How To Monitor Building Settlement / Heave
Read our guide on buildings are monitored for settlement or heaving upwards or downwards.
Article By: Tom Ayre | Last Update: April 2022
In this article, we are going to discuss 3 methods used to monitor a building for heave or settlement.
To clarify, heave is where the ground is pushed upwards and settlement is where the ground lowers. Both heave and settlement can cause serious issues with buildings.
The difficulty in monitoring a building for vertical movement is that you have to have precision equipment to do it accurately. Using a tape measure or laser simply won’t work if you are looking for precision.
The three methods described below are industry standard ways of monitoring movement. Let’s begin.
Table of Contents
A total station is a device that can accurately survey and record the position and height of an object. When checking for settlement / heave, targets can be installed on a building. This gives a fixed position that can be monitored and checked over time.
A total station is a very accurate method of obtaining vertical movement on the point it is checking. The total station requires a number of fixed points around the area that aren’t expected to move. These locations are used to each time to set up the device and give an accurate reading of height movement.
The monitoring targets fixed to a building are usually prisms or reflective targets.
- Height and position readings are very accurate, assuming you have suitable locations around the setup location.
- Settlement / heave measurement trends can be clearly shown. Areas can be highlighted where more or less movement is occurring.
- Simple to add many monitoring positions with low cost reflective targets / prisms.
- The total station requires a surveyor to visit the site each time, trends can only be observed between survey visits.
- Sometimes locations can be blocked by vegetation. This sometimes requires new points or clearance.
- Requires a fixed network of points around the setup area that do not move.
Surveying with a total station to check settlement / heave has been undertaken for a number of years. The methodology is easily repeatable on each visit, making the results very accurate and reliable.
Having a surveyor visit the site each time means data is only shown after each visit. The surveyor also needs a fixed network of points and a solid base to set the total station up on. Without these, accuracy is lost.
A dumpy level is a device that can be set to a very accurate horizontal plane, allowing precise height measurements to be taken using a measurement staff. When used in conjunction with datum markers around a building, a dumpy level can be a very accurate way of measuring settlement / heave.
To monitor the building, a number of fixed monitoring locations need to be established. To make it easy to take the measurements with the measuring staff, these points will need to be offset from the wall, such as a screw / wall plug or fixed level plate. It is on top of these the staff is placed and then the measurement recorded.
Like a total station, a dumpy level requires a set location that is assumed doesn’t move. It is from this point that all measurements are calculated and referenced back to.
- A dumpy level is very accurate when setup correctly.
- The setup process is relatively simple and results easy to calculate using addition and subtraction.
- Dumpy levels are relatively low cost and simple to use.
- A fixed location is required to set up back to. If this is blocked or requires a number of setups to reference back to, then accuracy can be lost.
- A dumpy level requires a site visit each time you need data. It also needs two people to operate. One on the dumpy level and one on the measuring staff.
- Requires a bit of office work to calculate the height changes.
A dumpy level is a very accurate way of surveying levels around a building. However, it does require some bulky objects / screws protruding from the building and also fixed positions to reference back to that cannot move.
The dumpy level method does require an on site visit and requires 2 people to undertake the task. A dumpy level is relatively low cost when purchasing other monitoring devices.
Tilt Beam Sensors
Tilt beam sensors installed in tandem with others can give you a movement profile over the length of a wall. By comparing precise tilt angles, you can gauge the extent and locations that movement is occurring.
The sensors are installed by either attaching them to a continuous beam along the wall or simple screwed using wall plugs / screws.
- Once installed, the sensors can wirelessly operate and send data back without a site visit.
- Batteries can last a long time (years sometimes) depending on how often you want data.
- Continuous flow of data can be every minute, hour, day etc.
- No direct way of measuring movement distances, as tilt sensors can only measure angles.
- Multiple sensors required and installed in a line to measure location and extent of tilt.
- One end of the sensors must be installed on to something that won’t move.
Tilt beam sensors provide a convenient way of capturing a lot of data without the need to continually visit the site. The biggest disadvantage is that the sensors can only record angular movement, which can sometimes be difficult to interpret in an up / down direction.
Often tilt sensors are installed alongside other movement monitoring techniques and can be used to observe early movement trends due to their precise angular measurements.
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