Soils

Pile foundations are subjected to vertical loads and significantly higher lateral loads due to wind, seismic effects, ocean waves and currents, and floating ice sheets. Applied vertical load on a pile is resisted by the skin friction and base resistance. The base resistance is provided by the soil layer and skin friction develops at the soil-pile interface. The lateral load on the pile is resisted by the soil-pile interaction effect, which is dependent on the pile and soil parameters. Published literature shows that a properly designed Pile-to-Pile Cap (PTPC) connection will offer significant lateral resistance to the applied loads. The soil-pile system behavior is highly non-linear which requires a detailed study on the soil-structure interaction considering multi-layered soil strata and their properties.
This Dissertation is divided into two parts: Evaluation of (A) the behavior and performance of PTPC connections, and (B) the load-displacement responses of a pile embedded in a multi-layered non-linear elastic soil strata subjected to static loads. A comprehensive literature review has been performed to study the factors affecting the PTPC connection performances and the load-displacement behavior of piles subjected to static lateral and axial loads considering soil-pile interactions. The objective of the study in Part A is to develop a PTPC connection design capable of producing adequate moment capacity of the pile by relying only on plain pile embedments without any special connection reinforcement details. The present study evaluates the local and global behavior of the PTPC connections with plain pile embedment through Finite Element Analyses (FEA).

Storing almost a third of the global soil carbon pool, wetlands are an essential component of the carbon cycle, and carbon-rich peat soil accumulates when carbon input through primary productivity exceeds output through decomposition. However, woody shrub encroachment in herbaceous wetlands can alter soil carbon processes, potentially diminishing stored carbon. To examine the effects of shrub encroachment on soil carbon, I compared soil carbon input through litterfall and fine root production, output through decomposition, and below-canopy microclimate conditions between Carolina willow shrub (Salix caroliniana) and herbaceous sawgrass (Cladium jamaicense) in the Blue Cypress Marsh Conservation Area (BCMCA), FL. To assess the level of production and its response to water level, I compared aboveground green biomass by measuring normalized difference vegetation index (NDVI) and photosynthetic stress by measuring photochemical reflectance index (PRI) between sawgrass and willow. I collected willow litterfall using litter traps and measured sawgrass and willow fine root production with fine root ingrowth bags. Litter decomposition was measured with decomposition bags deployed using a reciprocal litter placement design at BCMCA and incubated in a greenhouse to examine the effects of char and water level on decomposition. Above and belowground microclimate conditions were measured using sensors installed within sawgrass and willow canopies. Despite experiencing more photosynthetic stress, willow produced more green biomass than sawgrass. However, willow produced fewer fine roots than sawgrass and these roots were deeper within the soil. Willow litter decomposed faster even though sawgrass decomposition increased under drier conditions. Compared to the sawgrass canopy, the willow canopy had greater light availability, lower evaporative demand plus warmer and drier soils; however, litter decomposition did not differ between the canopies. These results suggest that willow encroachment can reduce the amount and alter the distribution of carbon within an herbaceous wetland, likely resulting in a net loss of soil carbon. Although willow encroachment may increase aboveground biomass carbon stocks, these stocks will likely be offset by a loss of soil carbon due to reduced fine root production and increased decomposition. Therefore, the transition from herbaceous wetland to shrub wetland will likely result in a loss of stored soil carbon.

Western Palm Beach County, FL is characterized by thick deposits organic soils at shallow depths. Because of their high void ratio and compressibility, these soils undergo large primary consolidation followed by extended periods of secondary compression causing excessive premature structural distress. Although soil stabilization has been largely used with remarkable results in soft, expansive and non-organic soils, limited research and practice exist in the implementation with highly organic soils. The main motivation of this research was to investigate the effects of cement stabilization on the compressibility behavior of organic rich soils, and develop mix design criteria for optimum cement contents necessary to induce the desired engineering behavior. This optimized mix design may provide guidelines for Deep Mixing Methods in organic soils.