Rectification of Tilted Columns of Track Hopper at NTPC- Singrauli by BBR India

M. B Ravi Kumar, Market Development Engineer, BBR India Pvt. Ltd., Bangalore

It has been a challenging assignment for BBR India Pvt. Ltd. apart from its core activity of prestressing, supply of Pot cu‎m PTFE bearings; the rehabilitation work assigned by NTPC has been the result of carefully selection, based on its past experience in executing such a critical job in a stipulated time.

NTPC's Singrauli (Shaktinagar) recently awarded the job of Track Hopper Plough Table Column repair to BBR India Pvt. Ltd. This was a critical assignment it had to be repaired on, while the system is in operation without disturbing routine productions. These track hoppers have been in existence and have been in service for almost 35 years and the plough table got tilted leading to a deflection in the supporting columns which are below the ground level.

BBR India's execution and design team was ready to accept challenge and quickly designed a solution and decided to take up this assignment, commitment to complete in just 3 months time. The plough table consists of a RCC slab of around 3.1 metre wide with a central beam, supported on columns which are at 4 meters c/c distance. The part of the plough table segments from column 30-40 was in a distressed condition due to tilting of the column supports. spaling of cover concrete, corrosion in rebars etc.

The plough table was to be rectified by * realignment of the plough table columns to proper position by pushing with jack units * rectification works on the concrete as per the methodology provided by the client's drawings.

The plough table columns which were in a tilted condition with the columns from 30-40 being out of plumb by app. 100 to 150 mm at top. The same has been realigned by pushing it by the required displacement to realign the columns to plumb using the hydraulic jacks at the top of the column, abutting the RC runner beam. The jacking (app 100 tons) was carried out by transferring the reaction to the side RC walls, through a steel strut. After the pumps were connected with the power supply, they were to be operated simultaneously so that all 11 jacks could move forward to push the columns in required direction.

Later once the columns were re-aligned, strengthening of the columns were done by jacketing method which involved the surface preparation methods for the concrete and for the reinforcements like chipping the entire column cover concrete, exposing the rebars, cleaning the corroded rebars, applying anti corrosive treatment for rebar by appropriate methods, providing extra reinforcements, shear connectors, epoxy injection treatment and finally micro concreting by increasing the column size. Finally once the strength is achieved, the jacks were released and the plough table is handed over for further usual operation.

Utmost safety has been taken care during the operation for not only human beings but also not to disturb the existing structures. It has been a tremendous experience both for NTPC and BBR India Pvt. Ltd, of achieving the success in the running operation conveyor belt without any hurdles and for such critical assignments one can certainly now rely on BBR India Pvt. Ltd. The whole team of NTPC under the leadership of its GM, Mr. J P Singh & DGM (O&M) Mr. S.K Datta has been extremely cooperative and helpful in executing the assigned work.