Geological Investigation for Canals
• Canal is an excavation along a predetermined route and at a pre-determined grade for water distribution.
• If the material bounding the excavation is relatively impervious, the canal will be unlined.
• Material subject to high seepage rates are traversed by lined canals.
• The lining may consists of compacted earth, concrete, bituminous material, masonry blocks, earth and bentonite mixture or any combination of these.
• For investigation of canal alignment, engineering geological survey are similar to roadways.
• Care should be taken that there should be no detrimental settlement of the canal into the underlying material.
• Side slopes should be stable.
• Bottom and side slopes should be sufficiently impervious with regard to permissible water loss.
• Longitudinal and transverse profiles along the chosen alignment are prepared and depths of cut and height of embankments determined.
• A surface engineering geological map encompassing a strip of about 50 m width along the canal alignment must be prepared.
• The location of outcrops and contacts between rock formation, between soil and rock and between different soil types should be shown.
• The accompanying report should describe the characteristics of the soils and rocks.
• Canals on strong rocks are the most stable even though, cutting through the rock require most work.
• For most canal test holes are placed about 300 m apart along the route center line, depth of which should be at least 4 m below the bottom of canal.
• Additional holes are placed where geological or topographical conditions sharply change and at the locations of major auxiliary concrete structures.
• As canals carry water to places where there is need, the seepage lost should be maintained to minimum.
• Permeability of the foundation material can be roughly estimated by performing pumping tests in drill hole.
• Highly pervious layers can be successfully located by geophysical methods.
• Existing slides should be mapped, and an estimate made of their influence on future canal construction and operation .
• If a canal is located in rock, a careful estimate must be made of the permeability of the rock.
• It is necessary to determine whether or not ground water can or does flow through fissures in the rock.
• If the groundwater flow is restricted owing to the tightness of the openings, drains in a lined canal should be indicated to remove excess ground water as the groundwater can cause frost heave or hydrostatic uplift of the lining.
• If the material bounding the excavation is relatively impervious, the canal will be unlined.
• Material subject to high seepage rates are traversed by lined canals.
• The lining may consists of compacted earth, concrete, bituminous material, masonry blocks, earth and bentonite mixture or any combination of these.
• For investigation of canal alignment, engineering geological survey are similar to roadways.
• Care should be taken that there should be no detrimental settlement of the canal into the underlying material.
• Side slopes should be stable.
• Bottom and side slopes should be sufficiently impervious with regard to permissible water loss.
• Longitudinal and transverse profiles along the chosen alignment are prepared and depths of cut and height of embankments determined.
• A surface engineering geological map encompassing a strip of about 50 m width along the canal alignment must be prepared.
• The location of outcrops and contacts between rock formation, between soil and rock and between different soil types should be shown.
• The accompanying report should describe the characteristics of the soils and rocks.
• Canals on strong rocks are the most stable even though, cutting through the rock require most work.
• For most canal test holes are placed about 300 m apart along the route center line, depth of which should be at least 4 m below the bottom of canal.
• Additional holes are placed where geological or topographical conditions sharply change and at the locations of major auxiliary concrete structures.
• As canals carry water to places where there is need, the seepage lost should be maintained to minimum.
• Permeability of the foundation material can be roughly estimated by performing pumping tests in drill hole.
• Highly pervious layers can be successfully located by geophysical methods.
• Existing slides should be mapped, and an estimate made of their influence on future canal construction and operation .
• If a canal is located in rock, a careful estimate must be made of the permeability of the rock.
• It is necessary to determine whether or not ground water can or does flow through fissures in the rock.
• If the groundwater flow is restricted owing to the tightness of the openings, drains in a lined canal should be indicated to remove excess ground water as the groundwater can cause frost heave or hydrostatic uplift of the lining.