Explain geological factors on alignment and stability of roads.

Road is an important infrastructure, the planning, designing, construction and maintenance of which are the major duties of Civil Engineers.  Geological consideration for the arrangement and stability of road can be explained under the following points:

1. Topography

2. Lithology

3. Geological structures

4. Weathering

5. Groundwater condition

Topography:

1.  A topographic map can be used to reveal the existence of various types of land features like valley, hills, in-flowing or out-flowing streams and their rugged topography, which are entirely responsible for the alignment of the road.

Lithology:

 The following points are to be considered:

1. Consolidated, competent massive rock is favorable and more stable since it requires less maintenance but it is costly and difficult to blast.

2. Unconsolida....

Road is an important infrastructure, the planning, designing, construction and maintenance of which are the major duties of Civil Engineers.  Geological consideration for the arrangement and stability of road can be explained under the following points:

1. Topography

2. Lithology

3. Geological structures

4. Weathering

5. Groundwater condition

Topography:

1.  A topographic map can be used to reveal the existence of various types of land features like valley, hills, in-flowing or out-flowing streams and their rugged topography, which are entirely responsible for the alignment of the road.

Lithology:

 The following points are to be considered:

1. Consolidated, competent massive rock is favorable and more stable since it requires less maintenance but it is costly and difficult to blast.

2. Unconsolidated incompetent rock is unfavorable and many complicated problem can arise in construction, but it is easy in blasting.

Geological Structures:

 If some plane of weakness like bedding plane, foliation plane, joint, shear zone are present in a rock in such a way that these planes are inclined towards the free side of the valley, then the rock has very high chance to fall along these planes. 

Joints:

It influences the stability of the cuts in the same way as the bedding planes. 

1. when joints are present in the large number, joints reduce even the hardest rock to a mass of loosely packed up blocks on the side of a cuts which could fall down. 

2. Even if the joints are few but are continuous and inclined toward the free side of cut, then there is a risk of slop during the presence of moisture. Jointed rocks are supported by the different retaining structures in the major road construction programme.

Faults:

1. Faults are the worst type of planes of potential failure and quite unfavourable.

2. Faults should not be left untreated in any case.

 Weathering :

1. Weathering can result on  undermining, rocks or debris fall etc  and hence is unfavourable.

2.  Better design is required when cuts pass through weathered zone of the rock.

Ground Water Condition:

 It is very necessary to find out the position of the ground water table of the site. Following points should be considered:

1. Ground water makes soil/rocks weak and unstable

2. Presence of aquifers,GWT at shallow depth makes the site hazardous.

3. Special consideration (drainage,lowering of GWT, etc.) are to be taken before construction of roads in such regions.