Study On The Consolidation Theory Of Soft Soil With Partially Penetrated Vertical Drains

As an efficient and economical method, vertical drains have been widely used to improve soft soil and the related consolidation theories were well developed. However, there are some cases in actual engineering projects where vertical drains can only be partially penetrated since the soft soil layer is so deep that it is impossible or not economical to penetrate it. This results in the studies on the consolidation theory of soft soil with partially penetrated vertical drains.The consolidation theory so far available for soft soil with partially penetrated vertical drains is all established on the hypothesis that the consolidation of soil beyond the tip of vertical drain is three dimensional with radial and vertical flows while the one of soil beneath vertical drain is one dimensional with vertical flow only. Obviously, due to the existing of vertical drain, three-dimensional seepage also exists in the soil beneath vertical drain. In order to overcome the shortcoming involved with the available theory and to make it closer to actual case, the consolidation theory of soft soil with partially penetrated vertical drains is studied further herein.In the present thesis, a new computational model which can consider three-dimensional seepage in the soil beneath vertical drain is established through assuming a virtual drain in the soil just below the tip of actual one. The analytical solutions for the consolidation of soft soil with partially penetrated vertical drains are obtained under both single-drainage and double-drainage boundary conditions. By using the solutions, the approximate methods so far available for the computation of average consolidation degree of soft soil with partially penetrated vertical drains were compared and discussed in detail, and the consolidation characteristics of soft soil with partially penetrated vertical drains are investigated.It has been shown that the rate of consolidation of the soft soil with partially penetrated vertical drain is increased with the increase of the drain length. However, it is slow down as the length exceeds some extent. Among the all approximate methods, the one proposed by G. R. Chen is closest to the analytical solutions given herein, and then is the one by K. H. Xie. While the consolidation degree is underestimated by the approximate method proposed by Hart, it is overestimated by the one commonly used in China.