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Research of observational method on the groundwater in the tunnel excavation using the SWING method
Tunnelling and Underground Space Technology Tunnelling and Underground Space Technology 21 (2006) 420
incorporating Trenchless Technology Research
www.elsevier.com/locate/tust
Research of observational method on the groundwater in the tunnel excavation using the SWING method Yuzo Ohnishi a, Hiroyasu Ohtsu b, Kenji Takahashi c, Toru Yasuda
c
a
c
Department of Civil Engineering System, Kyoto University, Kyoto, Japan b International Innovation Center, Kyoto University, Kyoto, Japan Department of Tunnel Engineering, Pacific Consultants Co., Ltd., Osaka, Japan
Groundwater poses problems for the construction of mountain tunnels in that measures to prevent or control face collapse and tunnel drainage are needed due to the large quantities of water inflow that result from the discontinuous nature of the ground. Groundwater problems in the surrounding environment include the chain reaction of damage to the surrounding water environment that occurs due to the drainage of groundwater and the impacts of groundwater on existing water resources. There have been many cases in which such problems have inevitably led to enormous cost overruns and missed deadlines. Numerical analysis has been a primary method to evaluate such groundwater problems, but it requires the time and effort of preparing ground models of a certain scale and processing the data. For this reason, in almost all cases, the evaluation of groundwater problems has relied on preliminary evaluation throughout, and reverse or verification analysis rarely been performed during the construction. Moreover, even with current analysis tools it is difficult to conduct impact evaluations that reflect the preceding excavation data. The SWING system is not a numerical analysis method using a ground model, as represented by seepage flow analysis or the modified tank model. Based on the water inflow incurred by actual tunnel excavation, the model is conducted with a unit slice volume of 50 m in the excavation advance direction, and a hydraulic equation is applied within this slice volume to determine the coefficient of permeability and the effective porosity. Furthermore, based on the hydraulic constant determined from preceding data, the range and volume of the drop in groundwater level and the drop in the quantity of marsh water are determined for the slice volume. Then, during tunnel construction, it is used to validate the results of predictions made against site measurements and the current impact of droughts. The SWING system was used to make predictions based on these initial settings. As the construction progressed, the excavated sections were reviewed based on the preceding construction data, and continued estimates of the as-yet-excavated sections were made. In the case study here, identification of the excavated sections and predictive evaluation for the as-yetexcavated section was done in about 2–3 h, including correction of the input data. In some cases, the results of drain boring at the face were retrieved rapidly and determination of the quantity of water inflow during the main shaft excavation and predictions of the effect of the accompanying drought were done instantaneously. Therefore, this system can be considered to be one of sufficient practical value. The difficulties in determining the stability and permeability of the ground prior to tunnel construction often result in inevitable groundwater-related troubles. In addressing these problems, the SWING system is expected to play an important role in future tunnel construction, in that it allows the observation and measurement of the surface water and groundwater produced both inside and outside the tunnel shaft in the course of construction, as well as the immediate feedback of the results in design and construction. Keywords: Tunnel; Groundwater; Observational method
doi:10.1016/j.tust.2005.12.064
incorporating Trenchless Technology Research
www.elsevier.com/locate/tust
Research of observational method on the groundwater in the tunnel excavation using the SWING method Yuzo Ohnishi a, Hiroyasu Ohtsu b, Kenji Takahashi c, Toru Yasuda
c
a
c
Department of Civil Engineering System, Kyoto University, Kyoto, Japan b International Innovation Center, Kyoto University, Kyoto, Japan Department of Tunnel Engineering, Pacific Consultants Co., Ltd., Osaka, Japan
Groundwater poses problems for the construction of mountain tunnels in that measures to prevent or control face collapse and tunnel drainage are needed due to the large quantities of water inflow that result from the discontinuous nature of the ground. Groundwater problems in the surrounding environment include the chain reaction of damage to the surrounding water environment that occurs due to the drainage of groundwater and the impacts of groundwater on existing water resources. There have been many cases in which such problems have inevitably led to enormous cost overruns and missed deadlines. Numerical analysis has been a primary method to evaluate such groundwater problems, but it requires the time and effort of preparing ground models of a certain scale and processing the data. For this reason, in almost all cases, the evaluation of groundwater problems has relied on preliminary evaluation throughout, and reverse or verification analysis rarely been performed during the construction. Moreover, even with current analysis tools it is difficult to conduct impact evaluations that reflect the preceding excavation data. The SWING system is not a numerical analysis method using a ground model, as represented by seepage flow analysis or the modified tank model. Based on the water inflow incurred by actual tunnel excavation, the model is conducted with a unit slice volume of 50 m in the excavation advance direction, and a hydraulic equation is applied within this slice volume to determine the coefficient of permeability and the effective porosity. Furthermore, based on the hydraulic constant determined from preceding data, the range and volume of the drop in groundwater level and the drop in the quantity of marsh water are determined for the slice volume. Then, during tunnel construction, it is used to validate the results of predictions made against site measurements and the current impact of droughts. The SWING system was used to make predictions based on these initial settings. As the construction progressed, the excavated sections were reviewed based on the preceding construction data, and continued estimates of the as-yet-excavated sections were made. In the case study here, identification of the excavated sections and predictive evaluation for the as-yetexcavated section was done in about 2–3 h, including correction of the input data. In some cases, the results of drain boring at the face were retrieved rapidly and determination of the quantity of water inflow during the main shaft excavation and predictions of the effect of the accompanying drought were done instantaneously. Therefore, this system can be considered to be one of sufficient practical value. The difficulties in determining the stability and permeability of the ground prior to tunnel construction often result in inevitable groundwater-related troubles. In addressing these problems, the SWING system is expected to play an important role in future tunnel construction, in that it allows the observation and measurement of the surface water and groundwater produced both inside and outside the tunnel shaft in the course of construction, as well as the immediate feedback of the results in design and construction. Keywords: Tunnel; Groundwater; Observational method
doi:10.1016/j.tust.2005.12.064