Dongwook Kim

Recently, many of new constructions or replacements of infrastructures are taking place at extreme regions, such as permafrost area or deserts. The extreme regions are largely classified into cold and hot regions. In these regions, climatic, environmental, and geographical factors cause ground deformation such as ground settlement. Ground deformation influences behavior of foundations and stability of the super structures. Especially plants are more critical to ground deformation because these facilities are very sensitive to differential settlement or vibration due to improper foundation designs. In this study, a new type of pile foundation named the environment-responsive pile foundation(ERPF) was verified in order to reduce the negative effect with ground deformation. The verification was performed through numerical analysis, as a result of numerical analysis, the positive effects of environmental-responsive pile foundations against ground deformation was identified. Additionally, the location and properties of the reinforcement were adjusted to maximize the effect of ERPF. Consequently, a low modulus of elasticity of the pile reinforcement material have the effects of reducing negative skin friction force within pile foundation.

Waterproof membranes have higher initial strength, faster construction, and better waterproofing than conventional sheet membranes. In addition, their polymer constituents have much higher interfacial adhesion and tensile strength than those of conventional materials. However, despite their advantages, waterproof membranes are not widely used in civil construction. This study evaluates the material properties and interface parameters of a waterproof membrane by considering the results of laboratory experiments and numerical analysis. Since the contact behavior of a membrane at its interface with shotcrete is important for understanding the mechanism of the support it offers known as a shotcrete tunnel lining, modeling should adopt appropriate contact conditions. The numerical analysis identifies the suitability and contact conditions of the waterproof membrane in various conditions.

In the present study, the overall stability of typical Korean composite caisson breakwaters that were initially designed following the conventional deterministic approach is investigated using reliability approaches. Therefore, the sensitivity of critical uncertainties regarding breakwater safety is analyzed. Uncertainty sources related to the structure, ocean conditions, and properties of the subsoil and rubble mound are considered in the reliability analysis. Sliding and overturning failures are presented as explicit equations, and three reliability methods, i.e., the mean value first-order second-moment, first-order reliability method, and Monte Carlo simulation, are applied in the evaluation process. Furthermore, the bearing capacity of the rubble mound and subsoil are analyzed using the discrete slice method conjugated with the Monte Carlo simulation. The results of this study establish that the sliding failure generally is the most frequent failure occurring among the above-mentioned overall stability failures (around 15 times more common than failures observed in the foundation). Additionally, it is found that the horizontal wave force primarily contributes to the sliding of the caisson body, whereas the friction coefficient is the main factor producing the resistance force. Furthermore, a much small probability of overturning failure implies that the overturning of a caisson around its heels uncommonly occurs during their lifetime, unlike other overall failure modes. Moreover, the failure in foundations may commonly encounter in the breakwater that has a high rubble mound structure compared with sliding mode. Particularly, the performance function of the all foundation bearing capacities presents a nonlinear behavior and positively skewed distribution when using the Monte Carlo simulation method. This phenomenon proves that simulation methods might be an appropriate approach to evaluate the bearing capacity of a breakwater foundation that can overcome several drawbacks of the conventional design approach.

A model for predicting shallow depth soil temperatures is important and effective to assess the changes in soil conditions related to global climate change and local disturbances. Shallow-depth soil temperature estimation model in cold region in Alaska is developed based on thermal response using air temperature and shallow-depth soil water content during active layer development period of 160 days from May to October. Among the seven soil temperature measurement sites, data from four sites were used for model development, and the remaining three sites were used for model validation. Near the middle of the seven measurement sites, air temperature is monitored at one location. The proposed model implemented concepts of thermal response and cumulative temperature. Temperatures and soil water contents were measured using automated remote sensing technology. Consequently, it was confirmed that the developed model enables fast and accurate assessment of shallow-depth soil temperature during active soil layer development period.

There are several options in determination of foundation types for offshore wind turbine towers. The foundation types are mainly determined based on the sea depth. For relatively shallow sea depth, jacket structure or monopile is one of most preferred offshore wind turbine foundation types. Foundations of wind turbines are more critical against lateral loads or moments compared to their vertical load; therefore, reliable assessment on their lateral behavior is important. As the existing design specifications of laterally loaded pile is developed based on the database from the experiments of lateral load test results of small-diameter piles. Validation of suitability of using the existing design specifications to design monopiles against lateral load is important. Therefore, in this study, review on offshore foundation design for wind turbine towers especially focusing on lateral behavior of monopile was conducted.

The validity of using the existing numerical p-y methods [American Petroleum Institute (API) and Reese methods] for the design of offshore wind turbines’ large-diameter monopiles in sands is questionable, as many researchers have raised concerns related to the diameter effects in p-y models. This study presents the development of experimental p-y relationships for large-diameter monopiles in dense sands based on results from centrifuge tests exhibiting a softer monopile behavior than those proposed by the API and Reese methods. The effect of socketing the tip of a pile in rock bearing layers was also investigated. The initial gradients of the p-y relationships in dense sand layers were shown to become significantly stiffer as the depth reaches the much stiffer and stronger rock-bearing layer. The lateral load-displacement curves obtained based on the developed experimental p-y relationships were found to be well matched with the measured lateral load-displacement curves; therefore, it was conclude...

Stable backfill materials for the heat sensitive structures of buried power cables, hot water pipes, and gas pipelines are suggested to have low permeability and high heat transfer characteristics. The hydraulic and thermal conductivities of backfill materials or clay liners are important parameters in proper design and construction of geotechnical structures involved with heat transfers. In this study, to investigate the optimal natural backfill or liner materials, thermal and hydraulic conductivities of kaolin–silica mixtures examined based on the results from laboratory tests under different consolidation conditions. From the experiment results, the thermal conductivity increases while hydraulic conductivity decreases with increasing density during consolidation process. As a result, back-fill materials with high kaolin content under low consolidation stress were desirable materials for burial of heat sensitive structures.