Highway Research Record

III. GEOTECHNICAL ENGINEERING
ON GOING PROJECTS
Monitoring and Instrumentation of Band Drain Work of Visakhapatnam Port Connectivity Road

Date of Start: February 2003
Central Road Research Institute, New Delhi (R, I)

Present Status and Progress
NHAI authorities are presently executing construction of 12 km length of road to provide connectivity to Visakhapatnam Port area under National Highways Development Programme. A part of this road passes through very soft marine clay area. To accelerate the rate of consolidation of marine clay, prefabricated vertical drains (Band Drains) are being installed at a spacing of 1.15 m distance in a triangular pattern. In order to monitor the progress of consolidation of the soil layer beneath the embankment pore pressure build up, settlement and horizontal spreading of sub-soil are being monitored using piezometers, settlement gauges and inclinometers. Presently first stage of construction (1.75 m height) and designated waiting period has been completed in about 1.7 km of the stretch and second stage loading is under progress.

Findings / Conclusions
Following interim observations/conclusions have been made based on the analysis of the data collected.
1) Marine clay deposits on which design preload had been applied have undergone about 80 per cent of consolidation. The     magnitude of settlement measured till date varies from 46 to 82 cm.
2) The inclinometers have shown lateral movement of subsoil varying from 40 to 120 mm. The lateral movement of sub-soil has     been observed at depths varying from 4 to 10 m.
3) Vane shear tests conducted after designated waiting period indicated strength improvement to the extent of 82 percent in     the top layer decreasing to 16 percent at 5 m depth.

Limitations
The instruments have been installed at selected locations. The data obtained at these locations are to be extrapolated to cover the entire stretch. This exercise may not be entirely accurate considering wide variations encountered in marine clay deposits and their properties.

Reports/Publications
1 U.K.Guru Vittal, P.Subramanya Prasad & Sudhir Mathur, ‘Instrumentation of road embankment on soft marine clay – a case study’, published in the Indian Geotechnical Conference, Warangal, Dec 2004