| Test Information | |
| Year | 1989 |
| Test Location | University of Houston Foundation Test Facility, TEXAS |
| Test Type | Large Scale |
| Reference | Dunnavant, T. W., & O'Neill, M. W. (1989). Experimental p‐y Model for Submerged, Stiff Clay. Journal of Geotechnical Engineering, 115(1), 95-114. |
| Purpose | The intent is to add to the data base, from which p-y models for design may be derived/tested, a new p-y criterion for piles submerged in stiff clay of different geological character. Three types of pile are taken into consideration: a small steel pile (see Dunnavant and O'Neill (a)), a large steel pile (see Dunnavant and O'Neill (b)) and a reinforced concrete pile (see Dunnavant and O'Neill (c)). |
| Keywords | p-y curves; lateral loads; saturated stiff clay; gap formation; scour; cyclic degradation; new p-y curve formulation |
| Soil Information | |
| Soil Type | Clay |
| Soil Description | The soils at the site are natural, overconsolidated, saturated clays of the Beaumont formation.The natural groundwater depth was 1.53 m below the pit, which has been flooded for five months prior to driving. |
| Soil Classification | CL to CH |
| Type of Soil Investigations | CPT, field Vane shear tests |
| Attachments |  Soil Properties-DATA |
 Profile of Undrained Shear Strength | |
E50 profile | |
Profile of Total and effective unit weights | |
| Pile Information | |
| Pile Material | Steel |
| Pile Placement Method | Driven open-ended |
| Material Properties | Length= 11.8 m; EI= 138 MN-m^2 |
| Pile Cross Section | Circular |
| Outside Section | 27.3 cm |
| Wall Thickness | 9.27 mm |
| Test Configuration | |
| Test Configuration | Single Pile |
| Pile Spacing | 6 m from Pile 2 (see Dunnavant and O'Neill (b)) |
| Head Boundary Condition | Free |
| Loading | |
| Type of Loading | Static One-Way Cyclic |
| Axial Load | N/A |
| Load Application | All tests were conducted with a water depth in the test pit of about 150 mm to simulate offshore or river- bottom conditions. Most pile loads were applied using two-way displacement-controlled cycling under free-head conditions. Cycle periods of from 1 to 100 s were used. Three loading series—"primary," "healing" and "sand"—were performed. P-y criteria were developed using the results of the primary series, while the healing series was performed after a gap had developed around the pile to investigate the effects of the lapse of time between major loading events. In the sand series, pile-soil gaps were filled with fine mortar sand to investigate changes in pile behavior caused by filling the gaps. |
| Test Results | |
| Max Top Displacement | to complete! |
| Attachments | Pile-Head Load- Deflection curves |
Load-Displacement curves DATA | |
| Analysis Method | |
| Type of Analysis | New p-y curves formulation: The term y50, the deflection corresponding to one-half of the /Jmax (static), is therefore not linearly dependent on the pile diameter, as has been suggested by others (e.g., Matlock 1970). |
| P-Y Curves Model | SOFT: Matlock (1970); STIFF A: Reese et al. (1975) ; STIFF B: Reese and Welch (1975); The cyclic SITE p-y curves were formulated for the case of 100 loading cycles. |
| P-Y Curves Derivation | Experimentally derived from the measured moment, pile-head deflection and pile-head slope through double differentiation and double integration. |
| Attachments | P-Y curves DATA |
Raw Static p-y curves for Pile 1 | |
Raw Static p-y curves for cycle 1 and 100; Pile 1; depth=1.27m | |
Comparison of Pile-Head Load-Deformation Predictions; Cycle 100, Pile 1 | |
| Conclusions | |
| Comparisons | The proposed criterion indicates slightly less stiff initial behavior but lower post-peak degradation than the "Stiff A" criterion for submerged stiff clays and, consequently, predicts considerably different pile-head behavior. The Site criterion fits the Cycle-100 data extremely well for Pile 1. |
| Outcomes | It is evident from the data for Piles 1 and 2 that significant degradation due to cyclic loading did not occur in the load-deflection curves until the head deflection reached about one percent of the pile diameter. The rapid rate of degradation at larger deflections appeared to be associated with the formation of a permanent gap around the pile due to (1) Plastic deformation of the soil; and (2) hydraulic scour during cyclic loading. The criterion appears particularly well-suited to the prediction of the behavior of piles of very large diameter. Test data indicated that appreciable cyclic degradation did not begin until the pile-head displacements had reached about 0.01 B, but, once started, did not appear to stabilize within 200 cycles. The principal source of degradation was the development of a permanent gap around the piles, intensified by hydraulic erosion. Rest periods between loadings after the opening of a gap between the pile and the soil resulted in weakened soil response, although this effect is not included explicitly in the proposed criterion. |
