The geotechnical properties of the young calcareous rocks of Southern Florida are presented on the basis of literature survey and a series of field and laboratory tests. The rocks covered are Miami, Key Largo and Fort Thompson lime-stones. The paper describes briefly the geology and lithography of the calcareous rocks and the successful methods of sampling them. The field tests included seismic refraction studies, uphole and crosshole wave velocity studies and Menard Pressuremeter tests. The laboratory tests comprised. of index tests and the strength-deformation evaluation tests. In addition to the usual unconfined compression tests usually utilized for evaluating the rigidity of rocks, this investigation provides the results of Ko -triaxial tests.
The range of values for porosity, compressive strength and modulus from various tests are presented. The discussion provides a reasoning of the difference in values obtained from various tests. The suitability of various tests in providing a representative mechanical behavior is discussed.
The soft porous lime-stones of the humid tropics and subtropics have been controversial as a suitable foundation material. Sowers (10) described interesting case histories of failures in limestone in Florida, which alerts the foundation engineer to be cautious with this material but presents little information as to its physical and engineering properties except the porosity of these lime-stones and solution activity. The intragranular porosity of these lime-stones and their effect on compaction has been discussed by Saxena et.al.(8). Based on performance records of many multistory buildings in Miami area, Leon (5), however, feels that these lime-stones are good foundation materials, but again with little information on the properties.
This paper attempts to provide the engineering properties of the weak calcareous rocks of Southern Florida found in approximately 30m. depth from the surface, around and south of Miami. These rocks are generally overlain by a thin veneer of unconsolidated marls and organic material and underlain by approximately 9Om. of quartz sands and silts of Miocene Age. The rocks in the upper layer are lime-stones of marine origin and consist of a sequence of three different variety of lime-stones called Miami limestone, Key Largo limestone and Fort Thompson lime-stones. The sands and silts below these rocks are known as Tamiami and Hawthorne Formations. A brief account of the formation is presented.
The rocks investigated are products of Pleistocene Age (4) and consequently are amongst the rocks of Pleistocene series. During Pleistocene time, many variations in the sea level occurred which were related to glacial activity to the north. Pleistocene sea levels were both higher and lower than the present elevation. The Pleistocene rocks of South Florida reflect this changing environment, consisting of limestone with variable lithology. The formations are, in places, discontinuous and interfingered. Ancient coral reefs and related deposits especially exhibit evidence of migration required by the ecological necessity of the corals to follow the shifting path of shorelines and nutrients. The areal extent of the rocks is presented.