Hill Roads Challenges and Control Techniques
Hill roads are the terms used to refer to the roads built in a country’s mountainous areas. India has a sizable amount of hilly regions; among the 28 states and 8 union territories, 9 states and 9 additional states have sizable hill areas, with the majority of these states being in hilly regions in the north and North East.
A fifth of the nation’s total land and nearly 3000 km of India’s international boundaries are entirely occupied by the Himalayan region. Some hilly regions have breathtaking natural scenery that draws tens of thousands of visitors from both domestic and foreign countries.
Because of their proximity to international borders and defense facilities, roadways in mountainous terrain are strategically important. The Indian road network crosses a variety of terrains, including hills and mountains.
On the other hand, hilly regions, including their road networks, are regularly impacted by flash floods caused by high intensity rainfall, cloud burst, and snow avalanche, resulting in the closure of many portions of road network. Furthermore, we hear about landslides and slope failures from various regions of the nation every year, which cost us countless human lives and enormous monetary damages due to the destruction of infrastructure and communities.
Design
We know that roads travelling over terrain with a cross slope of 25% to 60% are termed mountainous roads, while roads with a cross slope more than 60% are called steep roads. In other words, a hill road is a road that is laid in an area with a cross slope of more than 25%, i.e. the slope that is nearly perpendicular to the centerline of the highway alignment.
Road design in hilly places differs greatly from that in lowlands. Due to tough terrain, abrupt bends and curves, high slopes, and restricted roadway width, as well as other environmental and safety limitations, hill roads provide significant challenges in their alignment, design, construction, and maintenance.
In hilly areas, road links are generally provided on the basis of clusters or groups of villages as far as possible because the population of each village may be very low; however, the requirement of the hill road is decided based on administrative, developmental, strategic, other needs, and the obligatory points viz saddles, passes, valleys, river crossings, vertical and overhanging cliffs, forest and cultivated land, and other natural features like escarpments, slide prone, avalanche-prone.
Many times, for hill roads, the shortest distance parameters must be ignored in order to achieve simple curves and grades, prevent costly cuts or fills, and avoid long river crossings and obstructions.
Furthermore, the feasibility of road tunnels to minimize hill cutting while constructing an alignment for a hill road travelling through high land and avoiding passage through snow bound regions, Eco sensitive areas, crossing beneath water bodies, or crowded areas should be explored. The choice to construct a tunnel in a road system should be made with the lifetime cost and total savings for traffic in view, with the shortest possible route in mind.
Planning
The primary goal of hill road design is to find the quickest, most cost-effective, and safe route between the required places. However, when constructing hill road alignment, considerations such as snow melting faster on the sunny sides of the hills as compared to the shady sides of the hills should be considered.
As a result, it is advised that the hill road be aligned on the sunny side of the hills. Similarly, advantageous slopes are accessible in river valleys, making it economical to carry the alignment as far as feasible along the river valleys. Hilly locations prone to strong winds with speeds over 100 km/h should also be avoided as much as possible.
The cost of tunneling is determined by geology, tunnel location, tunnel length, and other site-specific parameters. Overall, tunnels may be the most cost-effective choice in the long term. Even a longer road length to accommodate gradients and bends may result in a lower operating cost. As a result, the controlling factor in determining the alignment of these hill roads will be operational cost savings and road safety.
A hill or mountain road’s effectiveness and usability are dependent on its right alignment. As a result, altering the alignment of hill roads requires extreme caution. A good alignment offers characteristics such as a stable and safe road, an easy gradient, low construction and maintenance costs, comfortable travel, and minimal vehicle wear and tear, among others.
In hilly terrain, the help of a Global Positioning System (GPS) or Differential GPS (DGPS), as well as modern technology, such as a drone, aerial, or mobile LiDAR, should be utilized for Alignment Survey.
Complications
On hilly terrain, landslides and erosion are regular hazards. Road development involves a lot of rock cutting, which disturbs the natural conditions and the balance of forces, resulting in slips, sinking, and landslides. Furthermore, rain falls hard on the hills, and because the slopes of the hills are relatively steep, the water rapidly reaches the roadside, causing drainage issues as well as slope erosion by loss of the top layer, resulting in the formation of gullies.
However, as time passes, the sills and gullies deepen and cause the slope to be overstepped, resulting in slope instability. Slope stability is largely determined by slope geometry, material strength characteristics, geological, geomorphological, and hydrological variables, among other factors.
The majority of the time, the solutions are a mix of several stabilizing methods ranging from surface slope protection to subsurface instability solutions. As a result, a multidisciplinary approach is essential for selecting slope stabilizing techniques. Vegetation has a vital role in slope stabilization. Planting dense natural vegetation along the slope helps to stabilize the shallow soils with root systems, avoids erosion, and reduces infiltration.
Deep fissures allow rainwater to enter the sliding mass, raising seepage pressure inside the mass and putting hydro-static pressure against the fissure or crack walls.
Slope treatment can also be accomplished by seeding. The asphalt mulch method may be used to prepare slopes into large seed beds. A sprayer is then used to disperse the asphalt mulch. The asphalt coating eventually disintegrates, with a carpet of green vegetation taking its place.
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