Ground Deformation Induced by Vacuum Consolidation

Abstract

The deformation characteristics of soil subjected to vacuum pressure are discussed and an approximate method is proposed for calculating settlement and lateral displacement of the ground induced by vacuum consolidation. Laboratory oedometer test results indicate that if the vacuum pressure alone is larger than the lateral stress required to maintain an at-rest ͑no horizontal strain͒ condition, there will be inward lateral displacement and the vacuum pressure will induce generally less settlement than a surcharge load of the same magnitude. In the case of field vacuum consolidation, the confining stress acting on a soil element can be regarded as consisting of two parts: Due to vacuum pressure and earth pressure. Assuming a value of the lateral earth pressure coefficient acting in the ground under vacuum consolidation ͑k ao ͒, somewhere between the active and at-rest values, an equation defining the depth-below which there will be no significant inward lateral displacement-is derived. Further, assuming that the volumetric strain induced by vacuum consolidation is the same as the one-dimensional consolidation induced by application of a surcharge load of the same magnitude, an approximate method is proposed for calculating the ground settlement and inward lateral displacement induced by vacuum consolidation. This method has been applied to two case histories reported in the literature, and it is shown that the field-measured data are simulated reasonably well, suggesting that the method may be useful for the design of vacuum consolidation projects.

Estimation of Influence Scope of Lateral Displacement of Soft Ground under Vacuum Pressure with PVD

“…If only the vacuum pressure is larger than the lateral stress required for a no horizontal strain condition, an inward lateral displacement is observed. Based on a series of test results, Chai et al [1] reported an approximate method for calculating the ground lateral displacement induced by vacuum pressure.…”

“…Table 2 lists the information needed to calculate the lateral displacement induced by vacuum consolidation by using the approximate method. Advances in Civil Engineering e method proposed by Chai et al [1] for calculating lateral displacement of the soil at the treated area boundary as a result of the vacuum-drain consolidation can be summarized as follows:…”

“…Figure 7 plots the variations in the LF, where the LF � 0 when χ � K 0 . A stress ratio (k) [1] was defined as…”

“…With several advantages over embankment loading, vacuum pressure applied to the processing of soft clay has a higher practicability, such as no fill material, shorter construction periods, and nonrequirement for heavy machinery. In addition, the vacuum preloading method does not add any chemical admixtures into the ground and is consequently an environmental-friendly ground improvement method [1,2]. However, owing to the principle effect of the vacuum preloading method, the treated area will not only induce vertical settlement and inward (toward the centre of the loading area) lateral displacement of the ground but also cause crack adjacent to the treated area.…”

“…e current methods for calculating lateral displacement of soil consist of the strain method (the horizontal displacement at the boundary is calculated based on the strain of the soil in the treated area) [1] and the method of determining the ratio of the settlement and lateral displacement [4]. It is noteworthy that the above methods are not used to solve the deformation of the soil influenced by the different lengths of a prefabricated vertical drain (PVD).…”