Highway Research Record

III. GEOTECHNICAL ENGINEERING
NEW PROJECTS
Ground Improvement Measures for Widening of Industrial Bypass Road at Visakhapatnam

Date of Start:May 2004
(i) Central Road Research Institute, New Delhi (R,I)
(ii) Visakhapatnam Port Trust (S)

Scope and Objectives
(i) Subsoil investigation by making boreholes in the 1.2 km stretch
(ii) Collection and testing of disturbed and undisturbed samples
(iii) Conducting field vane shear tests
(iv) Design of suitable ground improvement measure to be adopted

Methodology
The Visakhapatnam Port Trust (VPT) authorities are proposing to take up conversion of about 1.2 km length of existing industrial bypass road from two lane carriageway to four lanes. The existing two lanes run through marshy land with embankment height vary from 0.5 to 1 m. The subsoil in the region is soft marine clay and water table is almost at ground level. Based on the findings of sub-soil investigations, ground improvement measures were designed. The strength of sub-soil was found to be about 8 kPa and coefficient of consolidation was found to be 1 m2/year. World wide polymeric vertical drains commonly known as ‘Band drains’ are being adopted for accelerating consolidation of soft clayey soil and the same technique has been proposed. Band drains consists of a plastic core formed to create channels, surrounded by a thin geotextile filter jacket. Typically the size of band drains is 100 mm in width and 3 to 9 mm in thickness. The primary use of band drains is to accelerate consolidation and to decrease the settlement time of embankments constructed over soft soils. Band drains also accelerate the rate of strength gain of the in-situ soils. Band drains have been proposed at a triangular spacing of 1.25 m with preload height being limited to 1.70 m. The waiting period would be about 150 days after laying the embankment.

Conclusions
Ground improvement by using polymeric band drains is a promising technique in marine clay areas.

Significance/ Utilization Potential
The technique can be adopted in other areas having marine clay deposits. However the design would have to be modified keeping in view changes in properties of sub-soil.

Limitations
The rate of consolidation and strength gain in marine clay layer is proposed to be monitored using instruments.