Study On Effects Of Frequency On Dynamic Behaviors Of Loess Under Bilateral Cyclic Vibration

As the development of develop-the-west strategy, more and more construction involved with geotechnical engineering is being located in western loessial region. geotechnical engineering word in loessial region are often affected by dynamic loads, such as Seismic loads, traffic loads, blasting loads, etc.al. under natural condition, different kinds of dynamic loads differ from each other. Even if the type of loads is the same, different reasons causing loads lead to different frequency of vibration. As a result, frequency of dynamic loads on loess is not fixed, sometimes it is a combination of different frequencies. So it is significant for secure valuation of engineering and Seismic design to research the effects of frequency on dynamic behaviors of loess.In most of the recent research, simulating stress on 45o surface of sample by unidirectional vibration is usually aimed to study effects of horizontal dynamic stress without considering the vertical seismic loads. To take the actual situation into account in this test, bilateral cyclic vibration apparatus is used to analyze and research dynamic behaviors of loess by bilateral vibration under different frequency considering the truth that vibration frequency of dynamic loads in nature is not the same. On the basis of experimental results, dynamic strength curve(fdtlg~N relation curve), dynamic parameters, dynamic shear stress-dynamic shear strain relation curve(ddgt ~ relation curve) 、dynamic shear modulus-dynamic shear strain relation curve(ddG g~ relation curve) and initial dynamic shear modulus are obtained. Through analyzing those relation curves, conclusion of effects of external factors on dynamic behaviors of loess is stated as below:(1) fdtlg~N relation curve of loessThrough analyzing dynamic strength curve, the effects of consolidation confining pressure and frequency of vibration on dynamic strength is obvious. The higher the consolidation confining pressure is, the higher the dynamic strength under the same cyclic number is. The higher the lateral cyclic stress is, the lower the dynamic strength is. The higher the vibration frequency is, the higher the dynamic strength.(2)dynamic strength parameters of loessWhen other conditions are the same, dynamic strength parameters(dynamic friction angle dj and dynamic cohesive force dc) decreases as cyclic number increases. The effects of the lateral cyclic stress on dynamic friction angle dj and dynamic cohesive force dc is obvious. Under the same cyclic number, higher lateral cyclic stress causes lower dynamicfriction angle dj and dynamic cohesive force dc. Frequency affects dynamic friction angle dj and dynamic cohesive force dc to a certain extent. Under same cyclic number, higher frequency causes higher dynamic friction angle dj and dynamic cohesive force dc.(3) dd?? ~ relation curve of loessDynamic shear stress of loess d? increases as dynamic strain d? increases. The effects of consolidation confining pressure on dd?? ~ relation curve is obvious. The higher the consolidation confining pressure is, the higher the speed of dynamic shear stress increasing as increase of dynamic shear strain is. In the late stage close to damage criterion, the effects of vibration frequency on dd?? ~ relation curve is obvious. The higher the frequency is, the higher the speed of increase of dynamic shear stress is. In the primary stage, the effects of vibration frequency on dd?? ~ relation curve is not obvious.(4) ddG ?~ relation curve of loessUnder unidirectional vibration condition, dynamic shear modulus of loess decreases as dynamic shear strain increases. Under bilateral vibration condition, dynamic shear modulus decreases at first and then starts to increase. The effects of consolidation confining pressure on ddG ?~ relation curve of loess is obvious. The higher the consolidation confining pressure is, the higher the dynamic shear modulus under the same dynamic shear strain is. In the late stage close to damage criterion, the effects of frequency on ddG ?~ relation curve is obvious. Higher frequency causes higher dynamic shear modulus under the same dynamic shear strain. In the primary stage, the effects of vibration frequency on ddG ?~ relation curve is not obvious.(5) Loess’ s initial dynamic shear modulus 0GThe higher the consolidation confining pressure is, the higher the loess’ s initial dynamic shear modulus. There is a inflection point in effects of frequency on initial dynamic shear modulus, and the inflection point is located on frequency of 1Hz. When frequency is less than 1Hz, the loess’ s initial dynamic shear modulus decreases as frequency increases; when frequency exceeds 1Hz, increase of frequency causes increase of initial dynamic shear modulus.