UTEXAS4

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UTexas4 is a computer software application for computing the stability of earth and earth-rock slopes and embankments. UTEXAS4 has been written and is maintained by Dr. Stephen G. Wright of Shinoak Software, who is well-recognized as one of the leading experts in solving problems in soil strength and slope stability (Duncan and Wright, 2005).

UTexas4 has been considered one of the most sophisticated commercial software available to study the stability of slopes using a two-dimensional, limit-equilibrium method. The program has been widely used by the US Army Corps of Engineers and US Federal Highway Administration.

UTexas4 features unique random techniques for generation of potential failure surfaces for subsequent determination of the most critical surfaces and their corresponding factors of safety. The factor of safety is defined with respect to shear strength, i.e. the factor of safety is the ratio of the soil shear strength to the equilibrium shear stress. Values of the factor of safety at or less than unity are considered to represent instability and failure of the slope.


Features


UTexas4 is a slope stability computer program with a Windows-based graphical user interface for both entering and displaying the input data as well as displaying the results of computations. The user is provided with unique options to define irregular slope profiles. The UTexas4 program can be used to find the stability (factor of safety) of inhomogeneous slopes and embankments using both circular and noncircular slip surfaces.

Spencer's procedure of slices is used to compute the factor of safety. Automatic searches can be performed to locate the critical circular or noncircular slip surface with the lowest factor of safety. Searches with both circular and noncircular slip surfaces are fully animated to show each trial slip surface as they are tried along with the location of the slip surface which yields the lowest factor of safety. Also, a special, separate "interactive" search scheme allows the user to select trial slip surfaces, one by one, and compute the factor of safety for each surface. As the factor of safety is computed for each slip surface, contours of factor of safety are drawn and updated to guide locating the most critical slip surface with the lowest factor of safety. In this way engineers can see how the factor of safety changes with the location of the critical circle and eventually locate the most critical circle on their own and using their own judgment.


Unique method for profile definition
One of the three methods for searching circular failure surfaces
Evaluation scheme used for searching non-circular failure surfaces

Shear Strengths


    UTexas4 allows several representations for the soil shear strength, including
  • Conventional linear Mohr-Coulomb envelopes described by a cohesion intercept and friction angle
  • Linear increase in undrained shear strength below a horizontal reference datum
  • Curved Mohr-Coulomb envelopes

Shear strengths may be expressed in terms of either total stresses or effective stresses. The user can specify the tension crack if the tension crack presents a thread to the stability of the slope

Using conventional shear strength for soil properties
Using linear-increase of shear strength for soil properties
Using curved Mohr-Coulomb envelopes for soil properties

Integrated with EnFEM for finite element analyses

With the import function available in EnFEM , users can quickly import a UTEXAS4 data file and perform a Strength Reduction Finite Element Method (SRFEM) slope stability analysis within minutes. EnFEM reads the UTEXAS4 data file and automatically generates the slope geometry, distinct soil regions, material properties, groundwater table, tieback elements, surcharge loading, and boundary conditions based on the original UTEXAS4 model. EnFEM also uses an automatic mesh-generation function to display the mesh distribution on the screen, allowing users to preview and adjust mesh sizes if needed. In most cases, the user can initiate the computation without making any changes.

Benefits of using EnFEM for slope stability analyses are: (1) the critical slip surface develops automatically in SRFEM, and (2) SRFEM can consider failure mechanisms induced by soil-structure interactions.

When to use EnFEM for slope stability analyses?

(1) When the critical slip surface is complicated:
In this example, there is a stronger layer underneath a softer layer in this slope model. It is difficult to find an irregular slip surface with Limit Equilibrium Method (LEM).

Critical slip surface example

Softer layer over a stronger layer

(2) When the safety factor is limited by soil-structure interactions:
In this example, as soil mass slides down slope and the concrete facing is held relatively in place by the tieback, a slip surface can develop between soil and concrete facing. LEM can’t consider this type of failure mechanism.

Soil-structure slip surface example

Slip surface formed between the wall and soil elements

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