Back Analysis of Field Instrumentation Results During Reclamation & Ground Improvement Works- A Case Study-Paper

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The study evaluates settlement and consolidation of soft marine clay beneath a 27-hectare container-terminal yard reclaimed at Jawaharlal Nehru Port, Maharashtra. The site contains approximately 7–9.5 m of compressible clay over dense sand or weathered rock. Ground improvement involved prefabricated vertical drains and surcharge loading to accelerate consolidation.<br /><br />Settlement plates monitored ground movement during construction. The authors back-analyzed field data using two approaches: Asaoka’s method, which estimates ultimate settlement and horizontal coefficient of consolidation (Ch), and curve fitting, which calibrates theoretical settlement curves against measured results by adjusting compression ratio (CR) and consolidation coefficients. Results were compared with laboratory parameters.<br /><br />Curve fitting produced average CR values of 0.21 for the very soft clay and 0.18 for the soft clay, compared with laboratory values of 0.25 and 0.19. The authors conclude that laboratory parameters overestimated settlement. Back-analyzed Ch values were also slightly below laboratory estimates: 2.35 versus 2.34 m²/year for the very soft layer, and 2.85 versus 3.14 m²/year for the soft layer. They suggest disturbance and remoulding of the upper clay during land-based reclamation may reduce the effective average consolidation rate.<br /><br />For four monitored areas, Asaoka-derived Ch values ranged from 3.26 to 4.24 m²/year, while curve-fitting estimates ranged from 2.46 to 2.79 m²/year. Thus, Asaoka’s method consistently indicated higher Ch than curve fitting. Overall, the study demonstrates the value of field settlement monitoring and back-analysis for assessing ground improvement and checking laboratory-based design assumptions.

Keywords

soft marine clay

settlement analysis

consolidation

prefabricated vertical drains

surcharge loading

Asaoka method

curve fitting

ground improvement

container terminal yard

Jawaharlal Nehru Port