A new approach to improve soft ground in a railway station applying air-boosted vacuum preloading

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.