No abstract

A fundamental study of the undrained behaviour of sands under multiaxial loading is presented. The investigation was carried out using Fraser River and Syncrude sands in a hollow cylinder torsional shear device. Shear loading was carried out under strain control to capture the postpeak strain-softening characteristics of loose sands. It is shown that the undrained response of loose sands is highly dependent on the loading direction. The friction angle mobilized at phase transformation and steady state is a unique material property, independent of the mode of loading, direction of principal stress and initial consolidation stress, and void ratio state. There is no unique relationship between steady state strength and void ratio which is independent of stress path and the level of initial confining stress.Key words: anisotropy, hollow cylinder torsional shear, liquefaction, sand, simple shear, triaxial.

The potential for static and cyclic liquefaction of the sand that underlies the highly seismic Fraser Delta is assessed under simple shear test conditions, typical of an earthquake shaking. A comparison of liquefaction potential is also made between simple shear and conventional triaxial stress conditions. It is shown that the liquefaction potential of sand is profoundly influenced by the stress path. The reduction factors currently applied to the cyclic triaxial resistance for representing simple shear response may involve a large degree of conservatism in design. A direct measurement of soil behaviour under stress conditions typical of earthquake loading may thus have large economic benefits. Key words: sand, liquefaction, static, cyclic, triaxial, simple shear.

The effect of stress path on the steady state line of a liquefiable sand is investigated. Results from undrained triaxial compression and extension tests on water-deposited sands show that the steady state line of a given sand, though unique in the effective stress space, is not so in the void ratio – effective stress space. The sand is contractive over a much larger range of void ratios in extension than in compression. While a single steady state line emerges for compression loading, extension loading yields several lines, each characteristic to a given deposition void ratio. All these extension lines lie to the left of the compression line in void ratio – effective stress space. Thus at a given void ratio, steady state strength is smaller in extension than in compression, the difference increasing as the sand becomes looser. The implications of the results are discussed in relation to practical design. Key words: sand, liquefaction, steady state, stress path.

The effective stress response of a natural marine clay to slow undrained symmetrical cyclic reversal in shear stress is presented. The effects of cyclic principal stress difference amplitude, cyclic principal effective stress ratio amplitude, initial direction of loading, and step increase in cyclic stress level on the clay stress-strain response are studied under stress conditions of the triaxial test. Characteristic behaviour patterns are identified in terms of effective stresses.