TZ & QZ Curves¶

TZ Curves - API 2000¶

The TZ curves for all axial methods are developed in accordance with API WSD (2000) and takes into account whether they are for sand or clay. The shape of the TZ curves for sand and clay are shown in the figure below, (extracted from API WSD (2000)). Most methods (e.g. ICP) make similar recommendations for the treatment of calculated skin frictions in generating TZ and QZ curves. TZ curves for clays also include the residual effect as shown in the figure below.

Typical axial pile load displacement TZ curves, ref API WSD (2000)

TZ Curves for both compression and tension are presented in the tab “TZ Curves”.

TZ Curves - API RP2GEO¶

The shapes of the TZ curves for sand and clay according to API RP2GEO (2011) are shown in the figure below. Most methods make similar recommendations for the treatment of calculated skin frictions in generating TZ. TZ curves for clays also include the residual effect as shown in the figure below.

Typical axial pile load transfer-displacement TZ curves, ref API RP2GEO (2011)

The definition of the TZ curves recommended by API RP2GEO curves are given in the table below.

 $$\frac{z}{z_{peak}}$$ $$\frac{t}{t_{max}}$$ Clays Sands 0.16 0.30 0.30 0.31 0.50 0.50 0.57 0.75 0.75 0.80 0.90 0.90 1.0 1.00 1.00 2.0 0.70 to 0.90 1.00 >2.0 0.70 to 0.90 1.00

QZ Curves¶

The QZ curves for all axial methods take the same shape, whether for sand or clay, again according to the recommendations of API WSD (2000) and API RP2GEO (2011). The ultimate resistance in the QZ curve takes account of whether or not the pile is expected to behave in a plugged or unplugged manner at a particular penetration. This is carried out using the plugged or unplugged end bearing resistance as described in the section on axial capacity.

Pile tip load-displacement QZ curve, ref API WSD (2000)

The plotting of TZ & QZ curves can be controlled by specifying limiting depths on the output tab. A top depth limit and lower limit can be specified.

Pile tip load-displacement QZ curve, ref API WSD (2000)