Présentations Colloques

Oral Presentation
7.04
Session 7.04: Groundwater and man-made underground works
Van Hasselt Blanca
Analysis by cross plot method for anticipating seepage during operation of unlined underground storage caverns
The topic addressed in this presentation is on early detection of unconformity of the seepage evaluated during construction compared to the expected seepage during the operation of unlined underground storage caverns for LPG or Oil. A first objective is the early identification of potentially de-saturated joints and therefore the implementation of remedial actions while access is still easy to the underground works. A second objective aims at optimising the seepage pump capacity prior to starting operation.**The methodology is based on cross plot analysis of seepage rate versus the hydraulic margin. The combination of both these parameters allows for calculating the productivity of a system. Therefore, as long as the hydraulic boundary conditions remain unchanged, the seepage is following a linear correlation with the hydraulic margin. Any change in the correlation between both these parameters hints at a change in hydraulic boundary conditions or a change in saturation conditions. The considered case assumes that there is no significant change in permeability (either by clogging or grouting works, nor by washing out of joints) during the period over which this analysis is made.**Illustrations are presented for different stages of underground cavern testing and commissioning, by focusing on the seepage measurements during the water curtain system testing (full size hydraulic test, FSHT), seepage measurements during the access tunnel flooding (pre-CAT), and seepage measurements during the cavern acceptance test (CAT).**The main implications are-**- early detection of problems, such as de-saturated joints potentially leading to insufficient hydrodynamic containment, this to allow for remedial works when construction is still on-going,**- early evaluation of the final seepage for operation such as to allow for adapted seepage pump capacity for operation,**- management of groundwater around the underground facility by improving grouting works or adapting the future operating procedures.**
France