Application Of Geological Investigations: Roads And Highways

ROADS AND HIGHWAYS

Their planning, designing, construction and maintenance are among the major duties of civil engineers the world over.

geological investigations play important role in the design, stability and economical construction and maintenance of the roads.

Such investigations are aimed at providing full details regarding topography of the area, lithological characters of the rocks or soil and the ground water conditions.

Topography

Topography or the landform of a region is single most important factor that controls the selection of alignment of a road project.

Topographic maps would reveal the existence of various land features like valleys and the inflowing streams, the hills and their undulations, the plateaus and the plains with all their varying configuration from place to place.

Obviously, knowledge of all such features is not only important but very essential for a right alignment.

Preliminary surveys, including aerial surveys followed by detailed surveys are often necessary to obtain desired topographical

Lithological Character

Broadly speaking, ground may be divided into two types: consolidated, massive hard rock type and soft, unconsolidated type.

The Massive groups of rocks include all varieties of igneous, sedimentary and metamorphic rocks which can stand even with vertical slopes.

For making roads through them, however, these rocks require extensive blasting operations.

They cannot be simply cut out or dug out, Once cut, especially if they are free from joints and fractures and un favorably inclined bedding planes, these rocks stand erect for year without much maintenance.

The Unconsolidated group presents the engineer many complicated problems. Thorough soil investigations regarding their mode of origin, texture, structures, porosity, permeability, degree of compaction, consolidation characteristics or compressibility, etc all are requited to be known within broad limits to design safe.

and stable roads over them.

Residual soils are generally homogeneous and properties evaluated from selective bore hole samples might prove sufficient.

Geological Structures

The structural features of rocks, especially in those of sedimentary and metamorphic origin, have very important bearing upon the design of cuts as well as on the stability of the road as a whole.

A given rock might be quite hard and otherwise sound for a cut as road foundation.

But, if in the same rock some planes of weakness (such as bedding planes, joints, foliation, cleavage) are present in such a way that these are inclined towards the free side of the valley, the rock could likely fail along these planes.

Such structural features include dip and strike, joints, fault planes and shear zones.

Dip and Strike.

There may be three possibilities for making a cut in the inclined beds: it can be made parallel, at right angles or inclined to the dip direction.

The relative merits of the cut vis-a-vis its stability would be as follows assuming other things are favourable:

Cut is parallel to the dip direction: In such a case, the layers offer a uniform behaviour on either side of the cut and as such the risk of failure is minimal on this account.

Cut is made parallel to the strike, that is, at right angles to the dip direction. In some cases where the layers dip into the hill rather than

in the road, the cut is considered quite stable