Model Test Study on Bearing Capacity of Sandy Soil Foundations in Beach Areas

In this study, we investigate the bearing capacity characteristics and controlling mechanisms of coastal beach sand in Quanzhou Bay, Fujian Province, China. The results provide support for coastal engineering construction and vehicle trafficability assessment in beach areas, while field sampling, laboratory static plate load tests, and data-based modeling were conducted to examine the effects of moisture content, particle size distribution, and relative density on the bearing behavior of beach sand. In total, 52 groups of static load tests were performed, with the results showing that relative density is the dominant controllable factor affecting the bearing capacity of coastal beach sand. When the relative density increased from 40% to 65%, the ultimate load increased by 80%, and the deformation modulus increased by 139.9%. The optimal relative density range was approximately 52–65%, and the improved particle size distribution enhanced bearing performance. The ultimate load of well-graded sand was 60% higher than that of poorly graded sand, and moisture content showed a threshold effect, with the best mechanical performance occurring at a moisture content of about 7%, whereas excessive moisture content significantly reduced the bearing capacity. Under natural conditions, the proportional limit load of medium-dense coastal beach sand in Quanzhou Bay was approximately 200 kPa, the ultimate load was 250 kPa, and the characteristic value of bearing capacity was 125 kPa, while the dominant failure mode was general shear failure. A semi-empirical bearing capacity model was also developed; its average relative error was 10.35%, indicating that it has both physical meaning and engineering applicability. The findings provide a reference for foundation design evaluation in Quanzhou Bay and similar coastal beach areas.