Engineering Surveying

Engineering Surveying

Surveying

Surveying is the technique of determining the relative position of different features on, above or beneath the surface of the earth by means of direct or indirect measurements and finally representing them on a sheet of paper known as plan or map.

Leveling

          Leveling is a branch of surveying, the object of which is to. Find the elevation of a given point with respect to the given or assumed datum. Establish a point at a given elevation with respect to the given or assumed datum.

Object of surveying

1.      The aim of surveying is to prepare a map to show the relative positions of the objects of the surface of the earth.

2.      The map is drawn to some suitable scale. It shows the natural features of a country, such as towns, roads, railways ets.

3.      Maps may also include details of different engineering works, such as roads, railways, irrigation canals, etc.

Uses of Surveying

(i)                 Plans prepared to record property lines of private, public and government lands help in     avoiding unnecessary controversies.

(ii)               Maps prepared for marking boundaries of countries, states, districts etc., avoid disputes.

(iii)             Locality plans help in identifying location of houses and offices in the area.

(iv)             Road maps help travellers and tourist.

(v)               Topographic maps showing natural features like rivers, streams, hills, forests help in planning Irrigation projects and flood control measures.

(vi)             For planning and estimating project works like roads, bridges, railways, airports, water supply and waste water disposal surveying is required.

(vii)           Marine and hydrographic survey helps in planning navigation routes and harbours.

(viii)         Military survey is required for strategic planning.

(ix)             Mine surveys are required for exploring minearl wealth.

(x)               Geological surveys are necessary for determining different strata in the earth crust so that proper location is found for reservoirs.

Classification of surveying

1.      Plane surveying

2.      Geodetic surveying

Plane surveying

            Ordinary field and topographical surveying in which the curvature of the earth is disregarded — compare geodetic surveying. Plane surveying is done on an area of less than 250 km­². Plane surveying is conducted by state agencies like the irrigation department, Railway Department, etc.

Geodetic surveying

            Geodetic surveying is a specific type of surveying that takes the curvature of the Earth into account. These surveys cover large areas of land and provide high levels of accuracy. Geodetic surveying is conducted by the survey of Pakistan department, and is carried out over an area exceeding 250 km­².

AUTOMATIC LEVELS

                                           LEVELS AND TRANSIT-LEVELS

ELECTRONIC LEVELS

TOTAL STATIONS

THEODOLITES

SURVEYING EQUIPMENT ADAPTERS

TRIBRACHS

SURVEYING TRIPODS

SURVEYING RODS

SURVEYING POLES

 PRISMS

FIELD BOOKS

COMPASSES & CLINOMETERS

PLUMB BOBS

                             

               

Bearings

It is an angle made by the survey line with reference to some fixed meridian.

Bearings are classified into three types:

1.      True bearing

2.      Magnetic bearing

3.      Arbitrary Bearing

True bearing

The angle made by a survey line with reference to the meridian is known as true bearing. It always remains constant.

Magnetic bearing

The angle made by a survey line with respect to magnetic meridian is known as magnetic bearing. It changes from place to place.

Arbitrary Bearing

The angle made by the survey line with reference to arbitrary meridian is known as Arbitrary Bearing.

Designation of Bearings

1.  Whole circle bearing

The whole circle bearing (W.C.B) of a line is the horizontal angle measured clockwise from the North limb of the meridian.

2.  Reduced Bearing (RB) or quadrantal bearing (QB)

The quadrantal bearing (Q.B.) also known as reduced bearing (RB) of a line is defined by the acute angle which the line makes with the meridian. Thus, it depends on the quadrant in which the line presents

3.  Fore Bearing (FB) or forward bearing (FB)

The bearing of a line measured in the forwrard direction (i.e., along the progress of survey) is known as fore bearing.  Fore bearing = Back bearing ± 180°

4.  Back bearing or Backward bearing (BB)

The bearing of a line measured in the backward direction (i.e., opposite to the direction of progress of survey) is known as back bearing. Back Bearing = Fore Bearing ± 180°

Traverse

          Traverse is a method in the field of surveying to establish control networks. It is also used in geodesy. Traverse networks involve placing survey stations along a line or path of travel, and then using the previously surveyed points as a base for observing the next point.

Types of Traversing

Traversing can be further divided into two categories depending upon the type of instrument used,

• Open Traversing
• Closed Traversing

A closed traverse is one enclosing a defined area and having a common point for its beginning to end (For Example a close property boundary). An open traverse is one which does not close on the point of the beginning (For example: the line center survey of a highway, railroad, etc).