Shiv Shankar Kumar

One-Dimensional Effective Stress Non-Masing Nonlinear Ground Response Analysis of IIT Guwahati

Groundresponseanalysis(GRA)helpstoassesstheinfluenceofthesoilmediumonthepropagating shearwavesandindicatesaboutthecharacteristicsofthewavesreachingthegroundsurfacefromthe bedrocklevel.SuchastudybecomesimperativefortheurbanizedalluvialbanksofNorth-Eastern regionofIndia,whichislocatedinthehighestseismiczoneofthecountry.Conventionally,GRAis carriedoutbasedequivalentlinearapproach,whichbeingasimplisticapproachisunabletocapturethe nonlinearcharacteristicsofsaturatedsiltysandssubjectedtoseismicshaking.Thisarticlepresentsthe outcomeofseismicone-dimensionalnonlinearGRAofIITGuwahati(locatedonavaryinggeology inthesaturatedalluvialbanksofRiverBrahmaputra)consideringpore-waterpressuredissipation characteristicsandnon-Masingunload-reloadcriteria.Variousgroundresponseparametersobtained fromthestudyhelpsintheaccurateidentificationoftheearthquakeintensitybasedsiteamplification oftheregionexpressedthrougha2-Dmapping. KEywORDS 2-D Contour Maps, Amplification Factor (AF), Ground Response Analysis, Nonlinear Effective Stress Analysis, Non-Masing Criteria, Peak Ground Acceleration (PGA), Predominant Period, Response Spectra

Local Strain Measurements in Triaxial Tests Using On-Sample Transducers

Conventional triaxial tests mostly use external LVDTs attached to the actuator of automated triaxial system so as to measure the strain. However, these LVDTs measure the external strain applied and not the strain developed in the sample during shearing. This paper presents the use of on-sample transducer to measure localized strain in a soil sampled subjected to triaxial tests. Specimens prepared at two relative densities (30 and 90%) and three effective confining pressures (50, 100 and 150 kPa) were tested with displacement rates of 0.005 and 1.2 mm/min. It has been observed that the slower rate of loading poses significantly higher secant stiffness of soil. The use of on-sample transducers provides a wide range of strains, i.e., from low strain (~ 1 × 10−3%) to high strain (>1%), and can be used to evaluate the modulus reduction curve over the investigated wide range of strain. The capability of on-sample transducers can be effectively harnessed to evaluate the maximum shear modulus of a soil.