A study on water film in saturated sand

Available online at www.sclencedirect.comINTERNATIONAL" ScienceDirectJOURNAL OFSEDIMENTRESEARCHEL SEVIERIntematonal Joumal of Sedment Research 25 (01)221232ww.evercmlocate/jicA study on water flm in saturated sandLUX. B.' and CUI p?2Water film can serve as a sliding surface and cause landsides on gentle slopes. The development of“water film" in saturated sand is analyzed numerically and theoretically based on a quasi-three-phasemodel. It is shown that stable water films initiate and grow if the choking state (where the fluid velocitydecreases to near zero) remains steady in a liquefied sand column. Discontinuity can occur in pore watervelocit, grain velocity and pore pressure after the initiation of a water film. However, the discontinuityand water film can disappear once the choking state is changed. The key to the formation of water film isthe choking in the sand column caused by eroded fine grains.Key Words: Saturated sand, Water flm, Liquefaction1 IntroductionThe concept of“water flm" in sand containing an impermeable layer was first suggested by Seed (1987)in his attempt to explain slope failures observed in earthquakes. This“water film”can serve as a slidingsurface for post-liquefaction failure. This sliding surface can arouse landslides and debris flows on gentleslopes. The water film in saturated sand is a water gap due to non-uniform permeability of the sedimentwhere the pore water is trapped by relatively low permeable layers. Sand grains do not support oneanother. They suspend under the condition of zero effective stresses (Scott, 1986), and eventually settledown because they have a higher density than water. The rate of settlement is restricted by the fact thatwater must flow upward around the sand grains (Bose and Dey, 2009). If liquefiable sand deposits areoverlain by less permeable soils in a stratified deposit, the overlaying deposit can restrict the pore waterfrom passing through. If there is no downward drainage through the deposit, this relative flow betweenthe upward water flow and the settlement of grains at the interface, by continuity, must be equal to thevelocity of settlement at the upper liquefied sand surface (Ficgel and Kutter, 1994). Thus, anaccumulation of water in the form of a water gap forms at the interface. Feigel and Kutter (1994) andMalvick et al. (2008) performed centrifuge shake table tests to demonstrate the formation of water filmsin stratified sand. More recently, Kokusho (1999) performed shake table tests using sand samplescontaining a seam of non-plastic silt. Kokusho showed that water films formed beneath the sit layer. Inthis case, the column was subjected to horizontal dynamic loadings to simulate earthquakes. Experimentalobservations on the formation of water films in vertical columns of saturated sand contained in circularcylinders have also been reported by Zhang et al. (1999) and Peng et al. (2001). In both cases, care wastaken in preparing the sample by feeding wetted uniform sand continuously into a column of water toavoid intentional stratification. However, small heterogeneity still existed due to nonuniform settlementvelocity.These researches revealed that liquefaction is a necessary condition for water film initiation and growth.In Zhang's experiment (1999), a sand column in a circular cylinder was subjected to a vertical impact. ItDr., Laboratory for Hydraulic and Ocean Engineering, Institute of Mechanics, Chinese Academy of Sciences,Beijing 100190, China, E-mail: xblu@imech.ac.cnProf, Key Laboratory for Mountain Hazard and Earth Surface中国煤化工rzard and .Environment, Chinese Academy of Sciences, Chengdu 610041,_.ac.cnNote: The original manuscript of this paper was received in Feb.DHCNMHGevedinMay2010. Discussion open until Sept. 2011.Intemnational Jounal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221-232.221 -was found that small heterogeneity of saturated sand may be aggravated during the settlement of sandafter liquefaction. The water films occurred at the place where fine grains accumulated( Fig. 1).In the centrifuge experiments of Malvick et al. (2008), a stratified slope was born shaking. A thin layerof silt with a permeability of 3x10- 'm/s was embedded in the slope. The rest of the slope consisted ofNevada sand with a permeability of 5x10~'m/s. It was shown that the maximum increases of porepressure and displacement occurred immediately under the silt clay (Fig. 2) after shaking. This indicatesthat the water film forming under the silt clay is caused by the net inflow of water in this zone due to thehigh pore pressure. The low permeability layer of silt clay plays an important role in the formation ofwater film.In addition, Zheng et al. (2001), Lu et al. (2006) showed analytically that the water flm had to be justbeneath the fine sand layer. Malvick et al. (2006) discussed the development of water films using theconcept of localization.Fig. 1 Transverse water films In a sand column (Zhang ct al, 1999)400 after shaking(PtD)e)Fig. 2 Displacement and formation a water film a| 中国煤化工6)The formation mechanism of water flms in stratifed sandC N M H Gosity distributedcontinuously, is a process that has not been researched extensively. Inis paper reports the further analysis.222.Intermational Joumal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221-232of the formation mechanisms of water films on the basis of the above mentioned works.In this paper, a quasi-three-phase model is presented to describe the movement of liquefied sand.Although a full description is not available, a simple empirical model will be devised to explainqualitatively the main features observed experimentally. Then, theoretical analyses and numericalsimulations will be used to understand the mechanism of water films.2 Formulation of the problemFigure 3 shows a horizontal sand stratum, which is water saturated with porosity and other parameterschanging only vertically. The x axis is upward (Fig. 3).A set ofsimplified quasi-three-phase flow equations is presented in the following, under theassumptions that (1) the flow is one dimensional; (2) the inertia effect may be neglected; (3) only thesimplest form of interaction between water and grains is considered and; (4) the whole sand column isliquefied at the beginning. A broad grain size distribution means that some of the fine grains may bewashed away to become part of the percolating fluid or re-deposited later somewhere down stream(Alekseevskiy et al, 2008). This may tum an initially homogeneous sand column into an inhomogeneoussand column. The heterogeneity can aggravate with time and flow rate. The eroded grain mass is assumedto proportional to the relative velocity between water and grains but limited by the mass of fine grains inpores. Hence, the problem lies in properly describing the transport of these fine grains and its effect onpermeability.2.1 Erosion relationIn experiments the water films formed only when the grain size distribution was broad and containedfine grains. These experiments suggest that the fine grains should be flushed away by the percolatingwater. This results in the change of initial porosity and the turbidity of percolating water. Changes ininitial porosity and turbidity both alter the permeability.Fine grain mass transferred to water is assumed to be proportional to the relative velocity betweengrains and water, but inversely proportional to the fine grain mass in the percolating fluid. There is a limitto the amount of fine grains that can be transported (Fazli et al.. 2008; Wang et al, 2008; Ghodsian andVaghefi, 2009; Yu et al., 2009). Thus, the erosion relation is (Cheng et al., 2000):⊥(22 < 2.(x)if -<(.0)s-(1)p。\ Ot+心)-+(“一一)P1(+u, 2)sootherwise(2)p:atin which the first term“。on the right side of the first equation shows how the fine grains aretransferred to water, the second term -q describing deposition places a limit on the amount of fine grainsthat can be carried in the percolating fluid, q is the ratio of the volume of fine grains to porosity, Q isthe fine grain mass eroded per unit volume of the sand/water mixture, Pz is the density of the grains, uis the velocity of percolating fluid containing fine sand grains, u, is the velocity of sand grains, T andu' are the characteristic time and velocity in this problem, respectively, e(x,t) is the porosity, Q(x) isthe maximumof Q that can be eroded at x.2.2 Conservation equationsConsidering the erosion of fine grains, the pore is flled by two parts: one is the fine sand eroded fromthe skeleton q , and the second is pure water ε-q. Assuming that fine grains flow with the pore water,the mass conservation equations can be described by (Cheng et al.,. 2000)d-q)e+ 0(e-g)pu = 0(3)2xagp.. + aqp."=G=照中国煤化工(4)t201-8)e. + a(1-8)p,u_. GnYHCNMHG(5)aax°aIntermational Joumal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221-232-223-in which ρ is the density of water, G is the erosion-rate, e.g.. the mass of fine grains eroded from theskeleton in unit time.Combining Eqs. (3)- (5) yieldsau+(1-s)ks, =U()(6)in which U() is the flow rate of water per unit cross sectional area of the sand column.Flow direction of fluidcontaining fine sandQ90~PercolatingSkeletonfluid0➊0。The move direction of gainsFig.3 Sketch of the model (A sand column with parameters only vertically changeable isconsidered. The fine grains eroded from the skeleton move upwards with pore waterflow while the coarse grains settle downwards. )Considering the momentum transferred by the fine sand eroded from the skeleton, the momentumconservation equations are adopted as:[(e-g)p+qp.J[(0+-)-一.c2(u-u)_(7)k(s,q)[e-q)p+ qp,Ig8axax a(8)u-u)in which Eq. (7) is for percolating fluid and Eq. (8) for the total momentum. The last term on the rightside of Eq. (8) is the momentum of eroded fine grains. In Eqs. (7) and(8), p is the pore pressure, k isthe physical permeability (k=K1png，Pw is the density of the water, K is the Darcy's permeabilty,and g is the gravity acceleration), and σ。is the effective stress.Obviously, k increases positively with increasing E and decreasing q. For simplicity without lossof generality, k is assumed to be proportional to ε and inversely proportionalto q (Lu et al, 2006):k(e,g)=kof(q,c)=k(-aq+ Be)(9)in whicha,B are parameters and 1< β<< a. Since we think the choking state is mainly caused by theeroded fine grains, a is chosen to be much greater than B,中国煤化工sin q haveagreater influence than thatof ε.YHCNMHGIn experiments, the water flm sometimes forms and expands u wren usappycais. iuo uay be caused by-224-Intermational Joumal of Sediment Research, VoL. 25, No. 3, 2010, pp. 221- -232the formation or disappearance of choked states in the sand layer. Thus, two assumptions are adopted inthe following: (1) once the choking occurs, i.e., the permeability k drops to zero at any place, thechoking state remains unchanged; and (2) The choking state may disappear once the gradient of porepressure is over a critical value Pa .2.3 Discontinuity reltions and the conditions for formation of water flImsThe expansion of water flms depends on the discontinuity. Assuming the velocity of discontinuity isw,and using transformation of coordinate ξ=x- wI, which is often adopted in the analysis of discontinuity,e.g. shock wave (Lu et al, 2006), Eqs. (4)-(8) becomed(e-g) (u-w)=0Eq(u-w)=G(-s) (u, -w)=-Gd4(10)([(e-q)p+qp,ZJ(u-w)+ (1-s)p,u,(u, -w)+ L(p+o.)=-[(e -q)p+(1-8+q),]εd一00-0---0(0400where H is the interaction assumed to be proportional to the velocity difference between pore water andgrains and H=n2(u-u,)/k (Lu et al, 2004), σe is the effective stress.Then, five discontinuity relations may be obtained by integrating Eq. (10) along the discontinuity:pt=ρ~(e*-q*)(r+-w+)=(e- -q)(r-w)(-e*)4;-w*)=6-e)bu;-w-)(11)|ε* p*u*u*-w* )+(1-8*)p;uiw;-w*)+p* +σ: =|e p:u~(ur-w )+(1-ε )o;u,(,-w~)+p" +σ;p:tu -w"+p*=zp:br-w严+p~in which P. =ρ+2(p, -p), assuming that q/e and p. are constant at the discontinuity. In the waterflm (c=1), the water velocity is u, the pore pressure is p. Outside the water film (E≠1), theparameters are the porosity, the water velocity, pore pressure, grain velocity_ and effective stress&,u,p,ug,σe. Let u-山=U, w-u=W, with W being the velocity of discontinuity relative to thewater film.Then derive the following relationsu,=woru,-w=WeU+(1-ε)W=0op=p-p=p[{∪_w)} - w]=25E p.W(12)op-σ。=-pgWU=-εp.w2中国煤化工It is clear that W and U will both vanish when σ。 is zetCCHCNMHGvater flm in thiscase. The persistence or expansion of water films requil. .. .unimiv v-stress or otherInternational Joumal of Sediment Research, Vol. 25, No. 3, 2010, pp.221-232.225-conditions such as choking in sand.3 Initiation of water flmsBased on the model above, water film develops in a liquefied sand column (the effective stress and theshear stress are both zero), where coarse grains settle downwards and water with fine grains eroding fromthe skeleton move upwards.Consider the fixed boundary,ie., u and u, are both zero at x= 0 , then the total mass flow rate fromEq. (6) is:au+(1- 8)u, =U(1)=0 .(13)Using Eqs. (1), (2), (9) and (10), Eqs. (4), (5), (7) and (8) are reduced to8εtoue_1__u-q]at ax Tu*(1-ε)8q + auq_u-q(14)Dt ax:°[(e-q)_+q](+uE_ au(aε7“i-ε as?,)x’εa1-ε koP;J(q,E) (1-g)^Tu*(-E) ”-q)+T =(ε-q)(1-P)gIt is observed in experiments that water fiIm formation is so slow that the inertia effect can be neglected,thus Eq. (14) can be further simplified under the condition of erosion/re-deposition. It is reasonable totake T as the appropriate characteristic time. And let u，denote the characteristic velocity and let Ldenote the characteristic length of the problem, then Eq. (14) can be witen in a non-dimensional form interms of(15)The first two equations in Eq. (14) become0ε. Tu, OEu_ ;__ u,Ot L a“u*(1-8)(16)cq. Tu, aqu(，0tLa5u*(1-&)For Tg/un >>1, i.e, the gravity effect dominates and the inertia terms are negligible, the last equation ofEq. (14) becomes=(=e_ 919050510-12.15100 -)1.(17)u,when u, isu =koP,g(1- p/p,)(18)Thus, up to a factor near unit, u/(1-;) is the settlement velocity of grains in a uniform sand columnwith constant permeability coefficient hg. The problem now reduces to finding e(5,r) and q(5,r) as asolution to Eq. (16). The initial conditions are:e(E,0) = Eo(5), q(5,0)=0(19)In order to avoid complication due to consolidation wave (Scotter, 1986) from the bottom of the sandcolumn, the sand column is assumed long enough for water film development before the wave arrives.Then rewrite Eq. (16) as: .a. Buc(20)四+ oug_u_ 4中国煤化工6+- aσ。“u*(1-MHCNMHGwhich can be shown to be hyperbolic with the characteristic equatons as-226-Intermational Journal of Sediment Research, Vol 25, No. 3, 2010, pp. 221- 232The C characteristicd5_ . Bu。 audEq(21)The C* characteristics= ;Along the c and C+ characteristics, ε and q satisfyouaude亟=(+9)(_二i-g)it(22)aaεd_ εq=q-:dtqdrThen the solution is completely determined when the values of & and q are prescribed at 1=0 forAs for the initiation conditions of water films, consider frst the magnitude of the parameter u,T/L. Inthis equation, T is time for settlement, u, is the settlement velocity of sand grains and L is theinterval between two water films. In the experiments of Zhang et al. (1999) and Peng et al. (2001),T~20s and u,=10+~10~'m/s ，while L is 0.06m. Hence u,T/L ranges between 0.03~0.003.Therefore, when the initial non-uniformity of the sand column is small (δ <<1), the second term in Eq.(20) can be neglected until the non-uniformity becomes sufficiently large and concentrated at certainlocations. Consequently, for a limited period of time Eq, (20) can be further simplified toaε ___ u,σ"u*(-8)~ 9(23)q=u_ u,=“u*(1-8) 9which shows that ε and τ are periodic in ζ when so(n) is also periodic. Taking into accountquadrature, Eq. (17) yields8=6o(s)+q(24)lq(25)。4 1-6(5)-gEo(sXaq +aeo(c)- Bq)-qu. [e(Gc)+qFThis indicates that water films are likely to develop when q reaches the largest value in the shortesttime. In particular, it shows that water films would develop at equal intervals of x if the initial porositydistribution is periodic in x . However, this solution is not sufficiently accurate in describing how waterfilm expands because the non-linear terms in Eq. (20) will be no longer negligible.In the above discussions a number of constants are involved, say, a, β and h, are in dimensionlessform. In the following, the constraints will be put on these constants to ensure the development of waterfilms. Consider the case where the initial porosity at distances far greater than Tu, from s=0 isconstant, theneo(G)→6 as ζ→∞and eo(s)→e as s→-∞Water film may develop when the two parts of the sand column separate and this depends on the grainvelocity u, at large |s| as t→∞. According to Eq, (25), I→∞requires the denominator in theintegrand to be zero. This allows solving for porosity ε* and ε~ at s→∞from the followingequations as r approaches infinity中国煤化工6|1+2(acs* + Pet -(26)YHCNMHGThe corresponding grain velocity isInternational Journal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221-232- 227-5=等6-)|(0-a) (-)-xs](27)This places a constraint on a, β, h at given σ and 6. As an example, taking 6σ =0.408，εσ*=0.392，a=1 ，β=56 and h=14 ，it yields u; -uf =3.56x10-3 as τ- →∞withus*o-uro=3.2x10-3 as r→0.It follows that under the present condition one or several water films will eventually develop nears=0.4 Numerical results and discussionsThis section will solve Eq. (17) by using the finite differential method under two types of initialParameters adopted in simulation are: β=47~56， p, =2400kg/m2，P =1000kg/m2，u" =0.04 ,kg=4x10-m/s, a=1, K= =50.0, a=0.08, time step Or=9x10+, step length Qx =0.01, critical porepressure P。 = 0.25MPa，N=L/0x， L is the length of the sand column.(1) Condition 1: The initial porosity changes continuously. Assume that once a place is choked, the stateremains unchanged.Figure 4 shows that when a place is choked, the porosity below the place increases gradually up to 1.0. Awater film is believed to occur there and then expand.Figure 5 shows the variation of pore water velocity, which increases first because of the high hydraulicgradient and then decreases to zero following the decrease of porosity and permeability. Outside the waterfilm, the velocity changes lttle, suggesting that there should be discontinuities at the boundaries of waterFigure 6 shows the variation of the fine grains eroded from the skeleton. The fine fraction depends onthe velocity difference between pore water and grains according to Eqs. (1) and (2). Thus, the value of thefine fraction is small in the water film and places some distance away from the water film, but the value isbig near the water flm.Figure 7 shows the distribution of pore pressure. It can be seen that the pore pressure is discontinuous.The peak value occurs at the choked place and causes the upward percolation of pore water. Below thechoked place the pore pressure increases suddenly due to the blockage of pore water flow.Specifically, when the sand column is choked, the velocity of pore water decreases to near zero and ahigh hydraulic gradient forms at this place due to the very small porosity. Thus the pore water velocity,grain velocity and mass of eroded fine grains tend to be discontinuous. Beneath the choked place, there isa net inflow of pore water because it is difficult for the upward flow to pass through the place, so grainsthere must move downwards according to Eq. (6). Grains at the above part also move downwards and fillup at the choked place. Then, a water film eventually forms. The pore water beneath the choked placeflows upwards while the grains settle down. As this occurs, the water film becomes wider and wider at aexpansion rate equal to that of the discontinuity D=[(-ε* ): -(1-ε ):;/(1-e*)-(1-e )=u,, whereug",s* ,u; and ε~ denote the grain velocity and porosity at the two sides of discontinuity,ut =0,e*=1,uj;and 8" can be determined by Eq. (20). It can be seen that the expansion rate is the same as thesettlement velocity of grains which changes with other parameters of the sand column.(2) Condition 2: The porosity distribution is the same as that in condition (1), but the choking state maydisappear.Figure 8 shows that when a place is choked, the porosity there increases gradually until a water flmdevelops. However, when the pore pressure is over a critical value, the choking disappears. The porepressure, pore water velocity and grain velocity become smooth from the discontinuous state. At last, thewater film disappears.Figure 9 shows the velocity of pore water. The velocity tends to be discontinuous after a water flmdevelops and then becomes smooth when the choked place中国煤化工TYHCNMHG-228-Intermational Journal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221-2320.0050.0040.8 t「T Initial tirne2 30000dt3 100000r6+4 100000.0.0032一0.40.00221t= 0.09090.2 H0.0012t= 0.90093t= 13.50090.0十0.0002040806080100Fig. 4 Development of porosity under assumption 1Fig.5 Development of velocity of pore water under(here N equal L/Or )assumption I0.015-9000，0.012-120000.009 .X2,3-150001 t= 0.09090.006 .凸-180002t中0.9009一1-21000-24000-270004(30B0100:010Fig.6 Development ofq under assumption 1 Fig. 7 Development of pore pressure under assumption 1Figure 10 gives the distribution and variation of the eroded fine grains. The fine fraction decreasessharply in the water film and increases as the water film disappears due to the variation of pore watervelocity. After the water film disappears, the value of the fine fraction levels.0.700.653(0.600.55>0.501t=0.02t- 0.0553t=0.091t= 180.405t= 135000.3510 608(soNFig. 8 Development of porosity under assumption 2Fig. 9 Development of velocity of pore water underassumption 2中国煤化工Figure 11 gives the pore pressure, which increases quicklyMHCNMHGI decreases withthe disappearance of the water film.Intermnational Journal of Sediment Research, Vol. 25, No. 3, 2010, pp.221- -232.229-0.00883、 A-120000.00801t= 0.0550.00724a -160002t= 0.0911∞0.0553t四180.00642t=0.091-200004t- 1350031= 180.0056 .4t∞13500-240000.0048204(B01002(6(8(Fig. 10 Development of q under assumption 2Fig.11 Development of pore pressureunder assumption 2The water film forms in a similar way in both conditions. But when the pore pressure exceeds a criticalvalue, water can pass through the choked place, the grains above the choked place can settle down againand the pore pressure becomes smooth gradually. Then, the water film disappears.5 Comparison with the experimental resultsThe numerical results are compared with the experimental data of Kokusho et al. (2002) (Fig.12). InKokusho's experiment, a saturated loose sand layer of 200 cm depth sandwiches a seam of non-plastic siltin the middle (96 cm above the bottom). The initial void ratios at the upper, the middle and the lowerlayers are 0.924, 1.5 and 0.831, respectively, with corresponding permeability of 0.04 cm/s, 0.00018 cm/sand 0.04 cm/s. The thickness of silt seam is about 4 mm. The saturated sand is in a tube of 13 cm innerdiameter and 211.5 cm height. The one-dimensional sand layer is instantaneously liquefied by a loadingwith a steel hammer. The data are adopted in the simulation (Table 1). Figure 12 shows that the tworesults agree well, under the assumption that the water flm begins when the porosity is 10% higher thanthe initial porosity.6 ConclusionsTheoretical and numerical analysis have been carried out to investigate the development of water film insaturated sand. The main conclusions can be drawn as follows:Stable water film may exist in a sand column only if it is liquefied and choked by the eroded fine grains.The non-uniform grain size distribution along the depth of the sand column is an essential preconditionfor the development of water films. The transport of sand composed of fine grains by percolation tends toaggravate this non-uniformity. Liquefaction is necessary for water films.st9-1 Numerical results2 Kokusho's results050150200 250Development of water flm中国煤化工Fig. 12 The comparison of our results withMYHCNMHG- 230-Intermational Joumal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221-232Table 1 Parameters in Kobusho et al. (2002)SandThicknessRelative densityPermeabilityInitialMaximum of strain( cm)(%(cm/s)porosity(%)Upper layer sand103.6140.040.482.4Sandwich sand0.4L.8E-40.6Lower Layer sand96390.454.0.95The evolution of the pore water velocity, grain velocity and the amount of fine grains eroded from theskcleton were analyzed. A water film appeared when fine grains eroded from the skeleton andre-deposited downstream in the sand column to cause choking. The coarse grains from above werestopped while they move downwards bencath the choked place. In this way, water films developed. Thewater film tended to be wider and wider if the choked state was unchanged. Otherwise, the water filmdisappeared when the pore pressure gradient exceeded a critical value that caused the sand column fromchoked state to smooth state.AcknowledgementsThis study was supported by National Basic Research Program of China“Activity characteristics andformation rules of secondary mountain hazard of earthquake" (No. 2008CB425802) and Key Program ofChinese Academy of Sciences (No.KZCX2-YW-302-02). Prof. Li Yong polished the English.ReferencesAlekseevskiy N. I,, Berkovich K. M.. and Chalov R. s. 2008, Sediment transportation and accumulation in rivers.Intermaltional Joumal of Sediment Research, Vol. 23, No.21, pp. 93- -105.Bose S. K. and Dey S.2009, Suspended load in flows on erodible bed. Internaltional Joural of Sediment Research,Vol. 24, No. 3, pp. 315 -324.Cheng C. M., TanQ. M, Peng F. J. 2000, On the mechanism of the fornation of horizontal cracks in a verticalcolumn of saturated sand. ACTA Mechanica Sinica( English Serials), Vol. 17, No.1,pp. 1-9.Fazli M., Ghodsian M., and Salehi S. A. A.2008, Scour and flow field around spur dike in a 90° bend. IntermaltionalJournal of Sediment Research, Vol. 23, No. 1, pp. 56 -58.Fiegel, G L. and Kutter B. L.1994, Liquefaction mechanism for layered sands. Journal of Geotechnical Engineering,ASCE, Vol. 120, No. 4, pp. 737-755.Ghodsian M. and Vaghefi M.2009, Experimental study on scour and flow field in a scour hole around a T-shape spurdike in in a 90° bend. Intermaltional Jourmal of Sediment Research, Vol. 24, No.2, pp. 145-158.Kokusho T. 1999, Water film in liquefied sand and its effect on lateral spread. Jounral of Geotechnical andGeoenvironmental Engineering, No. I0, pp. 817- 826.Kokusho T. and Kojima T.2002, Mechanism for postiquefaction water film generation in layered sand. Jounral ofGeotechnical and Geoenvironmental Engineering, ASCE, Vol. 128, No. 2, pp. 129 137.LuX. B., Tan Q. M., Zheng ZM, Yu S. B., and Cui P. 2004, Liquefaction and displacement of saturated sand undervertical vibration loading. Acta Mechanica Sinica, Vol. 20, No.1, pp. 96- -105Lu X. B, Zheng Z. M, and Wu Y. R. 2006, Formation of water film in saturated sand. Acta Mechanica Sinica, Vol.22, No. 4, pp. 377-383.Malvick E. J, Kutter B. L., and Boulanger R. W. 2008, Postshaking shear strain localization in a centrifuge model ofa satuarted sand slope. Jounral of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 134, No. 2, pP.164- 174.Malvick E. J., Kutter B. L., Boulanger R. W., and Kulasingam R. 2006. Shear localization due to liquefaction. inducedvoid redistribution in a layered infinite slope. Jounral of Geotechnical and Geoenvironmental Engineering, ASCE,Vol.132, No.10, pp.1293-1303.Kokusho T. 1999," Water fIm in liquefied sand and its effect on lateral spread. Jounral of Geotechnical andGeoenvironmental Engineering,Vol. 125, No. 10, pp.817-826.Peng F. J.,. Tan Q. M., and Cheng Z. M.2001, Laboratory study on water flms in saturated sands. Acta MechanicaSinica, Vol. 16, No.1, pp. 48- 54.Seed H. B. 1987, Design problems in sand liquefaction. Joumal of Geotechical Engineering, ASCE, Vol. 113, No.8,pp. 827- -845Scott R. F. 1986, Solidification and consolidation of a liquefied sand column. Soils and Foundations, Vol. 26, No. 4,pp. 23-31.YuiG A., Wang Z. Y, Zhang K., Chang T. C. and Liu H. X.2009 Fffect of ingominee transport rateof bed load in mountain streams. Internaltional Joumal of Sedime中国煤化工260-273.Wang Z. Y, Wang G Q., and Huang G H.2008, Modeling of stiYHCNMHGI over large areas.Intemnaltional Joumal of Sediment Research, Vol. 23, No.3, pp.International Joumal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221-232-231-ZhangJ. F, Meng x. Y, Yu s. B., Tan Q. M, and Zheng Z. M. 1999, Experimental study on permeability andsettlement of saturated sand under impact loading. Acta Mechanica Sinica, Vol. 31, No. 2, pp. 230-237 (inChinese).Zheng Z. M., Tan Q. M., and Peng F. J. 2001, On the mechanism of the formation of horizontal cracks in a verticalcolumn of saturated sand. Acta Mechanica Sinica, Vol. 17, No. I, pp.1-9.中国煤化工MHCNMHG-232-Intemnational Journal of Sediment Research, Vol. 25, No.3, 2010, pp. 221- -232