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原文传递 Strength Envelopes for Florida Rock and Intermediate Geomaterials.

题名：	Strength Envelopes for Florida Rock and Intermediate Geomaterials.
作者：	McVay, M.; Song, X.; Wasman, S.; Nguyen, T.; Wang, K.
关键词：	Florida limestone, Conventional Triaxial Compression (CTC), Shallow foundation design, Bearing capacity, Strength envelope, Triaxial compression testing, Index testing and unconfined compression strength, Rock (Geology), Finite element code
摘要：	For the design of a shallow foundation on Florida limestone, a calibrated bearing capacity equation based on a material-specific strength envelope is required. In this study, two large data sets containing samples from across the state of Florida were studied. Data set #1 contained over 8,000 results of unconfined compression tests (qu), split tension (qt), and bulk dry unit weight (?dt), and set #2 with 570 results contained qu, qt, ?dt, as well as rock formation identification, carbonate content, and porosity components. The data sets show Florida carbonate rocks are porous to very porous with porosity up to 60% and median porosity of 37%. The data sets were used to develop strong correlations for qt and qu from bulk dry unit weight, carbonate content, and formation factor. Next, (conventional triaxial compression (CTC) testing (>300) with cell pressures up to 1,500 psi was performed to evaluate the ductile and brittle nature of Florida limestone. It was concluded that most of Florida’s near surface rocks are in the ductile range when subjected to confining stresses typical for shallow foundation loadings. Based on the test results, a threshold for rocks to change from brittle to ductile behavior has been identified. Most significantly, strength envelopes for the rocks in the study have been developed from all the triaxial results. In general, the envelopes show significant downward slope after reaching peak values, at much steeper rate than the envelopes for brittle rocks. Additionally, guidelines to establish the strength envelope for other rock formations in Florida are provided. Subsequently, a constitutive model representative of the nonlinear strength envelope of Florida limestone was implemented into a 2D and 3D finite element code, and simulations were carried out for potential shallow foundation scenarios (homogenous or rock over sand). Each characterization (B, B/L, and D/B) was simulated with the full range of expected strength properties. Finally, an analytical bearing capacity equation was developed for both the homogeneous and rock-over-sand scenario. The Florida bearing capacity equation was calibrated using the numerical simulation results, and it can be applied to any footing shape, depth from 0 to B, and any rock thickness, even rock overlying a soil layer, such as the case in south Florida, where cap rock Is usually encountered atop a thick sand layer.
报告类型：	科技报告