Chain and Tape Surveys Overview

Chain and Tape Surveys

Chain and tape surveys are critical components of land surveying, ensuring accurate measurements and settlement monitoring in infrastructure projects such as highways, bridges, railroads, pipelines, and buildings. This type of survey involves using chains to measure distances between points and tapes to assess horizontal distances. Let's dive deeper into the various aspects of chain and tape surveys.

Uses of Chain and Tape Surveys

Chain and tape surveys play a crucial role in determining the location, distance, and elevation of landmarks, which are essential for various applications, including:

• Construction: These surveys help to establish reference points, lines, and levels during the construction process.
• Land Development: They support planning and design activities by measuring parcel boundaries, site layout, and grading plans.
• Mining Operations: Accurate measurements performed with chain and tape surveys ensure efficient mining operations and safety compliance with regulations.
• Transportation Infrastructure: Surveying techniques involving chains and tapes aid in designing road alignments, bridge foundations, and railway tracks.
• Pipelines: Determining right-of-way corridors, slope stability, and avoiding hazardous areas require precise measurements made possible through these methods.

Chain Testing and Correction

To ensure accuracy, chain survey equipment undergoes rigorous testing procedures and calibration checks. Commonly used methods include:

Flexibility Tests

Chains are tested for flexibility by bending them manually or mechanically and observing if they return to their original shape without permanent deformation.

Interval Checks

Chain intervals are checked against established standards to verify their length and alignment.

Sagging Measurement

The sagging of chains is measured over varying lengths to determine any deviations from the expected linearity.

Corrections may be required based on the results of these tests to maintain precision in the measurement.

Principle of Chain Survey

Chain surveying follows the concept of triangulation, where angles are measured between two known locations by sighting through an instrument called a theodolite. The chain is laid out to each point, recording the distance between each station on the chain to obtain a series of three-dimensional coordinates. Triangulation enables the connection of all points within a project area to create a comprehensive picture of the site.

Terms Used in Chain Survey

Understanding the terminology associated with chain survey helps in better comprehension of the processes involved. Some key terms include:

• Surveyor's Chain: A tool consisting of links connected by pins, used to measure distances.
• Tape: A flexible, often ribbon-like material used to measure distances, usually horizontal.
• Link Length: The distance between adjacent pins on a surveyor's chain.
• Incremental Chain: A chain with variable link lengths enabling more accurate measurements.
• Flexible Tape: A PVC or fiberglass strip attached to a reel with even graduations.
• Interpolation: The estimation of intermediate points based on existing data.

Field Book Types

Field books serve as primary documentation tools for chain and tape survey work. Different formats include:

Graphic Scale Field Books

These field books contain a graphic scale representation of the site, allowing surveyors to record details accurately.

Grid Field Books

Grid field books have numbered squares arranged in rows and columns, helping surveyors to systematically organize and record data.

Alphanumeric Field Books

Alphanumeric field books include a grid format with letters and numbers, providing greater flexibility for recording various types of information.

Conclusion

Chain and tape surveys are integral to land surveying and infrastructure development, offering precise measurements and monitoring capabilities. By understanding the principles, techniques, and terminology associated with these methods, surveyors can effectively execute their tasks, ensuring the success of various construction and engineering projects.