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...

/pdf/behaviour-of-tire-shred-sand-mixtures-2u9smxp58l.pdf

Behaviour of tire shred - sand mixtures

The authors acknowledge the observations of discussers Decourt and Rodriguez-Roa regarding the adequacy of the bearing capacity equations used in the research. The authors cite the differing views of the discussers, pointing to the concern raised by discusser Rodriguez-Roa that the wide variance in results might serve to entirely discredit the usefulness of the bearing capacity equation; while noting the point of discusser Decourt, who, citing others in agreement, believes that discrediting the bearing capacity equation is precisely the point. However, the authors, themselves, state the belief that the bearing capacity equation, as seen in the forms emerging from current research, should be embraced. The authors add that the purpose of the bearing capacity equation is to calculate the limit or plunging load of the footing. They claim to have not used it beyond its designed purpose. As for discusser Decourt's point that the bearing capacity equation (the so-called triple N formula) is wrong, the authors explain that the equation, initially proposed for the indentation of metals, has evolved over time to include more realistic geotechnical and foundation engineering problems (i.e. shape and depth, along with base, ground, and load inclinations). In its present form, the authors note the bearing capacity equation has high empirical content, despite being derived from rigorous analysis at the beginning. Addressing discusser Rodriguez-Roa's point about using experimental data to determine the validity of the bearing capacity equation, the authors believe that the final solution to the question must first come from establishing a proper analytical basis, as explored by the authors (e.g., Salgado et al. 2004, Lyamin et al. 2006, Martin 2005). These examples rigorously calculate limit loads and then follow this with proper validation against well-performed, well-instrumented load tests on properly and completely characterized soils. The authors note that the bearing capacity equation, even its traditional forms, was never designed to compute ultimate loads defined on a basis of a specific settlement value. The discussers agree with discusser Decourt about the bearing capacity formula having limitations in its present form. At the same time, the authors also agree with discusser Rodriguez-Roa about retaining the concept of the bearing capacity equation as a tool for geotechnical and foundation engineers. The authors predict that practitioners in the near future will be provided with both an extremely useful and nearly exact version of the bearing capacity formula; one that will have a small, precisely known level of uncertainty.

Closure to “Estimation of Bearing Capacity of Circular Footings on Sands Based on Cone Penetration Test” by Junhwan Lee and Rodrigo Salgado

Drilled-displacement (DD) piles are a distinctive class of auger piles installed by using specially designed drilling tools. Although these piles are increasingly being used in different parts of the world, the available design methods rely on empirical rules. This paper outlines a promising approach to quantify shaft resistance of DD piles installed in sand. Finite element analyses (FEAs) performed in this study use a two-surface, plasticity-based constitutive model for sand and involve three distinct analysis stages: pile installation, removal of drilling tool from the ground, and loading of the pile. Based on FEA results, a set of equations that can be used in calculation of the limit unit shaft resistance of DD piles in sand is proposed. Moreover, the shaft resistance available for a DD pile is compared with that available for a nondisplacement (e.g., drilled shaft) and a full-displacement pile installed by monotonic jacking.

Recent Advances in Calculation of Shaft Resistance of Drilled-Displacement Piles

Experimental Study of Crushing in Cone Penetration Test in Silica Sand

Site Variability Characterization Using Cone Penetration Test Data

In view of the vast numbers of used tyres stockpiled across the USA and their problematic disposal characteristics, it makes environmental and financial sense to find ways of recycling them. This briefing paper describes a research project which was undertaken in Indiana to construct and test a soil-tyre embankment. Findings are outlined and recommendations made. (A)

Rodrigo Salgado

Papers

Closure to “Estimation of Bearing Capacity of Circular Footings on Sands Based on Cone Penetration Test” by Junhwan Lee and Rodrigo Salgado

Recent Advances in Calculation of Shaft Resistance of Drilled-Displacement Piles

Experimental Study of Crushing in Cone Penetration Test in Silica Sand

Site Variability Characterization Using Cone Penetration Test Data

Briefing: construction of tyre-shreds test embankment