Grouted Tieback with Friction

The Grouted Tieback with Friction support type in Slide, uses the same input parameters as the Grouted Tieback support type, with the following important difference:

The Shear Strength properties of the soil/grout interface of the Grouted Tieback with Friction support type are described below. For a description of all other input parameters, see the Grouted Tieback support topic.

NOTE: make sure that you have read the Overview of Support Implementation topic, for important information which applies to all support models in Slide.

Pullout Strength

The Pullout Strength options for the Grouted Tieback with Friction support type:

are the same as described for the GeoTextile support type. For a description of these options, see the GeoTextile support topic.

The area on which the shear force acts, for the Grouted Tieback with Friction support type, is defined by the Grout Diameter as described below.

Grout Diameter

The Grout Diameter for the Grouted Tieback with Friction support type, serves the following purpose:

Circumference = 3.14159 * Grout Diameter

Area = Circumference * Bond Length

image\groutdiameter.gif

Definition of frictional area for Grouted Tieback with Friction

Implementation of Grouted Tieback with Friction Support in Slide

Consider a grouted tieback which intersects a slip surface, as shown below.

image\support_tieback2.gif

Li  = bonded length of tieback within sliding mass

Lo  =  bonded length of tieback embedded beyond slip surface

Tieback (with Friction) Parameters

T  =  Tensile Capacity (force)

P = Plate Capacity (force)

 =  Interface Friction Angle (deg)

a  =  Interface Adhesion (force / area)

D = Grout Diameter

S  =  Out of Plane Spacing

At any point along the length of the tieback, there are 3 failure modes which are considered:

  1. Pullout (force required to pull the length Lo of the tieback out of the slope)

  2. Tensile Failure (maximum axial capacity of the tieback tendon)

  3. Stripping (slope failure occurs, but tieback remains embedded in slope)

The maximum force which can be mobilized by each failure mode, PER UNIT WIDTH OF SLOPE, is given by the following equations:

Pullout:                    Eqn.1

Tensile:                           Eqn.2

Stripping:         Eqn.3

If the Strength Model = Linear (Mohr-Coulomb), then the shear strength in Equations 1 and 3, is given by:

                              Eqn. 4

If the Strength Model = Hyperbolic, then the shear strength in Equations 1 and 3, is given by:

                          Eqn.5

where is the normal (effective) stress along the Grout / Soil interface. If pore pressure is considered, the Adhesion and Friction Angle parameters are for effective stress conditions.

See the GeoTextile support topic for more information about the Linear and Hyperbolic shear Strength Models.

NOTE: if the tieback Shear Strength is specified as Material Dependent, then the Pullout Force and Stripping force, are determined by integrating along the bonded length, to determine the force contributed by each segment of the bonded length which passes through different materials.

At any point along the length of the tieback, the force which is applied to the slip surface, is given by the MINIMUM of these three forces (Tensile, Pullout or Stripping).

Applied Force = min (F1, F2, F3)                Eqn.6

The Force Diagram for the Grouted Tieback with Friction support type, can have the same general shape as described for the Grouted Tieback support type. See the Grouted Tieback support topic for an illustration.