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

This paper presents, for sand, a formulation for a surface in stress space defining the onset of dilatancy based on the volumetric threshold strain concept, the expression for the small-strain shea...

Dilatancy-triggering surface for advanced constitutive modelling of sand

Coal combustion by-products of fly ash and bottom ash may be disposed separately, or may be commingled for disposal. Markets for any product, except high calcium Class C fly ash, are extremely limited. However, the other fly ash areas and the bottom ashes have been demonstrated to be excellent embankment materials. The research reported in this paper makes the economic use of these presently wasted materials more technically feasible. Where waste fly ashes and bottom ashes are disposed separately, there is a need to know the geotechnical behavior of explicit mixtures of them. Mixtures of optimal performance are thus identified and recommended. Where the products are commingled for disposal, it is usual to find that the fly/bottom mixture varies widely within the deposit. Thus, materials excavated for use are implicit mixtures, whose composition must be determined, and parameters measured. Compaction control of these mixtures becomes an issue because of their variability. The paper affords guidelines for the selection of fly/bottom ash mixtures, as well as the technology of controlling their compaction and predicting their behavior.

Building embankments of coal combustion fly ash-bottom ash mixtures

The standard penetration test (SPT) is the most commonly used in situ test for site investigation. The test procedure consists of driving a standard split-spoon sampler into the ground and measuring the number of blows required for penetration of the sampler at specific depths. Disturbed samples are retrieved and used for soil identification in the field and for performing index tests in the laboratory. Over time, many sources of errors were identified regarding the SPT equipment and testing procedure. The SPT-Torque test (SPT-T) is a modification of the original SPT procedure and consists of rotating the standard sampler while torque is measured after it is driven the required 0.45 meters. Purdue University developed the first automated torqueing hardware prototype in 2010 as part of this INDOT/ JTRP-funded research project. Glacial deposits are found across the majority of the state of Indiana. Glacial till is a highly variable soil due to the type of source material that it is composed of and the vast area that it covers. The developed SPT-Torque equipment was selected by INDOT for use in glacial till soils found within the state of Indiana. By performing torque tests, additional in situ data is collected, thereby improving engineering design. In this research, data collected from side-by-side field testing (SPT, SPT-T and CPT) at various sites in the state of Indiana were used in the development of blow count, torque, and cone resistance correlations for Indiana soils. Study Objectives

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Development of SPT-Torque Test Correlations for Glacial Till

One of the most important factors in earthwork-related design is the correct estimation of the water content of in situ soil because its mechanical response to loading and construction activities depends strongly on its water content at the time of construction. However, because the time between site investigation, design and construction phases varies substantially for any given project, initial estimates of soil water content may no longer apply. Occurrence of excessive soil moisture in the in situ soil at the time of construction leads to low strength, which inevitably results in constructability problems, particularly for fine-grained soils. If the strength of the foundation soil is too low, it is not capable of sustaining the loads due to construction activities. Changes in soil moisture over time have led to a larger number of change orders for INDOT. Once a change order is seen as necessary, INDOT engineers and contractors working at a jobsite have to then agree on how to proceed and spend extra time and effort to bring the water content of the in situ soil to the desired level or redo the design for current conditions before the construction process can actually begin. This report presents a methodology that can be used to estimate the water content of fine-grained soils (A-4, A-6 and A-7-6 according to the AASHTO classification system) found in Indiana near the ground surface (within the top 5 ft. [150 cm]) and to assess the impact of changes in water content of fine-grained soils on their constructability.

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Moisture-Strength-Constructability Guidelines for Subgrade Foundation Soils Found in Indiana

The Engineering of Foundations, Slopes and Retaining Structures rigorously covers the construction, analysis, and design of shallow and deep foundations, as well as retaining structures and slopes. It includes complete coverage of soil mechanics and site investigations. This new edition is a well-designed balance of theory and practice, emphasizing conceptual understanding and design applications. It contains illustrations, applications, and hands-on examples that continue across chapters. Soil mechanics is examined with full explanation of drained versus undrained loading, friction and dilatancy as sources of shear strength, phase transformation, development of peak effective stress ratios, and critical-state and residual shear strength. The design and execution of site investigations is evaluated with complete discussion of the CPT and SPT. Additional topics include the construction, settlement and bearing capacity of shallow foundations, as well as the installation, ultimate resistance and settlement of deep foundations. Both traditional knowledge and methods and approaches based on recent progress are available. Analysis and design of retaining structures and slopes, such as the use of slope stability software stability calculations, is included. The book is ideal for advanced undergraduate students, graduate students and practicing engineers and researchers. 

Rodrigo Salgado

Papers

Dilatancy-triggering surface for advanced constitutive modelling of sand

Building embankments of coal combustion fly ash-bottom ash mixtures

Development of SPT-Torque Test Correlations for Glacial Till

Moisture-Strength-Constructability Guidelines for Subgrade Foundation Soils Found in Indiana

The Engineering of Foundations, Slopes and Retaining Structures