Engineering Geological Assessment of Recurrent Landslides at Chakki Moad Along NH-05, Solan District, Himachal Pradesh, India

The Himalayas are a young mountain range, still being pushed upward by the slow, massive collision of two tectonic plates. This constant geological pressure creates steep slopes and fractured rock, making the region naturally prone to landslides. When heavy rain soaks into these slopes, or when human activity cuts into them to build roads, the ground can lose its grip and slide. For the people living and traveling in these mountains, understanding why these slides happen is not just an academic exercise; it is a matter of safety and survival. Engineers and geologists study the specific layers of rock, the direction in which they tilt, and the water that flows through them to figure out how to keep the ground stable.

In the Solan District of Himachal Pradesh, India, a critical stretch of National Highway-05 known as Chakki Moad has become a focal point for this kind of study. This road is the main link between the cities of Chandigarh and Shimla, carrying immense amounts of traffic, commerce, and tourists. Yet, for over a decade, this section has been plagued by recurrent landslides that block the road, damage infrastructure, and threaten lives. A recent systematic review by researcher Deepak Parkash Gupta examines exactly why this specific section of the highway is so unstable. The investigation reveals that the problem is not caused by a single factor, but by a perfect storm of weak rocks, active fault lines, heavy monsoon rains, and the necessary but disruptive work of widening the highway itself.

The area sits within the Lesser Himalaya, a zone defined by intense geological deformation. The ground here is made up of several distinct layers of rock, each with its own weaknesses. The oldest layers include the Subathu Formation, which consists of splintery shale and limestone that break down easily when wet. Above this lies the Dagshai Formation, made of soft, crumbly red sandstone and siltstone that disintegrates quickly. The topmost layer, the Kasauli Formation, is composed of stronger sandstone and gravel, but even this rock is heavily cracked and fractured. At Chakki Moad, these rock layers are not just sitting there; they are being squeezed and shifted by massive underground forces. The Main Boundary Thrust and the Surajpur Thrust, two major fault systems, have crushed and sheared the rock masses, creating zones of weakness where the ground is already broken before a landslide even begins.

What makes Chakki Moad particularly dangerous is the orientation of these rock layers. The beds of rock generally tilt downward toward the valley at an angle between 35 and 45 degrees. This is a critical detail because it means the layers of rock are parallel to the slope of the hill. When heavy rain from the monsoon season, which brings between 850 and 900 millimeters of rain annually, saturates the ground, the water seeps into the cracks and along these tilted layers. The water acts as a lubricant, reducing the friction that holds the rock in place. Because the layers are already tilted toward the road, the entire mass of rock and soil can slide down along these smooth, wet surfaces, much like a deck of cards sliding off a tilted table.

Human activity has only intensified this natural instability. To widen the highway and accommodate more traffic, engineers have cut into the hillsides, removing the natural support at the bottom of the slopes. This process, known as toe erosion, leaves the upper parts of the slope hanging without support, making them prone to collapse. Furthermore, the drainage systems along the road are often inadequate. Instead of flowing away, rainwater concentrates in gullies and seeps into the fractured rock, increasing the pressure inside the ground and further weakening the soil and rock. The combination of these factors has led to a cycle of failure. Records show major landslides in 2010, 2013, and again during the monsoon seasons of 2022 through 2026. Each event damages the road and nearby properties, only to be followed by repairs that are soon threatened by the next slide.

The study concludes that fixing this problem requires more than just clearing debris after a slide. The researchers argue that the instability is a cumulative result of weak geology, active tectonics, and human modification. To truly reduce the risk, a comprehensive approach is needed. This includes building better systems to drain water away from the slopes, both on the surface and deep underground. Engineers recommend installing retaining walls and rock bolts to hold the fractured rock together, as well as using vegetation with deep roots to help bind the soil. Continuous monitoring of the slope using modern instruments is also essential to detect movement before a major failure occurs. Without these integrated measures, the Chakki Moad corridor will likely continue to face disruptions, economic losses, and risks to human life, as the natural forces of the Himalayas continue to test the limits of the road built upon them.