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

Tire shred-soil mixture backfill for use in mechanically stabilized earth (MSE) walls has several advantages over traditional backfill materials: 1) good drainage, 2) high shear strength, 3) low compacted unit weight and 4) low lateral pressure exerted on retaining structures. This work presents the results of laboratory tests performed on tire shred-sand mixtures focusing on determining the properties required for their use as backfill in MSE wall applications. Three sizes of tire shreds are considered: tire chips with 9.5mm in nominal size, and tire shreds with 50-to-100-mm and 100-to-200-mm in length. The optimal mix proportions of tire shred-sand mixtures for enhanced mechanical response of the composite material are provided. Segregation of the materials in the tire shred-sand mixtures was investigated for various mix proportions. The effects of tire shred size, and tire shred-sand mixing ratio on the interaction between geogrids/ ribbed-metal strips and the mixtures are evaluated based on a series of laboratory pullout tests. Results indicate that the optimal mix proportion of tire shreds and sand is 25/75 and 30/70 (tire shred/sand) by weight, equivalent to approximately 40/60 and 50/50 (tire shred/sand) by volume for tire shreds with 50-100 mm and 100-200mm in length, respectively. This optimum mix proportion also ensures negligible segregation of the components of the mixture in the composite material. For all three shredded tire sizes considered, the pullout capacity of a geogrid embedded in the tire shred-sand mixtures prepared at the optimum mixing ratio is larger than that obtained for pure tire shreds. The pullout capacity of geogrid placed in samples prepared at optimum tire shred-sand mixing ratio is found to be higher for tire chip-sand mixtures than for tire shred-sand mixtures. This is mainly due to the crossing of the geogrid by the tire chips, which generates passive resistance during pullout. The size of tire shred has a negligible effect on the pullout response of ribbed-strip embedded in mixtures. Large-scale direct tests evaluated the shear strength properties of samples prepared at optimum tire chip-sand and tire shred (50 to 100 mm in size)-sand mixing ratios.

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Tire Shred Backfill in Mechanically Stabilized Earth Wall Applications

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Soil Damping and Its Use in Dynamic Analyses

Thecurrentstudyexaminesandquantifiesthelimitshaftresistanceofdrilledshaftsinstalledinclaythrough finite-elementanalyses that use an advanced two-surface-plasticity constitutive model for clay. The clay constitutive model used in this study reproduces the mechan- ical responseofclaysundermultiaxial loadingconditions,predictsbothdrainedandundrainedbehavioratsmallandlargestrains,andcaptures the drop in strength toward a residual value at very large shear strains. One-dimensional finite-element analyses are performed to simulate the essential stages of the installation and loading of drilled shafts in clay for different initial stresses, different overconsolidation ratios, and dif- ferent values of the difference between the critical-state and the minimum residual friction angles. On the basis of these simulations, equations for the shaft friction coefficient are proposed that can be used in the calculation of the shaft resistance of drilled shafts in clay. Predictions using theproposedequationscomparewellwiththedataderivedfromdifferent fieldpileloadtestsondrilledshafts.DOI:10.1061/(ASCE)GT.1943- 5606.0000803. © 2013 American Society of Civil Engineers. CE Database subject headings: Drilled shafts; Piles; Clays; Numerical models; Plasticity; Finite element method; Constitutive models. Author keywords: Drilled shaft; Nondisplacement piles; Shaft capacity; Clay; Numerical modeling and analysis; Two-surface plasticity.

Rodrigo Salgado

Papers

Tire Shred Backfill in Mechanically Stabilized Earth Wall Applications

Soil Damping and Its Use in Dynamic Analyses

Shaft Resistance of Drilled Shafts in Clay

Nonlinear analyses of laterally loaded piles – A semi-analytical approach

Bearing capacity of circular footings under surcharge using state-dependent finite element analysis