At the southernmost locale, Ingraham Park, the bioturbated facies is on the bottom, then a section of cross-bedding, with a final bioturbated section at the top of the formation. The stratigraphic sequence throughout the formation is alternating sections of the two faces. The oolitic facies can be further divided into a cross-bedded and a bioturbated facies. The bryozoan facies is comprised entirely of one species, Schizoporella floridana (Osburn 1914. The formation has two distinct facies - an eastern oolitic facies that form the Atlantic Coastal Ridge, and the bryozoan facies to the west, in the Everglades. Rainwater at this time flowed through the pore spaces allowing calcite to precipitate around the grains and formed the indurated rock (Halley and Evans). Sub-aerial exposure of the deposits occurred during the lowering of sea level during the Wisconsian. Osmond, Carpenter, and Windom (1965) and Broecker and Thurber (1965) through uranium-series dating concluded that the Miami Limestone is about 130,000 years old. The formation was deposited during the Sangamon interglacial and Wisconsin glacial stages as a narrow band of oolitic carbonate in a north-south trending barrier bar system along the eastern portion of present day Miami-Dade and Broward counties. The Miami Limestone, formerly known as the Miami Oolite (Sanford 1909), is one of three distinct Pleistocene rock formations in southeastern Florida.
This limestone has been subjected to minimum tectonism and it looks like an intact or massive rock mass that can be misinterpreted in the GSI application with subdesigned results with severe consequences to the projects.Virtual Field Trip of Selected Exposures of the Miami Limestone Miami-Dade & Broward counties, Florida These two parameters are the basis for calculating the total settlement and punching failure of shallow foundations.ĭetermination of the type of the structure and the surface conditions of the discontinuities in the Miami Limestone is a challenge because this lithology is jointless. FDOT requires the use of the FDOT Soil and Foundation Handbook (SFH) and American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specification to design bridge foundation.īased on AASHTO LRFD 2014 to define the elastic modulus of the rock mass ( E s) and the global rock mass strength (scm), the GSI should be determined using Figure 1. In recent years, the Florida Department of Transportation (FDOT) has been improving existing roadways and developing new projects where some bridges have been designed bearing on Miami Limestone. (1994) has been limited in the Miami Limestone and minimum information has been previously reported. The use of the Geological Strength Index (GSI) introduced by Hoek et. The Miami Limestone (formerly the Miami Oolite), named by Sanford (1909), occurs along the Atlantic Coastal Ridge in portions of Dade, Monroe, Broward and Palm Beach Counties. Additionally, statistical information about the geotechnical property indices, such as unit weight, unconfined compressive strength, modulus of elasticity and tension, as well as percentage of recovery and Rock Quality Designation (RQD) are included in this paper to have a better idea of the conditions of this limestone.
Based on the Hoek-Brown Criterion, the GSI values are used to determine the global shear strength of the rock mass to evaluate potential punching failure of shallow foundation for bridges through the Miami Limestone. This paper proposes a modified GSI table to characterize the Miami Limestone. Since the limestone is jointless, its appearance is like an intact or massive rock and estimate the GSI values could be wrong. The use of the Geological Strength Index (GSI) has not been commonly used to characterize rocks like Miami Limestone.
0 kommentar(er)
