Ground Improvement Using Geocell & Biaxial Geogrid for Raising of Existing Ashpond Bund of Thermal Power Plant Near Krishnapatnam, Andhra Pradesh by TechFab India Industries Ltd.

Manish Barot & Deeraj Reddy, Techfab India Industries Ltd.

Introduction :

Sri Damodaram Sanjeevaiah Thermal Power Station is located in Nelatur Village, near Krishnapatnam in Andhra Pradesh. The power plant is one of the coal-based power plants of Andhra Pradesh Power Development Company Limited (APPDCL).

APPDCL proposed to establish one unit of 800 MW super critical coal based Thermal Power Plant (Stage-II) as expansion plant to the 2x800 MW Sri Damodaram Sanjeevaiah Thermal Power Station (SDSTPS Stage-I). As a part of this expansion, Ashpond bund created up to 5m height at Stage-I needed to raise its height for another 5m.

The existing ash pond bund has been filled with fly ash. The pond ash is a non-plastic material and possess very low dry density as compared to natural soil. Since the entire segment of the new bund construction was supported on fly ash, it was very important to adopt any suitable ground improvement technique which can effectively improve the bearing capacity of fly ash at the base of the bund and also minimize and control the settlements of the proposed bund. This was the major challenge of this project.

Ground Improvement Solution :

Considering all the above aspects, TechFab India proposed ground improvement method using the Techcell Geocell (356x200), TechGrid Biaxial geogrid and Nonwoven Geotextile T200 as the best suitable solution.

Geotextile was laid below the TechGrid Biaxial geogrid and Techcell Geocell. It will act as separator and best filter media at the base of ash bund. This will also help to effective load distribution. And the purpose of providing TechGrid Biaxial geogrid was to ensure proper distribution of the load from the bund and reduce differential settlements. Techcell will also transfer the load pressure to wider area and hence reduces the pressure intensity on the fly ash to permissible limits.

Why Techcell Geocell is recommended?

•   The 3D confinement of Techcell geocell prevents movement and shearing of soil infill under cyclic loading, while reducing aggregate attrition. The confinement system also maintains soil compaction, thereby providing long term soil reinforcement and structural strength as well as improves moduli of infill materials, while increasing the bearing capacity of the underlying soil strata.

•   Techcell is the cellular confinement system created, manufactured and distributed by TECHFAB INDIA made from High Density Polyethylene stabilized with carbon black which has higher tensile strength and stiffness.

•   Techcell is expanded on-site to form a honeycomb like structure, which is in filled with granular infill which   creates unique cellular confinement system. Techcell will increase the shear strength of the confined soil, and increase load carrying capacity. With granular infill material and holes in Techcell wall, it enhances drainage and release pore water pressure.

•   Techcell is used for soil confinement, stabilization and reinforcement in wide variety of load support applications.

•   This system can be use full for embankment constructions over weak soils, overlarge parking areas, Storage areas; coastal areas, over poor sub grade for pavement constructions where ground improvement is require and need to control the settlement.

Execution at Site:

•   The work site was well prepared before the installation. The ground has been compacted in accordance with the project specification. All surfaces to be deployed was ensured to be free of all foreign and organic material or sharp objects

•   The rolls of Non-Woven Geotextile are unrolled and laid as per the markings. The adjacent rolls of geotextile were joined with necessary overlaps.

•   As per the design requirement Biaxial Geogrid was laid on the surface of Non-Woven Geotextile. Necessary overlaps were maintained for the adjoining rolls of geogrid.

•   Geocell sections were then stretched to maximum area and was allowed it to relax and install J-pins (permanent or temporary) to anchor the edge cells. Aligning and fastening the geocell was done by using hooks.

•   The Geocell system was filled with the infill material suggested and levelled to approximately 50mm above the cells. Compaction of infill material was done with Roller or compacter as per the project specification.

•   Proper side-to-side cell alignment has been maintained to prevent loss of cell infill material. Every surface of the panels was compacted well as per the specification.

•   After the completion of geocell installation, the ash pond bund was constructed to required height.

Conclusion :

The project is completed successfully within the stipulated time. The client was satisfied with product quality as well as quick material supply by TechFab India industries Ltd. The project included very strict quality control norms and involved visit to factory and checking the manufacturing process and quality control systems prior to approval of a source. TechFab's systematic quality control ensured easy source approval prior to dispatch.