Purpose of Temporary Benchmark

A temporary benchmark (TBM)/ Benchmark Surveying is a fixed point with a known elevation used for level control during surveys works and construction like excavation level, Back filling, screed top level, etc.

Purpose of Temporary Benchmark in Surveying | Benchmark Surveying

Benchmark Surveying

Nails in road seals, or marks on kerb & channel are commonly used as temporary benchmarks. Someone referred to as 'TBM' or 'SFL'. 'SFL' can be equal to plinth beam or DPC top level.

Temporary Benchmark (TBM)

The term benchmark, or bench mark, originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle-iron might be placed to make a "bench" for a leveling rod, thus ensuring that a leveling rod might be accurately repositioned within the same place within the future. These marks were usually indicated with a chiseled arrow below the horizontal line.

The term is usually applied to any item wont to mark some extent as an elevation reference. Frequently, bronze or aluminum disks are set in stone or concrete, or on rods driven deeply into the world to supply a stable elevation point. If an elevation is marked on a map, but there's no physical mark on the bottom , it'sa spot height.

The height of a benchmark is calculated relative to the heights of nearby benchmarks during a network extending from a fundamental benchmark. A fundamental benchmark may be a point with a precisely known relationship to the vertical datum of the world , typically mean water level . The position and height of every benchmark is shown on large-scale maps.

The terms "height" and "elevation" are often used interchangeably, but in many jurisdictions they need specific meanings; "height" commonly refers to an area or relative difference within the vertical (such because the height of a building), whereas "elevation" refers to the difference from a nominated reference surface (such as sea-level, or a mathematical/geodetic model that approximates the ocean level referred to as the geoid). Elevation could also be specified as normal height (above a reference ellipsoid), orthormetric height, or dynamic height which have slightly different definitions.

benchmark surveying

Type of Benchmark Surveying?

It is a relatively permanent point of reference whose elevation for some assumed datum is known. It is a starting and ending point in leveling. The following four types of bench-marks are commonly used.

1. GTS Benchmark in Surveying
2. Permanent Benchmark in Surveying
3. Arbitrary Benchmark in Surveying
4. TBM in Surveying (Temporary Bench Mark)

Permanent Survey Mark (PSM)

A Permanent Survey Mark (PSM) is a major reference mark placed by surveyors to assist them in repegging land parcels and extending new surveys. they are also used for project such as road construction, map production and mining development, etc.

PSMs are typically blocks of concrete approximately 200mm square and 300mm deep. They have a brass plaque or metal rod at the centre. Most are placed below ground level and aren't visible unless they have been marked with either a metal cover (usually in metropolitan areas) or a witness post and indicator plate (usually in areas being developed).