The present work stems from the design of a viaduct in South Wales, U.K., where full-scale pile testing was carried out to assess whether the proposed design methods would meet the required load capacity and settlement criteria for the working piles. Five fully instrumented large diameter bored cast in situ piles, up to 30 m deep, were installed in weathered mudstone and tested under vertical loading. A sixth pile, which had no shaft instrumentation, was formed with a voided toe. In conjunction with vast soil data from 218 site investigation boreholes, the extensive data produced from the load tests were analyzed to quantify the key parameters considered to influence load transfer and settlement behaviour. Each pile was first calibrated using four methods to establish the as-built stiffness, taking into account the nonlinearity of concrete and the effect of partial steel encasement. It is demonstrated that the current national norms for bored pile design in cohesive soil soft rock are overconservative for South Wales ground conditions. To ameliorate this, alternative methods are proposed, which lead to improved reliability and accuracy in shaft and base capacity assessment. In addition, a numerical model is developed that can be used to predict the complete load-settlement variation up to the ultimate state. The model is sufficiently expounded to allow its immediate application in pile design by geotechnical engineers.Key words: piled foundations, load tests, bearing capacity and settlement, Mercia mudstone.
This paper discusses the definition of, and the distinction between, deformability and ductility of reinforced concrete (RC) beams that are strengthened by advanced composites. The study examines the suitability of a new, design-based method for the determination of deformability, as well as an energy-based process, which is found to be suitable for quantifying the ductility levels of fibre-reinforced polymer (FRP)-strengthened RC members. Ten FRP-strengthened RC beams and four slabs have been load-tested to ultimate failure in the current study. The test results, together with the load–deflection data of an additional 26 beams from literature, form the basis of analyses and discussions. The paper concludes that high deformability does not necessarily lead to good ductility, as very brittle failure modes of such beams have been observed in the experimental studies and reported in literature. It was found that a ductility index of between 2·0 and 2·5 reflects 25–33% of elastic energy stored in the strengthened system. This level of elastic energy is considered to be the maximum acceptable in FRP-strengthened concrete flexural elements for ductile behaviour. It was also found that for ductile failure modes the deformability and ductility indices tend to converge, whereas for brittle behaviour the deformability index could be up to 33% higher. The results presented in this paper provide a rationale for the ductility considerations to be incorporated into the development of design equations for FRP strengthening.
This paper reports on the engineering properties and microstructure of concrete incorporating slate waste aggregates generated from roofing slate production in the UK. Various concrete mixtures were designed using different sizes of slate waste as aggregate replacement. Concrete produced with limestone aggregate was used as control. The results showed that concrete produced with limestone aggregate tended to fail predominantly through the interfacial zone between the aggregate surface and the cement paste and mortar, without any observed aggregate fragmentation. In contrast, the concrete made with slate waste aggregate showed signs of failure emanating from both the interfacial zone as well as from the cracking and subsequent fragmentation of the aggregates. The findings show that the concrete made with slate waste aggregates attained compressive strength of 25–30 N/mm2, splitting strength of 2–3 N/mm2 and elastic modulus of 25–32 kN/mm2 thus indicating potential for using slate waste as a replacement for limestone aggregate in most low- to medium-strength engineering applications.
An empirical method is developed for estimating the load transfer and deformation of drilled, in situ formed piles subjected to axial loading. Firstly, governing equations for soil-pile interaction are developed theoretically, taking into account spatial variations in: (a) shaft resistance distribution and (b) ratio of load sharing between the shaft and base. Then generic load transfer models are formulated based on examination of data from 10 instrumented test piles found in the literature. The governing equations and load transfer models are then combined and appropriate boundary conditions defined. Using an incremental-iterative algorithm whereby all the boundary conditions are satisfied simultaneously, a numerical scheme for solving the combined set of equations is developed. The algorithm is then developed into an interactive computer program, which can be used to predict the loadsettlement and axial force distribution in piles. To demonstrate its validity, the program is used to analyse four published case records of test piles, which other researchers had analysed using the following three computationally demanding tools: (a) load transfer (t-z), (b) finite difference and (c) finite element methods. It is shown that the proposed method which is much less resource-intensive, predicts both the load-settlement variation and axial force distribution more accurately than methods: (a-c) above.
A semi-empirical method has been developed which can predict the characteristics of large-diameter, bored, cast in situ piles in Mercia mudstone, at every stage of loading up to the ultimate state. The analysis is based on mathematical representation of: (a) the mobilization of shaft resistance and end bearing with increasing pile settlement; (b) the variation in load sharing between the pile shaft and base; (c) where present, the additional influence of compressible soil debris on settlement at pile base level; and (d) the effect of nonlinear stress–strain behaviour of concrete on pile compression, hence settlement. The predictive method has been validated against a large database of full-scale pile tests in Mercia mudstone and other cohesive soils. The database comprised test piles with or without instrumentation and having a wide range of diameters and lengths. In every case, the predictive capability is judged to be accurate and satisfactory. The method is also capable of dealing with special circumstances whereby a pile is specifically constructed to support load purely in shaft resistance or end bearing. The improved predictive capability of this method, in pile analysis, is expected to result in a more cost-effective construction.
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