Geological Investigation for Road Alignment
• Engineering geologist suggest the most favourable location line for the road after a preliminary engineering geological investigation.
• Further detailed study is carried out in the alignment thus fixed and necessary amendments are made
• As highways are linear structures, they often traverse a wide variety of ground conditions along their length.
• In addition, the construction of a highway requires the excavation of soils and rocks, and stable foundations for the highway, as well as construction materials
• Topography or landform of a region is single most important factor that controls the selection of alignment of a road project
• The ground beneath roads and, more particularly, embankments, must have sufficient bearing capacity to prevent foundation failure and also be capable of preventing excess settlements due to the imposed load
• Strong rocks can stand even with vertical slopes and when they are free from extensive joints and fractures and are inclined favourably then they are considered most suitable for road construction
• But construction in these rocks require extensive blasting
• On the other hand unconsolidated earth materials like soil, and fractured rocks need detailed investigation about their origin, texture, porosity, permeability, compaction and consolidation characteristics
• Building roads in the river terraces will be much economical than blasting through rocks but they may cause problems in the stability in some cases.
• The attitude of beds, joints and fractures are important in the road cut
• If cut is parallel to the dip direction, layers offer a uniform behaviour on either side
• If cut is parallel to strike, one side will have rock inclined towards the cut and another away from the cut, the latter one is considered stable
• Joint spacing, orientation, roughness, separation have a direct role in the strength of the rock mass and determine the vulnerability of rock mass
• In highway projects, jointed rocks are stabilized by artificial supports like breast wall, retaining walls and bolts.
• Fault zone is zone of crushing and shearing and adjacent rocks are generally fractured
• Weathered rocks have low strength which in many cases should be treated like soil.
• Landslide hazard zonation map should be consulted during the fixing of alignment
• Rock outcrops, soil area, major scarps, faults, fold, crushed and sheared zones, alluvial terraces, fans, debris, landslides should be marked in the detailed engineering geological map
• The map should also include hydrological data like streams and rivers
• Sites for bridges, culverts, causeway, crossings should also be marked and investigated.
• Further detailed study is carried out in the alignment thus fixed and necessary amendments are made
• As highways are linear structures, they often traverse a wide variety of ground conditions along their length.
• In addition, the construction of a highway requires the excavation of soils and rocks, and stable foundations for the highway, as well as construction materials
• Topography or landform of a region is single most important factor that controls the selection of alignment of a road project
• The ground beneath roads and, more particularly, embankments, must have sufficient bearing capacity to prevent foundation failure and also be capable of preventing excess settlements due to the imposed load
• Strong rocks can stand even with vertical slopes and when they are free from extensive joints and fractures and are inclined favourably then they are considered most suitable for road construction
• But construction in these rocks require extensive blasting
• On the other hand unconsolidated earth materials like soil, and fractured rocks need detailed investigation about their origin, texture, porosity, permeability, compaction and consolidation characteristics
• Building roads in the river terraces will be much economical than blasting through rocks but they may cause problems in the stability in some cases.
• The attitude of beds, joints and fractures are important in the road cut
• If cut is parallel to the dip direction, layers offer a uniform behaviour on either side
• If cut is parallel to strike, one side will have rock inclined towards the cut and another away from the cut, the latter one is considered stable
• Joint spacing, orientation, roughness, separation have a direct role in the strength of the rock mass and determine the vulnerability of rock mass
• In highway projects, jointed rocks are stabilized by artificial supports like breast wall, retaining walls and bolts.
• Fault zone is zone of crushing and shearing and adjacent rocks are generally fractured
• Weathered rocks have low strength which in many cases should be treated like soil.
• Landslide hazard zonation map should be consulted during the fixing of alignment
• Rock outcrops, soil area, major scarps, faults, fold, crushed and sheared zones, alluvial terraces, fans, debris, landslides should be marked in the detailed engineering geological map
• The map should also include hydrological data like streams and rivers
• Sites for bridges, culverts, causeway, crossings should also be marked and investigated.