A Case Study on Pressuremeter Test in Katni, Madhya Pradesh, India-Paper

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The Katni Grade Separator project in Madhya Pradesh required geotechnical investigation for a major railway corridor. The site geology consists of surface alluvium over residual limestone- and bauxite-derived soils, commonly hard, high-plasticity clay. At depths greater than about 10 m, obtaining undisturbed samples was difficult, and SPT-based strength correlations were considered uncertain for the local geology. The investigation therefore used pre-bored Menard pressuremeter tests (PMTs) to assess in-situ soil properties.<br /><br />Following two stages of borehole investigation, 32 PMTs were performed in eight boreholes at selected depths. Test data were corrected for hydraulic head, equipment compliance, and membrane resistance. Pressure–volume curves were interpreted to derive the pressuremeter modulus (EPMT), limit pressure (PL), and undrained shear strength (Su), using established cavity-expansion methods.<br /><br />Field execution was challenging. Gravel punctured probe membranes, while high-plasticity clay caused probes to stick and sustain damage during extraction. Pipe leaks and air in the measuring system also produced misleading volume readings. The team addressed these issues through equipment checks, monitoring volumeter behavior, modifying probe protection, and adjusting drilling and extraction procedures. Borehole diameter was critical: oversized holes shifted curves and could prevent adequate measurement of the plastic phase; gravel-filled gaps in undersized or poorly cased holes also distorted results.<br /><br />Limit pressures generally ranged from 20 to 45 bar. PMT-derived strengths were substantially higher than values inferred from SPT correlations, reaching 250–500 kPa at 12–15 m, 400–500 kPa at 15–20 m, and 500–700 kPa at 20–30 m. For design, however, strengths beyond 20 m were capped at 550 kPa, and other design values were informed by triaxial tests.<br /><br />The study concludes that PMT locations and depths should be selected using prior borehole data, equipment and borehole quality must be carefully controlled, and tests should continue until several readings are obtained in the plastic phase for reliable strength interpretation.

Keywords

Katni Grade Separator

Madhya Pradesh

geotechnical investigation

Menard pressuremeter test

PMT

high-plasticity clay

limit pressure

undrained shear strength

borehole quality

railway corridor