Abstract

Non-coaxiality of the principal stress direction and principal strain increment direction has been observed in both numerical modelling and experimental studies.The importance of non-coaxiality has been widely recognised in the geomechnical engineering.Without considering the non-coaxiality in the design may lead to an unsafe soil structure.Therefore,it is essential to understand the non-coaxial soil behaviour better and take it into account in the numerical modelling.

A new Hollow Cylinder Apparatus in Nottingham Centre of Geomechanics (NCG) has been employed in this study.A series of preliminary tests have been carried out to validate the reliability and repeatability of the testing results.

Three series of tests,including 24 tests on Portaway sand and 2 tests on Leighton Buzzard sand,were conducted to study the non-coaxial soil behaviour of granular materials.The three stress paths followed were monotonic loading along fixed principal stress direction,pure rotation of the principal stress axes with constant deviator stress and combined rotation of principal stress axes with increasing deviator stress.Portaway sand was chosen because it has been used in NCG to investigate granular soil behaviour.Therefore,stress-strain behaviour including non-coaxial behaviour can be observed and used by the other researchers in NCG to develop or verify numerical models.

The evidence of non-coaxiality has been obtained from the tests.In general,the non-coaxiality is relatively small in monotonic loading tests,but is more significant in the pure rotation tests and combined loading tests.The degree of non-coaxiality is affected by the density of the specimen,the stress path followed,the stress level and the material particle properties.