Study On Fully Softened Shear Strength Of Loess

In the stability analysis of loess landslides and slopes with finite deformation, residual strength parameters can be obtained by fully softed strength parameters of saturated natural loess indirectly. This paper summarizes the research achievements of scholars both at home and abroad about fully softed strength and takes the loess of Shanxi, Henan and Shaanxi provinces as the research objects for preparing saturated remolded samples by direct consolidation method and preloading consolidation method which are sheared in laboratory shear tests of different test methods and different test conditions, the test results obtained a set of values of strengths and strength parameters, which provide a certain reference for stability analysis. The specific contents that this paper completed are follows as:(1) Fully softed strength is the peak strength on the stress-strain curve of saturated remolded sample. It can be measured by shear test. The residual strength parameter can be approximately replaced with the peak strength parameter for stability analysis of loess landslides, which sovles the difficulty of acquisition of strength parameter that results from slide soils hard to distinguish and exploration methods such as drill hole,exploratory pits and shallow well difficult to sampling.(2) Prepare the sample by direct consolidation method and preloading consolidation method. Compared with direct consolidation method,samples prepared by preloading consolidation method have good saturated effect and uniform density, which can satisfy various test conditions.(3) Test results show that fully softed strength of loess is related to consolidation stress, rather than pre-consolidation stress, that is fully softed strength has nothing to do with density. The fully softed strength of saturated natural loess is close to the residual strength, its parameters can approximately replace the peak strength parameters of slide soils. Clay partical content affect the difference between fully softed strength and residual strength, the greater the clay partical content is, the bigger the difference is, the clay partical contents of the loess of the test sites are generally slow, so the loess particles can not occur obvious direction arrangement after big shear displacement, residual friction angle can be definited by reducing 1～3°on the basis of fully softed friction angle, with the clay partical content becoming larger, the reduction range increases.(4) Test method and test condition have little effect on fully softed strength and its parameters, the results of drainage repeated shear test is close to the ones of triaxial compression test, the range that shear rate,shear method and sample preparation method have an influence on fully softed friction angle is about 0～3°(5) The structural strength of saturated natural loess is related to clay partical content and consolidation stress, under low consolidation stress, the structural strength is small,with the consolidation stress increasing, the structural strength becomes large and its rangeability increases. The structural strength of saturated natural paleosol and its rangeability reduce with the consolidation stress increasing.