What are the implications of vibration, weakening or the removal of support?

There is often misunderstanding surrounding the application of and implications for insurance around the risks of Vibration, Weakening or the Removal of Support (VWRS). Should we include or exclude this cover on a given construction risk? Is the cost of this extension and the possible cost to collect additional information worthwhile?

Let’s examine the components of this extension in a public liability cover.

Vibration

This refers to the damage caused by any vibration.

Common causes of vibration on a construction site include heavy mobile plant (trucks, excavators and even cranes) jackhammers and some forms of piling (notably sheet piles and driven piles).

Weakening or the Removal of Support

This refers to damage caused when the supporting:

  • element / structure; or
  • ground,

is weakened or removed during construction operations.

Element / structure

This can include the removal of a vertical or lateral load-bearing wall, beam or foundation (or the weakening of it by cutting in to it or undermining it). It also includes the weakening or removal of any other element that provides support or stability to a structure. The process of underpinning is a prime removal of support risk, ironically carried-out to improve/strengthen support!

Ground

This can include any earth or rock (geological) excavation within the zone of influence of a structure supported by that ground. It could also be the ground itself (as opposed to a structure supported by the surrounding group) which collapses.

For example, excavation at the base of a slope (in certain soil conditions) can cause slippage of the uphill-slope due to weakening or removal of the support for the uphill “load”.  Retention system is required to assume the load, commonly in the form of:
a) Self-supporting embankments (“batters”) cut at an angle calculated for the prevailing geological conditions to prevent land slippage. For example, if the geology is rock, the angle can be steep, sometimes vertical, if the geology comprises soft soil, the angle will be shallow. If the angle of the batter is incorrect, and slippage occurs solely because of this, then support (of the land above) has technically been removed or weakened.
b) an installed piling system

Underpinning

An example of a construction activity that can contain all facets of VWRS risk, involving both structures and ground, is underpinning, where the supporting soil beneath (or alongside) an existing structure is excavated. Not only is the ground supporting the building weakened or removed, the excavation method will often involve some vibration.  Underpinning beneath an existing structure is often via a “hit and miss” system, where underpinning is installed at a gapped intervals along the perimeter to be supported, then the gaps are underpinned until the system becomes continuous.

Excavation

If an excavation is deep, is in rock and has close neighbours in old buildings (old buildings deteriorate over time and are generally not as well-founded / constructed as modern buildings), the vibration damage risk can be high. If rock hammers are used, the risk peaks, but is far less if rock-saws are used.

Shallow excavation in soft clay or soil, with no close neighbours, is a very low risk and the excavation will probably be effected using a bucket excavator.

Because VWRS can be a significant risk, most prudent underwriters would like to consider it before supplying terms (Note: Underwriters often request Geotechnical and Dilapidation Reports when the risk may be significant).

Many examples of litigation which arise from VWRS are emotively driven by third parties. People do not regularly inspect the exterior and interior walls of their homes and buildings – but they do when they feel vibration from earthmoving equipment operating nearby! It is t that they will discover previously unseen cracking (usually due to foundation settlement  or natural soil contraction) which are then attributed to neighbouring construction work.

Contractors who adhere to good risk management practice commission Dilapidation Reports as a matter of course where the potential of VWRS risks exist.