New methods for measuring the installation depth of prefabricated vertical drains

The installation depth of prefabricated vertical drain (PVD) is one of the key factors affecting the outcome of soil improvement when PVDs are used to accelerate the consolidation of soft soil. As PVDs are installed underground, it is difficult to verify the installation depth of PVDs for quality control purpose.In this note, three new methods that have been used in China for measuring the installation depth of PVD are introduced. The working principles of each method are described. The advantages and disadvantages of each method are discussed. An example is also given to illustrate the use of the methods in soil improvement projects.