（節(jié)選）港口航道與海岸工程外文翻譯--關(guān)于飽和沙中水膜的研究（原文）

1、 International Journal of Sediment Research, Vol. 25, No. 3, 2010, pp. 221–232 - 221 - International Journal of Sediment Research 25 (2010) 221-232 A study on water film in saturated sand LU X. B

2、.1 and CUI P.2 Abstract Water film can serve as a sliding surface and cause landslides on gentle slopes. The development of “water film” in saturated sand is analyzed numerically and theoretically based on a quasi-thre

3、e-phase model. It is shown that stable water films initiate and grow if the choking state (where the fluid velocity decreases to near zero) remains steady in a liquefied sand column. Discontinuity can occur in pore wat

4、er velocity, grain velocity and pore pressure after the initiation of a water film. However, the discontinuity and water film can disappear once the choking state is changed. The key to the formation of water film is

5、the choking in the sand column caused by eroded fine grains. Key Words: Saturated sand, Water film, Liquefaction 1 Introduction The concept of “water film” in sand containing an impermeable layer was first suggested by

6、Seed (1987) in his attempt to explain slope failures observed in earthquakes. This “water film” can serve as a sliding surface for post-liquefaction failure. This sliding surface can arouse landslides and debris flows

7、on gentle slopes. The water film in saturated sand is a water gap due to non-uniform permeability of the sediment where the pore water is trapped by relatively low permeable layers. Sand grains do not support one anot

8、her. They suspend under the condition of zero effective stresses (Scott, 1986), and eventually settle down because they have a higher density than water. The rate of settlement is restricted by the fact that water must

9、 flow upward around the sand grains (Bose and Dey, 2009). If liquefiable sand deposits are overlain by less permeable soils in a stratified deposit, the overlaying deposit can restrict the pore water from passing throu

10、gh. If there is no downward drainage through the deposit, this relative flow between the upward water flow and the settlement of grains at the interface, by continuity, must be equal to the velocity of settlement at th

11、e upper liquefied sand surface (Fiegel and Kutter, 1994). Thus, an accumulation of water in the form of a water gap forms at the interface. Feigel and Kutter (1994) and Malvick et al. (2008) performed centrifuge shake

12、table tests to demonstrate the formation of water films in stratified sand. More recently, Kokusho (1999) performed shake table tests using sand samples containing a seam of non-plastic silt. Kokusho showed that water

13、films formed beneath the silt layer. In this case, the column was subjected to horizontal dynamic loadings to simulate earthquakes. Experimental observations on the formation of water films in vertical columns of satur

14、ated sand contained in circular cylinders have also been reported by Zhang et al. (1999) and Peng et al. (2001). In both cases, care was taken in preparing the sample by feeding wetted uniform sand continuously into a

15、column of water to avoid intentional stratification. However, small heterogeneity still existed due to nonuniform settlement velocity. These researches revealed that liquefaction is a necessary condition for water fil

16、m initiation and growth. In Zhang’s experiment (1999), a sand column in a circular cylinder was subjected to a vertical impact. It 1 Dr., Laboratory for Hydraulic and Ocean Engineering, Institute of Mechanics, Chinese A

17、cademy of Sciences, Beijing 100190, China, E-mail: xblu@imech.ac.cn 2 Prof., Key Laboratory for Mountain Hazard and Earth Surface Process, Institute of Mountain Hazard and Environment, Chinese Academy of Sciences, Che

18、ngdu 610041, China, E-mail: pengxcui@imde.ac.cn Note: The original manuscript of this paper was received in Feb. 2009. The revised version was received in May 2010. Discussion open until Sept. 2011. International Journ

19、al of Sediment Research, Vol. 25, No. 3, 2010, pp. 221–232 - 223 - of the formation mechanisms of water films on the basis of the above mentioned works. In this paper, a quasi-three-phase model

20、 is presented to describe the movement of liquefied sand. Although a full description is not available, a simple empirical model will be devised to explain qualitatively the main features observed experimentally. Then,

21、 theoretical analyses and numerical simulations will be used to understand the mechanism of water films. 2 Formulation of the problem Figure 3 shows a horizontal sand stratum, which is water saturated with porosity and

22、 other parameters changing only vertically. The x axis is upward (Fig. 3). A set of simplified quasi-three-phase flow equations is presented in the following, under the assumptions that (1) the flow is one dimensional

23、; (2) the inertia effect may be neglected; (3) only the simplest form of interaction between water and grains is considered and; (4) the whole sand column is liquefied at the beginning. A broad grain size distribution

24、means that some of the fine grains may be washed away to become part of the percolating fluid or re-deposited later somewhere down stream (Alekseevskiy et al., 2008). This may turn an initially homogeneous sand column

25、into an inhomogeneous sand column. The heterogeneity can aggravate with time and flow rate. The eroded grain mass is assumed to proportional to the relative velocity between water and grains but limited by the mass of

26、fine grains in pores. Hence, the problem lies in properly describing the transport of these fine grains and its effect on permeability. 2.1 Erosion relation In experiments the water films formed only when the grain si

27、ze distribution was broad and contained fine grains. These experiments suggest that the fine grains should be flushed away by the percolating water. This results in the change of initial porosity and the turbidity of p

28、ercolating water. Changes in initial porosity and turbidity both alter the permeability. Fine grain mass transferred to water is assumed to be proportional to the relative velocity between grains and water, but invers

29、ely proportional to the fine grain mass in the percolating fluid. There is a limit to the amount of fine grains that can be transported (Fazli et al., 2008; Wang et al., 2008; Ghodsian and Vaghefi, 2009; Yu et al., 200

30、9). Thus, the erosion relation is (Cheng et al., 2000): ? ?? ? ?? ? ? = ? ?? ? ???? + ??? q uu uT xQ u tQ s s s1 1ρif ( ) ( )scsx Q Q x ρ ρ ε ≤ ≤ ? 0 ,(1) 0 1 ≤ ? ?? ? ???? + ??xQ u tQs s ρotherwise

31、 (2) in which the first term * uu u s ?on the right side of the first equation shows how the fine grains are transferred to water, the second term q ? describing deposition places a limit on the amount of fine gr

32、ains that can be carried in the percolating fluid, q is the ratio of the volume of fine grains to porosity, Q is the fine grain mass eroded per unit volume of the sand/water mixture, s ρ is the density of the grains

33、, u is the velocity of percolating fluid containing fine sand grains, s u is the velocity of sand grains, T and ? u are the characteristic time and velocity in this problem, respectively, ( ) t x, εis the porosity,

34、 ( ) x Qcis the maximum of Q that can be eroded at x. 2.2 Conservation equations Considering the erosion of fine grains, the pore is filled by two parts: one is the fine sand eroded from the skeleton q , and the secon

35、d is pure water q ? ε . Assuming that fine grains flow with the pore water, the mass conservation equations can be described by (Cheng et al., 2000) ( ) ( ) 0 = ?? ? + ?? ?xu qtq ρ ε ρ ε(3) xQ u tQ G xu qtqs s s ?? +