Foundation

CASE STUDY

Foundation Stabilization to Protect Reservoir Geomembrane, India

THE CHALLENGE

The design of a new compression station for the Gujarat State Petroleum Corporation (GSPC) included a power station and four cooling ponds. The facility located in Mallavaram, Andhra Pradesh is part of GSPCs gas pipeline transmission network expansion.

However the native soil of the site was comprised of non-homogeneous soft silty sand with a high water table. The subgrade had non-uniform bearing capacity. Hydrostatic pressure from the water and the self-weight of the earthen embankments on this soil could cause significant differential settlement. This would lead to excessive stretching of the lining, potential damage and even failure of the reservoir.

A ground stabilization solution was needed to improve the bearing capacity of the pond beds, which would distribute stresses more uniformly and limit differential settlements. This was critical for reliable, long-term performance.

The consulting firm, Engineering India Ltd (EIL), was tasked with coming up with a cost-effective foundation improvement solution for the ponds.

PROJECT AT A GLANCE

Application

Stabilize subgrade of water reservoir

Subgrade/Soil

Silty sand with very high water table

Location

Mallavaram, Andhra Pradesh, India

Installation

2013

Quantity

45,000 m2

Client

Gujarat State Petroleum Corporation (GSPC) is one of the leading oil and gas exploration, development and production companies in India, and India's only state government-owned oil and gas company.

Consulting Engineers Engineering India Ltd

Contractors Engineering India Projects Ltd

PRS-Neoweb Distributor Gorantla Geosynthetics Pvt. Ltd.

ABOUT PRS

PRS is the world’s leading supplier of cost-effective soil stabilization solutions. Combining unique proprietary technology with specialized engineering expertise, PRS delivers proven solutions for load support, slope and channel protection, earth retention and reservoir & landfill applications.

With a global network of fully owned subsidiaries and independent local distributors, PRS provides a full range of end-to-end support services. Since its establishment in 1996, PRS has implemented thousands of successful projects in over 45 countries worldwide.

CASE STUDY

CONVENTIONAL SOLUTIONS

Alternative solutions to create a uniform layer called for extensive subgrade replacement with a thick capping layer of quality aggregate. This solution was not cost-effective and does not deal with the high water table. Cement stabilization is too difficult to apply uniformly, its reliability over the long-term is questionable even in unsaturated conditions. Geogrids can not provide the same level of ground reinforcement and require imported higher cost aggregate.

PRS-NEOWEB™ SOLUTION

PRS-Neoweb geocells were chosen to strengthen the reservoir foundations, thereby providing protection for the geomembrane from underneath it. This differs from the more common use of PRS-Neoweb, which is placed on top of the geomembrane to protect it, usually with concrete infill. The PRS-Neoweb layer on the pond subgrade distributes vertical pressures laterally, thereby limiting differential settlement and improving its bearing capacity.

PRS-Neoweb 150 mm height was laid out over a non-woven geotextile and filled with 40 mm downsize aggregates. A layer of 50 mm aggregate and 50 mm sand was placed as a cushion between the PRS-Neoweb and the geomembrane. Two non-woven geotextiles were laid under and over the geomembrane for separation. The surface layer consisted of 150 mm thick concrete paving blocks set in 20 mm of cement mortar plaster on top of a 75 mm layer of sand.

PRS-Neoweb was also utilized on the slopes of the earthen embankments as well to maximize the geomembrane protection of the earthen embankments.

CLIENT BENEFITS

Engineering confidence – long-term reliability. Innovative solution – protecting the geomembrane from

the bottom up. Fast installation – easy and fast all-weather installation. Cost-effective – lower cost than alternatives. Multiple use – same PRS-Neoweb used for base

improvement and slope protection. Performance – guarantees long-term high bearing

capacity of the reservoir bed. Flexible solution – tolerates minor ground movement

without degradation or failure, including seismic activity.

Foundation Stabilization to Protect Reservoir Geomembrane, India

CASE STUDY

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* Design is valid only for Neoloy-based PRS-Neoweb™, and not applicable to HDPE or fabric geocells