The design of foundation in normal soil conditions is governed by bearing capacity, minimum depth of foundation and settlement. However, foundation design in karst regions needs to consider an additional criterion associated to the possibility of subsurface subsidence and ravelling sinkholes. Under this environment, alternative techniques are needed to improve the subsurface soil. In this study general background information is given to understand the geological characteristics of Central Florida and why this area is considered to be a karst region and susceptible to sinkholes formation. Traditional foundation design techniques on karst regions are addressed in this paper. Finally, the use of a network of three subsurface horizontal piles is proposed and the effect on stress increase and soil bearing capacity for footing due to the horizontal piles is investigated. Finite element computer software is used to analyze the stress distribution under different conditions and the results are discussed. The objective of this study is to determine whether or not horizontal piles under a circular footing at the sinkhole site is a viable solution to reduce the stress increase in the soil induced by the footing load. The horizontal piles located at a certain depth below the center of the footing intercepts the cone of pressure due to the footing load. Also, it is the purpose of this research to determine the effect on the soil bearing capacity for footing due to the proposed horizontal piles at the sinkhole prone area. In 1983 Baus, R.L and Wang, M.C published a research paper on soil bearing capacity for strip footing above voids. In their research, a chart for soil bearing capacity for strip footing located above a void was presented. However, in this paper we present a chart for circular footing size as a function void location and a design chart for circular footing size with a network of three underground piles. The result indicates that with the horizontal piles placed above the cavity, the stress increase caused by the footing load substantially decreases as compared to the situation of no horizontal piles, thus increases the soil bearing capacity for the normal design of footing size. The approach of using the horizontal piles placed in between the footing and the subsurface cavity is a new concept that has not been experienced previously. The results are strictly based on the analytical model of finite element program. Before full implementation for the construction practice, further research and experimental work should be conducted.

Unbonded post-tensioning tendons are an efficient and cost effective method of reinforcing concrete floor slabs, slabs-on-grade, parking garages, and bridge structures. However, the behavior of these structures is not well understood. There is concern that due to the lack of a significant amount of reliable research data on specimens reinforced in this manner, the commonly used design methods tend to significantly under-predict the strength. Four large, scaled, floor slab sections were constructed and destructively tested with the intent of more accurately understanding the strength of specimens reinforced with this method. Four test specimens represent a significant percentage of the current body of reliable research in this field. In order to accurately predict the design strength of these members, it is necessary to predict the increase in the reinforcing strand stress when the member is loaded to a flexural failure. This increase in strand stress was measured on each of the four laboratory tests which were performed. This allowed the strength of these concrete members to be more accurately predicted, and it was observed that the current design methods are significantly under-predicting this increase in strand stress as well as the flexural capacity of the members. The behavior of the deflection of the slabs in relation to the applied load was also analyzed, as well as the cracking behaviors. The four test specimens were combined with the available body of research data to complete the largest known database of members reinforced in this manner.