Abstract
The construction of an undersea tunnel below the Tsugaru Strait between Honshu and HokkaidoIslands in Japan through incipiently metamorphosed Miocene andesitic rocks have provided a remarkableopportunity to study the geochemical method to predict the gushing out of seawater into undersea tunnel, through fissures in zeolite facies metamorphosed rock mass from boundless overlying sea.
Close relathioship between discharge rate and K (and Ca) content of the seepage waters was found.K and Ca contents of the seepage waters generally increase and decrease respectively with the increase ofdischarging rate. The K content of seawaters, after extensively interacted with rocks, became extremelylow when the discharge rate is lower than hundred liter per minite. The Cl content of the seepage water canbe used to indicate the mixing ratio of seawater/meteoric water. Therefore, K×Cl value is proposed to bethe most important chemical parameter which clearly reflects physical properties of waters such as migrationvelocity of waters within the Miocene rock mass, water/rock ratio, water pressure and discharge rate.The variation of K and Cl contents of seepage waters from pilot bore holes and faces of tunnels providedcritical informations on how rapidly fluids are penetrating the rocks between the undersea tunnel and seafloor, permitting necessary precautionary measures to be taken to avoid disastrous entry of seawater.
