The sustainable performance of foundations of various urban buildings and infrastructures is strongly affected by groundwater level (GWL), as GWL causes changes in the stress state within soil. In the present study, the components affecting GWL were investigated, focusing on the effects of precipitation and river stage. These components were analyzed using a six-year database established for hydrological and groundwater monitoring data. Five study regions for which daily measured precipitation, river stage, and GWL data were available were compared. Different periods of precipitation, geographical characteristics, and local surface conditions were considered in the analysis. The results indicated that key influence components on GWL are different depending on the hydrological, geological, and geographical characteristics of the target regions. River stage had the strongest influence on GWL in urban areas near large rivers with a high ratio of paved surface. In rural areas, where the paved surface area ratio and soil permeability were low, the moving average showed a closer correlation to GWL than river stage. A moving average-based method to predict GWL variation with time was proposed for regions with a low ratio of paved surface area and low permeability soils.

Lightweight-foamed soils are mixed soils with foam and cement to enhance the solidity and lightness of soils. Marine wastes, especially waste fishing nets, can be additives to reinforce the engineering properties of lightweight-foamed soils. In this paper, lightweight-foamed soils reinforced with waste fishing nets were investigated. Dredged soil and waste fishing nets were collected and pre-processed for testing. For optimization, the water content, foam ratio, cement ratio, net ratio, net conditions, and curing days were evaluated with respect to workability, unit weight, and strength. The variables were narrowed down based on the performance criteria. The results found that a water content of around 100%, cement ratio of 20%, foam ratio of 5%, and net ratio of 4% with shredded nets provide the best engineering performance of lightweight-foamed soils. The use of nets presented a superior increase in critical strength rather than an obvious increase in peak strength. A normalized factor was used to predict the required strength of lightweight-foamed soils. Finally, this study proposes field implementation methods in terms of the initial conditions of soils and optimal conditions of soils, resulting in the depletion of waste fishing nets.