荷載作用下可液化地基中樁基礎(chǔ)的動(dòng)態(tài)行為畢業(yè)論文外文翻譯（英文）

1、Dynamic behavior of pile foundations under cyclic loading in liquefiable soilsAmin Rahmani ?, Ali PakDepartment of Civil Engineering, Sharif University of Technology, P.O. Box 11155-9313, Tehran, Irana r t i c l e i n f

2、oArticle history:Received 5 March 2011Received in revised form 12 September2011Accepted 13 September 2011Available online 11 November 2011Keywords:LiquefactionPile foundationsFully coupled three-dimensional dynamicanalys

3、isDynamic behavior of pilea b s t r a c tIn this paper, a fully coupled three-dimensional dynamic analysis is carried out to investigate thedynamic behavior of pile foundations in liquefied ground. A critical state bound

4、ing surface plasticitymodel is used to model soil skeleton, while a fully coupled (u–P) formulation is employed to analyze soildisplacements and pore water pressures. Furthermore, in this study, variation of permeability

5、 coefficientduring liquefaction is taken into account; the permeability coefficient is related to excess pore waterpressure ratio. Results of a centrifuge test on pile foundations are used to demonstrate the capabilityof

6、 the model for reliable analysis of piles under dynamic loading. Then, the verified model is used for aparametric study. The parametric study is carried out by varying pile length, frequency of input motion,fixity of the

7、 pile head, thickness of the liquefying soil layer and relative density of liquefying soil layer.Three different soil profiles have been considered in this study. In general, parametric studies demon-strate that fixity o

8、f the pile head, thickness of liquefying soil layer and frequency of input motion arethe most critical parameters which considerably affect piles performance in liquefied grounds.Crown Copyright ? 2011 Published by Elsev

9、ier Ltd. All rights reserved.1. IntroductionThe behavior of pile foundations under earthquake loading is an important issue that widely affects the performance of structures. Design procedures have been developed for eva

10、luating pile behav- ior under earthquake loading; however, application of these proce- dures to cases involving liquefiable ground is uncertain since the performance of piles in liquefied soil layers is much more complex

11、 than that of non-liquefying soil layer not only because the super- structure and the surrounding soil exert different dynamic loads on pile, but also because the stiffness and shear strength of the sur- rounding soil di

12、minishes over time due to non-linear behavior of soil and also pore water pressure generation. Liquefaction represents one of the biggest contributors to dam- age of constructed facilities during earthquakes [1]. This ph

13、enom- enon was reported as the main cause of damage to pile foundations during the major earthquakes such as Alaska, 1964, Loma-Prieta, 1989, Hyogoken-Nambu, 1995 [1]. Prediction of seismic response of pile foundations i

14、n liquefying soil layers is difficult, and there are many uncertainties in the mechanisms in- volved in soil–pile-superstructure interaction. However, in recent decades, a wide range of centrifuge and shaking table tests

15、 and also various numerical methods have been employed in order to provide better insights into the dynamic behavior of pile founda- tions in liquefiable soils. These researches can be divided intothree categories: field

16、 observations, laboratory tests, and numeri- cal modeling.1.1. Field observationsThese studies mainly investigate the distribution of the failure patterns, settlement and lateral displacement of piles. During Niigata Ear

17、thquake, 1964, many pile foundations failed to support structures due to the liquefaction of the surrounding soil. Accord- ing to Hamada [2], the ground in the vicinity of a four-storey build- ing moved approximately 1.1

18、 m, and the maximum lateral displacement of concrete piles with a diameter of 35 cm and length of 6–9 m was around 70 cm. The large amount of lateral displace- ment caused severe damage to the pile at the interface of th

19、e liq- uefied and non-liquefied layers. Mori et al. [3] conducted an excavation survey and internal inspection of the damaged piles of a silo which suffered severe damage due to the Hokkaido Nan- sei-Oki Earthquake, 1993

20、. They concluded that damage usually oc- curs at three different locations: at the pile head (for fixed-head piles), at a depth of 1–3 m below the pile cap (for free-head piles) and at the interface of the liquefied and

21、non-liquefied layers. This observation has been confirmed by others such as Tachikawa et al. [4], Shamoto et al. [5], and Onishi et al. [6].1.2. Laboratory testsThese studies include some dynamic centrifuge tests and als

22、o shaking table tests of pile-supported structures in which0266-352X/$ - see front matter Crown Copyright ? 2011 Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.compgeo.2011.09.002? Corresponding author. Tel

23、.: +98 21 6616 4225; fax: +98 21 6601 4828.E-mail address: aminrahmaani@gmail.com (A. Rahmani).Computers and Geotechnics 40 (2012) 114–126Contents lists available at SciVerse ScienceDirectComputers and Geotechnicsjournal

24、 homepage: www.elsevier.com/locate/compgeoinvestigations. Arulanandan and Sybico [35], based on the mea- surement of changes in the electrical resistance of saturated sand deposit during liquefaction in the centrifuge te

25、sts, concluded that ‘‘in-flight permeability’’ of saturated sand during liquefaction in- creases up to 6–7 times greater than its initial value. Jafarzadeh and Yanagisawa [36] by measurement of the volume of the ex- pell

26、ed water from saturated sand columns in shaking table model tests indicated that the average permeability coefficient during excitation is 5–6 times greater than its static value. Manzari and Arulanandan [37] used variab

27、le permeability in their numerical simulation. In their study, predictions of excess pore pressure and settlement were satisfactory, but lateral displacements were not simulated reasonably well. Balakrishnan [38] employe

28、d a fac- tor of 10 for increasing the permeability coefficient in numerical model in order to adjust the results of the simulation with the cen- trifuge test measurements for the soil settlement during liquefac- tion. Al

29、so, according to Taiebat et al. [39] and Shahir and Pak [40] using a constant value of permeability coefficient in numerical analysis results in a much smaller value of soil settlement compared to the measured value. Sha

30、hir and Pak [40] concluded that incorporation of permeability variation in the numerical model is necessary for capturing both pore pressure and settle- ment responses of a liquefiable soil mass. Therefore, in this study

31、, variation of permeability coefficient has been considered in numerical modeling of liquefiable layers using a formulation suggested by Shahir and Pak [40] in which a direct relationship between the permeability coeffic

32、ient and excess pore water pressure ratio (ru) was proposed. This relationship is as follows:kp ki ¼ 1 þ ða ? 1Þrb1 u During PWP build up phaseðru < 1Þkp li ¼ a During liquefied stat

33、eðru ¼ 1Þkp ki ¼ 1 þ ða ? 1Þrb2 u During consolidation phaseðru < 1Þð3Þwhere ki is initial permeability coefficient, kb is permeability coeffi- cient during excit

34、ation, ru is defined as the ratio of the difference ofcurrent pore pressure and hydrostatic pore pressure over the initial effective vertical stress (ru ¼ Du=r0 v0). a; b1; b2 are positive materialconstant. These pa

35、rameters are 20, 1.0 and 8.9, respectively for Ne- vada Sand [40]. This basically means that the permeability coeffi-cient increases up to 20 times during the initial liquefaction. It is to be noted that the proposed val

36、ue for a is consistent with the re-ported value by Balakrishnan [38] because the peak value of 20 is nearly equivalent with average value of 10. Validity and efficiencyof the proposed formulation can be found in Refs. [3

37、3] and [40].5. Pile–soil model developmentIn this research, soil layers are modeled by cubic eight-node elements with u–P formulation (called EightNodeBrick_u_p ele- ment in OpenSees framework) in which each node has fou

38、r de- grees of freedom: three for soil skeleton displacements and one for pore water pressure. Pile is modeled by beam-column ele- ments which have six degrees of freedom for each node: three for displacements and three

39、for rotations. A lumped mass on the pile head represents the superstructure. The finite element mesh is presented in Fig. 1. One of the important and difficult steps in numerical simulation of pile foundations in the soi

40、l media is the connection of pile ele- ments to the surrounding soil elements. In the present work, the connection is provided by means of rigid beam-column elements which possess the same physical properties of pile ele

41、ments. As shown in Fig. 2, these elements connect each pile node to sur- rounding nodes of soil elements at an equal depth. At the connec- tion point, soil element nodes slaved to the connection element node for three tr

42、anslational DOFs, while the three rotational DOFs of the connection element are left unconnected. Furthermore, slip- page between pile elements and surrounding soil elements is fea- sible in all directions by using zero-

43、length interface elements, which are defined by two nodes at the same location where the connection beam-column element is connected to the surrounding soil (as shown in Fig. 2). An elastic-perfectly plastic material mod

44、el is used for the interface elements. Some static field tests and also a centrifuge test, discussed later in this paper, were simulated in or- der to obtain suitable mechanical properties of the interface ele- ment. Bas

45、ed on these studies, Young’s modulus and yielding strain of this material are selected to be 2000 kPa and 0.04, respec- tively and are used throughout the main simulations of pile behav- ior in liquefiable soil layer. It

46、 is to be noted that values considered for these parameters lead to immediate yielding of interface ele- ment i.e. slippage at soil–pile interface can take place. However, further studies and simulations revealed that th

47、e ef- fect of interface elements was not that significant for the centrifuge test that has been simulated in this study. Comparing the numer- ical results of the model with and without employing interface ele- ments reve

48、aled a maximum difference of 5%. This can be specific to the kind of the problem that is studied in this research where the saturated liquefiable ground is horizontal and the soil is cohesion- less. Nevertheless, the abo

49、ve mentioned interface element proper- ties were employed to improve the quality of simulations and match the numerical results with the experimental values as much as possible. Due to the symmetry of the model, the mode

50、l is halved at the line of symmetry along the center-line of the pile, and all applied static loads are halved. Soil elements are coarser far from the pile and finer around the pile (see Fig. 1). Boundary conditions are

51、set in the following way:? Base of the mesh is fully fixed in all directions. ? At the side planes, parallel to the excitation direction, nodes are restrained from movement in the y direction, and at the ones, perpendicu

52、lar to the excitation direction, the nodes at equal depths are constrained to have equal displacements in the x direction to simulate free-field ground motion. ? All other internal nodes are free to move in any direction

53、. ? Pore water pressures are free to develop for all nodes except the ones at the level corresponding to the ground water table elevation.Simulations are carried out in three loading stages. In the first stage of loading

54、 where pile elements are not installed, self-weight,Table 1Material parameters used for Dafalias–Manzari Model [32,33].Parameter function Parameter index ValueElasticity G0 150.0 m 0.05Critical state M 1.14c 0.78kc 0.027