GEOLOGICAL INVESTIGATION FOR HIGHWAY, RAILWAY, BRIDGE AND TUNNEL-(Part 6)

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Detailed geological information needed of the Hilly Areas:

•Detailed geological information is required of the ground where the cutting and filling are to be carried out

• In the hilly or slanting areas, details about the stratification, various geological structural features and weathering and erosion are required

• Designing and excavation works in the rocks especially in the sedimentary rocks and the strata sloping towards the proposed highway, motorway, railway, etc should be very carefully managed

• Cutting in jointed and weathered rocks requires special attention especially with respect to:

• Type, nature and composition of the rocks

• Dip and strike of the strata

• Geological Structural Features

• Marshes, water-logged and water-soaked areas

Important Geological Information related to the Bridges:

• Crossing of a railway and road, two roads of different categories e.g. a small or ordinary road and highway or a highway (a very good quality fast road but inferior to a motorway) and motorway (an obstacle-free very high speed high quality highway), highway and runway (a road-way for aircrafts), etc needs a bridge to cross over

• Similarly, the crossing of the said facilities over a ravine, river, stream or other water channel, highly populated or commercial area or valley at lower elevation also needs a bridge to cross over

• Crossing (in form of a bridge) over a valley or depression without any water flowing through it, is called Viaduct

Scouring and Erosion:These terms are very similar in their meanings. The practical difference between them is Scouring is the removal of soil of the bottom or bed of a river or stream; whereas Erosion is removal of soil of the sides or banks of a river or stream

Higher velocities of the river produces deeper scouring.

• Scouring usually occurs under the obstructed water e.g. under the piers.  •Terzaghi proposed that the scouring depth in a river occurs at least 3 times the rise of water level above the mean water level of the river

Common methods to reduce the scouring: (i) Placing rip-rap (assemblage and a little compaction of broken stones placed in water or on soft or wet ground as a foundation)around the pier’s footing

(ii) Placing the foundation of the piers well below the probable scouring depth

Geological aspects of a bridge: Geological Investigation of the foundations of piers and abutments, back-fill and scouring depth are needed. Foundations of the piers are not always needed to rest on i.e. not always provided on the solid rock. Some bridges have their piers’ foundations supported on the stiff clay but provided below the probable scouring depth



About the author

MuhammadTayyab

Me from Pakistan and im the student of undergraduate;BS Electronics.

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