2. SLIP-SURFACE(s) is the second set and it depends on the program used (BE.EXE or GE.EXE)
6.1 MAIN DATA
2. SLIP-SURFACE(s) is the second set and it depends on the program used (BE.EXE or GE.EXE).
Slip surfaces of circular shape for BE.EXE (Bishop Extended method) are described in Section 7.
Slip surfaces for GE.EXE (General Method) of arbitrary or circular shape are described in Section 8.
The slip circle analysis by the Bishop Extended method and BE.EXE is usually done first.
After completion of the slip circle analysis by BE.EXE, you can read the same main data file by GE.EXE and check some non-circular slip surfaces, or compare the results computed by the extended Bishop's method with the result obtained by the General Method, which satisfies all equilibrium conditions, using SWITCH to… option.
6.1 MAIN DATA
Trial slip-surfaces may be used for either the right or left face of the slope. No restrictions are placed on the direction in which the slope faces. See Addendum 1, page 149. Positive direction of "x" is horizontal with coordinates increasing to the right hand side. The positive direction of "y" is upward.
The cross-section to be analysed is drawn in a convenient scale, basically as shown in Fig. 6.1 (simple slope, p.39), Fig.6.2 (slope with vertical crack, p.39) and Fig. 6.3 (moderate size problem, p.41).
It is recommended to use A-3 size millimeter paper or similar to draw moderate size and/or complex sections, and to follow the principles shown in Fig. 6.2. Draw your x & y axes. Writer's preference is to place "x" in such way that all or most points have positive values of "y" and that major part of the cross section is on the (+)ve side of "x" for the right face slope.
Smallest example for preparation of input data is given in Fig. 6.1, p.39 and Fig. 6.2, p.39. A moderate sized example for preparation of input data is given in Fig. 6.3, p.41.
Boundaries of the cross section, limits of soil zones and piezometric lines are approximated by a straight line segments.
* End points of line segments are numbered from 1 to "N",
* Zone boundary lines and piezometric lines are numbered from 1 to "L", and
* Soil zones are numbered from 1 to "M". If the shear strength of some material zone(s) has to be described with the nonlinear failure envelope, these material zones must be either numbered first, or all materials should be defined as they had the nonlinear failure envelope. Linear envelope can be described with nonlinear parameters by taking ∆φ=0 and with an nonzero value for parameter pN
The sequence of numbering of points and lines in the section is arbitrary.
Vertical lines are not needed for computational description of the cross section. If vertical line is prescribed, with the material definition in the range from 0 to the number of defined materials “M”, stability programs will warn you that this is not permitted. If, in spite of that, you start computation without making corrections, an error will be reported. However, if you want to have some vertical lines or any line of arbitrary orientation on your graph, you can prescribe to a line the material number outside the predefined range (0 to M). The negative material numbers are appropriate for such a purpose as they will show as discontinuous lines on the graphs on the screen and on HPGL plots, but will be ignored in computations. Such lines are called dummy lines.
ALL VALUES ENTERED IN THE PROGRAM MUST BE IN "SI" UNITS, in kN, m, (kilo-Newton, meter).
The unit weight of water is fixed value in the stability programs γw= 9,807 kN/m3.
MAIN DATA are entered after the first option is chosen in the INITIAL MENU of each stability program. The entering is performed in a "question and answer bases", or simply by following the screen instructions.
(i)
TITLE : is an alpha-numeric label giving the name of the problem. title. The suggested length of the title is not more than 40 characters, preferably less, if you wish to have a neat appearance on the screen. If you just press <Enter> without any title, the title will be automatically entered as "Untitled".
(ii)
COMNT : is the additional alpha-numeric comment to the problem with the suggested length as in (i). Make your comment as brief as possible. If you just press <Enter> without any comment, this label will remain empty.
(iii)
NUMBER OF POINTS (max.100) for the definition of the geometry of the cross section (N). Entering 0 (zero) or pressing only <Enter> will return you to the INITIAL MENU.
This comes handy if you initiated the procedure by not wishing to do so.
(iv)
NUMBER OF LINES (max.100) which describe the boundaries of the cross section, internal zoning and piezometric lines (L). Entering 0 (zero) or pressing only <Enter>
will return you to the INITIAL MENU.
(v)
NUMBER of MATERIALS (max.30) with different properties in the cross section, (M).
Entering 0 (zero) or pressing only <Enter> will return you to the INITIAL MENU.
(vi)
NUMBER OF MATERIALS WITH NONLINEAR ENVELOPES is the number of zones for which the soil shearing strength is to be described in the proposed unconventional manner (MN). Note that MN<=M. Advanced users would take MN=M, see (x) and (xi).
(vii)
TAILWATER LEVEL (YW) defines the "y" value of the free water surface (Fig. 6.3). In the case that such a level does not exist, some negative value, ("y" is positive upward) beyond the soil zone in consideration, should be given (Fig. 6.1 and Fig. 6.2). This level, if defined within the visible area of the screen, will be marked with a blue triangle on the extreme left or right side of the screen or graph. Soil zones beneath this level should be defined with the submerged unit weight ′γ in soil data set (x).
Note: Each time after entering (vii) or (viii) or (ix) or (x) and (xi) the following question will appear:
CONFIRM (Y/N) ?.
Pressing "Y" or "y" or only <Enter> would mean that you are satisfied with previous entries and you want to proceed with entering the next set of data. If you answer "N" or
"n", meaning that you are not satisfied with previous entries (you made some errors), the program will automatically offer you an opportunity to make corrections.
When you correct this group of data the program will offer you to continue entering the next group of data.
(viii)
COORDINATES x,y. Program asks the sequential entering of pairs of coordinates, separated by ",", starting from Point No. 1 and ending with Point No. N
(ix)
SOIL LIMITS AND PIEZ. LINES Program asks the sequential entering of definition of lines, described by the sequential number of end points T1,T2, and the material number MT beneath the line (T1,T2,MT). The strata beneath the lowest soil limit lines are assumed to extend down indefinitely. If the material number MT is entered as 0 (zero), then it describes a piezometric line. Note that only one piezometric line can be given for any vertical section, but several can be simulated using the option described in (x).
Vertical lines with 0≤ MT ≤ M are not allowed. If you really need a vertical line which separates soil zones, like for example in the description of the vertical tension crack, line 1-5 in Fig. 6.2, prescribe very small difference in x coordinates, say 0.001 to 0.01 meters.
Sequence of entering lines is arbitrary.
Note that the piezometric line will appear in blue color. Central point of each piezometric line segment will be marked with a small blue triangle.
If the material number (MT) beneath the line is either negative or larger then the number of materials M defined in (v), it will be the dummy line. Such a line will appear in the graphical displays, though discontinuous line on the screen and in the plotted graph, but it will be ignored in computations. Only a dummy line can be defined as a true vertical line.
(x)
SOIL PARAMETERS (Gamma, C, PhiB, PP) define unit weight γ , cohesion c′, or c , u the angle of the shearing resistance φ′ or φ′B or φu (in degrees), and the Pore Pressure indicator PP, respectively.
All soil unit weights for zones beneath the horizontal line corresponding to the tailwater level YW must be entered as submerged γ′=γsat -γw.
Strength parameters can be either in terms of total or effective stresses.
In the case that the shearing strength of material is to be described with nonlinear failure envelope, the parameter "PhiB" is the "basic angle of friction", (φ′B) and the additional PARAMETERS FOR NONLINEAR ENVELOPES (pNand ∆ ′φ ) will be entered with the next group of data (xi). Note that materials with nonlinear failure envelopes should be numbered first, or if sequence of is mixed, all materials should be treated as nonlinear.
In the case that φu=0, the value of c corresponds to y = 0, what permits the u description of the undrained strength linearly varying with depth, see PP option 3), in the next page.
The Pore Pressure indicator PP can be used in three ways:
1). PP>=0 Pore water pressure in the base of the slice will be computed by taking that r = PPu (pore pressure ratio), and the value of the pore water pressure will be computed from u = r xW / bu where W is the weight and b is width of the slice.
2). PP<0 Pore pressure is computed from piezometric line. Program calculates the height of the piezometric line above the base of the slice, or above the tail water level (whichever is smaller), multiplies it by the unit weight of water and by the absolute value of PP. In such a way, variable piezometric head in a single vertical section can be simulated. The piezometric line must be defined above all
materials that use this negative value of PP, otherwise, erroneous pore pressure will be implied.
3). PP is also used, in the case that φu=0, to define the gradient of the line describing the change of c with depth. Entering 0 (zero) would imply the constant u c value u with depth. Positive value means the increase of strength with the depth z, which is measured downward as positive from y=0, and the linear variation of the undrained cohesion is c (z) = c + PP z. See example in file CULIN.BG. u
You are advised to study the distribution of pore water pressures very carefully before defining these parameters in a most convenient and accurate way. Distribution of pore water pressures in some cases may become the most important and not always the simple part of input data preparation (see Bromhead 1986).
(xi)
PARAMETERS FOR NONLINEAR ENVELOPES are required when the number of nonli-near envelopes MN is larger than zero. Pairs of dPhi, (∆ ′φ ) and pN, (pN) values are required. Note that the basic angle of friction φ′B is defined as the value PhiB (or φ′) in the previous step (x). To describe the conventional Coulomb straight line, enter ∆ ′φ =0 and pN=1.
(xii)
DEPTH OF THE TENSION CRACK ? Enter the depth of the crack. In the case that the tension crack does not exists or if it is ignored, enter 0 (zero). If you want to introduce the tension crack at the top of the slope, refer to Addendum No.1, page 149, for further explanations.
(xiii)
NUMBER OF LINE LOADS if larger than zero, you will be asked to enter the pair of the coordinates for the point at which the line load is acting, and the intensity of each component in kN/m. Positive directions of components are in positive directions of corresponding axis. If the tension crack exists and if it is filled with water, the horizontal force of the water pressure will be inserted automatically as the first line load. You may find this option useful for description of anchor forces. Line loads will appear as dark red arrows on color monitor. The length of the arrow will be shown proportional to the load intensity.
(xiv)
NUMBER OF DISTRIBUTED LOADS in vertical direction are the surcharge loads (in kPa). If larger than zero, you will be asked to enter two point numbers, for which the location is defined in the list of coordinates (viii). Besides for the surcharge loads, this option is used if you want to describe the vertical tension crack. Soil above the depth of the crack is treated as the surcharge loading acting on the level of the tip of the crack. In the case that you have entered the depth of the tension crack >0, check Addendum 1, for details. If you have some other surcharge loads, beside due to the crack, the surcharge due to the crack must be entered as the first surcharge load. Surcharge loads are shown with dark red on color screen. The height of the strip representing the surcharge is
controlled by a value of the LOAD SCALE for which the default value 20 is used meaning that 20 kPa corresponds to 1 m. This LOAD SCALE for graphical presentation of the surcharge can be altered in BGP.EXE, page 132. However, this scale for the surcharge load due to the presence of the tension crack is governed by the description of the crack and not by this value of the LOAD SCALE that is applicable to all other surcharges.
(xv)
SEISMIC COEFFICIENTS kx, ky are two values expressing the components of inertia forces in terms of fraction of gravity. Most frequently, only horizontal acceleration kx is used, and the second value, ky is taken as zero. Note that the positive horizontal acceleration induces horizontal forces in the horizontal +x direction. If the slope is "left oriented", the negative value of kx shall normally cause the drop in the value of Fs and vice versa. Positive vertical inertia forces will act in (+)ve direction of "y" axis.
Program will automatically use the saturated unit weight for soils below the TAILWATER LEVEL (YW) for computation of inertia forces.
* * *
Entry (xv), described above, is supposed to be the last entry in the input stage and the graph will automatically appear on the screen.
The scale and the position of the cross section on the screen might need some adjustments, depending on the size of the section and position of the section with respect to origin. The option offered in the INITIAL MENU of BE.EXE is 6 ZOOM/ MOVE/ AXES/
MIRROR and in the second stability program GE.EXE is option 8 ZOOM/ MOVE/ AXES/
MIRROR. This set of options are also offered in several other menus. Available options are explained in the next page. The window showing the available options will appear as, for example, shown in Fig. 6.5, p.43.
* * *
As mentioned before, this set of main input data from (i) to (xv) can be entered in an identical manner using any of the two slope stability programs (BE.EXE or GE.EXE). After saving this set of data in a file, the same file can be loaded by any of the two slope stability programs. The data file formed by these programs will have an extension .BG added automatically to the users defined name when saved on the disk.
Three examples of input data are shown in the following pages 39 to 42 and included as files within this BGSLOPE 6.16 package. EXAMPLES of MAIN input DATA used in this Manual are stored in 8 files. File names are given in page 8 of this Manual. It is advisable for a novice user to load and/or print and/or examine these examples in some detail before attempting to use the package for solving his/her particular slope stability problem.
After performing adjustments shown as an example in Fig. 6.5 and 6.6, you are ready to enter slip surfaces, depending on the method selected, as described in Sections 7 & 8.
* * *
ZOOM/ MOVE/ AXES/ MIRROR… option is offered in several menus in this package. Its purpose is to control the graph on the screen as well as in graphic (HP-GL) files.
In any ZOOM/ MOVE/ AXES/ MIRROR window (Fig. 6.5 & Fig. 6.6, pages 43, 44) you can perform several adjustments using:
ZOOM controls the scale of the cross section. The scale is initially set automatically to 10, meaning that 1 meter of length corresponds to 10 pixels on the screen. It can be altered in by pressing + (plus on numeric key pad) to increase the size of the section, or - (minus on numeric key pad) to decrease the size. Scale increment (+) or decrement (-) is 1.02. The number in the left lower corner of the screen indicates the length of divisions on coordinate axes or on the scale bar. Cross-section loaded from the file will have the scale valid when the file was saved.
MOVE controls the position of the origin and the cross section on the screen. MOVE using arrows is performed in 5 pixel increments in both stability programs.
ARROWS TO MOVE Use arrow keys to move the origin in desired direction. Cross-section loaded from the file will have the origin valid when the file was saved.
letter A in Axes display is used as a toggle for showing or removing coordinate axes or the scale bar in the lower left corner of the screen. This option might give a neater appearance of the graph on the screen and on the drawing produced from the HP-GL, .PLT file exported by BGP.EXE. Cross-section loaded from the file will keep the consequences of this option when the file was saved. For example, compare windows shown in Fig. 8.14 (with axes, p.85) to Fig. 8.15 (no axes, p.86) or Fig.10.13 to Fig.
10.14, p.113.
letter R in miRror can be used to produce the mirror image, right slope becomes left and vice versa. (option rarely used).The sign of "x" of point coordinates is changed. Origin is moved in a new position - a mirror image of the point with respect to vertical line of the symmetry of the screen. This practically means that the whole graph has rotated for 180 with respect to the vertical center line of the screen. If you use the option twice in sequence, you will return to the initial orientation of the face of the slope. An example is shown in Section 9, Fig. 9.6 and Fig. 9.7, p.103.
letter C, in show Circles is an option offered in BE.EXE only. It works as a toggle. By pressing C you can make faster moves or zooms on the screen by not drawing slip circles in each step of the movement or in each change of scale. Press C again to see circles.
Fig. 6.1 Simple slope. Section, coordinate system, points and lines.
INPUT DATA for SIMPLE SLOPE shown in Fig. 6.1 above for the linear envelope.
BGSLOPE 6.16 Licensed: *****
Copyright: Dr M. Maksimovic 01-01-2006 Example 1 Simple slope
Linear envelope
NUMBER OF POINTS 4 NUMBER OF LINES 3 NUMBER OF MATERIALS 1
TAILWATER LEVEL -80 NUMBER OF SLICES 40 COORDINATES: SOIL LIM. & PIEZ. LINES:
Point x y Line T1 T2 MT 1 -10.000 18.000 1 1 2 1 2 12.000 18.000 2 2 3 1 3 36.000 9.000 3 3 4 1 4 60.000 9.000
SOIL PARAMETERS:
Mat. Gamma c PhiB PP 1 20.00 25.00 16.00 0.40 NUMBER OF LINE LOADS 0
NUMBER OF DISTRIBUTED LOADS 0
COEFF. OF SEISMICITY kx, ky 0.0000 0.000
In the Example 2, only the table with the soil parameters differs and looks like:
SOIL PARAMETERS:
Mat. Gamma c PhiB PP DPhi pN 1 20.00 0.00 16.30 0.40 48.10 28.20
Fig. 6.2 Simple slope with tension crack.
INPUT DATA for slope shown in Fig. 6.2 with tension crack + water.
BGSLOPE 6.16 Licensed: *****
Note that the horizontal force due to water pressure in the crack is entered (edited) to be QX=45 kN/m for the unit weight of water 10.0 kN/m3 though the program would calculate it as QX=44.13 kN/m for the unit weight of water 9.807 kN/m3.
Fig. 6.3 Geometry of cross sections for Examples 5 & 6.
INPUT DATA for the slope section shown in Fig. 6.3 with nonlinear envelopes.
Fig 6.4 Screen view of the cross section-start from default origin and scale
Fig 6.5 ZOOM/ MOVE... Start adjusting scale and origin to the whole section
Fig 6.6 ZOOM/ MOVE...Finished adjustments of scale of the whole cross section
Fig 6.7 SREEN VIEW. Finished adjustments of scale of the whole cross section