Mr. Pham Nguyen Hung - Chairman of PECC1’s Management Board (first from left) and Mr. Vu Van Dien - Manager of the Scheme (middle) representing the Company to receive award
Reporter: PECC1 received the award from FIDIC, can you provide some information to readers about this organization, Sir?
Mr. Pham Nguyen Hung: FIDIC is the voice of the global consulting engineers and a prestigious large organization in the field of infrastructure consulting. The FIDIC Award is annually granted with the aim of honoring projects making great contribution to the world economy and community. The nominees are technical consulting companies from various fields.
The FIDIC’s evaluation process includes many rounds, by comparing and evaluating among projects nominated from member countries. The reviewing council is formed from world well-known experts in the field of construction infrastructure consultancy. In 2018, Viet Nam was the only country in ASEAN whose project was granted the prestigious award of FIDIC. Therefore, the award for Huoi Quang Hydropower Project is not only an honor for PECC1 but also a great pride of the Viet Nam’s Power Engineering Consulting sector.
Reporter: Could you tell us about the difference as well as the complexity of Huoi Quang Hydropower Project compared to the others designed by the Company?
Mr. Pham Nguyen Hung: Huoi Quang Hydropower Project is a complex one with the first underground plant designed and supervised by local consultants. Previously, the underground machine room of Hoa Binh and Ialy Hydropower Plants were designed and supervised by consultants from Soviet Union. Huoi Quang Hydropower is the only hydropower project with the energy line including underground upstream and downstream surge tanks. The plant complex includes many items and is located inside the basalt-rock mountain with complex geological structure.
The plant’s elevation from the bottom of the foundation is 159m, but it had to be constructed in the condition that Son La Hydropower Project operated generation unit No. 1 at the end of 2010 with a rising water level of 215m (56m in water column difference). Therefore, the waterproofing design for the Plant area and construction solution for the outlet area is really difficult. With the efforts to overcome difficulties and determination to control the situation, PECC1 has proposed many construction solutions for items as well as appropriate solutions along with additional design calculations to ensure the construction progress and work safety.
Particularly, the construction drawing design of the underground hydropower plant shows thousands of pre-installed items, seepage drainage pipelines and components as well as the large underground cavity in the plant’s scale, requiring a force of key, experienced officials’ great attempts to competently apply 3D technology, ensuring the design of thousands of construction drawings with highest quality. So far, all the construction drawings have been properly performed on works, without missing any pre-installed detail. That is the most obvious demonstration, confirming the success in managing the design team, when Viet Nam self-designs the underground work for the first time.
Reporter: Could you tell us some specific initiatives in design consultancy for Huoi Quang Hydropower Project?
Mr. Pham Nguyen Hung: Some typical innovations can be shared such as: Hoa Binh Hydropower Plant or Ialy Hydropower Plant has separate ventilation tunnels, traffic and cable tunnels. It was recognized by PECC1 that existing of such tunnels increases the construction workload, while as required for safety, each tunnel need a tunnel arch-cover or other large areas of tunnel body but not used. In order to save cost for the investor, PECC1 has installed a ventilation section above the traffic tunnel, utilizing vacant space of the arch-cover. Cable tunnels are also arranged with cable ditches located under the tunnel floor and are arranged with insulating structures for the upper part. The rest of the tunnel body is divided into two parts, one part of it is utilized for ventilation, the other is used for emergency exit in case of incident. Thus, a intake ventilation tunnel and an intake tunnel are completely eliminated.
When the vertical ground of downstream surge shaft was being excavated down to the elevation of 208m, there appeared weak rock zone (tectonically destroyed which needs to be treated), to calculate for reinforcement of surge shaft, we had to deal with the problem of 3D deformation stress by the process of excavating down ground by the finite element method. This problem has been studied for a long time, but not yet completed. Thus, we hired Norwegian experts (with intensive experience in the field of handling underground work design) for calculation. However, after studying the parameters of the project, Norwegian experts said that this was surge shaft classified as a high pressure type in the world, with complex geological conditions, it needs a minimum of 6 months to complete the work. Thus, it will greatly affect the construction progress and related costs. Therefore, we have focused on studying the issue and after 3 months, we have found the solution.
Reporter: During the project implementation, how do international consultant experts assess the consultancy results of PECC1?
Mr. Pham Nguyen Hung: Exactly! During the survey, the preparation work of technical design for the project, PECC1 conducted measuring the natural stress by convergent measurement method. Thereby, the ratio of horizontal stress and vertical stress was determined at K=1.4. This is a very crucial parameter when calculating the underground work complex because the higher the horizontal stress is, the greater the disadvantage of supporting the high tunnel walls is.
After the design documents for the downstream surge shaft treatment was prepared by PECC1, local and foreign consultants have verified and wondered whether the figure was appropriate for North West area of Viet Nam or not. For ensuring the objectivity, EVN hired a third consulting unit introduced by foreign consultants, who is the professor from the Institute of Earth Crust’s Stress Studies, under the China Seismological Bureau, to measure the natural stress. Test measuring results show that the horizontal/ vertical stress ratio reaches 1.35, which is not much different from the survey results by PECC1.
During the design process of handing unfavorable geological conditions at the downstream surge shaft, PECC1 has received close guidance from EVN’s leaders. PECC1 has mobilized experienced engineers, working with high intensity. After the completion of design for handling unfavorable geological conditions at the downstream surge shaft by PECC1, we have sent the result to the Consultants for verification (Power Engineering Consulting Joint Stock Company 2 and Fichtner Consulting Engineers Co., Ltd. (Germany)). Finally, the result was verified and agreed by the former and the latter and approved by Viet Nam Electricity.
Reporter: Thank you so much!