Study On The Consolidation Theory For Vertical Drains Considering The Actual Shape Of Influence Zone

The analytical consolidation theories for vertical drains under the equal strain conditions, due to its practicality, is still the main foundation to guide sand-drain design. The existing theories have been based on that the influence zone of regular polygon in practice is reduced to a circle, the initial excess pore water pressure have uniform distribution and the horizontal permeability of soil within the smear zone is constant. However, in practice, the permeability coefficient of soil becomes variable, due to the effect of disturbance during the installations of vertical drains. Meanwhile, the distribution of initial excess pore water pressure is not always uniform along the depth of the foundation. Under new conditions, the consolidation theory for vertical drains is further studied in this thesis. The principal contents and original work are as follows:1. The consolidation problem for vertical drains, in which the influence zone is regular hexagon, is studied and the analytical solutions are given under single-drainage and double-drainage conditions. Then the general solutions of vertical drains that have arbitrary regular polygon-influence zone are obtained. By comparing with the variable consolidation theory for vertical drains, it is shown that under the same conditions, the solution of this thesis is slightly larger than the existing one, but the difference is very small. This indicates that the assumption that the influence zone of vertical drain is a circle adopted in the available theories is reasonable.2. The general analytical solutions are given to the consolidation problem for vertical drains considering the actual shape of influence zone and the variety of horizontal permeability coefficient of soil. Four types of variation patterns of the horizontal permeability which are likely to appear in practice are proposed, and the corresponding analytical solutions are derived. The results show that the variation patterns of permeability within the influence zone have significant effects on the consolidation behavior. In general, under the same conditions, the rate of consolidation is the fastest in pattern 3, while it is the slowest in pattern 4.3. Under the non-uniform distribution of initial excess pore water pressure, the consolidation problem for vertical drains considering the actual shape of influence zone is studied. A general analytical solution is obtained under different drainage conditions. The specific analytical solutions corresponding to trapezoidal distribution, triangular distribution, and inverse triangular distribution of initial excess pore water pressure are derived. The results show that the distribution form of initial excess pore water pressure has a great influence on the consolidation behavior. Under single-drainage condition, the consolidation is the fastest when the distribution of initial excess pore water pressure is inverse triangular, while it is the slowest when the distribution is triangular. But the rate of consolidation is independent of the distribution form of initial excess pore water pressure under double-drainage condition.