Development of P-y curves for a Well Graded Gravel

Abstract

Research work is conducted to investigate the possibility of using laboratory model tests to simulate lateral response of drilled shafts embedded in soft weathered rock and discern their P-y curve function. Eight lateral load tests on instrumented model piles embedded in an Aggregate Base Course (ABC) medium are performed to evaluate the P-y curves. The ABC material is selected to simulate the response of soft weathered rock encountered in the field. The laboratory-evaluated P-y curves are compared to data from full-scale field tests performed in weathered rock. The two key parameters evaluated are the modulus of subgrade reaction (kho) and the ultimate lateral resistance (Pult). Using the laboratory-measured data, in comparison to measured field behavior, correlations for the subgrade modulus as a function of depth, as well as simplified approximations of Pult are developed for weathered rock materials. Results indicated that a hyperpolic P-y function seems to best represent the measured laboratory P-y curves. A comparison between laboratory and field data indicated that the ABC testing medium appears to yield kho and Pult that behave in a fashion similar to weathered rock material. Accordingly, it seems that, when appropriately mixed, that ABC can be used to model SWR encountered in the field. A distribution of kho with applied confining stress is evaluated and compared to results from procedures proposed by Reese (1997) for weathered rock and Terzaghi (1955) for stiff clay. A relationship developed for the distribution of subgrade modulus as a function of depth compared well with field data. The relationship of Pult with depth as a function of Geological Strength Index (GSI) and friction angle is also presented. All results are viewed in the context of the field measured response.