TZPILE implements the well-known method of soil-structure interaction, commonly called the t-z method, where t-z and Q-w curves are used respectively for load transfers in side resistance and end bearing. The t-z and Q-w curves can be internally-generated for both driven piles and drilled shafts with the input of information on the supporting soil and on the geometry of the pile.

Curves of short-term settlement as a function of applied loads are essential for some engineering computations; for example, when refined input is needed for the analysis of piles in a group. If a field-load test is performed, the computed curves can be "calibrated" by modifying input information to TZPILE to reach agreement with the experimental curves. The calibrated, site-specific curves can then be used with TZPILE to design the production piles, which may vary from the test piles in geometry and stiffness.

The main output provided by TZPILE is pile-head movement as a function of applied load. However, for any given load, the program can also present the load and movement along the length of the pile. In addition, the program allows the user to specify the settlement profile if the user would like to consider negative skin friction caused by downdrag. The program will use iterative solution to find the soil reaction based on the relative movement between the soil and the pile at the depth of interest. The neutral depth, which separates the negative and positive skin frictions, will be generated.


  • Built-in axial load-transfer curves
    • Driven Piles
      • Clay (American Petroleum Institute, API)
      • Sand (API)
      • Clay (Coyle and Reese, 1966)
      • Sand (Mosher, 1984)
    • Drilled Shafts
      • Clay (Reese and O'Neill, 1987)
      • Sand (Reese and O'Neill, 1987)
  • Manually input linear or nonlinear load-transfer in side resistence (t—z) and end bearing (Q—w) as a function of depth.
  • Handle user-inputted soil-settlement profile that may be produced from downdrag. A pile will be subjected to downdrag when the soils in contact with the upper portion of the foundation move downward relative to the movement of the pile under its external loading. The resulting downward force from the near-surface soils will add to the force applied to the pile by the superstructure and can lead to excessive settlement of the foundation.
  • Specify shafts having different sectional properties (cross-sectional area and modulus of elasticity) with depth. This is helpful for controlled computations of elastic deformations.
  • A short-term, load-settlement curve is generated for the modeled pile using nonlinear soil models and elastic pile material deformation. TZPILE generates the load-vs-settlement curve based on the t—z (load-transfer in axial side resistance as function of movement) and Q—w curves (load-transfer in end bearing as function of movement) that are either generated internally by the program or specified by the user.
  • TZPILE automatically outputs the internally-generated nonlinear soil-transfer curves in skin friction (t—z curves) at quarter depths on each soil layer. This can be useful when the user needs the curve for input as spring on other models.
  • Specify modification factors on side friction (t—z curves) and/or tip resistance (Q—w curve) for each soil layer. This is useful for special analytical cases, such as hypothetical computations of load-vs-settlement for evaluations of losses of strength during pile driving or to match measured load-test data.
  • Graphs of load-distribution curves, axial load-vs-settlement curve, t—z curves, and Q—w curve are generated by the program.
  • Generate output including include program and data file information, running date and clean echo printing of all inputted parameters.