Roads and RailwaysGeological Considerations

Prepared By – Ghanshyam Prajapati

Geological Considerations• Roads and Railways are very important projects for

any countries and an index of its development.• Such investigations are aimed at providing full

details regarding:

• Topography of the area• Lithological characters of rocks• Structural features of rocks• Ground water conditions

Topography of the area• Topography is a field of geoscience and 

planetary science comprising the study of surface shape and features of the Earth.

• It is a map that shows and elevation field, meaning how high and low the ground is in relation to sea level.

• A topographic map, also known as a contour map, is a map that shows the shape of the land using contour line.

• It is an important factor that controls the selection of alignment of a roads or highway project.

Objectives• An objective of topography is to determine the position

of any feature or more generally any point in terms of both a horizontal coordinate system such as latitude, longitude, and altitude. Identifying (naming) features, and recognizing typical landform patterns are also part of the field.

• A topographic study may be made for a variety of reasons: military planning and geological exploration have been primary motivators to start survey programs, but detailed information about terrain and surface features is essential for the planning and construction of any major civil engineering, public works, or reclamation projects.

Techniques of topography

Direct survey• Surveying helps determine accurately the

terrestrial or three-dimensional space position of points and the distances and angles between them using leveling instruments such as theodolites, dumpy levels and clinometers.

Remote sensing

• Remote sensing is a general term for geodata collection at a distance from the subject area.

• Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to in situ observation.

Aerial and satellite imagery

aerial and satellite imagery can be used to identify and delineate terrain features and more general land-cover features

Photogrammetry

• photogrammetry is a measurement technique for which the co-ordinates of the points in 3D of an object are determined by the measurements made in two photographic images(or more) taken starting from different positions, usually from different passes of an aerial photography flight.

Radar and sonar

• Satellite radar mapping is one of the major techniques of generating Digital Elevation Models (see below). Similar techniques are applied in bathymetric surveys using sonar to determine the terrain of the ocean floor.

Lithological characters of rocks

• Geological surveys should provide all possible details regarding the composition ,texture , structure and origin of rocks.

• The ground may be divided into two parts-

• Consolidated rocks• Unconsolidated rocks

Consolidated Rocks• The consolidated rocks consist of igneous,

sedimentary, and metamorphic rock.• Igneous rock is formed through the cooling and

solidification of magma or lava.

Granite

• Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water.

• Examples:-• Sandstones Quartzite

• Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (1500 bars).

• Examples:-• Gneisses, Schits

Unconsolidated Rocks• In stratigraphy, bedrock is consolidated rock

 underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil.

Structural features of rocks

• The important structural features of rocks are given below

1. Dip and Strike2. Joints3. Faults

Dip And Strike• Strike and dip refer to the orientation or attitude

 of a geologic feature. The strike line of a bed, fault, or other planar feature, is a line representing the intersection of that feature with a horizontal plane.

• The dip gives the steepest angle of descent of a tilted bed or feature relative to a horizontal plane.

Cut is made parallel to dip of beds• When the cut is made in the direction of dip of

beds, the cut slope will have horizontal beds , and it will be the same on either side.

• Hence in such case , there is a little dangers of slippage.

• This condition is quite safe and preferable.

Cut is made parallel to strike of beds

• When a cut is made to the strike of beds , many complications do arise , firstly the strata plunge steeply across the cutting and secondly the slope of cutting is un equal on sides.

• In some cases where layers dip into the hills rather than in the road, the cut is considered quite stable.

Joints• Joints influence the stability of the road cut in the

same manner as the bedding planes.• Moreover, even the hardest rock becomes weak

by the presence of enormous joints in its body.• If the major sets of joints are prominently inclined

towards the free side of the cut , the danger of slippage of the blocks is always imminent.

Ground water condition• Groundwater is the water located beneath the

earth's surface in soil pore spaces and in the fractures of rock formations.

• A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. 

• The ground water in many cases can reduce the bearing capacity of the foundation soil.

• Swelling of the clayey soils under the influence of the capillary ground water causes still worst troubles, resulting in the formation of unevenness in the road surface.

• The ground water conditions of the area will also need to be investigated along the proposed alignment of the roadway and railway.

• This include determining the position of ground water table as well as water bearing properties of the various rocks occuring along proposed route

Thank You