Reservoir Slope Protection, Chennai, India

Reservoir Slope Protection, Chennai, India

Project Title Reservoir Slope Protection
Owner ARS Metals Ltd.
Location Chennai, India
Material Used StrataWeb® Geocell
Application Geomembrane liner protection on slopes and base of Raw Water Reservoir for Captive Thermal Power Plant using concrete filled StrataWeb®
Project Execution November 2012

Project Brief

ARS Metals, a large automated steel plant in Southern India, known for its best quality TMT reinforcement steel bars and mild steel billets had decided to take the innovative initiative to integrate it with a 2 x 60MW power generating plant. The power plant requires a 100,000 m3 raw water reservoir. The reservoir was lined with an HDPE geomembrane as a water seepage barrier. The geomembrane lined slope needed stability and protection from uplift. Since the slope involved was quite steep, the Strata Solution of using StrataWeb® geocells with a concrete fill proved to be the most technically superior and cost effective solution as compared to others.

Challenges

The slopes of the Raw Water Reservoir were constructed at steep angles, ranging between 45° and 60° due to spatial constraints. This became difficult to weigh the geomembrane down with concrete blocks, tiles or pcc. Furthermore, owing to the geomembrane, no anchoring could be done. Harvesting rain water into the reservoir during the on-coming winter monsoons was yet another necessity to commission the reservoir at the earliest.

Strata Solution / Design Solution:

Considering technical requirements and time and cost issues, StrataWeb® geocells were suggested as geomembrane liner protection. The steep slope angles necessitated StrataWeb® of lesser cell size; hence the SW35 style was used. High strength polypropylene tendons of 6mm diameter and having ultimate strength of 6kN were considered at 500mm c/c vertical spacing to hold the Geocells into position. High strength cable ties and pneumatic staplers were used for cell to cell and flap to flap connections between StrataWeb® panels.

StrataWeb® was also recommended over the base of the reservoir.

Procedure / Construction Overview

StrataWeb® panels of size 2.6m X 5.6m were used. At the base, adjoining panels were joined with stapler pins and were fully spread to cover the entire base. Concrete (M15 with 100mm slump) was placed within the cells of the StrataWeb® with a boom placer and dressing was done manually. The thickness of finished concrete was 100mm.

StrataWeb® was anchored in place at the crest. Anchoring was done through a trench, about 1000 mm wide and 500 mm deep. Concreting was done within the trench to secure the StrataWeb® system at the top. High strength tendons were passed through StrataWeb® along the 2.6 m direction (at 500mm c/c) with special precautions at the ends. The tendons passing through the ends had to be intertwined between the two ends in order to make it a single unit. The geocells along the other direction were connected to each other with high strength cable ties. Concrete (M15 with 100mm slump) was poured from top to bottom and made to flow on the slopes with manual dressing using spades and floats.

Results

In spite of heavy rain in Tamil Nadu during November and December which drastically reduced the tempo of work, the Project was completed successfully within the stipulated time schedule. No other solution could have been executed within a shorter period or lesser cost, considering the steep slopes (and the associated limitations) and the rain water accumulation issues at the base. The reservoir is now ready to store water for usage in the thermal power plant.