土木毕业英文论文翻译.docx

1、土木毕业英文论文翻译INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICSInt. J. Numer. Anal. Meth. Geomech., 23, 439449 (1999)SHORT COMMUNICATIONSANALYTICAL METHOD FOR ANALYSIS OF SLOPESTABILITYJINGGANG CAOs AND MUSHARRAF M. ZAMAN*tSchool of Civil Engineering and Environmental Science, U

2、niversity of Oklahoma, Norman, OK 73019, U.S.A.SUMMARYAn analytical method is presented for analysis of slope stability involving cohesive and non-cohesive soils.Earthquake effects are considered in an approximate manner in terms of seismic coe$cient-dependent forces. Two kinds of failure surfaces a

3、reconsidered in this study: a planar failure surface, and a circular failure surface. The proposed method can be viewed as an extension of the method of slices, but it provides a more accurate etreatment of the forces because they are represented in an integral form. The factor of safety is obtained

4、 by using the minimization technique rather than by a trial and error approach used commonly.The factors of safety obtained by the analytical method are found to be in good agreement with those determined by the local minimum factor-of-safety, Bishops, and the method of slices. The proposed method i

5、s straightforward, easy to use, and less time-consuming in locating the most critical slip surface and calculating the minimum factor of safety for a given slope. Copyright ( 1999) John Wiley & Sons, Ltd.Key words: analytical method; slope stability; cohesive and non-cohesive soils; dynamic effect;

6、planar failure surface; circular failure surface; minimization technique; factor-of-safety.INTRODUCTIONOne of the earliest analyses which is still used in many applications involving earth pressure was proposed by Coulomb in 1773. His solution approach for earth pressures against retaining walls use

7、d plane sliding surfaces, which was extended to analysis of slopes in 1820 by Francais. By about 1840, experience with cuttings and embankments for railways and canals in England and France began to show that many failure surfaces in clay were not plane, but signicantly curved. In 1916, curved failu

8、re surfaces were again reported from the failure of quay structures in Sweden. In analyzing these failures, cylindrical surfaces were used and the sliding soil mass was divided into a number of vertical slices. The procedure is still sometimes referred to as the Swedish method of slices. By mid-1950

9、s further attention was given to the methods of analysis usingcircular and non-circular sliding surfaces . In recent years, numerical methods have also been used in the slope stability analysis with the unprecedented development of computer hardware and software. Optimization techniques were used by

10、 Nguyen,10 and Chen and Shao. While finite element analyses have great potential for modelling field conditions realistically, they usually require signicant e!ort and cost that may not be justied in some cases.The practice of dividing a sliding mass into a number of slices is still in use, and it f

11、orms the basis of many modern analyses.1,9 However, most of these methods use the sums of the terms for all slices which make the calculations involved in slope stability analysis a repetitive and laborious process.Locating the slip surface having the lowest factor of safety is an important part of

12、analyzing a slope stability problem. A number of computer techniques have been developed to automate as much of this process as possible. Most computer programs use systematic changes in the position of the center of the circle and the length of the radius to find the critical circle.Unless there ar

13、e geological controls that constrain the slip surface to a noncircular shape, it can be assumed with a reasonable certainty that the slip surface is circular.9 Spencer (1969) found that consideration of circular slip surfaces was as critical as logarithmic spiral slip surfaces for all practical purp

14、oses. Celestino and Duncan (1981), and Spencer (1981) found that, in analyses where the slip surface was allowed to take any shape, the critical slip surface found by the search was essentially circular. Chen (1970), Baker and Garber (1977), and Chen and Liu maintained that the critical slip surface

15、 is actually a log spiral. Chen and Liu12 developed semi-analytical solutions using variational calculus, for slope stability analysis with a logspiral failure surface in the coordinate system. Earthquake e!ects were approximated in terms of inertiaforces (vertical and horizontal) defined by the cor

16、responding seismic coe$cients. Although this is one of the comprehensive and useful methods, use of /-coordinate system makes the solution procedure attainable but very complicated. Also, the solutions are obtained via numerical means at the end. Chen and Liu12 have listed many constraints, stemming

17、 from physical considerations that need to be taken into account when using their approach in analyzing a slope stability problem.The circular slip surfaces are employed for analysis of clayey slopes, within the framework of an analytical approach, in this study. The proposed method is more straight

18、forward and simpler than that developed by Chen and Liu. Earthquake effects are included in the analysis in an approximate manner within the general framework of static loading. It is acknowledged that earthquake effects might be better modeled by including accumulated displacements in the analysis.

19、 The planar slip surfaces are employed for analysis of sandy slopes. A closed-form expression for the factor of safety is developed, which is diferent from that developed by Das.STABILITY ANALYSIS CONDITIONS AND SOIL STRENGTHThere are two broad classes of soils. In coarse-grained cohesionless sands

20、and gravels, the shear strength is directly proportional to the stress level: （1）where is the shear stress at failure, the effective normal stress at failure, and the effective angle of shearing resistance of soil.In fine-grained clays and silty clays, the strength depends on changes in pore water p

21、ressures or pore water volumes which take place during shearing. Under undrained conditions, the shear strength cu is largely independent of pressure, that is=0. When drainage is permitted, however, both &cohesive and &frictional components are observed. In this case the shear strength is given by (

22、2)Consideration of the shear strengths of soils under drained and undrained conditions, and of the conditions that will control drainage in the field are important to include in analysis of slopes. Drained conditions are analyzed in terms of effective stresses, using values of determined from draine

23、d tests, or from undrained tests with pore pressure measurement. Performing drained triaxial tests on clays is frequently impractical because the required testing time can be too long. Direct shear tests or CU tests with pore pressure measurement are often used because the testing time is relatively

24、 shorter.Stability analysis involves solution of a problem involving force and/or moment equilibrium.The equilibrium problem can be formulated in terms of (1) total unit weights and boundary water pressure; or (2) buoyant unit weights and seepage forces. The first alternative is a better choice, bec

25、ause it is more straightforward. Although it is possible, in principle, to use buoyant unit weights and seepage forces, that procedure is fraught with conceptual diffculties.PLANAR FAILURE SURFACEFailure surfaces in homogeneous or layered non-homogeneous sandy slopes are essentially planar. In some

26、important applications, planar slides may develop. This may happen in slope, where permeable soils such as sandy soil and gravel or some permeable soils with some cohesion yet whose shear strength is principally provided by friction exist. For cohesionless sandy soils, the planar failure surface may

27、 happen in slopes where strong planar discontinuities develop, for example in the soil beneath the ground surface in natural hillsides or in man-made cuttings.Figure 1 shows a typical planar failure slope. From an equilibrium consideration of the slide body ABC by a vertical resolution of forces, th

28、e vertical forces across the base of the slide body must equal to weight w. Earthquake effects may be approximated by including a horizontal acceleration kg which produces a horizontal force k= acting through the centroid of the body and neglecting vertical inertia.1 For a slice of unit thickness in

29、 the strike direction, the resolved forces of normal and tangential components N and can be written as （3） （4）where is the inclination of the failure surface and w is given by （5）where is the unit weight of soil, H the height of slope, is the inclination of the slope. Since the length of the slide s

30、urface AB is, the resisting force produced by cohesion is cH/sin a. The friction force produced by N is. The total resisting or anti-sliding force is thus given by （6）For stability, the downslope slide force must not exceed the resisting force R of the body. The factor of safety, Fs , in the slope c

31、an be defined in terms of effective force by ratio R/T, that is （7）It can be observed from equation (7) that Fs is a function of a. Thus the minimum value of Fs can be found using Powells minimization technique18 from equation (7). Das reported a similar expression for Fs with k=0, developed directl

32、y from equation (2) by assuming that, where is the average shear strength of the soil, and the average shear stress developed along the potential failure surface.For cohesionless soils where c=0, the safety factor can be readily written from equation (7) as （8）It is obvious that the minimum value of Fs occurs when a=b, and the failure becomes independent of slope height. For such cases (c=0 and k=0), the factors of safety obtainedfrom the proposed method and from Das are identical.CIRCULAR FAILURE SURFACESlides in medium-stif clays are of