Evaluation of the Influence Caused by Tunnel Construction on Groundwater Environment: A Case Study of Tongluoshan Tunnel, China
Quantification of each factor included in the indicator system.
Value of Tonluoshan tunnel
[B1] physical geography
[C11] average annual rainfall (mm)
According to rainfall records from local meteorological station, the average annual precipitation is 1215.5 mm in the tunnel area.
[C12] average annual evaporation (mm)
According to evaporation records from local meteorological station, the average annual evaporation is 959.6 mm in the tunnel area.
[C13] area of catchment zone (km2)
Tongluoshan tunnel passes through strata consisting of carbonate rocks of high permeability in the core and clastic rocks of low permeability in the flanks of Tongluoshan anticline. When calculating the catchment zone of tunnel inflow, a region composed of local watershed around the route of tunnel in the flanks and the entire karst valley are included. Total area of the catchment zone of Tongluoshan tunnel then is determined to 38.4 km2.
[C14] coefficient of rainfall infiltration
Based on the geological investigation report, infiltration coefficient of rainfall in the outcropping carbonate rocks ( and ) reaches 0.55, with 0.20 in the coal measure strata (), while it is only 0.054 in the Jurassic clastic rocks ( and ). Due to statistics of outcrop in terms of different lithology, 44% of them are carbonate rocks, while 32% are coal bearing strata, and 24% are clastic rocks.
[C15] spatial relationship between the tunnel and geomorphology
Length consisting of the section between 32 K + 700 and 34 K + 200 and that between 35 K + 800 and 36 K + 300 is about 2 km, belonging to the type of side below the valley and river crossing, while the rest belongs to other type.
[C16] capacities of reservoirs and lakes on the ground (m3)
There are no reservoirs and lakes within 2 km from the tunnel axis except Jinzhong reservoir, which is about 9 km far from the tunnel axis, storing approximately 300 thousand cubic meters. Since karstification is well developed in the tunnel area and Jinzhong reservoir is the origin of Qingshuixi River, it is taken into consideration from a safe point of view.
[C17] flow of surface rivers (m3/s)
Qingshuixi River is the main surface river which may have hydraulic connection with the water inflow into tunnel.
[B2] geology and hydrogeology
[C21] carbonate rocks exposure ratio (%)
As mentioned above, this ratio is about 44% in the tunnel area.
[C22] water yield property of aquifers
Based on the longitudinal profile of Tongluoshan tunnel, area of rocks with poor water yield property occupies 62.37%, with middle standing 30.14%, while the left (7.5%) is considered as aquifer with very good water yield property.
[C23] water pressure on the tunnel (Mpa)
Average water pressure on the tunnel is estimated as 1.0 MPa.
[C24] development of folds
Tongluoshan anticline is the main fold developed in the tunnel area with fractures coming from geological and karstic process.
[C25] development of fracture zones
Fracture zone passed through by tunnel excavation is found moderately developed.
[C26] formation lithology
Based on outcrops in the tunnel area, mudstone, shale, and clay stand for 21% and sandstone and siltstone stand for 35%, while carbonate rocks occupy 44%.
[C27] location of tunnel in horizontal and vertical hydrodynamic zoning of groundwater
From a regional scale, Tongluoshan tunnel is located in runoff area in horizontal and stressful saturation zone in vertical zoning.
[B3] tunnel engineers
[C31] length of tunnel (km)
About 5.2 km.
[C32] area of disturbed range (m2)
About 185 m2 including two tunnels.
[C33] construction method
About 80% of the tunnel excavated by full face excavation using drilling and blasting method, while the others adopt benching tunneling using drilling and blasting method.
[C34] burial depth of tunnel (m)
Burial depth between 100 m and 300 m stands for 50%, while the others have a value less than 100 m. From some statistic data and hydrogeological condition in the tunnel area, moderate level is given.
[C35] measures for prevention of groundwater flowing into tunnel
Composite lining is the prevailing waterproof used by Tongluoshan tunnel, while 20% of which adopts external pregrouting.