Model tests of sand-free air booster vacuum preloading for saturated cohesive soil foundations

Sand-free air booster vacuum preloading is a novel ground improvement technique for treating saturated cohesive soil foundations. To understand the mechanical behavior of the saturated soft ground during its consolidation and drainage improvement with this measure, a series of laboratory physical simulation tests have been conducted for a typical air booster vacuum preloading unit with a geometric similarity ratio of 1:6, based on soft ground improvement in an expressway embankment project in Sichuan Province. The length, width, and height of the modeled ground in the tests were uniformly 1m. Three pressurization modes were involved in the tests, including traditional vacuum preloading (no pressurization), interval pressurization, and constant pressurization, and the variation characteristics of mechanical behavior of the improved ground were obtained. The test results show that the excessive pore pressure, ground settlement, and water discharge in the three modes show a rapid change during the early stage, followed by a gradual stabilization during the later stage. The interval pressurization mode has the best effect on the drainage consolidation. For interval pressurization, the excessive pore pressure fluctuates growingly by approximately 10% at the pressurization moment, and dissipates by about 3.1%−4.2% after a pressurization cycle. Compared with interval pressurization and no pressurization, in the constant pressurization mode, the excessive pore pressure increases by approximately 25% and decreases by 9%, the ground settlement reduces by 12% and increases by 25%, and the water discharge diminishes by 15% and rises by 9%, respectively. Water content and shear strength parameters of the improved ground significantly decrease and increase under the three modes, respectively. Based on the experimental results, an improved numerical modeling method for analyzing such problems was provided. The results of ground settlement obtained using the model test, numerical simulation, and theoretical analysis were generally consistent, with the numerical simulation indicating relatively effective consolidation during the early stage. The research results can provide references for practical engineering.