Short Answer:
A benchmark in leveling is a fixed reference point with a known elevation, used for surveying and construction. It helps in determining height differences between different locations. Benchmarks are usually marked on permanent structures like buildings, bridges, or specially built concrete pillars. They ensure accurate leveling measurements in civil engineering projects. Surveyors use benchmarks as starting points to transfer elevation data to other points, helping in road construction, land surveys, and drainage systems.
Detailed Explanation:
In leveling, a benchmark (BM) is an essential reference point used to measure elevations. It provides a fixed, known height above a standard reference, usually mean sea level (MSL). Benchmarks are used in surveying to ensure all elevation measurements are consistent and accurate.
Types of Benchmarks in Leveling:
- GTS Benchmark (Great Trigonometrical Survey Benchmark):
- Established by government agencies like the Survey of India.
- Found on permanent structures such as bridges or rocks.
- Provides high-accuracy elevation data for large-scale projects.
- Permanent Benchmark:
- Fixed points created by public works departments or municipal authorities.
- Found on buildings, roads, or concrete pillars for long-term use.
- Arbitrary Benchmark:
- A temporary benchmark chosen by surveyors for local projects.
- Not based on official data but used when no official benchmark is nearby.
- Temporary Benchmark:
- Created for short-term use in a specific construction site.
- Used when permanent benchmarks are too far from the project area.
Importance of Benchmarks in Leveling:
- Ensures Accuracy: Provides a reliable starting point for elevation measurements.
- Prevents Errors: Helps avoid mistakes in height calculations during construction.
- Saves Time: Eliminates the need to determine elevations from scratch every time.
- Supports Infrastructure Development: Used in road building, bridge construction, and land surveys.
Conclusion:
A benchmark in leveling is a fixed point with a known elevation, ensuring accurate height measurements in civil engineering. Different types of benchmarks serve various purposes, helping surveyors maintain accuracy in construction projects.