| Test Information | |
| Year | 2007 |
| Test Location | North Carolina, USA |
| Test Type | Large Scale |
| Reference | Cho, K. H., Gabr, M. A., Clark, S., & Borden, R. H. (2007). Field P-y curves in weathered rock. Canadian Geotechnical Journal, 44(7), 753-764. |
| Purpose | A better understanding of p-y curves for weathered rock. Three different sites have been analyzed: see Cho et al. (a) and (c) for further information. |
| Keywords | drilled shaft, weathered rock p-y curve, subgrade modulus, ultimate resistance, verification tests |
| Soil Information | |
| Soil Type | Rock |
| Soil Description | CALDWELL COUNTY- Alluvium, sandy saprolite, weathered rock and hard rock comprised the foundation material. Tan to brown, medium dense silty to fine coarse sand exists over the weathered rock layer. Note: for further information about soil properties see Cho et al. (a): Soil Information's attachments. |
| Soil Properties | Core size was an H and RQD values ranged from 12% to approximately 65% |
| Type of Soil Investigations | Boring holes |
| Pile Information | |
| Pile Material | Concrete |
| Pile Placement Method | Drilled Shaft |
| Material Properties | Short Shaft length= 4.00 m; Long Shaft length= 4.80 m. |
| Pile Cross Section | Circular |
| Outside Section | 0.762 m |
| Test Configuration | |
| Test Configuration | Single Pile |
| Pile Spacing | 7.6 m |
| Group Arrangement | Two single piles: a short pile and a long pile |
| Head Boundary Condition | Free |
| Loading | |
| Axial Load | N/A |
| Load Application | For each test, both short and long shafts were constructed apart from one another. The logic of pushing a short against a long shaft during testing was to ensure that the short shaft would incur large enough lateral displacement to define the lateral subgrade modulus at the depth of the weathered rock layers, while the long shaft would posses enough capacity to act as reaction member. The loading sequence consisted of applying the lateral load in increments of 45-90 kN, followed by an unloading in cycles. |
| Test Results | |
| Max Top Displacement | Short Shaft= 0.089 m of displacement; Long Shaft= 0.023 m at a maximum applied load of 1334 kN |
| Attachments |  Deflection vs Depth_long pile_Caldwell site_40-1530kN |
Deflection vs Depth_long pile_Caldwell site_84-1682kN | |
Deflection vs Depth_short pile_Caldwell site_40-1530kN | |
Deflection vs Depth_short pile_Caldwell site_84-1682kN | |
Load-Deflection curve_Caldwell site | |
 Deflection curves from slope inclinometer data_DATA | |
Top displacements from dial gages_DATA | |
| Analysis Method | |
| Software Used | LPILE (Reese and Wang 1997); BMCOL 76 (Matlock et al. 1981) |
| P-Y Curves Model | Reese (1997) for weak rock; Reese and Welch (1975) for stiff clay; Gabr (1993) for stiff clay |
| P-Y Curves Derivation | Strain measurement from the VW strain gages were recorded using a CR-10 data logger |
| Attachments | P-Y curves_long pile_Caldwell site |
P-Y curves_short pile_Caldwell site | |
P-Y curves DATA | |
| Conclusions | |
| Comparisons | The calculated shaft-top deflection responses determined from BMCOL 76 are in good agreement with the measured data for both shafts, with the exception of the Caldwell County test data. In the Caldwell County comparison, the back-calculated p-y curves from the short shaft used as input data for BMCOL 76 analysis were adjusted by removing data points corresponding to no solid contact. The weak rock model overestimated the resistance of the test shafts mainly because of the selection of parameters. The stiff clay model, with the recommended values underestimated the lateral load- displacement response and it is considered to be conservative for use in weathered rock profiles. |
| Outcomes | Reese (1997) led to good results in coral limestone as reported by Nyman (1980), but this approach didn't yield any reasonable lateral displacement estimations for the drilled shafts tested in Piedmont weathered profiles. A p-y curve procedure should take the geological components into consideration. |
