Introduction of Chain Surveying:
- In the realm of land surveying, chain surveying stands as one of the oldest and most reliable methods for obtaining accurate measurements.
- This traditional technique has been employed for centuries to map out boundaries, establish topographic features, and create detailed plans for engineering and construction projects.
Understanding Chain Surveying:
- Chain surveying is a basic technique used to measure distances and create accurate maps or plans of land areas.
- It involves the use of a measuring chain, also known as a surveyor’s chain, which consists of a series of connected links, typically made of metal, with standardized lengths.
- By carefully measuring distances between points on the ground using the chain, surveyors can accurately determine the relative positions and dimensions of various features.
Chain In Surveying:
- In surveying, a chain refers to a measuring instrument used to determine distances on the ground. The chain used in surveying is commonly known as a surveyor’s chain or Gunter’s chain. It consists of a series of interconnected links, typically made of metal, with a standardized length.
- The most widely used chain in surveying is Gunter’s chain, which consists of 100 links. Each link is approximately 20.1168 meters (66 feet) in length. The chain is made of durable material, such as steel, and is marked at regular intervals to facilitate accurate measurements.
- The chain is designed to be used in a linear fashion, with one end held at the starting point and the other end extended along the survey line. The surveyor moves along the line, keeping the chain taut and aligned with the measuring line. The distance between two points is determined by counting the number of full chain lengths (100 links) and any remaining links.
- To enhance accuracy, the chain is equipped with handles or rings at each end for surveyors to hold securely. It is crucial to ensure that the chain is properly stretched and aligned during measurements to minimize errors. Surveyors must also account for any sag or variation in the chain’s length due to environmental factors like temperature and tension.
- The chain is particularly useful in situations where precise measurements are required but high-tech equipment like total stations or GPS receivers may not be available or feasible. It provides a straightforward and reliable method for measuring distances in a variety of surveying applications, including land surveys, boundary determinations, and topographic mapping.
- In modern surveying practices, the chain has been largely replaced by electronic distance measuring devices (EDMs) and Global Navigation Satellite Systems (GNSS). However, the chain remains an essential tool in situations where traditional surveying methods are still employed or as a backup option in case of equipment failure.
Terminologies In Chain Surveying:
In chain surveying, there are several terminologies and terms that are commonly used. Here are some key terminologies in chain surveying:
- Chain: The chain refers to the measuring instrument used in chain surveying. It consists of a series of interconnected links, typically made of metal, with a standardized length. The most common chain used in surveying is Gunter’s chain, which consists of 100 links and has a length of 20.1168 meters (66 feet).
- Link: A link is a single unit of measurement in a chain. In Gunter’s chain, there are 100 links, and each link is equal to 0.201168 meters (0.66 feet). Links are marked at regular intervals along the chain to facilitate measurements.
- Offset: An offset is a perpendicular measurement from the main survey line to a point of interest. It is used to determine the position of objects or features that are not directly on the survey line. The offset is measured using a cross-staff or other measuring instruments and is recorded to accurately plot the positions on the map.
- Station: A station refers to a marked point along the survey line. It is a reference point from which measurements are taken. Stations are typically marked using ranging rods or other temporary markers and serve as the basis for subsequent measurements and calculations.
- Chainage: Chainage, also known as chaining or chaining distance, refers to the distance measured along the survey line using the chain. It is the cumulative length of the chain measured from the starting point or the reference station.
- Traverse: A traverse is a series of connected survey lines that form a closed loop or polygon. It is used to determine the boundary or shape of an area. The traverse includes a sequence of stations, and measurements are taken between successive stations to determine the lengths and directions of the survey lines.
- Bearing: Bearing refers to the horizontal direction of a survey line with respect to a reference point or meridian. Bearings are usually measured in degrees, minutes, and seconds clockwise from the north or south direction.
- Compass Rule: The compass rule is a method used to determine the interior angles of a traverse. It states that the algebraic sum of the interior angles of a closed traverse is equal to (2n – 4) right angles, where n is the number of sides of the traverse.
- Reducing the Bearings: Reducing the bearings refers to converting the observed bearings, which are measured relative to the magnetic north, to the true bearings, which are measured relative to the true north. This correction is necessary due to magnetic declination.
- Closing Error: Closing error, also known as misclosure, is the discrepancy between the measured distance or angles of a closed traverse and the calculated values based on the geometric relationship of the traverse. It indicates the accuracy of the survey and can be used to adjust the measurements.
- Main Survey Stations: Main survey stations, also known as primary control points, are fixed points established at key locations within the survey area. These stations serve as reference points for the survey and are typically marked with permanent markers such as concrete monuments or brass disks. Main survey stations are used as starting points for measuring distances and angles.
- Main Survey Lines: Main survey lines are the primary lines along which measurements are taken in a survey. They connect the main survey stations and form the framework of the survey. Main survey lines are typically established based on the project requirements and the topography of the area being surveyed.
- Check Lines: Check lines are additional lines that are measured to verify the accuracy of the survey. They are independent of the main survey lines and are usually positioned in a way that allows for cross-checking and validation of the measurements. Check lines provide an additional layer of quality control and help identify any errors or discrepancies in the survey data.
- Offsets: In chain surveying, offsets are measurements taken perpendicular to the main survey line. They are used to determine the position of features or objects that are located away from the main line. Offsets are typically measured using a cross-staff or other measuring instruments and are recorded to accurately plot the positions on the map.
- Tie Lines: Tie lines, also known as tie measurements, are additional measurements taken to connect the main survey lines or to link features of interest. They help to tie different portions of the survey together and ensure continuity and accuracy in the survey data. Tie lines can be used to cross-check measurements and provide additional reference points for plotting.
- Base Line: The baseline is a long, straight survey line established within the survey area. It serves as the reference line from which other measurements and calculations are made. The base line is typically measured with great precision using specialized equipment and techniques. It provides the foundation for trigonometric calculations and the determination of angles and distances in the survey.
Understanding these terminologies is crucial for effectively conducting and interpreting chain surveys. They form the vocabulary and framework for accurately measuring distances, angles, and positions in the field, ensuring reliable and precise survey data.
Equipment Used in Chain Surveying:
a. Surveyor’s Chain: The surveyor’s chain is the primary instrument used in chain surveying. It typically consists of 100 links, with each link measuring 20.1168 meters (66 feet) in length. The chain is made of steel and is marked at regular intervals, usually every 10 links or 20 meters (66 feet), for easier measurement.
b. Ranging Rods: Ranging rods, also known as ranging poles, are used to establish temporary reference points during the survey. These rods are typically made of wood or metal and are painted in bright colors for easy visibility. They are placed vertically in the ground to mark key points for measurement and to aid in maintaining straight lines.
c. Cross Staff: Cross-staff is a simple instrument used to measure right angles and facilitate perpendicular offsets during the survey. It consists of two perpendicular arms attached to a central pivot point. By sighting along the arms and aligning them with reference points, surveyors can measure and mark right angles accurately.
Procedure for Chain Surveying:
a. Reconnaissance: Before beginning the actual survey, a preliminary examination of the area, known as reconnaissance, is conducted. This involves studying existing maps, understanding the topography, and identifying the key points for measurement.
b. Station Marking: The survey starts by establishing the primary reference points or stations within the survey area. These stations are marked with ranging rods and serve as the basis for subsequent measurements.
c. Chain Measurement: Using the surveyor’s chain, the surveyor carefully measures the distances between the stations and other key points of interest. The chain is laid on the ground, with each end held firmly by the surveyors. The chain is then stretched taut and aligned with the measuring line, and the measurement is recorded.
d. Offsets: Offsets are used to measure distances perpendicular to the primary line. The surveyor uses the cross-staff to measure right angles from the main line to the features of interest. These offsets are recorded and used to plot the accurate positions of these features on the map.
e. Chaining Continuity: Chaining continuity refers to ensuring that the chain measurements are accurate and consistent. This is achieved by cross-checking the measurements and ensuring that the chain is free from kinks or deformities.
f. Plotting: After completing the fieldwork, the measurements are transferred to a drawing or mapping sheet. The surveyor carefully plots the stations, measured distances, and offsets to create an accurate representation of the surveyed area.
Applications of Chain Surveying:
a. Topographic Mapping: Chain surveying is widely used in creating topographic maps that accurately represent the elevation, contours, and features of a land area. These maps are essential for urban planning, infrastructure development, and environmental assessments.
b. Boundary Surveys: Chain surveying is employed to establish and demarcate property boundaries. By accurately measuring distances and angles, surveyors can determine the exact boundaries between properties, resolve disputes, and facilitate land transactions.
c. Engineering Projects: Chain surveying plays a vital role in engineering projects, such as road construction, pipeline installation, and building layout. It provides the necessary data to design and plan these projects accurately.
Advantages And Disadvantages of Chain in Survey:
Advantages of Using a Chain in Surveying:
- Cost-effective: Chains are relatively inexpensive compared to modern surveying equipment such as electronic distance measuring devices (EDMs) or Global Navigation Satellite Systems (GNSS). They offer a cost-effective solution for conducting basic distance measurements in surveying projects.
- Simple and Reliable: Chains have a straightforward design and operation, making them easy to understand and use. They provide a reliable method for measuring distances, especially in areas with limited access or challenging terrain where other advanced equipment may not be suitable.
- No Electronic Dependency: Unlike modern surveying instruments that rely on electronic components and signals, chains do not require batteries, power sources, or complex calibration. This eliminates the risk of electronic failures or signal interference, ensuring the survey can be conducted independently of external factors.
- Robustness: Chains are typically made of durable materials such as steel, which makes them resistant to wear, tear, and adverse environmental conditions. They can withstand rough handling and can be used in various field conditions, making them suitable for rugged terrains and challenging surveying environments.
- Versatility: Chains can be used in different types of surveys, including land surveys, boundary determinations, and topographic mapping. They are suitable for measuring straight distances, angles, and offsets, making them versatile tools in a surveyor’s toolkit.
Disadvantages of Using a Chain in Surveying:
- Limited Accuracy: Chains have limitations when it comes to achieving high levels of precision. The accuracy of measurements using a chain can be affected by factors such as sagging of the chain, errors in alignment, and difficulty in reading the markings. This makes them less suitable for surveys that require extremely precise measurements.
- Cumbersome and Time-consuming: Measuring distances using a chain can be time-consuming, especially over long distances or in complex terrains. The process of laying out the chain, ensuring it is properly aligned, and recording measurements can be tedious and may slow down the surveying process.
- Limited Range: Chains have a limited measuring range, typically up to a few hundred meters or yards. For larger-scale surveys or projects that require measuring longer distances, chains may not be practical and other methods such as EDM or GNSS should be considered.
- Manual Errors: Chain surveying relies on manual measurements, which can introduce human errors. Miscounts, misalignments, or misinterpretations of measurements can result in inaccuracies in the final survey data. Careful attention to detail and strict adherence to surveying procedures are required to minimize such errors.
- Lack of Advanced Features: Chains lack advanced features such as automatic data recording, integration with digital mapping systems, or real-time data processing, which are available in modern surveying instruments. These features can significantly enhance the efficiency and accuracy of surveying operations.
In conclusion, chain surveying remains an important method in the field of surveying, providing accurate measurements that form the foundation of land planning, boundary determination, and engineering projects. Its simplicity, reliability, and versatility make it a valuable technique, even in the modern era of advanced surveying technology. By understanding the principles, equipment, procedures, and applications of chain surveying, professionals in the field can confidently utilize this method to obtain precise measurements and contribute to the successful execution of various projects.