Direct surface methods for road alignment

Direct surface methods are field studies by the geologist at the ground surface. For a road in rock slopes they are used to find stable alignment and safe cut slopes.

1. Geological (field) mapping at 1:5,000-1:2,000: traverses along the proposed centre line and on both sides; record rock type, weathering grade, soil cover and its thickness.
2. Structural measurements: strike and dip of bedding, foliation and joints by Brunton compass; spacing, persistence, roughness, aperture and infilling are noted. Joint sets are plotted on stereonet to check planar, wedge and toppling failure with respect to the proposed slope direction.
3. Study of natural slopes and existing cuts: performance of old road cuts and natural scarps shows safe angles for each rock type.
4. Mapping of landslides, rock fall, debris flow, gullies and erosion zones; old slide scars and tension cracks on the road line.
5. Hydrogeological observation: springs, seepage zones and wet areas, stream crossings and flood marks.
6. Rock strength estimates: Schmidt hammer, hammer-blow tests and RMR classification of outcrops.
7. Locating construction materials, quarries and spoil areas.

The result is an engineering geological map and a slope-stability zoning of the route, used for choosing the alignment and designing cut slopes (e.g. about 0.25H:1V in hard rock and 1H:1V or flatter in weak rock).