| Test Information | |
| Year | 2006 |
| Test Location | Salt Lake City International Airport, Utah, USA |
| Test Type | Large Scale |
| Reference | Rollins, K. M., Olsen, R. J., Egbert, J. J., Jensen, D. H., Olsen, K. G., and Garrett, B. H. (2006a). “Pile spacing effects on lateral pile group behavior: Load tests.” J. Geotech. Geoenviron. Eng., 132_10_, 1262– 1271. |
| Purpose | Investigation of pile spacing effects on the lateral behavior on a pile group. For a different spacing and group configuration see Rollins et al. (2006) (b) and (c). |
| Keywords | pile groups; p-multipliers; clay; spacing; lateral loads; diameter effect |
| Soil Information | |
| Soil Type | Clay |
| Soil Description | Stiff clay with some sand layer |
| Soil Classification | CH, CL-ML |
| Soil Properties | Friction angle for sand layers= 36-38°. The water table was located 1.07 m below the ground surface. |
| Type of Soil Investigations | CPT, borehole shear tests, vane shear tests, SPT, cone pressuremeter tests |
| Pile Information | |
| Pile Material | Steel |
| Pile Placement Method | Driven closed-ended |
| Material Properties | ASTM A252 Grade 3: Fy=405 MPa |
| Pile Cross Section | Circular |
| Outside Section | 32.4 cm |
| Wall Thickness | 9.5 mm |
| Test Configuration | |
| Test Configuration | Pile Group |
| Pile Spacing | 5.65D |
| Group Arrangement | Box Arrangement |
| Test Columns | 3 |
| Test Rows | 3 |
| Head Boundary Condition | Free |
| Loading | |
| Type of Loading | Static Two-Way Cyclic |
| Axial Load | N/A |
| Load Application | Lateral load tests were performed on two isolated single piles to provide comparisons to the pile group tests. The load was applied at 0.39 m above the ground surface for the 3*3 pile group and at 0.48 m above ground for the other pile groups. For each deflection increment, 15 load cycles were typically applied to simulate the cyclic loading typical of a M7.5 earthquake (Seed et al. 1975) and to evaluate the change in lateral resistance due to cyclic loading. |
| Test Results | |
| Max Top Displacement | 6.5 cm |
| Deflection | 0.20 diam |
| Attachments |  Lateral Load-Deflection- DATA |
 Lateral Load- Deflection in 3*3 pile group | |
Lateral Load- Deflection for each row in 3*3 pile group | |
Lateral Load- Deflection of single pile | |
| Analysis Method | |
| Software Used | LPILE (Reese and Wang 1997) for single pile; FLPIER (Hoit et al. 1997); GROUP (Reese et al. 1996) |
| Group Efficiency Factor | 0.87-1.08 |
| P-Multipliers (lead, 2nd, 3rd, n-th rows) | 0.95, 0.88, 0.77 |
| Type of Analysis | Finite Difference (LPILE) and finite element (FLPIER) |
| P-Y Curves Model | Reese and Welch (1975) for stiff clay; Matlock (1970) for soft clay; Reese et al. (1974) for sand. |
| Conclusions | |
| Comparisons | P-multipliers provided by Reese et al. (1996) and Reese and Van Impe (2001) overestimate the lateral resistance for closely spaced pile groups and could lead to somewhat unconservative results; p- multipliers recommended by AASHTO (2000), the US Army (1993), and the US Navy (1982) significantly underestimate lateral resistance and could lead to extra foundation costs for foundations in clay; GROUP and FLPIER tended to underestimate the measured bending moment at depths below the maximum value. |
| Outcomes | 1. Average lateral load resistance was a function of pile spacing. Group interaction effects became progressively more important in reducing lateral soil resistance as pile spacing decreased from 5.65, to 4.4 to 3.3 pile diameters on centers; 2. The leading row piles in the groups carried the greatest load, while the second and third row piles carried successively smaller loads for a given displacement. However, the fourth and fifth row piles, when present, carried about the same load as the third row piles. The back row piles often carried a slightly higher load than the piles in the preceding row; 3.The lateral resistance was a function of row location within the group, rather than location within a row. This behavior has been observed in other full-scale tests in clay, but is contrary to expectations based on the elastic theory which predicts that piles located on the edges of a row will carry more load than those located within the group; 4. For a given load, the maximum bending moments in the trailing row piles were greater than those in the lead row due to group interaction effects, which essentially softened the lateral soil resistance against the trailing row piles relative to the leading row piles; 5. Cyclic loading reduced the peak load at the same deflection by about 15% after 15 cycles and about half of this reduction occurred after only one cycle. However, at deflections less than the peak, the reduction in lateral resistance was considerably greater due to gap formation; Cyclic loading also led to increases of 14–30% in the maximum bending moment for a given load with the smallest increases in the single pile and lead row piles and the greatest increases in the trailing row piles. |
