Case Study of Geotechnical Challenges Involving Ground Improvement and Successful Completion of Pile Foundations in a Rail Road Project in India-Paper

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The case study describes geotechnical challenges and ground-improvement solutions used on a 115 km railway project in Andhra Pradesh, India.<br /><br />Two tunnels, 0.96 km and 6.62 km long, crossed hilly forest terrain. About 500 m of tunnel had only 4–6 m of overburden, where conventional cut-and-cover construction was considered. Limited forest land, the time needed to acquire more land, and the risk of flooding from streams made that method impractical. Instead, the overburden was strengthened with cement grouting and 3,000 micro piles. Tunnel safety was further supported by controlled blasting, face treatment, lattice girders, spiling, shotcrete, and rock bolts. Instrumentation and surface surveys tracked movements; maximum settlement was 9 mm. The approach completed the work in five months rather than an estimated 17 and cost about INR 10 crore, compared with INR 25 crore for cut-and-cover, excluding additional land costs.<br /><br />A five-kilometre swampy section could not be accessed by construction vehicles. Lime was spread and mixed into the soil to improve access, then used for stabilization and embankment construction. The treatment enabled site access within 24 hours, with stabilization followed by mixing, compaction, and curing.<br /><br />At the River Pennar bridge, sand overlying deep clay caused pile-bore collapse during construction. Vibro hammers drove strengthened casing through the upper 8–10 m of sand before drilling. This method enabled successful completion of all 360 piles.<br /><br />The study concludes that carefully designed grouting and micropiles can provide an alternative to cut-and-cover tunnelling in shallow-cover conditions, while lime treatment and casing can address difficult ground conditions for embankments and pile foundations.

Keywords

geotechnical engineering

ground improvement

tunnel grouting

micropiles

cut-and-cover alternative

lime stabilization

swampy soil

pile bore collapse

vibro hammer casing

Andhra Pradesh railway