SETOFF

The computer program SETOFF analyzes foundation settlement of both, shallow and deep foundations, using commonly-accepted procedures. The total settlement of a foundation is generally composed of two parts, elastic and consolidation settlement. Elastic settlement occurs because of the pseudo-elastic nature of most soils and it occurs immediately on application of the foundation load. Consolidation settlement takes place as the pore space in the soil is reduced under the foundation loading and it may require a period of time to be fully developed. The elastic settlement may not be important because it takes place during construction as the structural loads are added. Because of this, some compensation for the elastic settlement may take place during construction. This does not mean, however, that elastic settlement should be overlooked.

For the above criteria, SETOFF computes the settlement under 100% consolidation (without elastic settlement that occurs during construction, which can be calculated by other programs like APILE and SHAFT), but will not provide the information for the percentage of consolidation versus time.


Methodology

The computations in SETOFF follow a conventional settlement analysis in which the soil profile is divided into a number of layers, the average stress increase from all of the foundation-loaded area is determined for each layer, and the change in thickness for each layer is computed using the appropriate compressibility for the layer. The foundation settlement is the sum of the changes in the layer thickness.

Analyses of consolidation settlement may be divided into three parts. The first part is the determination of the soil stratigraphy and the representative properties of the soil in each stratum. The second part is the computation of the stress increase at pertinent points in the subsurface soils due to the foundation loading. The third part is the computation of settlement using the data from the first two parts. The computer program SETOFF will perform the last two parts.

Foundation settlement is always very specific. The actual settlement observed in the field will depend on actual foundation loads and soil conditions and not on values assumed for design. The foundation loading used should be the actual sustained loads and not the maximum design loads. If the rebound from an excavation is to be computed, the input soil compressibility should adequately represent the action of the soil under reducing stress as well as increasing stress; this may not be the unmodified results from consolidation tests.

Features

  • The program allows users to enter shallow foundations as well as deep foundations. Each foundation loaded area is identified by a name with up to four alphanumeric characters.
  • For deep foundations, users can investigate the differences in settlement when modeling individual or grouped piles (by entering proper dimensions and length for the deep foundation data).
  • Settlement of deep foundations can be calculated for three different conditions that are selected by the user:
    • friction piles with fictitious footing located on the top of the friction zone
    • friction piles with fictitious footing located at 1/3 depth of the friction zone
    • end-bearing piles with fictitious footing located at the top of the firm strata.
  • Subsurface conditions can be specified by up to 50 layers and by up to 50 soil compressibilities. Incompressible sand layers can be specified in any intermediate or extreme location in the strata.
  • Users can calculate (outside SETOFF) and enter soil compressibilities into SETOFF in any of the following three methods:
    • Semi-log percent vertical strain vs. log applied pressure curve defined by up to seven straight-line segments which in turn are defined by up to eight points on the curve.
    • The slope of a semi-log percent vertical strain vs. log applied pressure curve.
    • The slope of an arithmetic percent vertical strain vs. applied pressure curve.
  • Settlement may be computed at up to 25 points defined by the user due to loads from up to 50 loaded areas.
  • Loaded areas may be:
    • rectangular and/or circular in shape,
    • in any order and combination,
    • placed at any depth, and
    • pressure for a loaded area may be negative to represent an excavation.
  • The program displays a three dimensional model of the soil stratigraphy and layout of the modeled foundations. This is a very useful view to check the locations, number of foundations and the soil stratigraphy. The 3D View toolbar allows users to manipulate the view of the soil and foundation model from different angles.
  • Enhanced data entry:
    • Standard Windows operations, such as dialog boxes, grid cells, clickable buttons, drop-down list of options, and pull-down menu choices are all incorporated in the program.
    • Most cells allow the use of mathematical equations to ease certain data entries (or for occasional unit changes).
    • Program allows for models in S.I. Units (Force in kN and Length in meters) or English Units (Force in lbs and Length in feet) or any other set of consistent Force/Length units that are entered by the user.