Abstract

The underground penstock of the 250 MW hydropower plant (HPP) in Laos was leaked seriously several times from 2012 to 2016 and it affected to operation the HPP. In this paper, the authors introduce the solutions to rehabilitate the water convey of the HPP by realigning the penstock and strengthening the reused parts of the penstock. The installation of a new spherical valve to control pressure in the penstock required to use high strength reinforcement with double corrosion protection for top of the existing Vertical Shaft No.1 of the penstock. DYWIDAG & UTRACON GROUP recommended the installation of permanent strand anchors with a double corrosion protection system (type “TWINCorr”) to strengthen the vertical shaft No.1. This includes the installation of non-corroding, high strength concrete plates for the anchor head to meet highest requirements of corrosion protection whilst keeping the anchors de- and re-stressable. For an easy, safe and reliable control of the anchor forces during tensioning, several strands were equipped with DYNA Force load sensors. To ensure the quality of construction, UTRACON GROUP used borehole endoscope to check groundwater, carter problem in borehole during strand installation. The anchorage has been working swimmingly with minor reaction to the changes of loading, and minimum working bond strengths can be derived. After 5.5 years without production, the HPP resumed full operation by the end of May 2022.

Introduction

A 250 MW hydropower plant (HPP) is located on a river in Southern Region in Laos. The HPP combines a 141.49 mil. m3 reservoir and a long water convey to generate electricity with working head 400-600 m. Waterway comprises of intake, headrace tunnel, surge tank, penstock and powerhouse to convey the maximum design discharge (Qmax) of 59.22 m3/s. The intake component is a tower shaped component of 52 m high, with ellipse shaped cross section. Headrace tunnel is a reinforced concrete lining component of 5862.6 m long, its water clearance cross section is in rounded shape with inner diameter D = 4 m. Surge tank is a restricted orifice surge tank with rounded cross section. The restricted orifice of 141.13 m high has inner diameter D = 4 m. The tank shaft is 43.3 m high with inner diameter D = 12 m.

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