P.G. Biddle

Case Study 6 [p99] was concerned with long-term recovery movement following removal of an oak tree. Results were presented for level monitoring over the period 1987 to 1993. At that stage recovery movements were still continuing.

In April 1999 I took a further set of readings on the level monitoring markers. The figure below provides an update for Case Study Figure 6.8 [p103]. It can be seen that further movements over the previous six years have been negligible, marker C recording further movement of only 4.5mm (i.e. an average of 0.75mm per annum). Furthermore, extrapolation of the movement between 1989 and 1993 suggests that most of this further movement would have occurred soon after 1993. The monitoring in spring and autumn of 1992 had previously shown that seasonal movements had ceased.

On the basis of this information, the building insurers (Legal and General) reinstated full insurance cover for subsidence and heave. Obviously this satisfactory final outcome has taken a long time to achieve, but it was known from the outset that there was a significant persistent deficit, and that recovery would take many years. The level monitoring, which was originally set up for diagnostic purposes, has allowed this process to be studied, and provided the essential information to enable reinstatement of insurance cover.