The construction of National Highway 66 (NH-66) in Kerala has been plagued by damages, raising serious concerns about the stability of the soil and the construction techniques employed. An expert panel has investigated the issue and is now calling for ground strengthening measures to prevent further incidents.
Several factors have contributed to the problems with NH-66. One major issue is the inadequacy of soil testing and the failure to consider the varied nature of the soil in Kerala. The highway passes through diverse terrains, including areas with loose soil, paddy fields, and regions with significant water flow. In many locations, the subsoil consists of soft, compressible, and water-saturated soils with low shear strength and bearing capacity, making them unsuitable for supporting heavy embankments.
The expert panel found that in some areas, red laterite stone has been sliced up to depths of more than six meters without proper soil strengthening or the construction of retaining walls. In other locations, ancient, broken rocks were exposed during excavation, increasing the risk of collapse. The panel also noted instances where the standard spacing between soil nailing rods was not followed, with wider gaps than recommended and missing rods.
Another significant problem is inadequate drainage and water management. The construction has obstructed natural drainage channels and watercourses, leading to increased pore water pressure and reduced soil strength. Poor drainage and continuous water infiltration from adjacent fields and streams have further exacerbated soil saturation, triggering progressive failure beneath the embankment.
The unscientific construction techniques used in some sections of NH-66 have also come under fire. In certain areas, the highway is elevated by as much as 50 feet, with interlock bricks placed on both sides and soil filled in between without proper compaction or reinforcement. This unstable soil has led to complete road collapses during heavy rains. The collapse of a section of NH-66 at Kooriyad, Malappuram, where the highway was built on a reclaimed paddy field without adequate subsoil drainage or geotechnical support, exemplifies this issue.
In light of these issues, the expert panel has made several recommendations for ground strengthening. These include improving slopes adjacent to the highway by building benches, providing sufficient width for each bench, and implementing specific engineering solutions tailored to the soil type and thickness in each area. The panel also emphasized the importance of proper soil testing to determine the appropriate depth and spacing for soil nailing rods, as well as the amount of shotcrete to be applied.
Following the collapse of the Kooriyad national highway, an expert panel submitted a report to the central government, highlighting lapses on the part of the construction companies. The panel recommended completely reconstructing the collapsed section of the road, including the protective wall, and emphasized the need for proper soil testing. The construction company KNR Constructions and the consultant company Highway Engineering Consultant (HEC) have been barred from future bidding, and the project manager has been suspended.
The National Highways Authority of India (NHAI) has also acknowledged lapses in the construction of the embankment at Kooriyad and other stretches of NH-66. The agency attributed the failure to the concessionaire's failure to ascertain ground conditions and increase ground-bearing capacity before commencing work.
To prevent future incidents, a system-wide safety audit of all ongoing NH-66 works in Kerala is being conducted, focusing on reinforced soil walls, slopes, and drainage structures. Any designs similar to the one used at Kooriyad will be reconsidered. The collapsed section at Kooriyad is being rebuilt as a flyover, an elevated bridge, recognizing that this design is better suited for flood-prone, weak soil areas.
