In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. Fibre Bragg grating (FBG) sensors have emerged as a reliable, in situ, non-destructive tool for monitoring, diagnostics and control in civil structures. The versatility of FBG sensors represents a key advantage over other technologies in the structural sensing field. In this article, the recent research and development activities in structural health monitoring using FBG sensors have been critically reviewed, highlighting the areas where further work is needed. A few packaging schemes for FBG strain sensors are also discussed. Finally a few limitations and market barriers associated with the use of these sensors have been addressed.

Fibre Bragg gratings in structural health monitoring—Present status and applications

The properties of clean sands pertaining to shear strength and stiffness have been studied extensively. However, natural sands generally contain significant amounts of silt and/or clay. The mechanical response of such soils is different from that of clean sands. This paper addresses the effects of nonplastic fines on the small-strain stiffness and shear strength of sands. A series of laboratory tests was performed on samples of Ottawa sand with fines content in the range of 5–20% by weight. The samples were prepared at different relative densities and were subjected to various levels of mean effective consolidation stress. Most of the triaxial tests were conducted to axial strains in excess of 30%. The stress-strain responses were recorded, and the shear strength and dilatancy parameters were obtained for each fines percentage. Bender element tests performed in triaxial test samples allowed assessment of the effect of fines content on small-strain mechanical stiffness.

Shear strength and stiffness of silty sand

This paper describes recent advances in stability analysis that combine the limit theorems of classical plasticity with finite elements to give rigorous upper and lower bounds on the failure load. These methods, known as finite-element limit analysis, do not require assumptions to be made about the mode of failure, and use only simple strength parameters that are familiar to geotechnical engineers. The bounding properties of the solutions are invaluable in practice, and enable accurate limit loads to be obtained through the use of an exact error estimate and automatic adaptive meshing procedures. The methods are very general, and can deal with heterogeneous soil profiles, anisotropic strength characteristics, fissured soils, discontinuities, complicated boundary conditions, and complex loading in both two and three dimensions. A new development, which incorporates pore water pressures in finite-element limit analysis, is also described. Following a brief outline of the new techniques, stability solutions ...

Geotechnical stability analysis

Scientific approaches to pile design have advanced enormously in recent decades and yet, still, the most fundamental aspect of pile design—that of estimating the axial capacity—relies heavily upon empirical correlations. Improvements have been made in identifying the processes that occur within the critical zone of soil immediately surrounding the pile, but quantification of the changes in stress and fabric is not straightforward. This paper addresses the degree of confidence we can now place (a) on the conceptual and analytical frameworks for estimating pile capacity, and (b) on the quantitative parameters required to achieve a design. The discussion is restricted to driven piles in clays and siliceous sands, with particular attention given to extrapolating from design approaches derived for closed-ended piles of relatively small diameter to the large-diameter open-ended piles that are used routinely in the offshore industry. From a practical viewpoint, we need design approaches that minimise sensitivity...

Science and empiricism in pile foundation design

Tire shreds and tire shred  soil mixtures can be used as alternative backfill material in many geotechnical applications. The reuse of tire shreds may not only address growing environmental and ec...

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Behaviour of tire shred - sand mixtures

Despite the fact that results of many instrumented pile load tests have been reported in the literature, it is difficult to find well-documented instrumentation procedures that can be used when planning a load testing programme. A load test programme designed to investigate various aspects of the design and behaviour of driven steel piles is discussed in the present paper. Although the literature contains information on load testing of instrumented piles driven in either sand or clay, limited information is available regarding their axial load response in transitional soils (soils composed of various amounts of clay, silt and sand). Results are presented for fully instrumented axial load tests performed on an H pile and a closed-ended pipe pile driven into a multilayered soil profile consisting of transitional soils. In addition, the load testing planning, the instrumentation of the piles, the testing methods and the interpretation of the pile testing data are discussed in detail in the context of this an...

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Instrumentation and axial load testing of displacement piles

Model pile load testing is effective to study the load-settlement behaviour of pile foundations given the controlled environment in which the testing is done. This paper reports a testing program in a large calibration chamber involving individual piles and pile groups installed in sand samples of three different densities. Tests on both nondisplacement and driven piles are evaluated to assess the influence of the pile installation process on pile load-settlement response. A method is proposed to predict the load-settlement response of a pile group based on the response of a single pile. The method is shown to produce estimates that are in good agreement with measurements. The influence of pile group configuration, pile spacing, soil density and method of pile installation is discussed.

Load-settlement behaviour of model pile groups in sand under vertical load

Most foundation solutions for transportation structures rely on deep foundations, often on pile foundations configured in a way most suitable to the problem at hand. Design of pile foundation solutions can best be pursued by clearly defining limit states and then configuring the piles in such a way as to prevent the attainment of these limit states. The present report develops methods for load and resistance factor design (LRFD) of piles, both nondisplacement and displacement piles, in sand and clay. With the exception of the method for design of displacement piles in sand, all the methods are based on rigorous theoretical mechanics solutions of the pile loading problem. In all cases, the uncertainty of the variables appearing in the problem and of the relationships linking these variables to the resistance calculated using these relationships are carefully assessed. Monte Carlo simulations using these relationships and the associated variabilities allow simulation of resistance minus load distributions and therefore probability of failure. The mean (or nominal) values of the variables can be adjusted so that the probability of failure can be made to match a target probability of failure. Since an infinite number of combinations of these means can be made to lead to the same target probability of failure, the authors have developed a way to determine the most likely ultimate limit state for a given probability of failure. Once the most likely ultimate limit state is determined, the values of loads and resistances for this limit state can be used, together with the values of the mean (or nominal) loads and resistances to calculate load and resistance factors. The last step in the process involves adjusting the resistance factors so that they are consistent with the load factors specified by American Association of State Highway and Transportation Officials (AASHTO). Recommended resistance factors are then given together with the design methods for which they were developed.

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2969&context=jtrp

Development of Load and Resistance Factor Design for Ultimate and Serviceability Limit States of Transportation Structure Foundations

A full-scale, double-wall, open-ended pipe pile with a diameter, B = 660 mm was densely instrumented with a combination of electrical-resistance and vibrating-wire strain gauges. The test pile was ...

Axial resistance of open-ended pipe pile driven in gravelly sand

Class F fly ash and bottom ash are solid residue byproducts produced by coal-burning plants. They are usually disposed off with a typical disposal rate of 80 % fly ash and 20 % bottom ash. To maximize the use of the coal ash, and thus significantly reduce the disposal problem that electric utility companies and our society in general face, the direct use of ponded or landfilled ash that is composed of high proportions of fly ash would be desirable. However, a general understanding of the behavior of high volume fly ash mixtures is needed. Although there have been investigations into the properties of separated single types of ash, the studies of the fly/bottom ash mixtures, especially with high fly ash contents, are very limited. Representative samples of class F fly ash and bottom ash were collected from two utility plants in Indiana and a series of extensive laboratory tests were conducted to obtain the mechanical properties of the mixture. Since the mechanical properties of ash mixtures are dependent on the mixture proportions, the investigations evaluate fly/bottom ash mixtures with different mixture ratios (with Fly ash contents of 50%, 75%, and 100%). The results obtained are merged with other considerations relevant to embankment design and construction and used to develop guidelines on coal ash utilization in highway embankments. In order to examine suitable fly/bottom ash mixture compositions and embankment geometries, slope stability analyses were performed on ash embankments with different geometries using the different properties of the ash mixtures with different mixture ratios. The limit equilibrium method was used for the stability analyses. Additionally, the corrosion potential to metal structures, which are commonly included in highway construction, is examined by performing corrosivity tests on the ash mixtures.

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Rodrigo Salgado

Papers

Instrumentation and axial load testing of displacement piles

Load-settlement behaviour of model pile groups in sand under vertical load

Development of Load and Resistance Factor Design for Ultimate and Serviceability Limit States of Transportation Structure Foundations

Axial resistance of open-ended pipe pile driven in gravelly sand

Determination of Ash Mixture Properties and Construction of Test Embankment - Part A