GENERAL DESCRIPTION SHAFT is a computer program used to evaluate the axial capacity and the short-term, load-settlement curves of drilled shafts or bored piles in various types of soils. In general, the majority of axial capacity methods used by SHAFT are based on the latest FHWA manual. In addition, several extra axial capacity methods are provided for clay shales, gravels, and gravelly sands.

SHAFT can analyze the axial capacity and settlement behavior of drilled-shafts in eight types of soil and rock models. SHAFT can accommodate any combination of soil and rock layers in a layered profile. The soils and rock models in SHAFT are the following:

• clay - cohesive geomaterial (FHWA), • sand - cohesionless geomaterial (FHWA), • clay - shale (Aurora & Reese), • strong rock - using either side resistance or end bearing

(FHWA), • strong rock - using both side resistance and end bearing

(for comparison), • decomposed rock/gravel (FHWA), • weak rock - cohesive intermediate geomaterial

(FHWA),• gravel - cohesionless intermediate geomaterial (Rollins

et al), and• gravelly sand (Rollins et al).

Design Charts for various shaft diameters

SHAFTA Program for the Study of Drilled Shafts Under Axial Loading

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ENSOFT, INC.engineering software3003 West Howard LaneAustin, Texas 78728

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LIST OF FEATURES In the past, many design engineers use a combination of the factor of safety method for geotechnical analysis of the founda-tion. The factor of safety method is termed the global approach and is often referred to as the allowable stress design (ASD) method. The LRFD method originated in structural engineer-ing and is termed the component approach. The LRFD method was accepted formally in 1994 by the American Association of State Highway and Transportation Officials (AASHTO) as a standard.

SHAFT provides options for computation of founda-tion capacity based on the ASD method or the LRFD method selected by the user. If the LRFD method is selected, the user should specify the resistance factors on side friction and tip resistance for each subsurface layers. SHAFT computes the side, end-bearing and total re-sistance for every foot of penetration and also predicts the load-vs-settlement curve of the top and bottom of the drilled shaft. Users can investigate capacities of drilled shafts of multiple diameters in one run and comparative output graphs thus helping on the selection of most economical sizing. New Design Charts allow users to select desired size and penetration of shafts based on desired pile capacity for specific pile-head movements. Profiles of the modeled shafts may be either straight-

sided or with underreams (bell).

Input of shaft dimensions and properties

LIST OF FEATURES (cont.)

SHAFTA Program for the Study of Drilled Shafts Under Axial Loads

Users may specify separate factors of safety for side resistance and for end bearing. The user can control the lengths of exclusion zones for side resistance at the top and/or bottom of the shaft to account for possible surface cracking in the soil due to moisture change or for other factors. SHAFT allows the computation of axial shaft resistance to uplift forces. The program can use any reduction factor speci-fied by the user for friction transfer in uplift of straight shafts.

The program produces output tables of load capacity values or bearing graphs, as a function of depth. These tables show axial capacity in side resistance and in end bearing, along with the sum of the two. The volume of concrete is also shown for each depth. The Technical Manual for SHAFT has the latest equations recommended in the referenced FHWA documents. The new Technical Manual is electronic and installed with the program. The theories for the methods of analysis are fully presented, along with the recommended technical procedures. More than thirty technical references are listed to provide additional information on the methods employed in the software program. The new User's Manual is a standard PDF file with descriptions of program input/output variables plus several reference ex-ample problems (input/output files installed with program). All charts along with background data can now be exported to external spreadsheets with pre-formatted tabs so users can further modify for presentation or other analytical purposes.

Other Software Features• For models in soils, SHAFT produces a single graph showing

the upper-bound, lower-bound, and trend (averaged) load vs. settlement curves for sand and clay layers.

• Axial load-transfer curves for side resistance (t-z curves) are provided by SHAFT on a text file for top, middle and bottom of each soil layer.

• A new chart option shows the soil profile along with the predicted shaft capacity as a function of depth.

• An option has been provided to allow analyses to include both axial side resistance and end bearing in rock sockets.

• Labels of vertical axis in result plots can be changed from Depth to Elevations for ease of evaluation/presentation.

Output Features• SHAFT produces graphics for the following: side resistance, end-bearing (tip) resistance, and total axial capacity as a function of shaft length (ultimate or with load factors).

• It also produces graphs of the short-term, load-settlement curve for any user-specified penetration.

• SHAFT generates output reports as plain text. A sample output file normally contains the following data:□ Printing of all input-data parameters (used for checking

inputted values).□ Summary results of skin friction. tip resistance, and ulti-

mate capacity as a function of depth.□ Tabulation of the approximate volume of concrete that

would be required per depth.□ Summary results of total allowable loads as a function of

depth (using inputted factors of safety).

Sample input/output screens

End bearing for various shaft diameters