ASDIP RETAIN now includes a new feature for User-defined lateral pressures. But what exactly is this, and how could this feature be useful in some cases? Isn't it better just to let the program calculate the pressures based on the backfill properties? This article will answer these questions in more detail.
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User-defined lateral pressures
Normally, the soils report includes the results of field and laboratory tests of the backfill material. These results may include soil properties, such as the moist density, saturated density, internal friction angle, cohesion, etc. With these parameters the structural engineer can calculate the soil lateral pressures based on well known theories, such as Coulomb or Rankine, which are triangular.
However, in some cases the soils report provides the lateral pressures, but may not provide the soil properties. Those pressures could be uniform, trapezoidal, triangular, etc, so it would be difficult to model those pressures in the software, particularly if it assumes that the pressures are triangular as in Coulomb and Rankine. In addition, back calculating the required properties that produce those pressures would be time consuming.
Fortunately, ASDIP RETAIN now includes a new feature that lets you specify the lateral pressures at the top and bottom of the wall directly in the program, without entering all properties. This will effectively model the pressures given in the soils report, and the software will use them in the wall design calculations.
To specify the pressures, you can now go to the Loads tab and then under the Backfill tab select the "User-defined Pressures" option. The user interface will show the fields to enter the pressures at the top and bottom of the wall.
In the example at the screen shot above, the lateral pressure diagram is a trapeze. The top pressure is 150 psf and the bottom pressure is 500 psf. The software then uses this diagram to evaluate the stability failure modes and complete the concrete design of the wall elements.
ASDIP RETAIN includes a new feature to let the user specify the soil lateral pressures directly. This is useful when the soils report provides the soil pressures rather than the soil properties. With the friendly user interface, the design can be completed and optimized with ASDIP RETAIN in minutes.
For engineering background please visit our blog post Cantilever Retaining Walls: Overview of the Design Process. For our collection of blog posts about retaining wall design, please visit Retaining Wall Design.
Javier Encinas, PE
ASDIP Structural Software