Surface and Structural Movement Surveys
Buildings or landscaped areas can be subject to movement such as land settlement or subsidence resulting in the need for one of the following three, regularly monitored surveys:
- Subsidence Survey – to check whether the levels of a floor or wall have sunk, risen or bowed.
- Levelling Survey – to check a localised grid of levels over a site to establish whether ground levels have sunk or risen.
- Settlement Survey – to check the levels of a floor after settlement has occurred, however this would presume there is data about the original floor or wall levels to compare new data with.
These types of survey are concerned with the level of acceptable undulation or structural movement across an area of land or within buildings. Catching movement early on ensures remedial costs are kept to a minimum and so pin pointing this with absolute accuracy is imperative.
Surveys of this type are often used to monitor anything from residential properties through to bridge construction or anything requiring the accurate construction of steel frameworks, dams, nuclear power stations and large factory sites. They are also used in built up areas or land experiencing high vibration from machinery due to mining, hydraulic fracturing or ‘fracking’ or where ground is being excavated for basements or underground car parks.
Subsidence surveys in constructed buildings
If you are concerned that your retaining walls aren’t robust enough or that land settlement has occurred, creating pooling of water, (for example, where a floor slab has sunk in the middle of a warehouse), it may be necessary for us to carry out a Levelling Survey or Subsidence Survey, mostly on behalf of a Consulting Structural Engineer. Examples of structural movement that could be surveyed and monitored in buildings could be subsidence, settlement, heave, sway, bulging walls, cracks or the expansion and contraction of constructed brickwork, blockwork or steelwork.
An initial survey will model and contour the face of the wall or floor to highlight any movement or deformation by establishing a series of permanent points along it. If the levels appear to be moving then a monitoring survey would be implemented to see how far and how quickly the movement is occurring.
A monitoring survey ensures that these permanent points are accurately resurveyed over an agreed period of time. We can then determine whether any movement has occurred as a result of land settlement or subsidence. To do this, we survey the permanent monitoring points using reflector-less instruments taking measurements on a suitable grid to allow us to compare data from previous visits. Over time, data is collected and can be presented in a variety of formats to show the level of movement that has occurred.
Examples of data presentation range from reports, contour models overlaid on top of each other, survey drawings or spread sheets for best interpretation.
Settlement or Subsidence Surveys of larger structures
Surveying land and buildings for structural movement is an area of surveying that has continued to grow due to the necessity to monitor and assess movement within potentially dangerous structures, such as, nuclear power stations, dams and large factories. Our surveying capabilities allow us to undertake complex schemes to identify 3 dimensional movement within a structure and throughout the structure as a whole.
Steel beams and rigid construction materials
Monitoring steel beam levels during construction ensures that there is no evidence of bend or twist in the steel guaranteeing accuracy at all stages of construction where necessary.
Where road level accuracy is essential in bridge building we are able to check how beams fit together in the construction of large infrastructure projects. Other uses of monitoring surveys include checking the accuracy of a standalone steel or concrete structure before proceeding onto the next stage of construction or checking pile positions during ground works.
In addition to improving accuracy levels during construction, a monitoring survey takes the uncertainty out of the project and reduces the need for costly and time-consuming remedial work. Reducing risk for our clients and keeping projects within budget and on time is of paramount importance.
Frequently Asked Questions
(1) How can we check whether my retaining wall is moving over time?
Permanent markers or targets can be fixed to the wall and surveyed for position and level over a set period of time. The results would show whether movement is occurring.
(2) How can I show whether my concrete floor slab has sunk?
We can carry out a detailed level survey across the slab and produce a contoured drawing which would clearly show the low and high areas.