Consolidation of band-shaped drain based on equivalent annular drain
LU Mengmeng1，2，ZHANG Qiang1，2，JING Hongwen1，2，WANG Bo1，2
(1. State Key Laboratory for Geomechanics and Deep Underground Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. School of Mechanics and Civil Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China)
Abstract：The existing theories for consolidation of band-shaped vertical drains were usually derived by converting the band-shaped drain into an equivalent circular drain using various equations. A common disadvantage of these studies is that either the circumference or the section area or even both of them of the band-shaped drain cannot be kept unchanged before and after conversion. Consequently，the actual amount of water flowing into and flowing out of the band-shaped drain cannot be reflected by the equivalent circular drain，which will inevitably lead to the misunderstanding of its consolidation behavior. In this context，a new equivalent annular drain is proposed to overcome the above disadvantage of the conventional circular drain. By considering three variation patterns of the horizontal permeability coefficient within the smeared soil zone，general analytical solutions are derived for the consolidation of band-shaped drain subjected to depth-dependent stress caused by time-dependent surcharge loading. Based on the general solutions，the detailed closed-form solutions are further derived for the cases of linearly distributed stresses along depth caused by instantaneously loading，linear loading，multi-stage instantaneously loading and multi-stage linear loading. Then，the effect of the annular drain is investigated by comparing its results to that of the circular drain. The results show that the circular drain is a particular case of the annular drain when the area reduction coefficient is taken as 1. The average degrees of consolidation predicted by the present solutions are mostly close to and slightly larger than that predicted by the Fellenius and Castonguay(1985) method based on the circular drain with equal cross-section area. The average degree of consolidation predicted by the annular drain is less than that predicted by the circular drain，moreover，the former is getting closer to the latter with the increasing in the area reduction coefficient. The difference in the average degree of consolidation predicted by the annular drain and circular drain diminishes with the reduction in the permeability of the band-shaped drain.
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2018, Vol. 37 
