Shear Strength Parameters for Silty-Sand Using Relative Compaction

 

Sadanand Ojha

Research Scholar, Department of Civil Engineering
Faculty of Technology, University of Delhi (Delhi Technological University Campus)
Bawana Road, Delhi-110042, India
e-mail: sadanand_ojha@yahoo.com

Ashutosh Trivedi

Professor, Department of Civil Engineering
Delhi Technological University
Bawana Road, Delhi-110042, India
e-mail: prof.trivedi@yahoo.com

 

 ABSTRACT

The strength behavior of silty sand can be interpreted from its relative compaction, mean confining pressure and relative dilatancy. The present work considers triaxial test results on silty sand at different relative compaction and confining pressure. The review of past results on shear testing indicates that strength parameter of clean sand and silts are often considered corresponding to relative density. There are serious problem associated with the estimation of relative density of the soil containing significant percentage of plastic and non-plastic silt. In fact, presence of plastic fines disallows the investigator to interpret relative density. Therefore it is pertinent to use relative compaction of the soil as considered in the present study to interpret the strength parameter of the soil containing fines. This concept is used for an analytic simplicity for generic application. This relative density assumption for the soil containing significant percentage of fines often leads to significant error in overall estimation of strength and deformation properties of silty sands. Previous researchers considered the stress strain response of silty sand based on critical state friction angle ?c, peak friction angle ?p; maximum and minimum void ratio (emax and emin) and empirical strength parameters Qb and Rb.The uncertainty in calculating the relative density for silty sands when fine contents is more than a certain limit gives error in computation of strength parameters of silty sand. Hence, the authors in the present study used the relative compaction instead of relative density and obtained the strength parameters Qaf and Raf. The results are compared with the back calculated values from the previously published studies. It is found appropriate to use the strength parameters Qaf and Raf for the soils containing significant percentage of fines.It was observed that the Yamuna sand containing silts has comparable values (25 to 40) of empirical shear strength fitting parameters (Qaf) at select relative compaction as shown in the present work in terms of Qaf and Raf. The value of Qaf and Raf has been analysed with reference to standard errors.

Keywords: Silty sand, relative compaction, relative density, strength parameters, critical and peak friction angle.

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