in liquefiable soil based on the results of dynamic centrifuge tests. The piles are end-bearing in dense sand, and are instrumented such that base, shaft and total pile load components can be measured. The data suggest that the overall co-seismic group settlement is accrued from incremental settlements of the individual piles as the group rocks under the action of the kinematic and inertial lateral loads. A Newmarkian framework for describing this behaviour is presented in which permanent settlement is incremented whenever the load in any of the piles exceeds the capacity of the soil to support the pile. This bearing capacity of the piles in liquefied soil is estimated based on measured dynamic soil properties during shaking and observations of the changes in load carried by the piles. The contribution of the pile cap in reducing settlement is also discussed. © 2008 ASCE.

The influence of tunnelling on piled foundations

A study of the influence of tunnelling on piled foundations was recently completed at the University of Cambridge. The study focussed on tunnelling near driven piles in dense sand and was carried out by means of centrifuge modelling. This paper presents a summary of the main findings, describing the mechanism controlling tunnelling-induced pile behaviour, a zone of influence around the tunnel where piles might be affected and recommendations for tunnelling near piles in practice. Both single piles and pile groups are considered.

A laboratory-scale buried charge simulator

An experimental technique has been developed in order to mimic the effect of landmine loading on materials and structures to be studied in a laboratory setting, without the need for explosives. Compressed gas is discharged beneath a sand layer, simulating the dynamic flow generated by a buried explosive. High speed photography reveals that the stages of soil motion observed during a landmine blast are replicated. The effect of soil saturation and the depth of the sand layer on sand motion are evaluated. Two series of experiments have been performed with the buried charge simulator to characterise subsequent impact of the sand. First, the time variation in pressure and impulse during sand impact on a stationary target is evaluated using a Kolsky bar apparatus. It is found that the pressure pulse imparted to the Kolsky bar consists of two phases: an initial transient phase of high pressure (attributed to wave propagation effects in the impacting sand), followed by a lower pressure phase of longer duration (due to lateral flow of the sand against the Kolsky bar). Both phases make a significant contribution to the total imparted impulse. It is found that wet sand exerts higher peak pressures and imparts a larger total impulse than dry sand. The level of imparted impulse is determined as a function of sand depth, and of stand-off distance between the sand and the impacted end of the Kolsky bar. The second study uses a vertical impulse pendulum to measure the momentum imparted by sand impact to a target which is free to move vertically. The effect of target mass upon imparted momentum is investigated. It is concluded that the laboratory-scale sand impact apparatus is a flexible tool for investigating the interactions between structures and dynamic sand flows. © 2013 Elsevier Ltd. All rights reserved.

Mechanical characterisation of hydrogel materials

Interest in hydrogel materials is growing rapidly, due to the potential for hydrogel use in tissue engineering and drug delivery applications, and as coatings on medical devices. However, a key limitation with the use of hydrogel materials in many applications is their relatively poor mechanical properties compared with those of (less biocompatible) solid polymers. In this review, basic chemistry, microstructure and processing routes for common natural and synthetic hydrogel materials are explored first. Underlying structure-properties relationships for hydrogels are considered. A series of mechanical testing modalities suitable for hydrogel characterisation are next considered, including emerging test modalities, such as nanoindentation and atomic force microscopy (AFM) indentation. As the data analysis depends in part on the material's constitutive behaviour, a series of increasingly complex constitutive models will be examined, including elastic, viscoelastic and theories that explicitly treat the multiphasic poroelastic nature of hydrogel materials. Results from the existing literature on agar and polyacrylamide mechanical properties are compiled and compared, highlighting the challenges and uncertainties inherent in the process of gel mechanical characterisation. © 2014 Institute of Materials, Minerals and Mining and ASM International.