Study On The Dynamic Characteristics Of Engineering Loess Slope Under Construction Inspires

As a marginal subject, dynamic responses of loess slopes are not only an important problem of engineering geology, but also of other subjects. Owning to the gulf between different subjects, it is arduous to study dynamic responses of loess slopes and the study is far from ripeness. And it has been studied and received more satisfied results in the field of dynamic response which caused by natural earthquakes, but for artificial earthquake, especially piling and dynamic compaction, lack research. So the research on the engineering vibrate to the loess slope is more practical significance. This article works for landslides in engineering loess slope of Zhengzhou-Xi'an passenger express railway through the combined research method of field tests, model tests, centrifuge model tests and numerical simulation, and investigates the response rules of acceleration, speed, transient displacement and amplification effect for loess slope in dynamic compaction. The research work has accomplished with the following achievements:1. To investigate the failure factors of the loess slope under external vibration, the dynamic responses of the loess slope excited by construction vibrations for railway subgrade solidified are tested and the differences between the dynamic data of the horizontal surface and that of the slope are analyzed. Research results show that:The loess slope has strong dynamic responses to the construction vibrations, and especially, the dynamic responses of the crest part of the slope are much stronger than that of the free field (horizontal surface). The topographic amplification effects should be one of the potential factors for the loess slope failure in the subgrade solidified process. Therefore, to ensure the stability of the slope and construction safety, it is critical important to adapt the preconditions for the slope enhance before the subgrade solidified.2. This article has accomplished the large model test for 1:20 loess slope, investigated the law of similitude, boundary condition treatment in the model test, studied the change rules of dynamic properties and dynamic response rules for loess slope in dynamic compaction, as well as the dynamic properties and dynamic response rules under the influence of the slope ratio. Results show that the amplitude of dynamic response increased with increasing slope ratio. The amplitude of dynamic response for loess slope in dynamic compaction fades out rapidly with the impact loading effect; the vibration cycle is less than 1s and the major frequency is between 25～45 Hz that no superimposed vibration will occur. The amplification effect on radial acceleration is more obvious for loess slope in dynamic compaction, the vertical vibration prevails at lower part of slope while radial vibration prevails at upper part of slope. There is amplification effect for response amplitude on impact vibration of on the ridge of loess slope. There is obvious amplification effect on slope for input acceleration along the slope, especially the most obvious amplification effect at the top of slope.3. The stability analysis and its protecting in the excavation and unloading course of loess slope occupy an important position in the slope engineering. One centrifugal model test of non-reinforcement slope and two centrifugal model test of soil nail reinforcement slope are performed on the centrifuge. The deformation characteristics, reinforcement effect of soil nails and change regularity of stability in the excavation and unloading course of loess slope are studied. Results of centrifuge model tests show that soil nailing can greatly increase the stability of loess slopes. Due to the anchoring effect of soil nail, the range of deformation is wider, but magnitude is smaller, and the largest deformation is not in the surface, but in the anchor region of the nailed slope. Non-reinforcement loess slope have the potential failure surface of about 40cm below its peak, the models were substantially stable against failure and deformation tends to steady after nailed. The unleveled length of soil nail reinforcement is superior to the level length on the occurrence of resistance to slope failure.4. Based on the characteristics of loess slope, through a lot of numerical simulations with FLAC3D, the paper comprehensively studies dynamic responses under the actions of piling, dynamic compaction, excavation and soil nail reinforcement in loess slope. Results finds that:inspired by piling, dynamic consolidation, the dynamic response (acceleration, velocity and displacement) value decreases with increasing of source distance in loess slope; The dynamic responses remarkably affected by the loess slope topographic, and especially, the dynamic responses of the variable angle part of the slope are much stronger than that of the free field. The gradient and shape of Loess slope have a certain influence to the dynamic response, the greater the slope gradient, the greater the dynamic response. As the excavation progressed, the stability of the slope, reducing gradually, but, the horizontal displacement of slope slightly decreases, plastic zone significantly reduced after soil nail reinforcement, and the reinforcement effects of long-ranging soil nail is relatively preferable. Numerical simulation results and test results are basically consistent, and the rules of dynamic responses in loess slope are mostly the same as each other, thus proved each of results.