Project settings — OGR Slip2D documentation

The Project Settings dialog holds the choices that apply to the whole analysis: units and failure direction, the methods of slices and their convergence, the groundwater method, the statistical and seismic analyses, partial factors and a few numerical controls. The settings are saved in the project file, so every project carries its own.

2.1.1Opening the dialog#

Choose Analysis → Project Settings… (Ctrl+J) or the toolbar button. The pages are listed on the left (General, Methods, Groundwater, Transient, Statistics, Random Numbers, Design Standard, Advanced, Seismic and Project Summary) and the buttons at the bottom act on all of them at once:

OK applies every page and closes the dialog; Apply applies them and leaves it open; Cancel closes it without applying what has not been applied yet.
Restore Defaults puts back the default value of every project setting.

The settings of the slip-surface search (surface type, search method, grid, filters, optimisation) are not in this dialog but in Surfaces → Surface Options… (Section 2.7).

Version 0.1.235

Restore Defaults takes effect immediately, before OK, and Cancel does not undo it. It also resets the settings that live outside this dialog: the whole Surface Options configuration, the slope limits and the moment axis go back to their defaults too.

The Project Settings dialog open on the Methods page: the list of pages on the left, the nine methods with check boxes, and the convergence options below them — Figure 2.1.1 Project Settings, Methods page.

2.1.2General#

Table 2.1.1 General page.

Field	Meaning	Default	Range or choices
Units	Unit system for display and input (Unit systems). The line below the list summarises its units.	Metric, stress as kPa	Six systems
Time Units	Unit of time	`d`	`s`, `min`, `h`, `d`, `mo`, `yr`
Permeability Units	Unit of hydraulic conductivity	`m/s`	`m/s`, `m/day`, `m/year`, `cm/s`, `mm/hour`
Failure Direction	Which way the sliding mass moves (Failure direction)	Right to Left	Right to Left, Left to Right
Max Materials	Largest number of materials the project may hold	20	1 to 500
Max Supports	Largest number of supports	20	0 to 500

Version 0.1.235

Max Materials is enforced when properties are imported from another project and by the scripting and agent interfaces, but not by the Define Materials dialog, where materials can be added beyond the limit. Max Supports is stored and not enforced anywhere.

Unit systems#

OGR Slip2D computes and stores every value in the SI system of the second row of Table 2.1.2 (m, kN, kPa, kN/m³). Choosing another system does not change the model: values are converted when they are shown and converted back when they are entered.

Table 2.1.2 The six unit systems, in the order of the list.

System	Length, force, force per length, stress, unit weight
Metric, stress as MPa	m, MN, MN/m, MPa, MN/m³
Metric, stress as kPa	m, kN, kN/m, kPa, kN/m³
Metric, stress as tonnes/m²	m, tonnes, tonnes/m, tonnes/m², tonnes/m³
Imperial, stress as tons/ft²	ft, short tons (2000 lbs), tons/ft, tons/ft², tons/ft³
Imperial, stress as ksf	ft, kips, kips/ft, ksf, kips/ft³
Imperial, stress as psf	ft, lbs, lbs/ft, psf, lbs/ft³

Version 0.1.235

The unit system reaches only the Define Materials dialog (unit weights, strength parameters, constant pore pressure and air entry value) and the Newmark displacement shown in the Interpret window. Coordinates, loads, supports, the water pressure grid and the remaining fields of this dialog are always entered and shown in metres, kN and kPa, whatever system is selected. With the default system there is no difference.

Failure direction#

The equations of every method are written for a mass that slides in a known direction (Section 3.1.5). The page shows a small sketch of the slope and an arrow for the option chosen:

Right to Left (the default): the sliding mass moves towards decreasing $x$ ; the crest is on the right and the toe on the left.
Left to Right: the mass moves towards increasing $x$ ; the crest is on the left and the toe on the right.

Set it before computing whenever the ground of the model falls to the right. The direction also decides the sense in which the horizontal seismic force and the support forces act.

2.1.3Methods#

The upper group, Methods (enable/disable), has one check box per method of slices: Bishop Simplified, Janbu Simplified, Janbu Corrected, Ordinary / Fellenius, Spencer, GLE / Morgenstern-Price, Corps of Engineers #1, Corps of Engineers #2 and Lowe-Karafiath. A new project has Bishop Simplified and Janbu Simplified enabled. Every enabled method runs its own search, so each has its own critical surface; if none is enabled, Compute runs Bishop Simplified. The methods are described in Section 3.2.

Table 2.1.3 Convergence Options group of the Methods page.

Field	Meaning	Default	Range or choices
Number of slices	Slices into which each trial surface is divided	25	3 to 500
Tolerance	Convergence tolerance on the factor of safety	0.005	10⁻⁶ to 1
Maximum iterations (scope differs by method)	Iteration budget; what it bounds depends on the method (below)	50	1 to 500
Interslice force function	Shape of $f(x)$ in GLE / Morgenstern-Price; enabled only when that method is ticked. $x$ runs from 0 at the left end of the surface to 1 at the right.	Half Sine	Half Sine, Constant, Trapezoidal, Clipped Sine
Interslice forces	Whether the interslice resultant whose inclination Lowe-Karafiath and Corps of Engineers #1 and #2 prescribe is the total force or the effective force with the water thrust applied separately; enabled only when one of those three is ticked	Total (water thrust included)	Effective (water thrust separated), Total (water thrust included)

The same Maximum iterations bounds a different loop in each family of methods:

Bishop Simplified, Janbu Simplified and Janbu Corrected: the iteration on the factor of safety, exactly as set.
Lowe-Karafiath and Corps of Engineers #1 and #2: the same iteration, but a value below 60 is raised to 60.
Ordinary / Fellenius: nothing, as the method has no iteration.
Spencer and GLE / Morgenstern-Price: the search for the interslice inclination; above 400 it is also the budget of the inner iteration solved at each step of that search, which otherwise keeps its 400 passes.

With Constant as the interslice force function, GLE / Morgenstern-Price is equivalent to Spencer. Total is the convention in which the published values of the three prescribed-inclination methods are given; Effective is the choice for a slope with water standing over it, where the total-force assumption makes the factor of safety depend on the depth of the water (Section 3.3).

2.1.4Groundwater#

The Basic group chooses how pore pressures are obtained; the Advanced group switches on one of three analyses that change them. How each method is used, and how the materials take their pore pressure from it, is the subject of Section 2.4.

Table 2.1.4 Groundwater page. The list of methods shows their identifiers as they are stored.

Field	Meaning	Default	Range or choices
Method	Source of the pore pressures: none, water surfaces (`water_table`, `piezo_line`), the $r_u$ coefficient (`ru`), a water pressure grid of total head, pressure head or pore pressure, or a finite-element seepage analysis, steady or transient	`water_table`	`none`, `water_table`, `piezo_line`, `ru`, `grid_total_head`, `grid_pressure_head`, `grid_pore_pressure`, `fea_steady`, `fea_transient`
Pore Fluid Unit Weight	Unit weight of water, $\gamma_w$	9.81 kN/m³	0.1 to 50 kN/m³
Default Hu	Coefficient $H_u$ applied to the vertical distance below a water surface, for materials that do not set their own	1.0	0 to 1
Auto Hu (compute from water-surface slope)	$H_u = \cos^2\alpha$ from the inclination of the water surface, for every material	off	—
Negative pore pressure cutoff / Cutoff value	Upper limit on the matric suction used in the shear strength of materials with unsaturated parameters	off / 100 kPa	0 to 10⁶ kPa
Advanced	One option at most: None, Transient groundwater, Calculate Excess Pore Pressure (B-bar method) or Rapid Drawdown analysis	None	Mutually exclusive
Drawdown method	Procedure of the rapid drawdown analysis; enabled only with that option	Effective Stress using B-bar	Effective Stress using B-bar; Duncan, Wright, Wong 3 Stage (1990); Army Corp. Eng. 2 Stage (1970); Lowe and Karafiath (1960)

The three advanced options cannot run together, which is why they are radio buttons. Rapid Drawdown analysis enables Boundaries → Add Drawdown Line and Groundwater → Drawdown Level Sweep…; all four drawdown procedures need the groundwater method water_table or piezo_line and at least one material marked with undrained behaviour, and the analysis refuses to run otherwise (Section 3.8). Transient groundwater enables the Transient page and Groundwater → Transient Groundwater….

2.1.5Transient#

The solver options of the staged transient seepage analysis. The page is greyed out until Transient groundwater is chosen on the Groundwater page and applied; the stage times and the per-stage Calculate SF flags are edited in Groundwater → Transient Groundwater… (Section 2.9).

Table 2.1.5 Transient page.

Field	Meaning	Default	Range
Transient groundwater	Read-only: On, or Off with a pointer to the Groundwater page	Off	—
Stages defined	Read-only: number of stages and how many compute a factor of safety	0	—
Tolerance	Convergence tolerance of the transient solver	10⁻⁵	10⁻⁹ to 1
Maximum iterations	Iterations per time step	30	1 to 1000
Number of time steps	Time steps per stage; Auto derives it from the element size and the storage, so that the water front crosses about one element per step	Auto	Auto, 1 to 100 000

2.1.6Statistics#

Switches on the probabilistic and sensitivity analyses run by Statistics → Compute Statistics. The random variables themselves are defined in Statistics → Random Variables…; both are described in Section 2.10.

Table 2.1.6 Statistics page.

Field	Meaning	Default	Range or choices
Probabilistic analysis	Sample the random variables and compute the distribution of the factor of safety	off	—
Sensitivity analysis	Sweep each random variable across its range	off	—
Analysis type	Global Minimum re-evaluates the deterministic critical surface for every sample; Overall Slope repeats the whole search for every sample, which is much slower	Global Minimum	Global Minimum, Overall Slope
Sampling method	How the samples are drawn	Monte Carlo	Monte Carlo, Latin Hypercube
Number of samples	Samples of the probabilistic analysis	1000	1 to 1 000 000
Sensitivity intervals	Equal intervals into which each variable's range is divided for the sensitivity sweep	50	2 to 500

The commands of the Statistics menu stay greyed out until one of the two analyses is ticked here.

2.1.7Random Numbers#

Table 2.1.7 Random Numbers page.

Field	Meaning	Default	Range or choices
Generation	Pseudo-random is reproducible: the same seed gives the same answer. Random takes its seed from the clock, so successive runs differ.	Pseudo-random	Pseudo-random, Random
Seed	Seed of the pseudo-random stream; disabled with Random	10116	0 to 2 147 483 647
Share one Latin Hypercube stratification across variables	Sample $i$ falls in the same stratum of every variable, so the variables move together; no effect on Monte Carlo	off	—

The seed governs the probabilistic and sensitivity analyses and the searches that draw surfaces at random (Slope, Block, Path and Simulated Annealing). The Grid Search and Auto Refine enumerate their surfaces, so nothing there is random. Keep the pseudo-random generator for results that go into a report: they can be reproduced exactly.

2.1.8Design Standard#

Partial factors, off by default: switching them on changes every factor of safety the model has given so far, so it is an explicit choice. When they are applied, the analysis works on a factored copy of the model (the project itself is not changed) and the value it reports is an over-design factor, which must exceed 1, rather than a factor of safety. The status bar, the Results dock and the analysis notes say so. The procedure is explained in Section 2.11 and Section 3.12.

Table 2.1.8 Design Standard page.

Field	Meaning	Default	Range or choices
Apply partial factors	Switches the design standard on	off	—
Design standard	Loads a set of factors; enabled when the box above is ticked	None	None; Eurocode 7 — DA1 Combination 1; Eurocode 7 — DA1 Combination 2; Eurocode 7 — DA2; Eurocode 7 — DA3; Custom
Permanent actions, Variable actions	Factors that multiply the actions	1.0	0.1 to 10
Cohesion, tan(friction angle), Undrained strength cu, Shear strength (other models)	Factors that divide the strength, by category of strength model	1.0	0.1 to 10
Unit weight	Factor that multiplies the unit weights	1.0	0.1 to 10
Resistance	Factor that divides the whole resistance	1.0	0.1 to 10

Choosing a standard loads its factors (Table 2.1.9); the factor fields can only be edited with Custom.

Table 2.1.9 Factors loaded by each standard (EN 1997-1, Annex A).

\gamma_{G}

\gamma_{Q}

: permanent and variable actions;

\gamma_{c'}

\gamma_{\phi'}

\gamma_{cu}

\gamma_{\tau}

: cohesion, tan φ′, undrained strength and other models;

\gamma_{\gamma}

: unit weight;

\gamma_{R}

: resistance.

Standard	γG	γQ	γc′	γφ′	γcu	γτ	γγ	γR
DA1 Combination 1	1.35	1.5	1.0	1.0	1.0	1.0	1.0	1.0
DA1 Combination 2	1.0	1.3	1.25	1.25	1.4	1.25	1.0	1.0
DA2	1.35	1.5	1.0	1.0	1.0	1.0	1.0	1.1
DA3	1.35	1.5	1.25	1.25	1.4	1.25	1.0	1.0

Limitations in 0.1.235

The permanent-action factor is not applied: the weight of the soil carries no action factor, every distributed and line load is multiplied by the variable factor, and the analysis notes say so when the permanent factor differs from 1. The action factors loaded for DA3 are those of set A1 (1.35 and 1.5), where a slope under DA3 takes set A2 (1.0 and 1.3). The Shear strength (other models) factor is not an EN 1997-1 factor: OGR Slip2D sets it equal to the tan φ′ factor of the same set.

2.1.9Advanced#

Numerical and admissibility controls of the limit-equilibrium run. The defaults suit most models.

Table 2.1.10 Advanced page.

Field	Meaning	Default	Range
Tensile stress check / Percentage of slices	Rejects a surface with tension on a slice base, checked after the factor of safety has converged, over a percentage of the slices counted from the toe	off / 95 %	1 to 100 %
Use enhanced particle swarm algorithm	At the end of each iteration of the Particle Swarm search, the particles with the highest factors are scattered again	on	—
Accelerate convergence (Steffensen, scope differs by method)	Aitken extrapolation of the iteration on the factor of safety. Used by Bishop Simplified on circular surfaces and by both Janbu methods; the other methods do not use it.	on	—
Search surfaces in parallel / Processors to use	Splits the surfaces of a search across several processes; the result is identical, only the time changes. The line below shows how many processes the percentage gives on this computer (at most 8).	on / 50 %	1 to 100 %
Initial factor of safety	First trial value of the iteration: a starting point, not a lower bound	1.0	0.001 to 100
Minimum lambda, Maximum lambda	Range searched for the interslice scale factor $\lambda$ of Spencer and GLE / Morgenstern-Price	−0.1, 6.0	−10 to 10
Maximum base angle on weak-layer clips	Steepest slice base allowed on a surface that a weak layer has clipped; 90° switches it off	80°	1 to 90°
Check m-alpha < 0.2	Rejects surfaces on which $m_\alpha$ falls below 0.2 (Whitman & Bailey, 1967); applied to Bishop Simplified, both Janbu methods, Spencer and GLE / Morgenstern-Price	on	—

Surfaces rejected by the m-alpha check keep their factor of safety and stay in the results; they are only barred from being the critical surface. In a purely cohesive soil the check amounts to a ceiling of 78.5° on the inclination of the slice base, which is tighter than the default 80° of the weak-layer ceiling. Narrowing the lambda range below 1.5 can exclude the solution: the validation circle the program is checked against needs $\lambda = 1.49$ (Section 3.3).

2.1.10Seismic#

What a seismic run reports beyond the factor of safety. The seismic coefficients themselves are set in Loading → Seismic Load… and the acceleration records in Loading → Seismic Records… (Section 2.5.4).

Table 2.1.11 Seismic page.

Field	Meaning	Default	Range or choices
Critical acceleration: Compute Ky for all surfaces	For every surface, the horizontal seismic coefficient $k_y$ that brings it to the target factor of safety; surfaces are ranked by it	off	—
Target factor of safety	Factor of safety that defines $k_y$ ; enabled with either analysis	1.0	0.001 to 100
Permanent displacement: Newmark displacements	Displacement of a rigid sliding block, integrated from a record above $k_y$	off	—
Seismic record	Record to integrate, listed with its peak acceleration and duration	(none)	Records of the project
Displacements computed using	Polarity of the record	Maximum of both polarities	Maximum of both polarities, Direct polarity, Inverse polarity, Average of both polarities
Direction: Allow upslope displacement	Off: the resistance to upslope movement is taken as infinite and the block only moves downslope	off	—
Scale record by a factor of	Multiplies the accelerations of the record; 1 uses it as recorded	1.0	0.0001 to 1000

With either analysis on, the critical surface reported is the one with the lowest $k_y$ , which in general is not the one with the lowest factor of safety. A Newmark run needs a record: with (none) selected the run says so instead of reporting a displacement. The record, polarity, direction and scale fields are enabled only with Newmark displacements ticked (Section 3.9).

2.1.11Project Summary#

Table 2.1.12 Project Summary page.

Field	Used in	Default
Project Title	Title of the PDF report	Untitled Project
Author	PDF report and Analysis → Info Viewer	pre-filled
Company	PDF report	pre-filled
Analysis	Free description of the analysis	empty
Comments	Free text, one comment per line; blank lines are dropped	empty

Note

In version 0.1.235 the Author and Company of a new project come pre-filled with the name and institution of the program's author. Replace them with your own before generating a report with File → Generate Report… (Section 2.12).

In OGR Slip2D

Every field of the dialog is written to the settings block of the .ogr file (Section 5.4), so reopening a project restores the configuration it was analysed with. The surface search settings travel in the same block, under search.

Source: ogr_core/project/settings.py · ogr_gui/dialogs/project_settings_dialog.py