In one rock cavern for crude oil storage with the water barrier system, clay grouting (non-pressurized clay grouting) method was employed in order to control groundwater and to reduce an amount of seepage flow. Before applying this method to the construction, indoor and in-situ tests were performed to confirm clay clogging mechanism and effects of clay grouting.
Dans une cavite dans la roche destinee au stockage du petrole brut avec le système de barrière d'eau, une methode de stabilisation du sol par argile (stabilisation par argile sans pression) a ete employee afin de contrôler les eaux souterraines et reduire le volume des infiltrations. Avant d'appliquer cette methode à la construction, des essais en laboratoire et sur Ie terrain ont ete realises pour verifier Ie mecanisme de colmatage à l'argile et les effets de stabilisation du sol par argile. ZUSAMMENFASSUN: In einer Felsbetthöhle fuer Rohöllagerung mit Wasserstausystem wurde ein druckloses Toninjektionsverfahren zur Grundwasserkontrolle und Reduzierung von Sickerströmung angewendet. Vor der praktischen Anwendung wurden im Labor und am Ort Pruefungen ausgefuehrt, um den Tonverschluβmechanismus und die Wirkung der Toninjektion sicherzustellen.
In Japan, the construction of underground crude oil storage plants (3 sites - 5 million kiloliters) for national petroleum stockpiling was started in 1987, and all plants were completed in 1994. At present, oil installation has also been completed. The water barrier system is employed to prevent leakage of oil and petroleum gas at these three storage plants. The bedrock of the Kuji site, one of the three sites, consists of granite, but this is considerably fractured, and the average permeability coefficient is very large, (7.6 × 10–8 m/sec). Accordingly, difficulty in the construction due to excessive water leakage had been anticipated. However, in case extensive drawdown of groundwater level around caverns occurred during construction, it might be difficult to raise the groundwater table again after completion. Furthermore, remained unsaturated zone around caverns has possibility to invalidate functions of the artificial water barrier. Therefore, the caverns were excavated under the active water barrier system in order to prevent the excessive drawdown of groundwater level. In addition to this, it was necessary to reduce the amount of seepage in order to decrease the operation cost for wastewater disposal system after completion. Considering the above-mentioned requirements, the non-pressurized clay grouting method was employed, using the seepage flow from water barrier system to the caverns. Since the effect of the clay grouting has been confirmed, an outline of the process and its results are reported in this paper.
Generally, grouting means pressurized injection of hardening materials such as cement into cracks around boreholes. On the other hand, clay grouting stated hereafter is a non-pressurized grouting utilizing seepage flow directed toward caverns. Clay particles carried into fissures or fractures by seepage flow plug those flow path slowly and widely. As a result impermeability of extensive rock mass including caverns can be uniformly improved. Concretely speaking, clay grouting is accomplished in the following way. First, water barrier tunnels and water barrier boreholes are excavated prior to excavating the storage caverns. Then, while the caverns are being excavated, water is poured into the water barrier facilities in order to prevent the groundwater level from falling excessively. In the clay grouting method, clay is mixed with this water and applied to the rock through the water barrier facilities. The sequence of cavern excavation is as follows:
the top heading,
arch enlarging,
first stage bench cut,
second stage bench cut,
third stage bench cut.
