Reinforcement of Base Embankment on Soft Soil at Navi Mumbai, Maharashtra, India.

Project Data

Project	Reinforcement of Base Embankment On Soft Soils, Coastal Road
Location	Navi Mumbai, Maharashtra, India
Client	City & Industrial Development Corporation of Maharashtra Ltd. (CIDCO)
Products used	Mirafi® PET800/50 High Strength Reinforcement Geotextiles

Overview

To facilitate smoother traffic flow and direct connectivity with Jawaharlal Nehru Port (JNPT), Navi Mumbai Special Economic Zone and Nodal areas, a 6-lane wide coastal road from NH4B near Navghar to Sector-63 at Dronagiri, Navi Mumbai was proposed. The 6-lane coastal road would make up 8.3km of the highway. Land acquisition for the construction work was first carried out for 5.4km of the road. This was followed by the construction of the road embankment of 52m at around 4.5m height.

The road alignment passed along soft soils with poor load carrying capacity and was of high compressibility. This makes the serviceability and stability of the embankment a major concern.

Solution

The proposed site of the road alignment passed along very soft to soft clays having a depth up to 9m. A total settlement of around 1.7m was anticipated with 90% consolidation to occur in about 20 years.

It was proposed to accelerate the consolidation process within 9 months of the construction phase by using prefabricated vertical drains (PVDs). The drains were driven up to the depth of the soft soil at a spacing of 1m in a staggered manner. The PVDs facilitated the draining of the water, from the foundation soil, vertically upward to a 300mm thick horizontal granular drainage blanket placed above the ground level.

High strength geotextiles were placed over the drainage blanket. These geotextiles provided reinforcement to support the pre-loaded embankment soil against rotational failure during the consolidation process. The design required that geosynthetics having a tensile strength of 400kN/m within 5% strain be used to meet the serviceability requirements.

Installation

Mirafi® PET 800/50 (tensile strength 800kN/m) high strength polyester woven geotextiles was used to provide stability to the embankment within the serviceability criteria. These geotextiles were laid with the roll direction running across the entire width of the embankment. No sewing of the geotextiles was allowed in this direction. Adjacent geotextiles were laid in a similar manner and their edges were sewn together using a portable stitching machine making a joint at every 5m along the length of the embankment.

Locally available granular soil was laid in stages over the high strength geotextile reinforcement until the desired embankment height was reached.

Performance

The foundation soil had consolidated within the design time period using prefabricated vertical drains while Mirafi® PET800/50 high strength geotextiles had enabled the rapid construction of the embankment over the foundation soil without any signs of distress and had helped achieved the required design settlement.