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 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 usually
takes place during construction as the structural
loads are added. Because of this, some compensation for the
elastic settlement may also be provided during construction. This does
not mean, however, that elastic settlement should be
overlooked.
The SETOFF software from ENSOFT computes the settlement that is
expected under 100% consolidation at any user-defined location
(in plan view of the site or in depth). However, SETOFF doesn't
provide 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 user-specified 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 user-inputted 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 user-specified names.
For deep foundations, SETOFF users can easily investigate the
differences in settlement when modeling a system with individual or
with grouped piles (by entering proper dimensions and length
for the deep foundation data).
Settlement of deep foundations can be calculated for
three dif ferent 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 curve of vertical strain (or void ratio) vs. applied
pressure curve (.
The slope of a semi-log vertical strain
vs. applied pressure curve.
The slope of an arithmetic 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.
