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This paper contains the findings of an extensive subsurface investigation for the Metropolitan Dade County's Rapid Rail Transit System. The first 35 km (21 miles) of the system have been studied in depth with the view of providing foundation design parameters for an entirely aerial dual-rail guideway. This guideway is commonly supported by single piers founded on shallow spread footings. Closely controlled rail and vehicle to platform tolerances demand accurate prediction of the surficial calcareous strata performance. A major portion of the transit alignment is underlain by a porous oolitic limestone, generally encountered near the ground surface and ranging in thickness from 3 to 12 m (10 to 39 ft). The shallow footings bear upon the upper surface of this calcareous formation. There is much local variability in the thickness and quality of the soil/rock. Four types of deposition modes have been identified (transverse glades and marine tidal shoals, cross-bedded marine oolites, freshwater deposits, and thin weathered uncemented limestones), and are important strength determinants. The elastic properties of the Miami calcareous formations were obtained from extensive laboratory tests on 10-cm (4 in.) inside-diameter cores. These tests included unconfined compression tests, modulus of elasticity, direct uniaxial tension tests, splitting cylinder (diametral compression tests), modulus of rupture (tensile failure stress in bending), shear strength, and punching shear strength (resistance to diagonal tension failure). These tests are shown in tables that include variability with depth. Permeability and electrical resistivity results are also included.
Calcareous rocks, modes of deposition, unconfined compressive strengths, diametral compressive strengths, modulus of rupture, punching and shear strengths, unit dry weights, porosities and specific gravity, small-scale and prototype footing tests, anchor pullout tests
Chief geotechnical engineer, Kaiser Engineers, Miami, Fla.