Ground Stabilization using Deep Soil Mixing Technique for an Approach Ramp-Paper

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The project required a 120 m-long railway approach ramp to rise approximately 6 m and connect a new ground-level line to an existing elevated metro line. The reinforced-concrete box structure imposed ground pressures of 75–280 kPa. Because the existing embankment fill was relatively compressible, untreated settlements were estimated at about 50 mm—above the project limit of 20 mm, including a maximum of 10 mm after track installation.<br /><br />Deep Soil Mixing (DSM) was selected instead of piled foundations as a cost-effective, low-vibration ground improvement solution. Designed in accordance with the Federal Highway Administration’s 2013 guidance, the scheme used 2.0 m-diameter cement-mixed columns in a grid beneath the structures. The columns had a target unconfined compressive strength of 0.75 MPa and were spaced 2–4 m apart according to loading requirements. The design accounted for column crushing and used area replacement ratios to meet settlement and capacity criteria.<br /><br />A 0.5 m-thick granular load transfer platform (LTP), reinforced with two layers of biaxial geogrid, was installed above the treated ground to distribute structural loads evenly. Quality verification included column coring and strength testing, plate-load testing of the LTP, and a zone load test on four trial columns. Under a maximum test pressure of 250 kPa, the trial section recorded an average settlement of 16 mm.<br /><br />The trial results supported the selected DSM-and-LTP system as a means of carrying the specified loads while controlling settlement to the project requirements.

Keywords

Deep Soil Mixing

DSM

railway approach ramp

settlement control

ground improvement

load transfer platform

geogrid reinforcement

cement-mixed columns

elevated metro line

foundation design