The influence of shearing velocity on the shear strength of soil

Posmična čvrstoća jedno je od najvažnijih mehaničkih svojstava tla prilikom građenja. Uvjetovana je vrijednošću maksimalnog posmičnog naprezanja koje tlo može podnijeti prije sloma. Prekoračenjem posmične čvrstoće dolazi do klizanja jedne čestice uz drugu, što uzrokuje slom tla. Posmična čvrstoća tla za efektivna naprezanja predstavlja kombinaciju dreniranih parametara čvrstoće: kuta unutrašnjeg trenja (φ) i kohezije (c) koje definira Mohr-Coulombov zakon sloma. Određuje se “in situ“ i laboratorijskim pokusima. Izravan posmik se smatra najstarijim i najjednostavnijim laboratorijskim pokusom određivanja posmične čvrstoće tla. U prvoj fazi pokusa uzorak se konsolidira pod određenim vertikalnim naprezanjem, a u drugoj fazi smiče zadanom brzinom koja ovisi o uvjetima dreniranja, propusnosti i debljini uzorka. Nekoherentna tla se smiču velikom brzinom, dok je za koherentna tla iznos brzine manji. Brzina smicanja i uvjeti dreniranja utječu na veličinu parametara čvrstoće tla. Rad se temelji na uspoređivanju i prikazivanju utjecaja različitih brzina smicanja na posmičnu čvrstoću nisko plastične gline u uređaju za izravni posmik.Shear strength is one of the most important mechanical properties of soil during construction. It is conditioned by the value of a maximum shear stress that a soil can withstand before failure. Exceeding the shear strength causes one particle to slide next to another, which results in soil failure. The shear strength of soil for effective stresses is a combination of drained strength parameters: internal friction angle (φ) and cohesion (c) defined by Mohr-Coulomb failure law. It is determined “in situ” and by laboratory experiments. Direct shear is considered to be the oldest and the simplest laboratory experiment which is used for determining the shear strength of soil. In the first phase of an experiment, a sample is consolidated under a certain vertical stress, and in the second phase it is sheared at a given velocity depending on drainage conditions, permeability and thickness of the sample. Incoherent soils are sheared at high speed, while for coherent soils lower velocity is needed. Shear velocity and drainage conditions affect the magnitude of soil strength parameters. The paper is based on the comparison and demonstration of the influence of different shear velocities on the shear strength of low plastic clay in a direct shear device