Bearing capacity of circular footing on geocell-sand mattress overlying clay bed with void

The potential benefits of providing geocell reinforced sand mattress over clay subgrade with void have been investigated through a series of laboratory scale model tests. The parameters varied in the test programme include, thickness of unreinforced sand layer above clay bed, width and height of geocell mattress, relative density of the sand fill in the geocells, and influence of an additional layer of planar geogrid placed at the base of the geocell mattress. The test results indicate that substantial improvement in performance can be obtained with the provision of geocell mattress, of adequate size, over the clay subgrade with void. In order to have beneficial effect, the geocell mattress must spread beyond the void at least a distance equal to the diameter of the void. The influence of the void over the performance of the footing reduces for height of geocell mattress greater than 1.8 times the diameter of the footing. Better improvement in performance is obtained for geocells filled with dense soil. (C) 2008 Elsevier Ltd. All rights reserved.

Prediction of Ultimate Capacity of Laterally Loaded Piles in Clay: A Relevance Vector Machine Approach

This study investigates the potential of Relevance Vector Machine (RVM)-based approach to predict the ultimate capacity of laterally loaded pile in clay. RVM is a sparse approximate Bayesian kernel method. It can be seen as a probabilistic version of support vector machine. It provides much sparser regressors without compromising performance, and kernel bases give a small but worthwhile improvement in performance. RVM model outperforms the two other models based on root-mean-square-error (RMSE) and mean-absolute-error (MAE) performance criteria. It also stimates the prediction variance. The results presented in this paper clearly highlight that the RVM is a robust tool for prediction Of ultimate capacity of laterally loaded piles in clay.

Pozzolanic properties of rice husk ash, burnt clay and red mud

In this paper materials like rice husk ash, burnt clay and red mud are examined for their pozzolanic properties. Rice husk ash, obtained from various sources, is analysed by X-ray diffraction. Compressive strength properties of lime-pozzolana mortars with rice husk ash, burnt clay and red mud as pozzolana are studied. Influence of grinding of rice husk ash and intergrinding with lime are also investigated. Combination pozzolana with partial replacement of burnt clay and red mud by rice husk ash are examined for their pozzolanic properties. Long term strength behaviour of lime-pozzolana mortars is investigated to understand the durability of lime-pozzolana cements.

Anionic clay-Pt metal nanoparticle composite through intercalation of hexachloroplatinate in nickel zinc hydroxysalt

Nickel zinc hydroxysalt–Pt metal nanoparticle composite was prepared by intercalation of the anionic platinum complex, [PtCl6]2− in nickel zinc hydroxysalt through ion exchange reaction and subsequent reduction of the platinum complex by ethanol. Powder X-ray diffraction and microscopy studies indicate that the process of reduction of the platinum complex in the interlayer region of the anionic clay takes place topotactically without destroying the layers.

Effect of soil variability on the bearing capacity of clay and in slope stability problems

Site-specific geotechnical data are always random and variable in space. In the present study, a procedure for quantifying the variability in geotechnical characterization and design parameters is discussed using the site-specific cone tip resistance data (qc) obtained from static cone penetration test (SCPT). The parameters for the spatial variability modeling of geotechnical parameters i.e. (i) existing trend function in the in situ qc data; (ii) second moment statistics i.e. analysis of mean, variance, and auto-correlation structure of the soil strength and stiffness parameters; and (iii) inputs from the spatial correlation analysis, are utilized in the numerical modeling procedures using the finite difference numerical code FLAC 5.0. The influence of consideration of spatially variable soil parameters on the reliability-based geotechnical deign is studied for the two cases i.e. (a) bearing capacity analysis of a shallow foundation resting on a clayey soil, and (b) analysis of stability and deformation pattern of a cohesive-frictional soil slope. The study highlights the procedure for conducting a site-specific study using field test data such as SCPT in geotechnical analysis and demonstrates that a few additional computations involving soil variability provide a better insight into the role of variability in designs.

Influence of drying on the liquid limit behaviour of a marine clay

The possible mechanisms of particle aggregation and reduction in liquid limit of the Cochin marine clay on drying are investigated. Mineralogical analysis showed the absence of halloysite in the marine specimen. Experimental results also ruled out the possibility of cementitious material being responsible for particle aggregation and reduction in clay plasticity on drying. The presence of calcium and magnesium as the predominant exchangeable ions and of a high pore salt concentration facilitates strong interparticle attraction and small particle separations; the latter leads to development of significant capillary stresses that permits an intimate contact of particles and growth of strong van der Waals' and Coulombic bonds.

pH mediated delamination of anionic clay-like nickel-zinc hydroxysalt in water through intercalation of zwitterionic p-aminobenzoate ions

p-aminobenzoate could be intercalated into the anionic clay, Ni3Zn2(OH)(8)(OAc)(2)center dot 2H(2)O at a high pH (similar to 10). When the pH was reduced to similar to 7 while washing colloidal dispersion due to delamination was observed. The development of partial positive charge on the amine end of the intercalated anion causes repulsion between the layers leading to delamination and colloidal dispersion of monolayers in water. The layers could be restacked from the colloid to form the parent solid either by increasing the pH or by evaporation.

Indentation of sintered alumina clay composite - an experimental discussion of a combined Boussinesq and blister stress field approach

Surface elastic strain field generated in conical indentation of sintered alumina clay composite was measured to verify the suitability of a superposed combination of Boussinesq and blister stress fields, used previously for analysing the indentation problem. The residual strain measured in the elastic hinterland is used to estimate the blister field strength without any reference to stress relation within that field. The approach may be useful in fracture studies of brittle materials.

Revised Cam-Clay Model

The Cam-clay models, or any other plasticity-based models, do not make distinction between the mode of stress transfer in coarse- and fine-grained soils. An examination of behavior at micro level in fine-grained soils, from the consideration of load transfer through physico-chemical interactions, suggests that the plastic compressions result from the grouping of particles into larger clusters and that elastic compressions result from the decrease in the spacing between particles. During shearing, these clusters gradually get dismembered, releasing the locked-in energy. The effect of such dismembering of clusters can be easily incorporated into the original Cam-clay model, and better predictions can be obtained with the associated flow rule, itself, for both normally and over consolidated states. The method essentially defines the hardening of yield surfaces with internal changes in the spacing between particles, instead of changes in externally observed plastic strains. The approach describes the behavior of over consolidated soils as yielding along successfively hardening Roscoe surfaces with gradually varying plastic properties.

Influence of Osmotic Suction on the Soil-Water Characteristic Curves of Compacted Expansive Clay

Unsaturated clays are subject to osmotic suction gradients in geoenvironmental engineering applications and it therefore becomes important to understand the effect of these chemical concentration gradients on soil-water characteristic curves (SWCCs). This paper brings out the influence of induced osmotic suction gradient on the wetting SWCCs of compacted clay specimens inundated with sodium chloride solutions/distilled water at vertical stress of 6.25 kPa in oedometer cells. The experimental results illustrate that variations in initial osmotic suction difference induce different magnitudes of osmotic induced consolidation and osmotic consolidation strains thereby impacting the wetting SWCCs and equilibrium water contents of identically compacted clay specimens. Osmotic suction induced by chemical concentration gradients between reservoir salt solution and soil-water can be treated as an equivalent net stress component, (p(pi)) that decreases the swelling strains of unsaturated specimens from reduction in microstructural and macrostructural swelling components. The direction of osmotic flow affects the matric SWCCs. Unsaturated specimens experiencing osmotic induced consolidation and osmotic consolidation develop lower equilibrium water content than specimens experiencing osmotic swelling during the wetting path. The findings of the study illustrate the need to incorporate the influence of osmotic suction in determination of the matric SWCCs.

Influence of Starch Polysaccharide on the Remolded Properties of 2 Indian clay Samples

The reported presence in marine clays and the recognized role of polysaccharide as a bonding agent provided the motivation to examine the role of starch polysaccharide in the remoulded properties of nonswelling (kaolinite) and swelling (bentonite) groups of clays. The starch polysaccharide belongs to a group of naturally occurring, large-sized organic molecules (termed polymers) and is built up by extensive repetition of simple chemical units called repeat units. The results of the study indicate that the impact of the starch polysaccharide on the remoulded properties of clays is dependent on the mineralogy of the clays. On addition to bentonite clay, the immensely large number of segments (repeat units) of the starch polysaccharide create several polymer segment - clay surface bonds that cause extensive aggregation of the bentonite units layers. The aggregation of the bentonite unit layers greatly curtails the available surface area of the clay mineral for diffuse ion layer formation. The reduction in diffuse ion layer thickness markedly lowers the consistency limits and vane shear strength of the bentonite clay. On addition to kaolinite, the numerous polymer segment - clay surface bonds enhance the tendency of the kaolinite particles to flocculate. The enhanced particle flocculation is responsible apparently for a small to moderate increase in the liquid limit and remoulded undrained strength of the nonswelling clay.

Potential-distance relationships of clay-water systems considering the Stern theory

This paper deals with the use of Stem theory as applied to a clay-water electrolyte system, which is more realistic to understand the force system at micro level man the Gouy-Chapman theory. The influence of the Stern layer on potential-distance relationship has been presented quantitatively for certain specified clay-water systems and the results are compared with the Gouy-Chapman model. A detailed parametric study concerning the number of adsorption spots on the clay platelet, the thickness of the Stern layer, specific adsorption potential and the value of dielectric constant of the pore fluid in the Stern layer, was carried out. This study investigates that the potential obtained at any distance using the Stern theory is higher than that obtained by the Gouy-Chapman theory. The hydrated size of the ion is found to have a significant influence on the potential-distance relationship for a given clay, pore fluid characteristics and valence of the exchangeable ion.