Flaws in design, implementation led to collapse of reinforced earth walls of NH 66 in Kerala: expert panel

The deficiencies in design, implementation, and quality assurance resulted in the collapse of reinforced earth (RE) walls that were constructed as part of the national highway (NH) 66 in Kerala, an investigation has concluded.

The four-member expert panel appointed by the National Highway Authority of India (NHAI) concluded that “there was a noticeable lack of consistent monitoring, third-party quality checks, and post-construction verification such as confirmatory boreholes, pull-out testing of reinforcements, and performance audits, as mandated in standard codes. This has resulted in premature failures, subsidence, and visible distress in multiple RE wall segments and cut slopes across the alignment.”

The RE walls had caved in, and cracks appeared in many stretches of the road, giving rise to safety concerns and traffic snarls. Kerala witnessed widespread public protests following the damage caused to the NH.

The report concluded that the RE walls “have either been constructed or are currently under construction without implementing ground improvement measures or partial replacement of the subsoil with reinforced fill or partial replacement of the subsoil with reinforced fill and geosynthetic reinforcement as basal reinforcement. In many locations, the groundwater table is at ground level,” according to the report submitted to NHAI a few days ago.

“It is crucial to implement ground improvement measures, or there may be potential settlement issues in the future. Therefore, monitoring the RE wall is essential to evaluate the total settlement of the structure,” the report pointed out.

The “systematic absence of geological input in the planning and execution of the highway alignment and associated structures, particularly in zones comprising lateritic terrain, weathered rock, paleo-river valleys, backwater/tidal flats, and high cut slopes particularly in reaches built over paleo-fluvial deposits, tidal flats, and active backwater zones attributed to lack of consideration of geological complexities,” it pointed out.

Though the NHAI and the Geological Survey of India (GSI) had entered into a memorandum of understanding on Jan 31, 2024 for “technical collaboration for geotechnical, geological, and landslide risk-related support, it has been noted with concern that the services and expertise of GSI have not been utilised in the planning, DPR preparation, or construction stages of NH 66,” the report said.

The panel has suggested to “mandatorily engage geosciences experts or specialised agencies like GSI in all the highway projects” since the “failure of highway slopes and associated infrastructure, particularly in hill and mountainous areas, is mostly dictated by the inherent geological complexities.”

“Geosciences experts or specialised agencies like GSI shall be engaged during project inception for route alignment feasibility, at the detailed project report stage for geological mapping, terrain classification, and slope-risk zoning, in the pre-construction phase for site-specific investigation, foundation validation, and material characterisation and during the construction phase for on-ground monitoring, slope remediation design, and dynamic advisory support,” prescribed the committee.

The panel suggested “immediate geological consultation and slope risk re-evaluation” for vulnerable and failure-prone stretches for the ongoing and future works under NH-66.”