Fundamental basis of single-point liquid limit measurement approaches

The liquid limit is defined as the point at which a clay’s behaviour changes from liquid to plastic. This transition is in reality gradual, rather than sudden. The definition of when this transition has been crossed must therefore be determined based on some arbitrary criterion. The percussion cup method of determining liquid limit in the manner suggested by Atterberg and subsequently standardised by Casagrande determines liquid limit as the water content at which 25 standard blows are required to cause closure of a standard groove. In order to speed up the determination of the liquid limit, a single-point method is defined in ASTM D4318, and in many other codes, to interpret liquid limit from groove closure at a different numbers of blows by assuming a relationship between water content and the number of blows required for groove closure. These methods differ considerably between different codes of practice currently in use worldwide. This paper examines the procedures for single-point determination of the liquid limit and offers some fundamental explanations that underpin the applicability of these procedures. This paper demonstrates that the variation in single-point liquid limit procedures suggested by various codes of practice can be attributed to the variability of liquid limit devices, rather than to variation in the soils being tested.This is the author's accepted manuscript. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0169131714004062?np=

The undrained strength - liquidity index relationship

A database of 641 fall cone tests on 101 soil samples from 12 countries has been analysed to determine the best mathematical relationship linking undrained shear strength with liquidity index. From the database, it is shown that the use of a linear relationship linking liquidity index and the logarithm of undrained shear strength that uses the commonly assumed 100-fold factor increase in strength from the liquid to plastic limit overpredicts the measured data of soil strength. The use of a factor of about 35 for the ratio between the strength at liquid limit and that extrapolated to the plastic limit is shown to be more realistic. Logarithmic liquidity index is examined and found to also correlate strongly with the logarithm of undrained shear strength; however, it is shown that no great statistical improvement is present compared with the semi-logarithmic formulation. When considering data of individual soils a power law fitting is statistically shown to be the preferred mathematical function.The authors gratefully acknowledge Dr Kevin Stone of the University of Brighton for providing a copy of the thesis by B. Kyambadde. Thanks to Professor Malcolm Bolton for his helpful comments. Thanks to Dr Sarah Allen for her help with the translation of the Swedish version of Atterberg’s original paper. The authors also thank all the reviewers of this paper for their insightful comments and helpful suggestions.This is the author accepted manuscript, which can also be found on the NRC Research Press website here: http://www.nrcresearchpress.com/doi/abs/10.1139/cgj-2013-0169#.U7awT_ldXH

Categories of SHM deployments: Technologies and capabilities

The findings of an extensive literature survey focusing on bridge structural health monitoring (SHM) deployments are presented. Conventional, maturing, and emerging technologies are reviewed as well as deployment considerations for new SHM endeavors. The lack of published calibration studies (and quantification of uncertainty studies) for new sensors is highlighted as a major concern and area for future research. There are currently very few examples of SHM systems that have clearly provided significant value to the owners of monitored structures. The results of the literature survey are used to propose a categorization system to better assess the potential outcomes of bridge SHM deployments. It is shown that SHM studies can be categorized as one (or a combination) of the following: (1) anomaly detection, (2) sensor deployment studies, (3) model validation, (4) threshold check, and (5) damage detection. The new framework aids engineers specifying monitoring systems to determine what should be measured and why, hence allowing them to better evaluate what value may be delivered to the relevant stakeholders for the monitoring investments.This work was partly funded by EPSRC Grant No. EP/K000314/1: Innovation Knowledge Centre for Smart Infrastructure and Construction.This is the final version of the article. It first appeared from American Society of Civil Engineers via http://dx.doi.org/10.1061/(ASCE)BE.1943-5592.000073

Use of fall cones to determine Atterberg limits: A review

This paper reviews the percussion-cup liquid limit, thread-rolling plastic limit (PL) and various fall-cone and other approaches employed for consistency limit determinations on fine-grained soil, highlighting their use and misuse for soil classification purposes and in existing correlations. As the PL does not correspond to a unique value of remoulded undrained shear strength, there is no scientific reason why PL measurements obtained using the thread-rolling and shear-strength-based fall-cone or extrusion methods should coincide. Various correlations are established relating liquid limit values deduced using the percussion-cup and fall-cone approaches. The significance of differences in the strain-rate dependency on the mobilised fall-cone shear strength is reviewed. The paper concludes with recommendations on the standardisation of international codes and the wider use of the fall-cone approach for soft to medium-stiff clays in establishing the strength variability with changing water content and further index parameters. </jats:p

Analysis of fiber-optic strain-monitoring data from a prestressed concrete bridge

This paper presents data from fiber-optic strain monitoring of the Nine Wells Bridge, which is a three-span, pretensioned, prestressed concrete beam-and-slab bridge located in Cambridgeshire in the United Kingdom. The original deployment at the site and the challenges associated with collecting distributed strain data using the Brillouin optical time domain reflectometry (BOTDR) technique are described. In particular, construction and deployment issues of fiber robustness and temperature effects are highlighted. The challenges of interpreting the collected data as well as the potential value of information that may be obtained are discussed. Challenges involved with relating measurements to the expected levels of prestress, including the effects due to debonding, creep, and shrinkage, are discussed and analyzed. This paper provides an opportunity to study whether two commonly used models for creep and shrinkage, adequately model data collected in field conditions.This work was supported by the following EPSRC grants: EP/D076870/1, Smart Infrastructure: Wireless Sensor Network System for Condition Assessment and Monitoring of Infrastructure; EP/I019308/1, Innovation Knowledge Centre for Smart Infrastructure and Construction; and EP/K000314/1, Innovation and Knowledge Centre for Smart Infrastructure and Construction - Collaborative Programme Tranche 1

Minding the geotechnical data gap:appraisal of the variability of key soil parameters for slope stability modelling in Saint Lucia

Identification of failure thresholds and critical uncertainties associated with slope stability often requires the specification of geotechnical parameter values for input into a physically-based model. The variation of these parameters (including mechanical soil properties such as effective friction angle and cohesion) can have a significant impact on the computed factor of safety. These uncertainties arise from natural variations in soils, measurement techniques, and lack of reliable information. Researchers may use statistical analysis coupled with numerical simulation to determine possible ranges of slope factors of safety and the relative influence of geotechnical and other parameters, such as topsoil depth and rainfall. This study investigates the variation of geotechnical parameters observed on the island of Saint Lucia in the Eastern Caribbean. A database of particle size distributions, in-situ moisture contents, Atterberg and direct shear box test results is compiled from 91 samples of tropical soils in Saint Lucia. A study of various probability distributions shows that the Weibull distribution may be favoured for the effective friction angle of the Saint Lucian soils considered based on the Akaike information criterion, employed as an estimator of the relative quality of statistical models dealing with the trade-off between goodness-of-fit and simplicity of the model

Railway bridge structural health monitoring and fault detection: state-of-the-art methods and future challenges

Railway importance in the transportation industry is increasing continuously, due to the growing demand of both passenger travel and transportation of goods. However, more than 35% of the 300,000 railway bridges across Europe are over 100-years old, and their reliability directly impacts the reliability of the railway network. This increased demand may lead to higher risk associated with their unexpected failures, resulting safety hazards to passengers and increased whole life cycle cost of the asset. Consequently, one of the most important aspects of evaluation of the reliability of the overall railway transport system is bridge structural health monitoring, which can monitor the health state of the bridge by allowing an early detection of failures. Therefore, a fast, safe and cost-effective recovery of the optimal health state of the bridge, where the levels of element degradation or failure are maintained efficiently, can be achieved. In this article, after an introduction to the desired features of structural health monitoring, a review of the most commonly adopted bridge fault detection methods is presented. Mainly, the analysis focuses on model-based finite element updating strategies, non-model-based (data-driven) fault detection methods, such as artificial neural network, and Bayesian belief network–based structural health monitoring methods. A comparative study, which aims to discuss and compare the performance of the reviewed types of structural health monitoring methods, is then presented by analysing a short-span steel structure of a railway bridge. Opportunities and future challenges of the fault detection methods of railway bridges are highlighted

A simple prediction model for asphalt surface texture incorporating mix gradation and air voids

This paper presents the results of a preliminary study that seeks to show how asphalt grading and air voids are related to the texture depth of asphalt. The fiftieth percentile particle size (D50) is shown to be a good predictor of texture depth measurements from a collected database of field and laboratory studies. The D50 is used to normalise collected texture data and this 'relative texture' is shown to correlate with air voids. Regression analyses confirm that air voids should be included along with a measure of gradation in the interpretation of asphalt surface texture.The derived formulae are used to develop correlation charts