| The loess has a wide distribution in our country. It was commonly seen in the earthquake-prone central western regions. The formation of the special conditions determines its special structural system, and shows the special engineering properties. Xi’an is an important city in loess region, with the rapid development of economy and the expansion of city, urban underground rail transit construction becomes inevitable demand. As present, the subway station, tunnel and other underground structure seismic problems in the loess region are not in-depth study. How to embody the Xi’an loess geological conditions and reflect the dynamic characteristics of loess in the subway underground structure seismic response analysis and seismic design is still in the blank. Based on above situation, this study adopts the method of soil dynamics, conducts the dynamic experimental study for the unsaturated loess of Xi’an, to meet the requirements of the subway underground structure seismic analysis of the loess dynamic characteristic parameters.In this paper, Chang’an District of Xi’an loess as the research object, made three different moisture content remodeling samples and natural moisture content undisturbed sample, conducted the dynamic triaxial tests under different consolidation pressures. Analyzed the unsaturated loess’ s variation of dynamic stress ~ dynamic strain relation, dynamic modulus, damping ratio and dynamic strength, and the test results of remodeling loess and undisturbed loess were compared. Studies have shown that: remodeling loess’ s dynamic stress ~ dynamic strain relation is in line with hyperbolic relationship, and by the influence of the moisture content is more obvious, the smaller the moisture content, the greater the slope of the curve in the elastic stage. With the increase of confining pressure, remodeling loess’ s dynamic stress ~ dynamic strain curves also will be increased height. Moisture content and confining pressure have a significant impact on remodeling loess’ s maximum dynamic modulus. In the same confining pressure, moisture content increases, the maximum dynamic modulus decreases; in the same moisture content, confining pressure increases, the maximum dynamic modulus increases. Remodeling loess’ s damping ratio is mainly in the range of 0.05 to 0.15, and along with the change of moisture content is not obvious but with the increase of confining pressure has a tendency to increase. Dynamic strength test to the loess sample to achieve εdf=0.65% as a failure criterion. The test got remodeling loess’ s dynamic shear strength index under natural moisture content and different vibration damage times. Soil disturbance has a significant influence on the loess dynamic parameters. Compared with the remodeling loess, the dynamic parameters and dynamic strength index of undisturbed loess were improved.In this paper, dynamic triaxial tests obtained the dynamic modulus, the damping ratio, dynamic strength and other dynamic characteristic index of unsaturated loess in Xi’an, provide relevant dynamic characteristic parameters to the seismic research and design of Xi’an subway. Meanwhile, a similar sampling loess, without tests, with the empirical formula to obtain the corresponding dynamic characteristic parameters. |
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