Settlement and Prediction of Subgrades in Tidal Flat Areas under Repeated Water Levels

The engineering geological conditions of the Xiapu tidal flat in a subgrade project in Fujian are analyzed. The numerical simulation software Plaxis^2D is exploited to study the settlement development of deep and thick grounds in tidal flats under repeated water levels. The growth mechanism of the consolidation degree in each phase is analyzed, and the consolidation degree prediction formula is proposed. The evolution of pore water pressure of subgrades in tidal flats is introduced, and the mechanism of pore water pressure growth under repeated water levels is revealed. The settlement prediction system is developed for deep and thick grounds in tidal flats under the repeated water levels according to the gray prediction method GM(1, 1). The correctness is verified by numerical calculation results. Results show that subgrades produce differential settlement under repeated water levels. In the subgrade project in Fujian, the settlement on the top right side of the embankment is larger than that on the left side, and the settlement difference is approximately 36 cm. The settlement rates on the right and left sides of the embankment are 9.43×10^-5 and 4.35×10^-5 m/day, respectively. The development of the consolidation degree during the loading and consolidation process can be well described by the power function form. The application of the power function expression is recommended. In the phase of repeated water levels, the logistic function expression is recommended for the consolidation degree. In terms of the development of pore water pressure, the pore water pressure of the subgrade on the right side is greater than that on the left side under repeated water levels. The pore water pressure on the right side of the subgrade suddenly increases to 120 kPa, and the pore water pressure is increased to 113 kPa at the center of the subgrade. The pore water pressure of the subgrade on the left side is 10 kPa. The pore pressure is higher than 3 kPa when it is first loaded. On the basis of gray theory, the settlement prediction system for deep tidal flat roadbeds under repeated water levels can control settlement error within 5% and can thus be applied to engineering practice.