Vertical facing panel-joint gap analysis for steel-seinforced soil walls

This paper reports the results of a numerical parametric study focused on the prediction of vertical load distribution and vertical gap compression between precast concrete facing panel units in steel-reinforced soil walls ranging in height from 6 to 24 m. The vertical compression was accommodated by polymeric bearing pads placed at the horizontal joints between panels during construction. This paper demonstrates how gap compression and magnitude of vertical load transmitted between horizontal joints are influenced by joint location along the height of the wall, joint compressibility, and backfill and foundation soil stiffness. The summary plots in this study can be used to estimate the number and type (stiffness) of the bearing pads to ensure a target minimum gap thickness at the end of construction, to demonstrate the relative influence of wall height and different material component properties on vertical load levels and gap compression, or as a benchmark to test numerical models used for project-specific design. The paper also demonstrates that although the load factor (ratio of vertical load at a horizontal joint to weight of panels above the joint) and joint compression are relatively insensitive to foundation stiffness, the total settlement at the top of the wall facing is very sensitive to foundation stiffness. This paper examines the quantitative consequences of using a simple linear compressive stress–strain model for the bearing pads versus amultilinear model that is better able to capture the response of bearing pads taken to greater compression. The study demonstrates that qualitative trends in vertical load factor are preserved when a more advanced stress-dependent stiffness soil hardening model is used for the backfill soil as compared with the simpler linear elastic Mohr–Coulomb model. Although there were differences in vertical loads and gap compressionwith the use of both soilmodels for the backfill, the differenceswere small and not of practical concern.Peer ReviewedPostprint (author's final draft

Landsat Satellite Image Segmentation Using the Fuzzy ARTMAP Neural Network

This application illustrates how the fuzzy ARTMAP neural network can be used to monitor environmental changes. A benchmark problem seeks to classify regions of a Landsat image into six soil and crop classes based on images from four spectral sensors. Simulations show that fuzzy ARTMAP outperforms fourteen other neural network and machine learning algorithms. Only the k-Nearest-Neighbor algorithm shows better performance (91% vs. 89%) but without any code compression, while fuzzy ARTMAP achieves a code compression ratio of 6:1. Even with a code compression ratio of 50:1 fuzzy ARTMAP still maintains good performance (83%). This example shows how fuzzy ARTMAP can combine accuracy and code compression in real-world applications.Office of Naval Research (N00014-92-J-401J, N00014-91-J-4100, N00014-92-J-4015); National Science Foundation (IRI 90-00530

Post-stressed concrete foundation may reduce machinery vibration

Post-stressing concrete mat foundation reduces excessive vibrations in machinery. The mat is stressed in compression after the machinery is mounted, thus closing any cracks in it, altering the distribution of the soil subgrade reaction on the mat, and changing the mat-subgrade natural frequency

Quantifying the effect of matric suction on the compressive properties of two agricultural soil using an osmotic oedometer

International audienceThe compaction of cultivated soils by agricultural machines considerably affects both the structure and physical properties of soil, thus having a major impact on crop production and the environment. The soil mechanical strength to compaction is highly variable both in time and space because it depends on soil type (texture), soil structure (porosity) and soil moisture (suction). This paper is devoted to the effect of soil suction on the compression index Cc which is one of the mechanical parameters that describes the soil mechanical strength to compaction. We used an oedometer compression tests with suction control implemented by using the osmotic technique to study the compression index of a loamy soil and a sandy soil. Soil samples were prepared by compacting soil powder passed through 2 mm sieve, to a dry bulk density of 1.1 or 1.45 Mg m-3. The mechanical stress and the suction ranges considered corresponded to field conditions, with vertical stress less than 800 kPa and suction less than 200 kPa. The results show that the compression index Cc changed little with suctions ranging from 10 to 200 kPa for the two soils at different initial densities. By contrast, the variation of Cc is significant when soil suction is close to zero for the loamy soil at an initial dry bulk density of 1.1 Mg m-3. From a practical point of view, this variation in compression index with suction is a useful result for modelling soil strain due to traffic and predicting the compaction of cultivated soils

Compaction behaviour of clay

This paper presents an experimental study of the compaction behaviour of non-active clay. One-dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using Trento high-capacity tensiometers. At lower water contents, a transistor psychrometer was used to measure post-compaction suction. Samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses. Three water content regions were identified in the compaction plane depending on whether post-compaction suction increased, decreased or remained constant as the degree of saturation was increased at constant water content. Hydraulic paths of specimens subjected to loading-unloading cycles at constant water content have clearly shown that post-compaction suction may increase as the degree of saturation increases. This non-intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour. To this end, a coupled mechanical water retention model was formulated. Irreversible one-dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress, modified suction and void ratio. Irreversible hydraulic 'wetting' paths were modelled by a boundary surface in the space suction, degree of saturation, and void ratio. This study was completed by investigating the pore size distribution of compacted samples through MIP tests

Investigation of gold nanorods as a sensing material in plasmonic sensor for triclopyr butotyl detection

Gold nanorods (GNRs) have a unique optical property of metal nanoparticles (MNPs) due to the localised surface plasmon resonance (LSPR) effect, which depends on the size, shape and dielectric property of the surrounding medium. LSPR, or commonly known as the plasmonic effect, refers to the optical phenomena resulting from the interaction of free electrons on a nano-sized metal surface with incident light at specific wavelengths. The plasmonic effect of rod-shaped nanoparticles shows dual absorption bands corresponding to transverse surface plasmon resonance (t-SPR) and longitudinal surface plasmon resonance (l-SPR). These two bands are sensitive to size changes and the surrounding medium’s refractive index. In GNR formation, particles size, homogeneity and shape are crucial elements to be investigated during the synthesis process. Therefore, three parameters are studied in this research, which are centrifugation speed, seed solution concentration and growth solution ageing period. Through the variation of parameters during the synthesis procedure, the optimum GNRs with a surface density of 74.81 %, an average length of 59.80 ± 0.53 nm and an average width of 14.14 ± 0.19 nm produce an aspect ratio of 4.23 ± 0.36 via the seed�mediated growth method (SMGM). The optimum GNR sample is prepared by adding 10 µl of a seed solution into a raw growth solution and left undisturbed for 20 hours and then centrifuged at a rotational speed of 5000 rpm. The optical spectrum from that sample exhibits two plasmon bands at the transverse axis of 535.02 nm and the longitudinal axis of 782.65 nm. For sensing application, the GNRs are used as a sensing material to detect the targeted analyte, namely triclopyr butotyl (Cଵଷ Hଵ଺ClଷNOସ). The sensitivity, stability and repeatability of GNRs in deionized water and triclopyr butotyl medium is studied by observing the changes in the absorption intensity and the peak position of the plasmon resonance. The optical response of 10 % triclopyr butotyl without GNRs shows no significant peaks and proves that GNRs are able to increase the ability of detection through the plasmonic effect. In sensitivity testing, it is found that the presence of triclopyr butotyl changes the absorption intensity and shifts the resonance peak position of the GNRs. The vi detection limit of GNRs is as low as 3 %. Furthermore, the GNRs depict good response during 600 seconds of the stability test. Moreover, the fast response and recovery time in the change of medium observed in five cycles show good repeatability of GNRs

The plastic limit of clays

The plastic limit of soils was first described by Atterberg in 1911. The thread-rolling test was standardised at the US Public Roads Bureau in the 1920s and 1930s, and has subsequently become one of the standard tests of soil mechanics. This paper reviews the original definitions of plastic limit as proposed by Atterberg, and proposes that the brittle failure observed in the plastic limit test is caused by either air entry or cavitation in the clay. Critical state soil mechanics is used to show that the observed range of undrained shear strengths of soils at plastic limit is consistent with this hypothesis. The fallacy that strength at plastic limit is a constant is highlighted, and the implications for geotechnical practice are discussed. </jats:p