Predection Of Water Inflow For The Tunnel Wall Rocks With Highly Pervious Zone And The Disposal Principles

The effects of tunnel construction on the wall rocks include the development of adisturbance zone around excavations and the alteration of ground water circulation systemaccordingly. When a highly pervious section is excavated, the influx of groundwater into theexcavations generally occur, and water inflow may incur wall rock collapse. In the principlesof sustainable development, the magnitude of groundwater inflow due to tunnel constructionshould be controlled to meet the environmental requirements and to realize risk controlobjects.The prediction of highly pervious sections in the wall rocks is one of the key focus forthe survey and design in tunnel engineering, since the water inflow during tunnel constructionis mainly related to the highly pervious sections. A recommended classification for the highlypervious sections, in terms of engineering geology and hydrological geology conditions, isproposed as the followings:①highly pervious section controlled by rock mass penetrability;②highly pervious section controlled by fracture zones;③highly pervious section controlledby faults;④highly pervious section controlled by the structure in a fold;⑤highly pervioussection controlled by a composite of structures. A highly pervious section type may include afew sub-types.The success of the design and construction of a tunnel requires a rational prediction forthe wall rocks water inflow. However, a significant difference between the water inflowpredicted from a conventional calculation and the practical water inflow is generally realizedduring tunnel construction. The difference can be generally attributed to the hydrologicalgeology model, which is used to calculate the predicted water inflow, is far from thehydrological geology conditions in the practical wall rocks. It is well recognized that thewater inflow is mainly related to the highly pervious section in wall rocks. The properties of ahighly pervious section depends on the conditions of engineering geology, hydrologicalgeology, groundwater recharge, the features of the designed tunnel. A comprehensiveprediction method for the water inflow of a highly pervious section is proposed, with theseconditions as index. For the wall rocks water inflow prediction of the steeply pervious zone,the proposed semi-analytical method to calculate the maximum instantaneous water inflowand the stable water inflow. A case history from a extra-long highway tunnel in Qinling mountain, with serious waterinflow during tunnel construction, is used to check the proposed composite prediction method.The calculated water inflow using semi-analytical method is generally in accord with thepractical water inflow observed during tunnel construction. The analysis on the features of thewater inflow of the case history indicate that the proposed comprehensive prediction methodis, at least, proper for the prediction of water inflow of the highly pervious section controlledby faults, with a high dip angle.Finally, a design procedure is proposed for the disposal measures of wall rocks waterinflow of tunnel and underground structures, in terms of guiding the survey and design of thestructures. In the proposed design procedure, the main factors include the predicted waterinflow, groundwater allowable discharge and the environmental effect of the groundwaterdischarge.