Development of a model pile for heat transfer experiments in the centrifuge

Conventional energy piles use embedded plastic pipes to circulate a fluid through solid concrete which enables transfer of heat into, or out of, the ground as required. Such piles are relatively low efficiency owing to the poor conductivity of the concrete in which the pipes are embedded. They are also known to be susceptible to damage during construction and their adoption as a sustainable energy source has, as a result, been limited. A novel method of heat transfer, which is much less susceptible to damage during construction, and has been found in field trials to be more energy efficient, exploits the significantly higher conductivity of water in a rotary augured hollow, cast in-situ, or precast pile. In such a pile the plastic pipes are placed in the water filled central void of the pile. Such an arrangement will lead to the ground around the pile experiencing a lower range of temperature variation compared with standard energy piles and the influence of this effect on pile capacity will be explored. In order to model multiple cycles of temperature variation to which the ground around a prototype pile may be subjected it is necessary design experimental apparatus that is capable of rapid heating and cooling and with high thermal conductivity materials. The paper will describe the design of a model pile which incorporates an immersed heating element capable of bringing the pile temperature to a specific maximum value and a means of quickly purging the heated water to return the pile temperature to the desired minimum value whilst the pile carries a constant axial load in the centrifuge

Disseminated tuberculosis in a patient treated with a JAK2 selective inhibitor: a case report

Background Primary myelofibrosis is a myeloproliferative disorder characterized by bone marrow fibrosis, abnormal cytokine expression, splenomegaly and anemia. The activation of JAK2 and the increased levels of circulating proinflammatory cytokines seem to play an important role in the pathogenesis of myelofibrosis. Novel therapeutic agents targeting JAKs have been developed for the treatment of myeloproliferative disorders. Ruxolitinib (INCB018424) is the most recent among them. Case presentation To our knowledge, there is no evidence from clinical trials of an increased risk of tuberculosis during treatment with JAK inhibitors. Here we describe the first case of tuberculosis in a patient treated with Ruxolitinib, a male with a 12-year history of chronic idiopathic myelofibrosis admitted to our Institute because of fever, night sweats, weight loss and an enlarging mass in the left inguinal area for two months. Conclusion Treatment with Ruxolitinib may have triggered the reactivation of latent tuberculosis because of an inhibition of Th1 response. Our case highlights the importance of an accurate screening for latent tuberculosis before starting an anti-JAK 2 treatmen

Tests of varied sample preparation methods for centrifuge modelling

Centrifuge modelling is an established technique capable of investigating the ground’s response to complex geotechnical events. Centrifuge models are often created from reconstituted soil, with well-defined boundary conditions and known soil parameters. Clay soil models may be prepared by mixing clay powder with distilled water to form a slurry. This slurry is placed within a soil container and subjected to a vertical stress (usually in a consolidation press or consolidated inflight). This creates an isotropic model but there is a fundamental difference between this soil model and naturally occurring soil deposits. The structure and fabric present within a naturally occurring clay is not reproduced by this preparation process. It is well-established that structure and fabric in naturally deposited soils are as significant in their effect on soil behaviour as, for instance, the stress history. Inherent structure and fabric within clay soils creates anisotropy which can vary with depth, this is particularly apparent when considering the permeability. Creating a soil model for centrifuge modelling with representative permeability anisotropy would allow for a better representation of consolidation driven events and the ability to observe long-term behaviour of complex geotechnical events. Currently, there are limited methods of doing so, leading to a considerable gap in knowledge associated with the behaviour of layered ground. This paper describes the development of the equipment and experimental procedure for quantifying the structure developed by different sample preparation techniques for centrifuge modelling

A numerical model to study the response of piles under lateral loading in unsaturated soils

The interaction between a laterally loaded pile and the surrounding soil is typically limited to the shallower soil layer. Often, this zone is above the water table and therefore the interaction takes place under unsaturated conditions. The available evidence is scarce but suggests that unsaturated conditions play a major role on the pile’s response. The actual mechanisms governing the soil–pile interaction under unsaturated soil conditions are not understood entirely, and this paper provides a useful insight on this topic. The analysis is carried out with a fully coupled three-dimensional numerical model, the soil behaviour is simulated with a Modified Cam Clay Model extended to unsaturated conditions. The model accounts for the increase in stiffness and strength of unsaturated soils as well as the volumetric collapse upon wetting. The constitutive model is calibrated on the laboratory data and validated against centrifuge data with satisfying agreement. The results highlight the substantial differences in the soil reaction against the pile depending on different water saturation profiles. The study also shows that the influence of unsaturated conditions on the pile response increases as the pile’s flexibility increases. Comparing the findings with currently available design methods such as the p-y curves, it is found that these do not adequately describe the unsaturated soil reaction against the pile, which opens the door for new research in the field. The proposed numerical model is a promising tool to further investigate the mechanisms underlying the soil–pile interaction under unsaturated soils

Numerical modelling of the response of an unsaturated silty soil under wetting and gravitational loading processes

This paper presents the results of a numerical study aiming at simulating the response of an unsaturated fine-grained soil under wetting and gravitational loading processes. This study is based on the results of some centrifuge tests carried out to assess the influence of partial saturation on the laterally loaded pile response. The hydro-mechanical behaviour of the silty soil is described using a constitutive model adapted to unsaturated conditions. The model predictions are compared with the measurements provided by LVDTs and laser transducers in the first phases of the experimental study. Besides validating the model, the numerical study aimed at investigating the influence of the after-compaction conditions on both the displacement field and the evolution of the more significant state variables during imbibition and gravitational loading processes. Finally, an additional analysis is conducted to determine the effects of the pile installation on the soil response

Centrifuge Modelling of Long-term Tunnelling Ground Movements

The increasing demand for public transport provision in cities has resulted in a requirement for enlarged public transport infrastructure. Where underground railways represent an important component of these systems, tunnel construction will inevitably lead to some degree of ground movement that can cause damage to surface structures and buried structures and services. It is important, therefore, that in the design of tunnels in urban environments these ground movements are predicted reliably. Predicting short-term ground movements resulting from tunnelling is standard when assessing the potential for damage to adjacent infrastructure. However, long-term tunnelling-induced ground movements and how these develop are understood less well and a research programme, based on geotechnical centrifuge modelling, is being conducted to improve our fundamental scientific understanding of this. The first stage of the programme has been to develop an apparatus that simulates the construction of a tunnel with a lining of known stiffness and permeability and allows construction ground loss to be replicated correctly. This paper describes the initial development of the apparatus along with results and analysis that demonstrates the suitability of the technique for the proposed study. The results obtained were observed to represent the short-term settlements that might be expected above a tunnel excavated in clay. The results also prove the modelling technique suitable for application in a full parametric study in which the geometry and boundary conditions of the model will be varied together with the permeability of the tunnel liner

Physical modelling of piles under lateral loading in unsaturated soils

In this paper, selected aspects of an experimental study conducted in a geotechnical centrifuge are discussed. The tests aimed to explore the effects of partial saturation of soil on the response of a single pile subjected to a combination of lateral force and bending moment under drained conditions. The soil used in the experiments is a low plasticity silty soil, named B-grade kaolin, characterized by a relatively high permeability compared to the typical values for clayey soils. Two different elevations of the water table and its effects on the pile response under loading are studied. The data show a marked influence of soil partial saturation on the pile response, both under working loads and ultimate loads. In particular, under working loads, the displacement of the head of the pile is appreciably lower than that measured under saturated conditions

A low-cost miniature immersible pore water pressure transducer

The ability to measure pore water pressure accurately in geotechnical models is vital for allowing researchers to quantify effective stress and, frequently, its temporal variation. The earliest use of electrical devices to measure pore water pressure in specific locations within a model employed a standard laboratory pressure transducer located outside the boundaries of the model connected to tubing inserted into the model. However, this technique was superseded by the development (some 40 years ago) of submersible miniature pore water pressure measuring devices that could be located within a model to measure pore pressure directly at specified locations. In particular, miniaturisation allowed these transducers to be used in small scale centrifuge models. This facilitated, across the full spectrum of geotechnical engineering modelling, both enhanced understanding of mechanisms, by permitting quantitative analysis, and validation of numerical techniques. The earliest miniature transducers, the PDCR81 device manufactured by Druck, rapidly became universally adopted by the geotechnical modelling community. The production of this device was halted about 10 years ago, but other manufacturers have developed similar miniature pore water pressure transducers. Whilst the newer devices have been demonstrated to be effective their unit cost is relatively expensive; owing to the low volume of manufacture. This can result in forced limitations in the number that may be in a model, or a reluctance to use them in zones of models where they might be damaged. The requirement for a cheaper but equally reliable device prompted the work described in this paper. This is now achievable because of the development for the consumer market of a mass produced robust, immersible pressure device that has a very low unit cost. The paper will describe the development of a miniature transducer, employing this device, that can be located within models in a similar way to the PDCR81

Experimental technique for creating enhanced capacity piles in a centrifuge environment

none3The paper describes experimental techniques developed in the geotechnical centrifuge facility at City, University of London to test bored pile foundations with profiled bores designed to increase pile capacity. Improvements were made to existing equipment to ensure accurate measurement of the load displacement response at working loads and potential errors quantified.openLeonardo Maria Lalicata, Andrew McNamara, Sarah Elizabeth StallebrassLalicata, LEONARDO MARIA; Mcnamara, Andrew; Elizabeth Stallebrass, Sara