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

This paper presents the results and analyses of uniaxial compression experiments performed on three silica sands. The sands have comparable particle-size distributions, but their particles differ in morphology and strength. Cylindrical samples of the three sands were compressed in a loading device placed inside an X-ray microscope (XRM) and scanned at multiple stress levels during uniaxial compression. 3D tomography data of the samples obtained from the XRM at different stress levels were then analyzed to obtain the distributions of particle size, particle morphology, and interparticle contact normals within the sample. Results indicate that: (1) the compressibility of the sands loaded under uniaxial compression is closely tied to particle morphology and strength and (2) the anisotropy in the orientations of interparticle contact normals generally increases with axial stress; however, this increase is limited by the occurrence of particle crushing in the sample.

Effect of particle characteristics on the evolution of particle size, particle morphology, and fabric of sands loaded under uniaxial compression

The filter paper technique consists of obtaining the equilibrium water content of a filter paper that is either in direct contact with a soil sample or inside an airtight container together with th...

/pdf/calibration-of-whatman-grade-42-filter-paper-for-soil-14jp8pc2s5.pdf

Calibration of Whatman Grade 42 filter paper for soil suction measurement

This paper deals with the performance of mixtures of asphalt, pyrolyzed carbon black (CB{sub p}), and two aggregates (limestone and slag) Marshall mix design was performed to determine the optimum binder content at 5% of air voids The range of the optimum binder content was 42%--55% for limestone mixtures and 63%--78% for slag mixtures, respectively Dynamic confined creep tests, gyratory tests, resilient modulus tests, indirect tensile tests, and Hamburg wheel tracking tests were carried out using mixtures at the optimum binder content The test results indicate that the use of CB{sub p} in asphalt pavements increases Marshall stability, decreases permanent strain, decreases the mix strain rate at 50 C and 138 kPa confinement, increases resilient modulus and tensile strength, and increases the stripping inflection point These results suggest that CB{sub p} improves asphalt pavement performance

Use of Pyrolyzed Carbon Black as Additive in Hot Mix Asphalt

The Dynamic Cone Penetrometer (DCP) is a device that is used in the construction industry for the assessment of in situ soil compaction quality. Over the past few decades, numerous correlations have been developed between the DCP test results and soil strength and stiffness parameters. This paper proposes a comprehensive set of criteria and recommendations for quality control (QC) of compacted subgrade that take into account the inherent statistical variability of DCP test results. For the development of the QC criteria, a new statistical methodology is used to extract representative test values from the raw field DCP test data. In order to use the proposed QC criteria, soils are first classified into two broad categories (fine-grained and coarse-grained) depending on their fabric and response to compaction efforts. Test results indicate that (i) for fine-grained soils, the DCP test values have good correlation with the plasticity index (PI), which is indicative of the type and amount of clay cont...

Quality assurance and quality control of subgrade compaction using the dynamic cone penetrometer

This paper presents a semianalytical solution for axially loaded pile groups in multilayered, linear-elastic soil profiles. The piles in the group can have circular, square, or rectangular cross sections. The soil displacement surrounding a pile group is linked to the axial displacement experienced by each of the piles in the group. The method is based on assigning a displacement decay function to every pile in the group and then summing up for all piles in the group the product of the axial displacement of each pile and its associated decay function. The governing differential equations describing the response of the soil and piles are derived by applying the principle of virtual work and calculus of variations to the pile–soil system. The governing differential equations predicting the response of the piles are solved analytically using the method of eigenvalues and eigenvectors, whereas the differential equations describing the soil decay functions are solved numerically using the finite-differ...

Rodrigo Salgado

Papers

Effect of particle characteristics on the evolution of particle size, particle morphology, and fabric of sands loaded under uniaxial compression

Calibration of Whatman Grade 42 filter paper for soil suction measurement

Use of Pyrolyzed Carbon Black as Additive in Hot Mix Asphalt

Quality assurance and quality control of subgrade compaction using the dynamic cone penetrometer

Analysis of Axial Loading of Pile Groups in Multilayered Elastic Soil