The sabkha soil spreads extensively in the Arabian Gulf Coast region. Sabkha is known as a geotechnically problematic soil because of its loose density, soft consistency, high salinity and water content, and occurrence of fine sands and clays. It is generally highly compressible and requires ground improvement for highway and railway construction. The purpose of this study is to provide a guideline for dynamic compaction to improve the bearing capacity of the coastal sabkha deposit. The ground behavior during dynamic compaction was evaluated for various compaction energy conditions using numerical analysis, and field dynamic compaction tests were also performed and compared with the numerical analysis results. It was found that the bearing capacity of sabkha deposit can be effectively improved by dynamic compaction. However, care must be taken to ensure that excessive porewater pressure is sufficiently dissipated during the application of dynamic compaction because the permeability is pretty low due to the high salt content in groundwater in the sabkha area.

Numerical pile segment analyses were conducted using an advanced soil model to investigate the development of side resistance and the soil behavior around a micropile installed in sand and subjected to static axial loading. A series of static pile segment analyses were performed for micropiles and Conventional Drilled Cast-In-Place (CDCIP) piles considering effects of pile installation, relative density of sand and pile diameter. Results of analyses were used to determine the effects of pile installation, pile diameter, and relative density of sand on static shear behavior of a micropile and changes in effective stresses and volumetric strains in the soil adjacent to the interface. Relatively high side resistance and stiff t-z response were characteristic features of a micropile compared with CDCIP piles. Results of static numerical pile segment analyses for micropiles were compared and found to exhibit good agreement with pile loading tests and design methods.

The use of piled raft foundations has been considered as an economical alternative to conventional deep foundations because a portion of the applied load is thought to be transferred to the raft. In analyzing the behavior of a piled raft as a settlement reducer, an accurate estimate of settlement of the system should be made, based on the adequate understanding of nonlinear behavior of piles in layered soils as well as the interaction between the raft, soils, and piles. This study developed a computer program incorporating an approximate hybrid analysis method for the practical design of piled raft foundations. In the presented method of analysis, the interactions between pile-soil, raft-soil, pile-soil-pile and raft-soil-pile are considered, and the effect of nonlinear behavior of piles and the interactions between piled raft components and soil are investigated by comparing with 3-dimensional FEM program analysis results.

Considering the case of fabricating a UHSFRC (ultra-high strength fiber-reinforced concrete) beam with the method of one end placing and self-flowing to the other end, it was intended to simulate the variation of the fiber orientation distribution according to the flow distance and the variation of the resultant tensile behaviors. Then the validity of the simulation approach was shown by comparing the simulated results with experimental ones. A three-point bending test with a notched beam was adopted for the experiment and a finite element analysis was performed to obtain the simulated results for the bending test considering the flow-dependent tensile behavior of the UHSFRC. From the simulation for the fiber orientation distribution according to the flow distance, it could be found that the major change in the fiber orientation distribution took place within a short flow distance and most of the fibers became nearly aligned to the flow direction. After some flow distance, there was a not-so-remarkable variation in the fiber orientation distribution that could influence the tensile behavior of the composite. For this flow region, the consistent flexural test results, regardless of flow distance, demonstrate the reliability of the simulation.

Sinkholes are the most common geohazards occurring in east Central Florida (ECF). To understand the sinkhole formation and karst hydrogeology within the ECF region, it is necessary to investigate the sinkhole triggering factors. The main purposes of this study are: (1) to develop a decision-tree based model for sinkhole hazard assessment, which accounts for multiple sinkhole affecting factors; and (2) to construct a sinkhole hazard map of east Central Florida (ECF) using the developed decision tree model. The decision-tree model, a popular classification method in data mining, accounted for five identified factors including geology formation/epoch, overburden thickness, hydraulic head difference, groundwater recharge rate, and proximity to karst features. In this study, the recorded 757 sinkhole locations in ECF were randomly split into 70:30 for training and validation purposes, respectively. The performance test of a produced sinkhole hazard map was carried out with a density analysis where density values should increase from the very low to the very high hazard class.