Study On The Loading Rate Effect On Deformation And Strength Characteristics Of Q₃ Loess

Loess is a kind of the Quaternary sediments, widely distributed in arid and semi-arid regions of northern. Due to its special formation of environment and process, it is a typical structural soil, with obvious structure. With the implementation of the country’s western development strategy, the quantity and scale of foundation engineering construction is increasing in the loess region, and a variety of engineering properties of loess are getting more attention. In the midst of these, the loading rate effect is of great importance to engineering practice. However, previous studies on the loading rate effect were more concentrated in sands. In a small amount of research related to the loading rate effect on loess, the loading rate was just a factor in the study of the loess’ structure. Thus there is a big space for research of the loading rate effect on loess and its further research is necessary.Based on this, the paper take Q3 loess which is located in an area around Dayan Pagoda in Xi’an as the research object, researched on loading rate effect on loess through triaxial shear tests of different loading rate. Above all, on the basis of triaxial tests of undisturbed sample, the paper made the stress-strain curve and got the shear strength, and according to Mohr-Coulomb theory, got the shear strength parameters of different samples by fitting stress plane, and then obtained the influence of loading rate on stress-strain curve、shear strength and shear strength parameters of undisturbed sample. Secondly, on the basis of triaxial tests of disturbed sample, using the same method to get its influence, and then compared with the influence of undisturbed sample. At last, the paper obtained the curve of structural strength exerting which can be expressed by the difference of stress-strain curve between undisturbed sample and disturbed sample and defined the structural strength by reality, and then analyzed the influence of loading rate on the curve of structural strength exerting and structural strength.Through above research the following main results have been got:(1) Loading rate have significantly influence on the stress-strain characteristics of undisturbed soil samples, and high loading rate、low confining pressure and low water content can lead to strain softening phenomenon, but the strain softening of disturbed soil hasn’t been observed in all of the tests.(2) There’s a critical loading rate in the influence of loading rate on the shear strength. The shear strength increases with the increase of loading rate when loading rate is less than the value, but reduces with the increase of loading rate when loading rate exceeds the value. Regardless of the undisturbed soil and disturbed soil has this feature.(3) The influence of loading rate on shear strength parameters c and φ is not the same. With the increase of loading rate, there’s the same critical loading rate in the influence of loading rate on the cohesion c that c increases when loading rate is less than the value but reduces when loading rate exceeds the value and the friction angle φ reduces. Both undisturbed and disturbed soil are showing the above features, but the influence on disturbed soil is significantly less than the undisturbed soil.(4) The curve of structural strength exerting is largely consistent with the stress-strain curve of undisturbed soil. With the increase of loading rate, the structural strength also shows the features that first increase and then reduce, and there’s the same critical loading rate.