PileGroup Validation - Example 8. Centrifuge lateral load test of a 2x2 pile group in soft clay (Taghavi et al. 2014)

This example is based on the centrifuge lateral load test of a 2 × 2 pile group founded in soft clay reported by Taghavi et al. (2014). The piles in the groups were spaced at 7.0 pile diameters and had a 2×2 symmetrical configuration in plan and were fixed to a rigid cap placed above the ground level. The model pile was fabricated from a hollow steel tube instrumented with six pairs of strain gauges at different levels to enable bending moment measurements along the pile.

The outside diameter of the pile was 9.5 mm and the wall thickness was 0.9 mm with the total length of 666.6 mm. The Young’s modulus of all piles was 182 GPa. All tests were conducted at a centrifugal acceleration of 30 g. For this analysis, an external diameter of 0.285 m, a wall thickness of 0.027 m, and a total length of 19.998 m were used. The free length, defined as the distance from the point of lateral loading to the ground surface was 3.9 m. A horizontal load was applied at the top of the pile. The layout of the pile group is shown in the figure below.

Figure 8-1 Pile group layout for Example 8

The ground profile and soil properties adopted in this example are shown in the table below. The groundwater table is assumed at the ground surface level.

Table 8-1 Soil layer and soil properties for Example 8 (after Taghavi et al. 2014)

The figure below shows the three-dimensional view of this 2 x 2 pile group modelled in the PileGroup program.

Figure 8-2 Three-dimensional view of 2 x 2 pile group

The figure below shows the soil layer information, pile group and pile cap loads defined in the program. It shows the thickness values for all the layers and also the pile lengths.

Figure 8-3 Soil layers, soil properties and pile cap loads defined for this example.

For this example, the pile group effect option “Automatically generated P-multipliers for pile group effect (Reese & Van Impe, 2001)” was adopted, as shown in the figure below. Since the pile space is 7 diameters, the P-multiplier should be 1.0 for this example based on this option.

Figure 8-4 Pile group effect option adopted for this example

The following figure presents a comparison of the bending moment profiles for the 2 × 2 pile group under lateral loading for the pile cap movement of 45 mm. The results obtained from the analysis using the PileGroup program are shown together with the measured field data reported by Taghavi et al. (2014) and the predictions using the GROUP program (Reese et al. 1996). The numerical predictions from PileGroup show excellent agreement with both the experimental measurements and the predictions from the GROUP program.

Figure 8-5 Comparison of measured bending moment profile with computed results using PileGroup when the pile top movement is 45 mm

References:

1. Reese, L. C., & Van Impe, W. F. (2001). Single Piles and Pile Groups Under Lateral Loading. CRC Press / Balkema, Rotterdam, The Netherlands.

2. Taghavi, A., and Muraleetharan, K. (2014). “Simulating centrifuge model tests of laterally loaded pile groups in CDSM-improved soft clay using a nonlinear Winkler model.” Geo-Congress 2014: Geo-Congress Technical Papers, American Society of Civil Engineers, pp. 1254–1263