How to Choose a Ground Anchor
Ground anchors (also called tiebacks or earth/soil/rock anchors) are a key element in maintaining the safety and integrity of structures that may collapse or fail. The proper installation and monitoring of ground anchors can be vital in maintenance optimization and even in avoiding accidents in tunnels, retaining walls, embankments and similar structures where large loads need to be transferred to the ground.
At the same time, it is important to choose a ground anchor that is best suited to the requirements of a project, since there are several options. On top of these options, it is also important to design anchor heads to enable future controls and to define the procedure that will have to be followed for checking the remaining load of the anchor. This blog briefly describes each one and, critically for project developers, reviews the return on investment for different ground anchor control methods based on their intended use.
For the purposes of this analysis, the key issue for project managers is what level of ground anchor monitoring will be required, since the systems and frequencies involved can have a significant impact on cost. In our e-book on Load Monitoring for Ground Anchorages, we describe three main options for monitoring ground anchors, depending on the design of the anchor:
- A lift-off procedure with grip on anchor tails.
- A lift-off procedure with grip on a threaded anchor plate.
- A load cell procedure.
Methods for checking ground anchor loads
The two lift-off procedures have similar return-on-investment profiles in terms of ongoing monitoring, since they both require site visits, special equipment and a manual intervention on the part of a technician. However, the load cell option offers two potentially cost-saving advantages. One is that load cells can be read directly by a technician, without requiring special stressing equipment to make a reading.
And the second is that the load cells can be integrated into a wireless monitoring system so readings can be taken remotely, in near-real time, at whatever interval is required by the project. There is one further monitoring option, which is not to monitor the ground anchors at all. For obvious reasons, this is only recommended in situations where lack of monitoring has negligible risk, for instance because the structure in question does not pose a safety hazard.
Our e-book on Load Monitoring for Ground Anchorages includes a cost analysis of five load control options for an example of a wall with 100 ground anchors:
- Doing nothing.
- Carrying out an annual load control of 10 anchors using a lift-off procedure, over three years.
- Carrying out an annual load control of 10 anchors using a manual load-cell reading procedure, over three years.
- Carrying out a quarterly load control of 10 anchors using a manual load-cell reading procedure, over three years.
- Carrying out hourly readings of 10 anchors using load cells connected to a wireless monitoring system, over three years.
In terms of total cost, option A was unsurprisingly the best, followed by C then B then E and D. But on a per-reading basis, E was 2,175 times more cost-effective than the next-best option. Thus, it is clear that in situations where having access to regular load control data is crucial, the integration of load cells with a wireless monitoring system is your best option.
- For further information on smart ground anchors, read our e-book on Load Monitoring for Ground Anchorages.