Open Access Test Analysis on the Dynamic Performance of Frozen Silty Clay

Transcription

1 Sen Orers for Reprints to 830 The Open Civil Engineering Journal, 2015, 9, Open Access Test Analysis on the Dynamic Performance of Frozen Silty Clay Zheng Bin 1, Xu Yang 2, Zheng Shanshan 1 an Qu Shuying 1,* 1 School of Civil Engineering, Yan Tai University, Yan Tai, China; 2 City Builing Inustry Management Office, Fu Shan District, Yan Tai, China Abstract Currently, over half of China s trunk railways are locate in permafrost regions. But to tackle the railway subgrae isease has always been the ifficulty in the railway construction there. The influence that the ynamics performance of frozen silty clay has on permafrost subgrae is an important component in the researches towars permafrost subgrae. In this paper, the ynamics performance of frozen silty clay in permafrost regions is stuie base on the inoor ynamic triaxial test at a low temperature, an at the same time, by stuying the influence that several factors like cyclic matrix, confining pressure, temperature an frequency have on relevant ynamics parameters, basis can be provie for the transformation an settlement mechanism of permafrost subgrae as well as for the analysis towars the permafrost s influence on vibration response uner train loa, an it offers much reference value to permafrost subgrae s esign. Keywor: Confining pressure, ynamic parameters, ynamic triaxial test, permafrost, steppe loaing. 1. INTRODUCTION Frozen soil is a special form of soil which is ivie into two types: permafrost an seasonal frozen soil. The former is the kin of soil which is frozen for more than three consecutive years, an generally, the freeze-thaw cycle takes place within several meters of its surface as the season changes. While the latter, seasonal frozen soil, usually refers to the one freezes within only a few meters on the surface, an often melts in summer an freezes in winter. The permafrost occupies about a quarter of the worl s lan area, an nowaays, over half of the trunk railways in China--one of the countries with large frozen soil areas in the worl [1], are constructe in frozen soil regions. With the complete avance of the national infrastructure construction, the railway construction in frozen soil area has been promote year by year [2]. However, a series of problems associate with that have cause the attention of scholars both at home an abroa. The Mechanics of Frozen Groun publishe in 1930 by.. [3] lai the founation for permafrost researches. Base on the ynamic triaxial test at a low temperature, T Chaichanavong [4] i a research on the ynamic property of ice an frozen soil; Li J C [5], base on the ynamic triaxial test at a low temperature, i researches towars the relationship between frozen soil s ynamics parameters an their influencing factors; while Ting J M [6], together with other colleagues, stuie the ynamic strength characteristics of frozen san on the basis of many ocument statistics. Moon-Young Kim [7] prove by experiments that the cementing power between soil an ice is much larger than that between soil an water. Zhu Yuanlin an He Ping [8] i a triaxial creep test on the frozen silt (loess in Lanzhou) s axial vibration uner ifferent confining pressures, an put forwar the triaxial creep moel when the frozen soil was uner vibrating loa, meanwhile, they iscusse the physical significance an change rules of all the parameters in the moel. Xu Xueyan [9, 10], through carrying out large numbers of ynamic triaxial tests at a low temperature, figure out how to etermine the frozen soil s stress-strain relationship, parameters an ynamic elastic moulus. Meanwhile, she was the first person in China who figure out the ynamic poisson's ratio of the frozen soil, an provie the numerical values of ynamic elastic moulus, ynamic poisson's ratio, ynamic shear moulus an ynamic amping ratio, an at the same time illustrate the relationship between these parameters an the temperatures as well as vibration frequencies of the frozen soil. Zhao Shuping [11] foun that the frozen soil s ynamic elastic moulus increases with increasing frequency or ecreasing temperature, an reaches a maximum in the vicinity of the saturate water content, while its ynamic amping ratio ecreases with increasing frequency or ecreasing temperature, an rises slightly when water content gets higher. Shi Yehui [12] teste the high-temperature permafrost boy of Qinghai-Tibet railway uner ifferent confining pressures, frequencies, temperatures an moisture contents, an foun that its elasticity moulus is mostly influence by temperature, while fluctuates as the confining pressure changes, an increases with increasing frequency. Zhu Zhanyuan [13-15], together with other people, carrie out stuies on the ynamic constitutive relation an mechanics parameters of the frozen clay in Beiluhe roabe of Qinghai Tibet Railway an i researches towars the influence that the permafrost has on subgrae s vibration response, as well as towars the preiction of ynamic settlement cause by the train s long-term running. Base on this, he also iscusse the ynamic response characteristics of the permafrost subgrae uring the train s running. In orer to stuy the mechanical property of / Bentham Open

2 Test Analysis on the Dynamic Performance The Open Civil Engineering Journal, 2015, Volume the contact surface of frozen soil-concrete, Lv Peng [16] invente a ynamic-loa irect shear apparatus that can be operate uner low temperature. Base on the common irect shear apparatus, he installe the ynamic loaing system an the temperature control system to make it an installation that can carry out ynamic-loa irect shear test on the frozen soils uner minus temperature, thus measuring the ynamic parameters of the permafrost. Xu Xiangtian [17], together with other people, use the low temperature triaxial apparatus an its control software from the national key laboratory for permafrost engineering to carry out various isobaric tests as well as triaxial shear loaing an unloaing tests towars the frozen soil sample. From these, Xu got a clear unerstaning about the application range of frozen soil s mechanical test metho an the influence that the equivalent shear stress has on frozen soil s volume eformation. Base on this, he mae a testing program on equal-p of frozen soil an mae great contributions to increasing the accuracy of frozen soil s mechanical test as well as exploring its mechanical properties. As can be seen from the above research finings, currently, there are few stuies focusing on the ynamics problems cause by rail traffic loa, such as the vibration input mechanism an reaction behavior of permafrost subgrae uner the train s high-spee running, the eformation an settlement mechanism of permafrost subgrae uner long-term vibration loa, as well as the influence that the permafrost has on vibration response, etc. In this paper, base on the inoor ynamic triaxial test at a low temperature, the ynamics performance of frozen silty clay in the Amo test section, which is locate in the GA Loeb Valley, part of the permafrost region of the Qinghai-Tibet Plateau, is stuie, an the influence that several factors like temperature, confining pressure, water content an frequency have on its ynamic parameters is also analyze. 2. MATERIALS AND METHODOLOGY 2.1 Test Instruments an Performance The MTS-810 ynamic triaxial material testing machine is use in this test with a maximum axial loa of 100kN. The test instrument is shown in (Fig. 1) Physical Properties of the Sample an Specimen Preparation The silty clay along the Qinghai-Tibet railway is use in the test, an its physical parameters are shown in Table 1. Base on the Stanar for Soil Test Metho [18] an Coe for Measurement Metho of Dynamic Properties Subsoil [19], the reconstitute cyliner specimen, whose stanar iameter an height is 61.8 * 125mm an average ensity is 1.8g/cm3, is prepare in this test. Samples are seale an fixe by copper-forme mol in batches an are store in the quick-freezing thermotank for over 24 hours. Then seale by rubber membranes, they are store for at least 12 hours in the thermotank which is set uner controlle temperature in a way to ensure the temperature of the sample meets the requirement. The temperature error in the thermotank is ±0.1, an the prepare samples are as (Fig. 1) shows. a. MTS-810 material testing machine b. Prepare frozen soil sample Fig. (1). MTS-810 material testing machine an prepare frozen soil sample Test Conitions During the test, the samples are quickly installe in low temperature ynamic triaxial test machine an are put into the low temperature pressure chamber to consoliate for 5 min. The loaing proceure of every sample is ivie into 4 steps: the consoliation process, the axial static loa application process, the axial static loa keeping process an the axial ynamic loa application process. Among them, the axial ynamic loa is a pressure - pressure sine wave uner classifie cyclic loaings, an vibrates 12 circles in every cyclic loaing, which is shown in (Fig. 2). The class for the loaing is over 12. With the same ynamic loa, all the test specimen are stuie comparatively, an the result is shown in Table 2. The termination criterion is that the axial eformation reaches 20% an the controlle conitions in the test are shown in Table 3. Fig. (2). Diagram of axial grae cyclic compressive stress loaing.

3 832 The Open Civil Engineering Journal, 2015, Volume 9 Bin et al. Table 1. Physical parameters table. Soil property Liqui limit (%) Plastic limit (%) Plasticity inex (%) Dry ensity (g/cm 3 ) The optimum water content (%) Qinghai Tibet clay Table 2. Dynamic loa class of permafrost s ynamics parameters ( 3 = 0.3MPa ). Loa classes n min /MPa max /MPa (n+1) /MPa n Table 3. The test conitions of permafrost kinetic parameters. Specimen number Temperature(T/) Confining pressure ( 3 /MPa) Moisture content (%) Frequency (Hz) cycle inex YTX YTX YTX YTX YTX YTX06-9 YTX07-7 YTX YTX09 Saturation 12 YTX YTX YTX12 Saturation YTX YTX YTX YTX YTX RESULTS ANALYSIS AND CONCLUSION The ynamics parameters of permafrost often inclue ynamic elastic moulus, ynamic shear moulus an amping ratio. An in this paper, the ynamic shear moulus an amping ratio of frozen silty clay are mainly analyze an iscusse Dynamic Shear Moulus of Frozen Soil The ynamic stress-strain relationship of subgrae soil uner traffic loa can be shown by equivalent linear moel. The ynamic shear moulus an the amping ratio are two important parameters to measure the ynamic performance. The hysteretic curve of frozen soil uner ynamic loa is as (Fig. 3) shows. The ynamic shear stress amplitue an ynamic shear strain amplitue of every loaing class are calculate through the following formulas. Every time the ynamic loa circulates, a elaye curve, as (Fig. 3) shows, will be forme. When rawing the hysteresis loop, Harin suggeste to use the hyperbolic curve, as formula (1) shows, to fit the relation curve (backbone curve) of the soil s shear stress amplitue an shear strain amplitue.

4 Test Analysis on the Dynamic Performance The Open Civil Engineering Journal, 2015, Volume (a) (b) Fig. (3). Determination of ynamic shear moulus an amping ratio. = (1) a + b An the ynamic shear moulus G is efine as the average slope of the elaye curve an the ynamic moulus of elasticity E is calculate in terms of the ynamic stress an ynamic strain that are shown in the (Fig. 3). = ( 1+ μ) (2) = 2 (3) G = (4) E G = 2(1 + μ) (5) E = (6) Through combining formula 5 an formula 6, formula 7 can be conclue. = 2 (1 + μ) G (7) In the formula: Axial ynamic strain amplitue; Axial ynamic stress amplitue; μ Dynamic Poisson's ratio [20, 21]. Uner ifferent temperatures, confining pressures an water contents etc., the relation curves of ynamic shear stress amplitue, ynamic shear strain amplitue an ynamic shear moulus of the frozen soil can be rawn by the above-mentione formulas. The curves are shown in (Fig. 4-11). As can be seen from the figures, the ynamic shear strain amplitue is from to 0.007, the ynamic shear stress amplitue from 0.1MPa to 2.1MPa, an ynamic shear moulus from 152MPa to 804MPa. As the ynamic shear strain amplitue increases, the ynamic shear stress amplitue also rises. The relation curve can be ivie into initial linear perio, meium-term nonlinear perio, an later approximately linear perio. The influence that ynamic shear moulus has on ynamic shear strain amplitue is quite complicate an shoul be analyze through ifferent factors Temperature When the confining pressure is 0.3MPa, moisture content 14.5% an frequency 2Hz, uner five ifferent negative temperatures, the backbone curves of frozen soil are as (Fig. 4) shows. As can be seen from the figure, temperature plays a significant role in the backbone curve. Uner the same ynamic shear strain amplitue, the ynamic shear stress amplitue increases as the temperature falls from -3 to -11, with the final value reaching 2.03MPa from 0.87MPa. Fig. (4). Backbone curves of frozen soil uner ifferent temperature conitions. Uner five ifferent temperatures, the changing curves of the ynamic shear moulus an the ynamic shear strain amplitue are presente in (Fig. 5). As shown in the figure, when uner the five ifferent temperatures, an with the increase of the ynamic shear strain amplitue, the ynamic shear moulus first rises, then levels off an then slows own in the en. As the temperature falls from -3 to -11, the ynamic shear moulus increases significantly with the final value reaching from 423.5MPa to 782.2MPa. This is because with the same water content, lower temperature will cause more free water to crystallize, resulting in stronger bining power between the soil grains an crystals. There-

5 834 The Open Civil Engineering Journal, 2015, Volume 9 Bin et al. fore, the soil becomes more rigi, resulting in the increase in the ynamic shear moulus. will weaken. With the increase in the confining pressure, the soil grains will be islocate by force with ecreasing soil porosity, resulting in the strengthening of the soil structure an the increase in ynamic shear moulus. But that oesn t mean this irect proportion will last all the time. After the soil is consoliate to a very close extent, the increase of the strength will not be that obvious. Fig. (5). Relationship between ynamic shear moulus an ynamic shear strain amplitue uner ifferent temperature conitions Confining Pressure When the temperature is -5, moisture content 14.5% an frequency 2Hz, uner four ifferent confining pressures, the backbone curves of frozen soil are as (Fig. 6) shows. As is known from the figure, the confining pressure oesn't have a significant influence on the curve. Uner the same ynamic shear strain amplitue, as the confining pressure increases from 0.3MPa to 1.2MPa, the ynamic shear stress amplitue keeps rising. However, when the confining pressure is between 0.6MPa an 1.2MPa, the ynamic shear stress amplitues are very close to each other. Fig. (7). Relationship between ynamic shear moulus an ynamic shear strain amplitue uner ifferent confining pressures Frequency When the temperature is -5, confining pressure 0.3MPa, an moisture content 14.5%, uner four ifferent frequencies, the backbone curves of frozen soil are shown in (Fig. 8). Uner the same ynamic shear strain amplitue, the ynamic shear stress amplitue increases with increasing frequency. However, when the frequency is 1Hz, it will be much smaller than those uner other frequencies, an its ynamic shear strain amplitue varies wiely. Fig. (6). backbone curves of frozen soil uner ifferent confining pressures. Uner four ifferent confining pressures, the changing curves of the ynamic shear moulus an ynamic shear strain amplitue are presente in (Fig. 7). As is shown in the figure, the confining pressure plays a significant role on the ynamic shear moulus. When the confining pressure is between 0.3MPa an 1.2MPa, the ynamic shear moulus will increase with increasing confining pressure. However, when the confining pressure is large enough, this kin of influence Fig. (8). Backbone curves of frozen soil uner ifferent frequency conitions. Uner four ifferent frequencies, the changing curves of the ynamic shear moulus an the ynamic shear strain amplitue are as (Fig. 9) shows. It is presente in the figure that when the frequency is 0.5Hz, 2Hz an 4Hz respectively an uner the same ynamic shear strain amplitue, the y-

6 Test Analysis on the Dynamic Performance The Open Civil Engineering Journal, 2015, Volume namic shear moulus will rise as the frequency rises. But when the frequency is 1Hz, it will be smaller than those uner other frequencies. Uner the four frequencies, as ynamic shear strain amplitue increases, the ynamic shear moulus first rises an then rops. An when the frequency is 1Hz, the ynamic shear moulus ecreases to a larger extent than those uner other frequencies. Loaing frequency can reflect the loaing rate, which will get higher with increasing loaing frequency, meanwhile, the time for the plastic flow of the grains an ice in the soil will be shortene. The increase in the soil s rigiity will weaken its eformability, thus its ynamic shear moulus will increase. Otherwise, the loaing rate will slow own with ecreasing loaing frequency, then the eformability of the soil will be strengthene an the ynamic shear moulus will ecrease. If the frequency is 1Hz, it might have something to o with the natural vibration frequency of the soil itself. When the water contents are 14.5% an 15.5% respectively, the two curves are very close to each other since there is little ifference. While in the saturate conition, uner the same ynamic shear strain amplitue, the ynamic shear stress amplitue from the first preparation metho will be larger than that from the secon one, an so as the final ynamic shear stress amplitue. (a) Fig. (9). Relationship between ynamic shear moulus an ynamic shear strain amplitue uner ifferent frequency conitions Moisture Content To control the moisture content is a har task when preparing the samples. In this test, two methos are aopte to prepare samples with ifferent moisture contents. The first one is to etermine the contents of soil an contents of water respectively accoring to the require moisture content, an then to mix the two materials together. The saturate sample is mae from the sample with 14.5% water content, by vacuum pumping an water filling, an the corresponing test results are shown in (Fig. 10a) an (Fig. 11a). The other one is to prepare the samples with 14.5% water content an through rying or humiifying them, other samples with ifferent water contents can be prepare. The saturate sample is mae from the sample with 11% water content, also by vacuum pumping an water filling. In this way, the soil grains are equally istribute, an the results are shown in (Fig. 10b) an (Fig. 11b). When the temperature is -5, frequency 2Hz, an confining pressure 0.3MPa, with four ifferent water contents that are mae by the two preparation methos above, the backbone curves of the frozen soil are shown in (Fig. 10a) an (Fig. 10b). As can be seen from the figures, uner the same ynamic shear strain amplitue, the ynamic shear stress amplitue increases as the water content gets higher. (b) Fig. (10). Backbone curves of frozen soil uner ifferent moisture contents. Uner four ifferent moisture contents, the relation curves of ynamic shear moulus an ynamic shear strain amplitue of the frozen soil samples mae through the two ifferent preparation methos are shown in (Fig. 11a) an (Fig. 11b). Accoring to the figures, uner the same ynamic shear strain amplitue, the ynamic shear moulus will rise with increasing water content. The main reason is that as the water content gets higher, more free water in the soil boy will crystallize uner the same minus temperature. These crystals will refill the soil skeleton, contributing to increasing acting forces among the soil grains. In this way, the soil is strengthene an its ynamic shear moulus increases. However, the ynamic shear moulus with 15.5% water content is smaller than that with 14.5% water content. Because in general, the number of crystals in the soil boy will increase with higher water content, an so as the soil s rigiity

7 836 The Open Civil Engineering Journal, 2015, Volume 9 Bin et al. an its ynamic shear moulus. But when the water contents are almost the same, their influence on ynamic shear moulus will not be that remarkable. Because the curves rawn from the two ifferent preparation methos are quite similar to each other. When in saturate conition an uner the same ynamic shear strain amplitue, the ynamic shear moulus in (Fig. 11a) is larger than that in (Fig. 11b). The reason lies in that in the first metho, the soil grains are relatively larger, an so as the small openings among the grains, meanwhile, large amounts of crystals among the grains are concentrate, resulting in the increase of the soil sample s rigiity. Therefore, its ynamic shear moulus is also larger. (a) In equivalent linearization moel, the amping ratio is the function of ynamic shear strain amplitue. Through calculating the ata from the test, the relation curves of the amping ratio an ynamic shear strain amplitue uner ifferent influencing factors can be rawn as (Fig ) show. As presente in the figures, the relationship between the amping ratio an various factors is quite complicate-- when the amping ratio is between 0.1 an 0.55, as the ynamic shear strain amplitue increases, the amping ratio of frozen soil, in general, first ecreases an then increases Temperature When the confining pressure is 0.3Mpa, the moisture content 14.5% an the frequency 2Hz, uner five ifferent temperatures, the relation curves of the amping ratio an ynamic shear strain amplitue are presente in (Fig. 12). Accoring to the figure, with the increase of the ynamic shear strain amplitue, the amping ratio first ecreases an then increases significantly, an in the mile phase, the increase becomes slow. With the same ynamic shear strain amplitue, as the temperature gets lower, the amping ratio of frozen soil ecreases ramatically, the same as the maximum amping ratio. This is because as the temperature rops, the unfrozen-water content in frozen soil also gets lower, causing bigger bite force among the soil grains an the increase in the soil s strength an rigiity. At the same time, the eformability of the frozen soil is lessene, leaing to even lower energy consumption. Therefore, the amping ratio ecreases ramatically. (b) Fig. (11). Relationship between ynamic shear moulus an ynamic shear strain amplitue with ifferent moisture contents The Damping Ratio of Frozen Soil The amping ratio can be calculate by formula (4), among which A L means the area of ynamic shear stressynamic shear strain hysteresis loop, an A T means the triangle area forme through the lines connecting the central point of hysteresis loop an the maximum point of shear stress an strain values. The formula is as follow [22]: AL μ = 4A L (8) Fig. (12). Relationship between amping ratio an ynamic shear strain amplitue uner ifferent temperatures Confining Pressure When the temperature is -5, the moisture content 14.5% an the frequency 2Hz, uner four ifferent confining pressures, the relation curves of the amping ratio an ynamic shear strain amplitue are shown in (Fig. 13). It can be seen from the figure that as the ynamic shear strain amplitue increases, the amping ratio first ecreases an then increases markely an finally levels off. With the same ynamic shear strain amplitue, the amping ratio of frozen soil is enhance, but not that ramatically, along with the increase of the confining pressure. When the confining pressure is between 0.6Mpa an 1.2Mpa, its influence is not that

8 Test Analysis on the Dynamic Performance The Open Civil Engineering Journal, 2015, Volume remarkable. The increasing confining pressure can graually melt the ice crystals in the frozen soil, resulting in higher unfrozen-water content, thus, the eformability of the frozen soil is strengthene, causing more energy consumption. Therefore, the amping ratio increases. (a) Fig. (13). Relationship between amping ratio an ynamic shear strain amplitue uner ifferent confining pressures Moisture Content When the temperature is -5, the confining pressure 0.3MPa an the frequency 2Hz, uner the conition of four ifferent moisture contents an by the two samplepreparation methos above, the relation curves of the amping ratio an ynamic shear strain amplitue are as Fig. (14a) an (Fig. 14b) show. Accoring to the figures, the relationship between the amping ratio an the moisture content is quite complicate an the istinction of the relation curves got from the two ifferent preparation methos is quite remarkable. In (Fig. 14b), the amping ratios uner ifferent moisture contents are relatively close to each other; the curves representing 14.5% an 15.5% moisture content respectively are very close to each other since their moisture contents iffer little; but when the moisture content is 12.5%, the final amping ratios in the two figures are quite ifferent from those uner other moisture contents. If the soil is saturate, the first preparation metho is usually a goo choice an when the ynamic shear strain amplitues are the same, the amping ratio of the frozen soil will be smaller than that from the secon preparation metho. The reason lies in that the soil grains in the first metho are relatively bigger, an the small openings among grains are much larger as well as there are more crystals which are relatively concentrate among the grains. Thus, the soil sample is more rigi, resulting in less eformability an less energy consumption. As a result, the amping ratio is smaller than that of the secon metho Frequency When the temperature is -5, the confining pressure 0.3MPa an the moisture content 14.5%, uner four ifferent frequencies, the relation curves of the amping ratio an ynamic shear strain amplitue is as (Fig. 15) shows. (b) Fig. (14). Relationship between amping ratio an ynamic shear strain amplitue with ifferent moisture contents. Fig. (15). Relationship between amping ratio an ynamic shear strain amplitue uner ifferent frequencies.

9 838 The Open Civil Engineering Journal, 2015, Volume 9 Bin et al. It can be conclue from (Fig. 15) that with the increase of ynamic shear strain amplitue, the amping ratio first ecreases an then increases. An when the frequency is 1Hz, the amping ratio is smaller than those uner other frequencies. The reason may be that the loaing frequency then is close to the soil s natural vibration frequency. CONCLUSION Base on the experiments an ynamics performance analysis towars the frozen silty clay in Amo test section of Qinghai-Tibet Plateau. The followings can be conclue: (1) Uner ifferent factors like temperature, confining pressure, moisture content an frequency, the ynamic shear strain amplitue of the frozen silty clay is from to 0.007; the ynamic shear stress amplitue is from 0.1MPa to 2.1MPa; while the ynamic shear moulus is from 152MPa to 804MPa an the amping ratio, 0.1 to The ynamic shear stress amplitue increases along with the rise of the ynamic shear strain amplitue, but the relationship between the ynamic shear moulus an the ynamic shear strain amplitue is quite complex--the amping ratio first ecreases an then increases later. (2) Temperature plays a significant role in the backbone curve of frozen soil. When the temperature falls from -3 to -11, the final ynamic shear stress amplitue will increase from 0.87MPa to 2.03MPa. As the temperature rops, the ynamic shear moulus is enhance markely, with the final value reaching 782.2MPa from 423.5MPa. As the temperature falls own, the bining power between the soil grains an crystals will be stronger an the ynamic shear moulus will increase. Uner the same ynamic shear strain amplitue, the frozen soil s amping ratio will ecrease remarkably along with the rop in the temperature. (3) The influence of the confining pressure on backbone curve is not quite remarkable. When the confining pressure increases from 0.3MPa to1.2mpa, uner the same ynamic shear strain amplitue, the ynamic shear stress amplitue will keep rising. The confining pressure is a more critical factor on the ynamic shear moulus. However, when the confining pressure is large enough, its influence will eventually weaken. As the confining pressure rises, the grains will be islocate with force, making the soil more rigi an the ynamic shear moulus to increase. Uner the same ynamic shear strain amplitue, the amping ratio increases with rising confining pressure, even though the increase may not be that obvious. (4) Uner the same ynamic shear strain amplitue, the ynamic shear moulus will rise with increasing water content. When uner saturate conition, the soil grains are relatively large, an so as the small openings among the grains, meanwhile, the crystals among the grains are concentrate together, causing the increase in the soil sample s rigiity. Therefore, its ynamic shear moulus is larger an the amping ratio is relatively smaller. CONFLICT OF INTEREST The authors confirm that this article content has no conflict of interest. ACKNOWLEDGEMENTS This work is supporte by the national natural science fun ( ), The 2015 science an technology innovation fun for grauates of Yantai University (01061). REFERENCES [1] Y. Zhou, D. Guo, an G. Qiu, China Permafrost, Science Press, Beijing, 2000, pp [2] G. Cheng, Z. Sun, an F. Niu, Application of the roabe cooling approach in qinghai-tibet railway engineering, Journal of Col Regions Science an Technology, vol. 53, pp , [3].. 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