Fluid flow assessment of double-chambered settling basin caverns during the operational conditions

• The influence of fluid flow within rock mass joints during operation and emptying conditions in the double-chambered settling basin caverns is analyzed. • A leakage assessment is conducted to determine the potential for water leakage from the caverns during the dry season. • The stability of the cavern is evaluated under long-term operational conditions involving fluid flow. The stability of the underground structures is critical for ensuring safe and efficient operation in hydropower projects. A key challenge is understanding how fluid flow through discontinuities in the surrounding rock mass influences the performance of underground structures like tunnels and caverns. This study investigates the stability of double-chambered settling basin caverns in a Hydropower Project in Nepal, focusing on the behaviour of fluid flow under operational conditions using a hydromechanically coupled discontinuum modelling approach. A representative numerical model is developed based on site-specific rock mass and joint properties, supported by laboratory tests on intact rock samples. The analysis shows that the maximum normal displacement induced by fluid flow in the joints is 6 mm, which is insufficient to cause instability. A leakage assessment is also performed to evaluate water flow from the caverns into the surrounding rock mass under different operating conditions. The maximum leakage is found to be 1.64 lt/min/m from a 3 m wide weakness zone, slightly exceeding the recommended limit of 1.5 lt/min/m. The results highlight the importance of comprehensive evaluation of fluid-rock interaction to ensure the long-term stability and serviceability of settling basin caverns. To the best of author’s knowledge, the influence of fluid flow through joints in water-filled underground settling-basin caverns has been rarely studied.