When it comes to land surveying, prisms systems are used to secure control points at a comfortable and accessible height in order to provide pinpoint accuracy. Prisms are mounted on surveying poles and are used with electronic distance measuring instruments, also referred to as EDMs, for improved accuracy.
A land surveying prism is designed to reflect the EDM beam back to its source both at a wide-angle and with high precision. Prisms help to reduce the beam from scattering as it needs to be reflected back in total, which results in a measurement that is more accurate and at a longer range.
Land Surveying Prisms Application
Land surveyors and engineers use survey prisms to measure the change in position of a target that may or may not is moving. For that reason, survey prisms are used in a wide range of monitoring applications.
Rail Monitoring
Rail monitoring is often necessary for approval of any project in the vicinity of a rail track or when creating various rail assets. To be eligible to seek an agreement, a line and level correlation survey must be conducted. This will provide the contractor with essential information about the exact positioning of the running rails, potential tunnel structure, and the proposed development of the project.
The data from the survey should be connected with the existing topographic or a measured building survey. This allows for the potential prediction of the potential impact on any rail infrastructure.
Settlement Monitoring
Settlement monitoring is a process that involves taking exact measurements of fixed monitoring points found on an existing structure or structures. Usually, some baseline measurements are initially taken from a remote benchmark location, which is not subject to movement from other construction. It is repeated periodically in order to document any potential movement.
Surveyors use high-tech equipment to detect both horizontal and vertical settlements from fixed monitoring points. The data gathered will be recorded and included within a comparative certified report. It is also useful to add photographic documentation of the conditions of the exterior and the interior of structures to determine any initial and subsequent measurement changes.
Displacement Monitoring
Land displacement monitoring is capable of detecting any vertical land displacements over a wide area usually in millimeter accuracy. This service is supposed to provide periodical observation and allows you to understand any potential land subsidence and deformation.
Displacement monitoring is required in order to determine the magnitude, the style, and the extent of landslide movements. The data collected from monitoring landslides is crucial in informing emergency risk assessment, which is more than important during periods of adverse weather. When it comes to design projects, information gathered on the direction of movement and erosion rate is very valuable.
Deformation Monitoring
Deformation monitoring is a systematic measurement and tracking of alteration in the shape or the dimensions of an object that comes as a result of stress created by various loads. This type of survey is crucial in logging measured values that could be used for added computation, predictive maintenance, and deformation analysis.
Deformation monitoring is primarily connected to applied surveying, but also has its ties in civil engineering, geology, construction, and mechanical engineering. The measuring devices will depend on the application, the situation, and the chosen method.
Convergence Monitoring
Convergence monitoring is something that can be done during the construction of a tunnel. As the excavated area will deform in time due to the weight of the surrounding, making this type of monitoring is something that is necessary. There are several factors that can affect how a tunnel may deform. Most of the deformation occurs around the excavated areas. This means that the amount that the tunnel converges could pose a safety risk to on-site workers and the overall stability of the project.
Post-construction convergence monitoring is usually done as risk management. It involves detecting structural movements, cracks, and in some cases potential hazards. Early warning detection is the best possible prevention when it comes to risk reduction.
Types of Optical Survey Prisms
There are several types of prisms that are used in correlation with total stations. Depending on the need, situations, and sometimes personal likings, surveyors have a variety of prisms to choose from. The most common ones include:
- Mini Prisms
- 360-Degree Prisms
- Standard Prisms
- Dual Prisms
Surveyors will be able to pick one based on several factors. One of them is whether you need an L-bar prism, a rail clip prism, a road prism, a reference prism, or simply lightweight prisms that can be carried around and stored easily. Other factors of determining which prisms to use are simpler and come depending on the price, accuracy, maximum range, reflectivity, prism diameter, and application.
Performing standard optical survey monitoring is most suitable with an L-bar prism. Railroad tracking monitoring requires a rail clip prism. Roadway monitoring will of course demand using a road prism. Doing any reference back sights, long-distance monitoring, or the monitoring of a moving target is done best with a reference prism. Finally, if you are working on surfaces that should not be penetrated or are very sensitive to impact and other outside factors, a lightweight prism will do the job.
Land Surveying Prisms FAQ
For added analysis, check out these most asked questions.
What is a prism in land surveying?
Survey land prisms are used to measure the changes in a position of a seemingly moving target. They have a wide range use starting with rail monitoring, settlement monitoring, displacement monitoring, deformation monitoring, and all the way to convergence monitoring.
How accurate is a survey prism?
The accuracy of a prism is determined by the physical location of the prims within its canister and holder. Most brands have an accuracy of 1 mm or less.
How does an optical survey prism work?
A survey prism is designed to reflect an EDM beam back to the source at a wide angle of incidence and with high precision. Prisms will reduce the scatter of the beam and reflect it back to the total which will result in more accurate measurements and allow for long-range measurements to be made.
What is a mini prism in surveying?
Mini prisms are usually attached to a prism pole or a static surface with the aim of acting as focal points for a variety of EDMs, accounting for improved accuracy. It is essentially a small optical device used for surveying and geodetic measurements, with its small size helping to provide better positional accuracy.
