NATIONAL HIGHWAY / NH 66 / KERALA CAVES IN - WHY ? JOHN KURIEN, Ex CGM, NABARD & Senior Consultant Earth Scientist

 John Kurien, former CGM,NABARD and Senior Consultant Earth Scientist writes on  the latest hazard in NH 66 in Kerala where roads disintegrate as fast as they are built.

Geomorphic and Geological safe guards for Capital Intensive  Geometric Highway Constructions in Coastal ecosystems.

 

Recent reports of large-scale earth subsidence along near-vertical highway abutments in the high-level laterite regions of northern Kerala—especially prior to the onset of the southwest monsoon—highlight the urgent need for geotechnical scrutiny in highway construction practices. These failures point to inadequately engineered cut-and-fill embankments, often rising 5 to 12 meters above the surrounding terrain. The ongoing construction of NH66, a 45-meter wide six-lane expressway, demands adherence to stringent Indian Road Congress (IRC) and Indian Standard (IS) protocols regarding earthworks, pavement design, drainage, and structural integrity. Given the ecological sensitivity and complex terrain of Kerala’s coastal belt, construction must be managed with meticulous attention to geomorphic and hydrological contexts to prevent anthropogenic disasters.

              Some critical issues and safe guards to be followed in construction management of major Geometric Highway projects which are highly sensitive to physiographic, geological , ecological and drainage in the coastal undulatory terrains warrants meticulous adherance to technical boundary conditions that will have to be followed to ward off such manmade catastrophes.

1. Physiographic Safeguards

The alignment of NH66 traverses a north-south corridor from Kasaragod to Parassala, intersecting numerous intermontane hills, valleys, and west-flowing rivers. The affected stretch—especially between Nileshwar (Kasaragod) and Kuttipuram (Malappuram)—features rolling topography and experiences over 2500 mm of annual rainfall. This high precipitation induces significant surface runoff, exacerbating risks associated with embankments as high as 12 meters, often constructed across valleys and former paddy fields.

The region's dendritic drainage pattern, characterized by steep gradients and high-capacity rivulets, demands engineered solutions to counteract the hydrostatic pressures accumulating on earthen embankments, especially under monsoon-saturated conditions. Ensuring long-term stability requires design practices that respect the natural topography and drainage behavior of the terrain.

2. Geological Safeguards

The geological profile of northern Kerala consists largely of tertiary sedimentary formations in Kasaragod and lateritic mantles in Kannur, Kozhikode, and Malappuram, underlain by crystalline bedrock. These overburdens contain various swelling clays, such as illite and montmorillonite, which present high risk of volumetric expansion upon saturation.

Use of these soils for highway embankments necessitates rigorous compaction protocols. Earth fill layers must be limited to 0.5-meter thickness, compacted with rollers and vibratory equipment, and tested in laboratories to understand mineral behavior under hydrodynamic stress. For embankments exceeding 3 meters in height, construction must comply with advanced IRC compaction and consolidation standards, ensuring stability under fluctuating moisture conditions.

3. Ecological Safeguards

The construction of NH66 through the ecologically fragile western coastal strip mandates comprehensive Environmental Impact Assessments (EIA) conducted by accredited agencies. The coastal terrain, marked by unique agro-climatic zones, endemic flora and fauna, and tectonic activity, requires cautious intervention.

Thick embankments over natural valleys—many of which are former wetlands or paddy fields—disrupt surface runoff and groundwater flow, leading to ecological imbalance and potential disaster. Fragmentation of ecosystems, soil degradation, and altered hydrology may result from poorly planned fill operations. Infrastructure must be planned with an eye toward maintaining ecological continuity and minimizing impact on natural drainage patterns.

4. Drainage and Hydrological Safeguards

Sustainable infrastructure in Kerala must consider its unique tripartite physiographic structure: highlands, midlands, and coastal plains. The region's complex weathering patterns, influenced by alternating monsoon and dry seasons, significantly affect sediment transport and deposition.

The high silt load and diverse composition—ranging from sand and clay to breccia and pegmatites—require careful engineering of drainage structures like culverts and bridges. These must provide sufficient venting capacity to allow free passage of sediment-laden water and prevent waterlogging in low-lying areas.

Where highway alignments cross valleys or seasonal water channels, elevated viaducts anchored to bedrock are preferable to solid embankments. This design approach preserves natural water flow and prevents buildup of hydrostatic pressures that could compromise structural integrity during peak monsoon periods.

Conclusion

Construction of high-speed highways in Kerala’s coastal belt must go beyond mere compliance with generic engineering standards. The unique interplay of geomorphology, geology, hydrology, and ecology necessitates tailored, site-specific safeguards. The recent failures observed along NH66 serve as stark reminders of the consequences of neglecting these factors. By embedding scientific insight and environmental stewardship into every phase of infrastructure planning and execution, we can ensure that such capital-intensive projects remain both safe and sustainable in the long term.

John Kurien
(1970 batch Geologist of GSI and later Sr.Hydrogeologist of CGWB 
CGM NABARD.
Retired in 2007 )

Affirms
Reading the newspaper reports, I have casually scribbled the article with my experience in Infrastructure Projects without any research