Reservoir Slope & Liner Protection with StrataWeb® at Gandhidham, Gujarat
|Principal Client||OPG Power Ventures|
|Consultant||Aquatherm Engineering Consultants|
|Application||Reservoir Slope and Liner protection|
|System Offered||StrataWeb® Geocells|
|Project Execution||May 2013|
A 2x150 MW Thermal Power Plant is being constructed near Gandhidham, Gujarat by OPG Power Ventures. A raw water reservoir has been constructed with a storage capacity of 50,000m3, to stockpile and ensure constant supply of water. It was lined with 250 micron geomembrane to render the bottom and side slopes impervious. The geomembrane lined slopes required protection from external damage and uplift pressures. Conventionally, a plain cement concrete lining is placed above the goemembranes. However, due to the weight of concrete tiles or green concrete as the case may be, the liner tends to slide down and collect at the toe which renders the system inadequate. Since the side-slopes were steep, using StrataWeb® geocells with lean concrete infill proved to be a technically superior and cost effective solution.
Problem and Objective
Strata Geosystems (India) Pvt Ltd was appointed in May 2013, to take up the work of raw water reservoir slope and liner protection with concrete in-filled StrataWeb®. The side-slopes of the reservoir were steep, at a gradient of 1V : 1.5H. No anchoring using spikes was possible owing to the geomembrane lining. Hence the weight of entire mass of geocells along with the in-filled concrete was required to be suspended at the top from anchors in trenches. The reservoir was required to be completed in time to fill up rain water during the fast approaching monsoons thus requiring urgency in execution.
The work commenced in May 2013. StrataWeb®, style SW660 was used. The concrete thickness was evaluated to prevent uplift of the geomembrane and hence the depth of StrataWeb® was designed to be 75mm.
Along the slope, high strength polypropylene tendons were used at regular horizontal spacing to suspend the in-filled geocells from anchors at the crest. Tendons were also intertwined between two adjoining panels along the row to hold the panels together. The panels along the column were connected to each other with high strength cable ties.
Over the base of the reservoir, the panels were fully spread to cover the entire base. Adjoining panels were joined with stapler pins and cable ties.
Concrete of grade M15 with 100mm slump was placed with a placer boom. Concreting was done first within the anchor trenches to secure the StrataWeb® panels at the top. Concrete was poured from top to bottom and made to flow along the slopes. Dressing was done manually using spades and floats. Thickness of the finished concrete was 100mm. Concrete in-fill was later done over the base of the reservoir with an overfill of 25mm.
Benefits to Clients
Green concrete normally cannot be placed directly on sloping geomembrane. Geocells offer a technical solution by providing cellular pockets to hold the green concrete in place. Since the concrete is not cast continuous because of geocells, ungainly cracks in concrete are avoided.
Besides these technical advantages, geocells make it easy for fast installation to meet strict deadlines. . The StrataWeb® solution is a fast and all-weather installation solution. No skilled labour is required. These factors resulted in substantial savings in money and resources.