ESTIMATION OF SETTLEMENTS OF DRILLED PIERS AT WORKING LOADS.

O'Neill and Reese (1999) suggest the following methods for computing axial settlements for isolated drilled piers:

1. Simple formulas
2. Normalized load-transfer methods

The total settlement St  at the pier head at working loads may be expressed as (Vesic, 1977)

The equations for the settlements are

Table 17.7 Values of Cp for various soils (Vesic, 1977)

Normalized Load-Transfer Methods
Reese and O'Neill (1988) analyzed a series of compression loading test data obtained from full-sized drilled piers in soil. They developed normalized relations for piers in cohesive and cohesionless soils. Figures 17.18 and 17.19 can be used to predict settlements of piers in cohesive soils and Figs. 17.20 and 17.21 in cohesionless soils including soil mixed with gravel.

The boundary limits indicated for gravel in Fig. 17.20 have been found to be approximately appropriate for cemented fine-grained desert IGM's (Walsh et al., 1995). The range of validity of the normalized curves are as follows:

 Figure 17.18 Normalized side load transfer for drilled shaft in cohesive soil (O'Neill and Reese, 1999)

Figure 17.19 Normalized base load transfer for drilled shaft in cohesive soil (O'Neill and Reese, 1999)

Figure 17.20 Normalized side load transfer for drilled shaft in cohesionless soil (O'Neill and Reese, 1999)

Figure 17.21 Normalized base load transfer for drilled shaft in cohesionless soil (O'Neill and Reese, 1999)

 

Figures 17.18 and 17.19
Normalizing factor = shaft diameter d
Range of d = 0.46 m to 1.53 m
 

Figures 17.20 and 17.21
Normalizing factor = base diameter
Range of d = 0.46m to 1.53m

The following notations are used in the figures: