A New Approach to Improve Soft Ground in a Railway Station Applying Air-Boosted Vacuum Preloading

Abstract

Conventional vacuum preloading usually does not meet the requirements to improve soft ground in railway stations due to its long duration and unstable drainage performance. This is because of the drainage capacity reduction over a prolonged period. To overcome these disadvantages, a new approach, called air-boosted vacuum preloading, was proposed to deal with the soft ground. To introduce the air-boosted vacuum preloading, principles of this new technology were first introduced in this paper, and then the whole process of the construction was listed. In order to verify the effectiveness of the proposed new method, four different sections were set up through measuring the settlement, the pore water pressure, and the groundwater table in a test field. The results showed that a more rapid improvement in the soils parameters was reached, especially in the vane shear strength and the compression modulus. Although the boosted action reduced the vacuum pressure to a certain degree, pressure differences between soils and the prefabricated vertical drains became much larger with the process of boosting, which lead to accelerate drainage. Preloading settlement of the boosted sections was greater than that of the conventional sections within the booster tube depth and was less beyond that depth. Similarly, the overall post-construction settlement was identical for both methods. Air-boosted vacuum preloading was thus recommended to treat soft soils for tight schedule projects.

Recent Developments in the Vacuum Preloading Technique in China

“…The air booster vacuum preloading technique was proposed to solve the shortcoming of the conventional vacuum preloading technique in that the PVDs' drainage capacities were often reduced due to the clogging of the filter sleeves. The effectiveness of this method was verified by the field practices [31,32] and laboratory model tests [33][34][35]. The principle of the air booster vacuum preloading technique is schematically shown in Figure 10.…”

Evaluation of Heating Time on Vacuum Preloading Treatment

“…Many new composite methods are proposed for these problems. The electro-osmotic combined vacuum preloading method [9][10][11][12][13][14] is to improve the effect of vacuum preloading reinforcement by adding a current field in the soil and making the pore water in the soil flow from the anode to the cathode under the action of the electric field; the air booster vacuum preloading method [15][16][17][18][19][20][21] is to improve the drainage efficiency by injecting high-pressure gas into the soil through a booster pump to form a greater pressure difference between the soil and the drains, and the high-pressure gas can produce fine cracks and form new pore water drainage channels. Moreover, there is strong ramming combined with the vacuum preloading method [22][23][24], mounding combined with the vacuum preloading method [25,26], and the graded vacuum preloading method [27][28][29][30], a method of adding chemical additives to modify and/or solidify the clays [31,32].…”

Numerical Simulation of Vacuum Preloading for Reinforcing Soil inside Composite Bucket Foundation for Offshore Wind Turbines

“…The results have shown that the new method exhibits similar efficiencies to the conventional vacuum preloading method. Shen et al [15] put forward an air-boosted vacuum preloading method to deal with the soft ground with less reinforcement time compared with the traditional vacuum preloading method, and the effectiveness of the proposed new method verified by field tests. There is currently limited few research into the vacuum preloading technique combined with bucket foundations.…”