Geology/Construction Roads and bridge
Dear sir ,
what is the geologist role in Road ,Piling and Bridge construction ?
The geologist possesses knowledge of rocks, soil, and subsurface structure that a civil engineer does not possess.
For instance, a ridge or mountain side might have dipping beds that have very defined bedding planes. Those bedding planes can be lines of weakness in the dipping ridge that can result in failure of the whole hillside. So if a road was built parallel to the dipping bed, the entirety of the road could be subject to failure if the whole side of the ridge were to fail and a landslide occur.
Knowing this, the geologist would recommend that the road cross the ridge perpendicular, and then turn and run parallel to the ridge but in the valley below and away from the hazard area. If the ridge does fail, only a small section of the road would be destroyed, and could easily be rebuilt once the debris is removed. Only a relatively small section would be affected.
Geologists also know where the best substrate material is. They can locate sources of good sorted sand for roadbed material that would not be prone to compaction after the road in laid. They can show the engineers where the best drained soils are in order to avoid areas high in clay that might result in shrinkage and swelling that would result in heaving and failure of the road surface.
Pilings need to be set in bedrock, so the geologist can locate where and at what depth it occurs so pilings can be driven in, or excavations can be made to set the pilings on a dressed surface.
The geologist can also look at the seasonal runoff in rivers and creeks and calculate the maximum flow rate and thereby provide the engineer with data with which he can calculate the minimum strength needed for the pilings to withstand annual flow pressures in the river or creeks over which the bridge needs to be built. This will also give information on the erosional capability of the water flow, to alert the engineer to the possibility of the bridge pilings being undercut or weakened by the water flow.
Erosion of the banks of the river is also important, and can be determined by the geologists knowledge of the flow regime of the river and its likelihood to erode the banks where the bridge is anchored.
For instance, down stream of a dam is a bad place for a bridge. The reason is, water always carries a load. It carries it until is stops at which time the load, the sand gravel and mud drops out of suspension as the water stops moving.
When the water starts moving again, it picks up a new load. So water released from a dam to generate hydroelectric power, has no load, if left it all in the bottom of the reservoir behind the dam. But as soon as it hits the river channel down stream it starts to pick up a new load, and it erodes the river channel causing erosion of the banks and the bottom of the river bed.
Another thing is the shape of the river. You do not want to build a bridge on a curving section of a river, because the curve is due to the river actively eroding the outside of the curve or meander. Building a structure there is asking for the water to undercut one side of the bridge.
Efforts to prevent this usually take the form of rip rap, or large boulders of hard rock placed along the bank, and around the pilings to prevent erosion. They do not always work.