We went to Middle Marsyangdi Hydropower for the ” Dam and Spillway Maintenance Project” undertaken by Lama-Venus-Himalayan JV. We performed the project procedure in various stages. Thus, in this blog, I will be writing about the work schedule we performed from start to completion of the project, Dam Spillway Structure Maintenance & Rehabilitation Work of Middle Marsyangdi Hydropower Station.
Overall, the project had to repair or replace existing reinforcement bars, perform concreting on the spillway floor and two exposed walls of the dam. And, finally, apply a high abrasion-resistant coat on the radical gate surface of the spillway.
Introduction to Project
Client: Nepal Electricity Authority (NEA), Middle Marsyangdi Hydro Power Station, Siudibar, Lamjung
Contractor: LAMA- VENUS- HIMALAYAN JOINT VENTURE, Kathmandu
Contract Identification No: MMHPS – 2076/77–CT-04
Location: Siudibar, Lamjung
Project: Dam Spillway Structure Maintenance & Rehabilitation Work of Middle Marsyangdi Hydropower Station (MMHPS)
Features of Middle Marsyangdi Hydropower Station
Run-of-River (ROR) Hydroelectric Plant*
Turbines: 2x 35MW
Installed capacity: 70 MW
ROR* – Running water is diverted from a flowing river and guided down a channel, or penstock, which leads to the powerhouse.
Following is the step by step working procedures of the project
Insurance of the overall project
Insurance of the overall project is done. It includes insurance of both Life and Nonlife aspects of the project. Life Insurance features insurance of project members, staff, workers, whereas non-life includes insurance of heavy and costly machines and equipment. Costly machinery covers Concrete Mixture, Concrete Pump, Excavator, Submersible water Pumps, Crane, 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 client, Nepal Electricity Authority.
Testing of Materials
Different construction materials to be used on-site are tested for their various properties before use. Reinforcement Bars, Cement, Sand, Aggregates, are tested in the lab to check their tensile and compressive properties. Whereas, for high abrasion resistant materials like Epoxy Chemicals, the Factory Test Certificate is the final.
The M60 Grade concretes’ mix design is done in the lab and a copy is sent to NEA.
Temporary housing, offices, laboratory, storeroom, workshops, workers camp, toilets, etc., that are essentially required on-site are set up.
Delivery and Installation of Plant & Machineries
Different Construction materials like Cement, Sand, Aggregates, Admixtures, MS pipes, Epoxy Materials, and other chemicals are delivered and stored on Site.
Machinery installed at the site are;
- Concrete Mixer
- Submersible Water Pumps
- Bar Bending Machine
- Sand Blasting Machine
- Bar Cutter and bar bender Machine
Access Road Construction
Aggregate armoured and stabilized pathway for heavy construction vehicles to reach the site and also to deliver construction materials to the site is constructed.
Large submersible pumps are fitted to pour out the water off the spillway as you can see in the pictures below.
Construction Coffer Dam
Large and small coffer dams are constructed for dewatering, diversion, and damming. The primary purpose of a cofferdam is to restrict water to flow back to the spillway and create a dry environment for a project to proceed.
Removing Sand Deposit and Debris
After continuously pumping out water, Sand deposits and debris are then removed. It is a very slow process and takes months to fully remove the sand deposits from the site.
Pre-Construction Joint Survey
A pre-construction survey of the access road, water and sand deposit level, the existing condition of the spillway, pier, ramp, roller bucket is done.
The preconstruction survey report is then submitted to the client.
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 main purpose of chipping off concrete is to increase the surface roughness, so bonding between fresh and old concrete is good.
Erection of Double 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 an 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 for previously used coupling.
Metal plates were installed in the lower portion of the spillway, to protect concrete from corroding.
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.
Handover of the project
After the completion of the project, the project is handed over to the Client in a small ceremony.
Here’s the short Youtube Video from the project,