Experimental Investigation on the Dynamic Shear Modulus and Damping Ratio of Aeolian Soils

Transcription

1 2016 International Conference on Power Engineering & Energy, Environment (PEEE 2016) ISBN: Experimental Investigation on the Dynamic Shear Moulus an Damping Ratio of Aeolian Soils Shengyang Feng a, Xiangyang Li b, Shuyun Wang c, Zhi Chen School of Environmental Protection an Safety Engineering, University of South China, Hengyang, , China a fengsy_usc@qq.com, b @qq.com, c @qq.com, @qq.com Keywors: Aeolian soils, Dynamic shear moulus, Damping ratio, Confining pressure Abstract. Dynamic shear moulus an amping ratio are two main parameters for escribing the ynamic performance of aeolian soils. This paper presents the influence of the confining pressure, the consoliation ratio an the vibration frequency on the ynamic shear moulus an the amping ratio of aeolian soils with a series of ynamic triaxial tests. Experimental results show that the ynamic shear moulus of aeolian soils increases with the confining pressure an the consoliation ratio, while the amping ratio ecreasing with them; both of the ynamic shear moulus an the consoliation ratio increases with the vibration frequency, but the influence is less than that of the confining pressure an the consoliation ratio. Introuction Aeolian soils, eriving from the esert, are carrie by the win, while the win weakening or encountering obstacles, they will be eposite. Aeolian soils are mainly istribute in the northeast an northwest of China. Many researchers [1~3] have reveale that aeolian soils possess weak ynamic performance, an founation at aeolian soils probably will encounter the earthquake-inuce liquefaction. But at present, stuies on the ynamic characteristic of aeolian soils are scanty. Dynamic analysis for aeolian soils may not be carrying out without its ynamic constitutive moel, of which the ynamic shear moulus an the amping ratio is the most important parameters. In aition, the ynamic shear moulus an the amping ratio are the necessary parameters for seismic response analysis, an also they are essential content for the seismic safety evaluation[4]. In orer to obtain the ynamic shear moulus an the amping ratio of soils, from 1960s, many researchers have researche the two parameters. Harin et al. [5~8] stuie influence factors of soils ynamic characteristic base on numbers of experiment atum with improve ynamic triaxial apparatus, an they presente the formula of the ynamic shear moulus an the amping ratio of soils. Zhai [9] propose a function relationship between the ynamic shear moulus an the epth, an evaluate the ynamic shear moulus using the fuzzy probability. Liang et al. [10] stuie the effect of the mixing ratio an the confining pressure on the ynamic shear moulus an the amping ratio. Analysis of the ynamic shear moulus an the amping ratio is very important, but because of soils iversity an test apparatus restriction, this problem is very complex. There are numerous influence factors of the ynamic shear moulus an the amping ratio, of which the confining pressure, the consoliation ratio an the vibration frequency are the main factors [11]. In this paper,

2 the influence of the confining pressure, the consoliation ratio an the vibration frequency on ynamic shear moulus an amping ratio of aeolian soils was analyze by a series of ynamic triaxial tests, an the mechanism was also iscusse. Experiment Summary Soil specimens. Soil specimens were taken from Fuxin City, Liaoning Province in China, 2 meters below groun. Physical an mechanical properties of the soil specimens are shown in Tab. 1. From Tab.1, soil grain size less than 0.05mm makes up 88.8% of the total mass, an the plasticity inex is 11.9, so the soil specimens can be ientifie as silty clay which is representative aeolian soils. Table 1. Physico-mechanical properties of unisturbe aeolian soil. ensity ρ/g.cm -3 water content w/% specific gravity G s granular component(%) 0.1~0.05mm 0.05~0.01mm 0.01~0.005mm <0.005mm liqui limit(%) plastic limit(5) plasticity inex Experiment scheme. In orer to research the influence of the confining pressure, the consoliation ratio an the vibration frequency on the ynamic shear moulus an the amping ratio of aeolian soils, ifferent confining pressure, consoliation ratio an vibration frequency were conucte in the ynamic triaxial test, incluing confining pressureσ 3c =100kPa, 150kPa, 200kPa, consoliation ratio k c =1, 1.5, vibration frequency f=1hz, 5Hz. Accoring to the above experiment scheme, we have mae 12 soil specimens, which the iameter is 3.91cm, an the height is 8cm. Particularly, for maintaining soils initial conitions, it is unable to isturb soil specimens. The ynamic triaxial apparatus in this paper is DDS-70 vibration triaxial apparatus (Fig.1). Figure 1. DDS-70 vibration triaxial apparatus.

3 Experiment Results an Analysis Experiment results. In the experiment process, the tension sensor an the isplacement sensor of DDS-70 respectively monitor ynamic stress E an ynamic strain ε, an it will acquire an raw the relation curve of E ln. We can use the following formula to convert E, ε to G,, an then raw the relation curve of G ln, shown in Fig.2. The conversion formula can be written as: (1 ), E G, 2(1 ) (1) Where is poisson ratio, for saturate soil, Figure 2. The relation curve of G ln of aeolian soils in ifferent experimental conitions. Accoring to the following formula, we can calculate the amping ratio λ, an then the relation curve of ln can be obtaine as Fig.3.

4 A0 (2) 4A Where A 0 an A respectively are the hysteresis loop area of E ~ε an the triangle area below the line from the original point to the large amplitue point shown. Figure 3. The relation curve of ln of aeolian soils in ifferent experimental conitions. Influence of the confining pressure. From Fig.2, we can see when the consoliation ratio k c an the vibration frequency f remain invariant, while the confining pressure 3c is ifferent, the ynamic shear moulus G increases with 3c. The reason is that the plastic strain of aeolian soils in low confining pressure is increasing faster than that in high confining pressure. The amplification of G is relate to the ynamic tangential strain, that is, G is more larger when is more smaller. Three relation curves of G ln are closer when is increasing, so it inicates that in the

5 conition of larger, the confining pressure has little influence on G. As shown in Fig.3, the amping ratio ecreases with the confining pressure when other factors are constant. The reason is that in soil ynamics, energy loss is expresse by the amping ratio, an when the confining pressure increases, contacts among aeolian soils particles are more closer so that wave travel path increases, then energy loss in wave travel path will augment, so obviously the amping ratio increases. Decreasing amplitue of the amping ratio is also relate to the ynamic strain, an it ecreases with the ynamic strain increasing. Influence of the consoliation ratio. As shown in Fig.2, the ynamic shear moulus is increasing with the consoliation ratio when other factors are constant. The reason is that aeolian soils are kin of loose sity clay with few clay particles [12]. In larger initial shear stress, aeolian soils particles easily slip towar more stable conition. In constant confining pressure, when the consoliation ratio is increasing, that is the mean stress /3( 2 ) is increasing, m 1 1c 2c accoringly the ynamic shear moulus will be increasing. In aition, Fig.3 shows that the amping ratio will ecrease with the consoliation ratio increasing k c, an ecreasing amplitue of the amping ratio is increasing rapily with the ynamic strain. Influence of the vibration frequency. As shown in Fig.2, the higher the vibration frequency is, the larger the ynamic shear moulus is. The reason is that in constant vibrating loa, the higher the vibration frequency is, the easier the tangential eformation expans, so the smaller the ynamic shear moulus will be. But, increasing amplitue of the ynamic shear moulus is not much when the vibration frequency increasing an the influence of the vibration frequency on the ynamic shear moulus is inferior to the confining pressure an the consoliation ratio. Fig.3 shows that the higher the vibration frequency is, the larger the amping ration in the same ynamic shear strain is, an the amping ratio is increasing with the ynamic shear strain. Conclusions The ynamic shear moulus an the amping ration of aeolian soils in ifferent confining pressure, consoliation ration an vibration frequency show the following characteristics: the ynamic shear moulus increases with the confining pressure increasing, but the amping ratio ecreases with the confining pressure increasing; the ynamic shear moulus increases with the consoliation ratio increasing, while the amping ecreasing; both of the ynamic shear moulus an

6 the amping ratio increase with the vibration frequency increasing, but the influence of the vibration frequency is much smaller than other two factors. Meanwhile, this paper exists some shortage: the ynamic shear moulus obtaining by the ynamic triaxial test in this paper was converte uner hypothesis that the poisson ratio of aeolian soils is constant, so that is more or less not conforme with the real case, but uner conition of small strain, changing amplitue of the poisson ratio is small, so this hypothesis is reliable. Acknowlegment This work was finance by the scientific research project of Hunan province eucation epartment (NO. 15C1191) an the PhD Initial Founation Program of University of South China (No.2014XQD22). References [1] Dickson B L, Keith M Scott, Recognition of aeolian soils of the Blayney istrict, NSW: implications for mineral exploration, Journal of Geochemical Exploration 63 (1998) [2] Igwe C. A. Clay, Dispersion of Selecte Aeolian Soils of Northern Nigeria in Relation to Soicity an Organic Carbon Content, Ari Lan Research & Management 15 (2001) [3] Zhang K, Chen Q, Zhao K, et al, 16S rdna PCR-RFLP analysis an phylogeny of bacteria isolate from swamp an meaow aeolian soils in the Zoige Plateau,Sichuan,China, Acta Ecologica Sinica 30 (2010) [4] Xie Dingyi, Developing Situation an Problems of Soil Dynamics in China, Northwest Seismol Gical Journal 29 (2007) 94~95. [5] Harin B O, Black W L, Vibration moulus of normally consoliate clay, Journal of Soil Mechanics & Founations Div, [6] Harin B O, Drnevich V P. Shear moulus an amping in soils, Journal of the Soil Mechanics an Founations Division98 (1972) [7] Harin B O, Black W L, Closure on vibration moulus of normally consoliate clay, Journal of Soil Mechanics & Founations Div, [8] Harin B O, Drnevich V P, Shear moulus an amping in soils: measurement an parameter effects (terzaghi leture), Journal of the soil mechanics an founations ivision 98 (1972) [9] Zhai Ruicai, Research of ynamic shear moulus of soft clay 18 (1996) [10] Liang Xu, Cai Yuangqang, Stuy on the elastic moulus an the amping ratio of compostie founation, China Civil Engineering Journal 37 (2004) 96~101. [11] Yuan Xiaoming, Sun Yue, Sun Jing, et al, Laboratory experimental stuy on ynamic shear moulus ratio an amping ratio of soils, Earthquake Engineering an Engineering Vibration 20 ( 2000) [12] Zhang Xiangong, Liu Gongxun, Yu Cong, et al, Testing stuy on structural character of aeolian soil in western area of Liaoning Province, Rock an Soil Mechanics 29 (2008)