Effects of Silt Content on Dynamic Properties of Solani Sand

In the present article, the results of cyclic triaxial tests conducted on Solani sand, collected from the bed of Solani River near Roorkee, are presented. Results of strain controlled undrained tests carried out as per ASTM D3999 for determinations of dynamic soil properties are presented. The variations of shear modulus with shear strain are reported. Remoulded samples were prepared with different percentage of silt contents and tested. The effects of silt content on shear modulus of Solani sand at different shear strain are evaluated. This effect is studied at two relative densities. It was found that the effect of silt content is significant on both shear modulus and damping ratio

Nonlinear Dynamic Behavior of Pile Groups: Effects of Plasticity of Soil

The effects of material nonlinearity of soil on dynamic behavior of a single pile and pile groups are investigated. An advanced plasticity based soil model, HiSS, is incorporated in the finite element formulation. To simulate radiation effects, proper boundary conditions are used. The model and algorithm are verified with analytical results that are available for elastic and elasto-plastic soil models. Analyses are performed for seismic excitation as well as for loads applied on the pile cap and the effect of nonlinearity is investigated. Effects of spacing between piles are investigated. It was found that the effect of soil nonlinearity on the seismic response is very much dependent on the frequency of excitation. At low frequencies, its effect is significant but at higher frequencies it is negligible. For the loading on a pile cap, the nonlinearity decreases the dynamic stiffness of the soil-pile system. Effect of nonlinearity on the dynamic stiffness is shown to be sensitive to the spacing between piles. Nonlinearity suppresses wave interference effects among piles and thus reduces the stiffness significantly at excitation frequencies where the group effect is most important

Effect of Plasticity of Soil on Seismic Response of Pile Foundation: Parametric Study

Much of the reported research on the dynamic analysis of pile foundations assumes linear behavior of soil that may not be valid at strong excitations. In this paper material nonlinearity of soil caused by plasticity and work hardening is considered for the dynamic analysis of pile foundations. An advanced plasticity based soil model, HISS, is incorporated in a finite element technique. Analysis is carried out in the time domain. The algorithm is verified with available analytical results and then linear and nonlinear responses of a single end bearing pile are compared. Effects of different frequencies of excitation (harmonic) and ratio of rigidity of soil and pile have been investigated

Liquefaction Studies of the Solani Sand Reinforced with Geogrid

In this paper, a study on liquefaction resistance of Solani sand reinforced with geogrid sheets is reported. Tests were carried out on shake table (vibration Table) with sand samples prepared at relative density of 25% without and with geogrid sheets. In this investigation biaxial synthetic geogrid sheets having the dimension equal to plan dimension of the shake table tank were used in three different combinations of 3 layers, 4 layers and 5 layers at different depths within the sand sample. The liquefaction parameters such as maximum pore water pressure (Umax), maximum pore water pressure built up time (t1) and pore water pressure dissipation time (t3) were measured with the help of transparent piezometer tubes and stop watch for each combination of geogrid sheet corresponding to various levels of accelerations varying from 0.1g to 0.4g. In each test, the frequency of dynamic load was kept constant (5Hz). The liquefaction resistance of sand was evaluated in- terms of pore pressure ratio. Tests results indicate that on inclusion of geogrid sheets into the sand samples, the Umax decreases and t1 and t3 increases. It was also observed that on increasing the number of geogrid sheets, Umax decreases further and this decrease is significant at small amplitude of excitation. The average increase in liquefaction resistance of sand was found to be about 31 % in case of 5 layers of Geogrid sheets at 0.1g acceleration

Computing the Similarity Between Moving Curves

In this paper we study similarity measures for moving curves which can, for example, model changing coastlines or retreating glacier termini. Points on a moving curve have two parameters, namely the position along the curve as well as time. We therefore focus on similarity measures for surfaces, specifically the Fr\'echet distance between surfaces. While the Fr\'echet distance between surfaces is not even known to be computable, we show for variants arising in the context of moving curves that they are polynomial-time solvable or NP-complete depending on the restrictions imposed on how the moving curves are matched. We achieve the polynomial-time solutions by a novel approach for computing a surface in the so-called free-space diagram based on max-flow min-cut duality

Floral induction in a photoperiodically insensitive duckweed, Lemna paucicostata LP6

The effects of 20 amino acids and two amides were studied on the flowering of a photoperiodically insensitive duckweed, Lemna paucicostata LP6. Alanine, asparagine, aspartate, cystine, glutamate, glutamine, glycine, lysine, methionine, proline, serine, and threonine induced flowering under a photoperiodic regime of 16 hours light and 8 hours darkness. Among these, glutamate and aspartate were found to be the most effective for flower induction. These acids could initiate flowering even at 5×10-7 molar level, though maximal flowering (about 80%) was obtained at 10-5 molar. Change in the photoperiodic schedule or the pH of the nutrient medium did not influence glutamate- or aspartate-induced flowering. The low concentrations at which glutamate and aspartate are effective suggests that they may have a regulatory role rather than simply acting as metabolites