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Abstract To reveal the stress-contraction pattern of loess in shearing，undisturbed specimens were obtained from the backwall of a typical landslide in Heifangtai. Three series of triaxial tests were carried out，including isotropically consolidated undrained tests and isotropically consolidated drained tests for saturated loess，and constant water content tests for unsaturated loess. The stress-strain relationship and the critical state strength of the loess are explored. The state parameter and the contractive/dilative behavior of the loess are investigated. The stress-contraction/dilation rules of the loess are studied based on classical dilatancy equations. The findings are as below： firstly，the saturated soil shows a unique critical state line which could represent the major stress level corresponding to the thickness of Heifangtai loess，while the unsaturated soil at 94 to 100 kPa suction shows a roughly parallel critical state line. Secondly，the loess commonly demonstrates a tendency of contraction or contractive deformation， but can also shows a tendency of dilation or dilative deformation which is affected by its initial void ratio and intial stress level. Thirdly，the undisturbed loess can be depicted by the soil state parameter，and can also demonstrate the phase transformation behavior from contraction to dilation. Fourthly，the contractive behavior of the loess can be generally reflected by the dilatancy equation in the Cam-clay model.
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2015, Vol. 34 
