Tutorial 3: Slope stability and soil nailing walls
Deep Excavation LLC
DeepEX 2015 – Advanced course
1
INTRODUCTION
DeepEX is a software program for braced excavations in soils with 2D limit-equilibrium and non-linear analysis
methods, and structural verification of all elements (with AISC, ASD, Eurocodes).
It offers the ability to analyze walls with multiple braces (tiebacks) in multilayered soils.
The non-linear analysis considers elastoplastic behavior for the whole soil-wall-support system.
The program also offers the ability to perform traditional limit-equilibrium analyses.
The graphical interface is completely interactive and the input is simplified to a great extend.
The program utilizes archives of wall types, structural and soil materials, ground anchors etc.
The analysis can be performed in either an utlimate state or at a service state (allowable design or LRFD).
The program offers the ability to automatically set all critical settings according to the desired design methodology.
The program also offers the ability to perform slope stability analyses with soil nails.
Corso Paratie, Milano 30 settembre 2009
DeepEX 2015 – Advanced course
2
Import
DXF
Slope tab
Launches
Options
Options for design approach (load
combination)
Select this check to Quick tool
perform slope
for analysis
stability analysis method
for current stage. (Bishop,
Spencer,
MP)
Quick tool for Draw tools for
type of failure slope center,
surface, and radius, etc.
radius search
DeepEX 2015 – Advanced course
Soil nailing
options
Press to perform
only slope
calculations (after
general analysis has
been performed)
Review of all slope options: 1. Method
1. Select this
button
2. Select analysis
method
3. Parameters for
Morgenstern-Price
method
Max number of iterations
Convergence tolerance (typical 0.1% or
0.01%)
Preliminary slice width
Minimum number of slices
DeepEX 2015 – Advanced course
Review of all slope options: 2. Center
Center location can be a point or a
rectangular grid.
The coordinates can be exact or relative to
the top left coordinates of the left wall.
Option: “Use only one point for the
analysis”, then one center point will be
used.
Rotation angle is used in Rectangular
search option.
DeepEX 2015 – Advanced course
Review of all slope options: 3. Radius search
Radius location can be a point or a rectangular
grid.
In the default option the radius search starts
from the bottom of the left wall to the bottom
of the model.
Option: “Use single radius search”,
to use
one radius.
Option: “Specify exact radii limits”,
use a
starting and an ending
radius.
Option: “Specify exact coordinates”, the
radius will vary from
a user specified
starting point
to a user specified ending
point.
DeepEX 2015 – Advanced course
Review of all slope options: 4.
Active/Passive
Within this tab the user can specify an active
angle and a passive angle limit. These angle
limits can be searched within a range from the
initial active or passive limit angle.
Select the “Use block analysis” option to force
the failure surface to be a block type. In this
case, you will have to define a starting point
and an ending point.
DeepEX 2015 – Advanced course
Review of all slope options: 5. Supports
Support resistance can be included within a slope stability analysis.
Researchers are recommending that caution is exercised when
support reactions are applied. In specific, with inclined ground
anchors, vertical slope or wall movements can result in the
relaxation of anchor force and thus the stabilizing support
contribution can be reduced.
-“Include support reactions”, will include the support reactions as
calculated from the wall analysis.
-“Include support service capacities”, will include the minimum
design capacity of a support. This option is most consistent with all
design approach methods such as EC7 etc.
-“Include support ultimate capacities”, will include the minimum
ultimate capacity of a support.
-“Ignore support forces” will ignore all support reactions.
DeepEX 2015 – Advanced course
Review of all slope options: 6. Misc
Wall shearing: When a failure surface intersects a wall, then the shear
capacity of the wall can be included in the analysis. This shear
capacity is always limited by the net soil resistance below the cut
point (passive-active, but to a depth that is automatically limited to
account for wall stiffness and displacement compatibility).
When the project is designed with an allowable approach, then the
ultimate wall capacity can be reasonably used. In this case, the wall
shear capacity is multiplied by the appropriate factor to obtain the
ultimate wall capacity.
Soil-shear on Vertical faces of end and start slices:
This option is used in Bishop analyses. Within this tab, if vertical faces
are encountered in the start or end, the shear and horizontal loads on
vertical faces can be calculated from at-rest or active earth pressures.
The number of vertical intervals, controls the points where the
pressures will be integrated to give the total force.
Include tieback shear on slice base: In Bishop analysis: When a ground
anchor fixed part intersects a slice then this option increases the
normal reaction and available shear at the intersected slice.
Review of all slope options: 7. 3D Loads
From this tab we can control how 3D loads are included in the
slope stability analysis.
The default option looks within the horizontal support spacing
limits and includes the 3D loads only found within.
Otherwise, 3D loads can be included within specified limits
from a minimum to a maximum out-of-plane coordinate
relative to the base wall.
DeepEX 2015 – Advanced course
Review of all slope options: 8. Tension crack
From this tab we can control the tension crack simulation.
Tension crack depths can be automatically calculated, if a
layer has cohesion or undrained shear strength. Otherwise,
the user can specify his own tension crack depth.
The tension crack can be filled with water if the last check box
is selected (recommended option).
DeepEX 2015 – Advanced course
Review of all slope options: 9. Automatic
search
When the automatic search option is selected, the search
limits for the slope stability must be defined.
Once the analysis is completed, it is important that we
examine where the critical slip surface is located in relation to
our search limits.
It is also important that we carefully choose the number of
points that will be adjusted. It might be ideal to first select
fewer points, that are later refined as we get a better handle
on the critical global stability surface.
DeepEX 2015 – Advanced course
Slope stability example.
• Typical example for generating a slope stability analysis
• Select one point center and rectangular search
• Define single radius and two radii limits.
Soil F
Soil properties: F
A. General
Soil name: F (this appears in the boring)
Description: Sand Detailed soil description.
Soil type: Sand
gt = 120 pcf : Total unit weight
gdry= 120 pcf : Dry unit
c‘ = 100 psf : Effective cohesion
F’ = 32 degrees : Effective friction angle
V = 0.35 Poisson’s ratio
D. Bond
Ultimate bond for soil nails= 50 psi
Press OK
Project geometry
Soil nails placed at 5 ft horizontal.
Change model limits
Edit the tieback sections
Rename tieback section 4-Strand to nail
.
1 and use #9 rebar in a 4inch hole
Select Grade 60 steel
(if not available you will have to define
from material properties)
Double click on left points and define
coordinates
Right click on the main wall and
deactivate it
Click on draw nail
group to draw soil
nails
Then draw from the
top to the bottom on
the vertical face
Click on soil nail tables and
change nail dimensions
Select one point for
the center of the
slope stability circle.
Click the mouse on
the screen where
desired (track the
moving cross).
Select one circle
radius.
Move mouse near excavation bottom (failure surface redraws
dynamically as the mouse moves). Select the excavation bottom
as show below.
Press calculate