Prediction and Analysis of Vertical Additional Force of Shaft Wall in Topsoil Containing Multiple Aquifers during Drainage

Studying the additional force in topsoil containing multiple aquifers can have a significant impact on predicting shaft wall fracture and guaranteeing shaft safety, as the aquifer number increases as drainage occurs. In this study, a numerical model calculating the effect of drainage on additional force in topsoil, containing multiple aquifers, was established on the basis of several practical engineering cases. The changes in the stress displacement of the shaft wall was analyzed during three different stages of shaft construction using typical parameters, and the effects of the various factors on the additional force variation under different water level gap conditions, depending on whether the drainage was synchronized or unsynchronized, were studied. The results indicate that the increment in the additional force, with an increasing water level gap in the central aquifer, is obviously larger than that in the bottom aquifer, and the difference in the maximum additional force between these two aquifers is approximately 0.6 MPa. The increasing number of central aquifers results in a higher increment in this force, which reaches 12 MPa with an increasing number of central aquifers. Meanwhile, a threshold value (about 0.6~0.7 H) exists for the depth of a central aquifer in terms of its effect on the additional force.