ABSTRACT
Secondary compression or creep is an important aspect in the design of earth structures on top of soft soils. The key question in such design is the development of pore pressures and settlement with time. In the beginning the soil deformations are delayed due to the low hydraulic conductivity of the subsoil. This causes an increase of the pore pressures. Gradually water starts flowing off, excess pore pressures decrease and settlements develop. Generally, the design of earth structures on top of soft soils is a rather onedimensional problem. GeoDelft has developed a one-dimensional software program MSettle for prediction purposes. A few other dimensional effects, like load distribution, are incorporated by approximation. The combined process of consolidation and creep is progressing very slowly. In order to limit the excess pore pressures and to accelerate the settlement rate, often a system of vertical drains is applied. Such a system may consist of small permeable vertical synthetic strips or massive granular walls containing drainage pipes. The flow to the vertical drains has a significant horizontal component. This makes it difficult to incorporate it directly in the one-dimensional approach of the MSettle program. Of course, a two dimensional extension is feasible. However, this violates the character of the program: simple and fast. Therefore, an attempt is made to express the horizontal flow into a leakage term, which can be incorporated straight forwardly.
