We went to Middle Bhotekoshi Hydropower for the ”Sub-contract for the Repair of Dam and Weir Surface Maintenance Project” after successfully completing the similar nature of the project in Middle Marsyangdi Hydropower. We, Venus Construction and Waterproofing Pvt. Ltd., performed the project procedure in various stages.
Thus, in this blog, I will be sharing the work schedule we performed from start to completion of the project, repair of dam and weir surface of Middle Bhotekoshi Hydroelectric Power Station. Furthermore, we successfully concluded the project amid the covid 19 pandemic that saw a few project members catch the virus, including me.
Overall, the project had to repair or replace existing reinforcement bars to perform concreting on the dam’s four spillways and exposed walls and apply a high abrasion-resistant coat on all four spillways.
Introduction to Project
Client: Nepal Electricity Authority (NEA)
Contractor: Guangxi Hydroelectric Construction Bureau Middle Bhotekoshi Hydroelectric Engineering Management Department
Sub – Contractor: Venus Construction & Water Proofing Pvt. Ltd.
Contract Identification No: GHCB -MBK/CH.2021 -03
Location: Chakubazar, Sindhupalchowk
Features of Middle Bhotekoshi Hydro electric power Station
(Project is Under Construction as of June 2021)
Run-of-River (ROR) Hydroelectric Plant*
Turbines: 3 x 34 MW
Installed capacity: 102 MW
Following is the step by step working procedures of the project
In our first impression, the inability to withstand a season monsoon by the newly constructed spillway was a little bizarre. However, inspecting more of the site condition, the extensive nature of the river’s boulders, and the high discharge it has on the monsoon seems to be the main reason for the damage. We also noticed that the two spillways on either end were more destructed and needed more repair.
Insurance of the overall project
Insurance of the overall project is done. It includes insurance of both Life and Non-life aspects of the project. Life Insurance features insurance of project members, staff, and workers, whereas non-life includes heavy and costly machines and equipment insurance. Furthermore, Costly machinery covers Concrete Mixture, Concrete Pump, Sand Blasting Machine, Bar Cutter, Bar Bender, etc.
After the insurance of the project is done. A copy of the insurance policy is then sent to the contractor, Guangxi Hydroelectric Construction Bureau Middle Bhotekoshi Hydroelectric Engineering Management Department.
Testing of Materials
Different construction materials to be used on-site are tested for their various properties before use. As most of the materials were supplied by the contractor, we had only Cement, Sand, and Aggregate to be tested in the lab to check their tensile and compressive properties. At the same time, the Factory Test Certificate was the final for high abrasion-resistant materials like Epoxy Chemicals.
The M60 Grade concretes’ mix design was done in the lab and a copy was sent to the client.
As it was a covid hot time and subcontracting, the contractor provided us with Temporary housing, storeroom, workers camp, toilets, etc., that are essentially required on-site.
Delivery and Installation of Plant & Machineries
Different Construction materials like Cement, Sand, Aggregates, Admixtures, MS pipes, Epoxy Materials, and other chemicals were delivered and stored on Site. Whereas, different heavy machinery like cranes, excavators, JCB, Trucks were provided to us by the contractor.
The machinery we installed at the site were;
- Concrete Mixer
- Bar Bending Machine
- Sand Blasting Machine
- Bar Cutter Machine
A submersible pump was fitted to pour the water off the spillway to create a dry environment for project work.
Pre-Construction Joint Survey
A pre-construction survey of the existing condition of the spillway walls is done to find the thickness of concrete that was swiped away and re-concrete.
The preconstruction survey report is then submitted to the contractor.
Cutting Broken Reinforcement & Demolition work
Existing worn-out reinforcement bars are cut off using a gas cutter and grinder. Also, the existing concrete surface is chipped off by the chipping machine until loose soft concrete is removed. The primary purpose of chipping off concrete is to increase the surface roughness, so bonding between fresh and old concrete is good.
Erection of Scaffolding
Class B MS pipes are erected to assist in chipping, drilling, anchoring, concreting, and epoxy work.
Corrosion Treatment Work
Corrosion treatment of existing reinforcement bars is done to protect rebars from rust.
Drilling and Anchoring Work
Holes of 28 mm or 25 mm diameter and 30 mm or 40 mm depth are drilled using a drilling machine. The hole is cleaned using an air blower, and the anchor rod is anchored using a chemical, Anchor – fix.
Welding Reinforcement bars
Existing worn-out Reinforcement bars are replaced by new Reinforcement bars of the required diameter. Here, we used both lapping and welding to replace worn out bars.
High Strength concrete work
Firstly, the rebars are provided with sufficient cover using different size cover blocks. The concreting surface is then cleaned by an air compressor or water jet. Next, the framework is provided for casting using a tie rod or any other suitable way. Finally, high-strength M60 grade Concrete or micro concrete is poured on the surface. The required number of cube sets is prepared as a sample of the concrete casting.
A vibrator is then properly used to eliminate air bubbles by vigorously shaking the freshly poured concrete. The framework is also frequently inspected to prevent leakage of mortar and deflections.
The applied framework is removed after 3 to 5 days and the concrete surface is cured for 7 days.
Application of Epoxy
The epoxy application area is firstly cleansed using the sandblasting machine. The resulting surface is then coated with primer, and a high abrasion-resistant epoxy coating is applied on the surface. The thickness of the epoxy is maintained as 10 -15 mm but may vary from surface to surface.
Post-Construction Survey And Documentation Work
After the completion of concrete works, a joint survey is conducted to measure the exact quantity of concrete.
Finishing & Site Clearance
After concreting and epoxy coating is completed, dismantling of Scaffolding, demobilization of plant & equipment, and construction materials are done.