Noriyuki Ohira

Groundwater Recovering Engineering for Underground Structure and its Effects

Recently, constructions of highway in a city have been built in semi-groundstyle as one of environmental methods against noise pollution. However, in some cases, these constructions can influence harmfully on the groundwater environmental protection, because they intercept the groundwater flow system.Semi-underground highway of Touhoku Line in Nerima section intercepted the aquifer, which was expected that the maximum water table rose 3m at up-stream and went down 2m at down-stream. Therefore, groundwater recovering countermeasure was necessary.Based on the results of field surveying observation and numerical simulation, this paper explains the groundwater recovering countermeasure and its effects which can respond well to the underground structure, hydrogeological conditions and the variations of water table.As results, we took following steps by considering both situations in nature and in heavy rain.(1) Walls used for S. M. W (Soil Mixing Wall) in up-stream and down-stream were cut 3m and 3.5 m depth from the ground surface, respectively;(2) Underdrain was constructed;(3) The connected conducts with 200mm in diameter were installed in every 50m; and(4) Discharges in downstream was conducted through infiltration boxes or recharging wells set every 50m.During the construction, maximum water table rose in 1.5m at up-stream and went down in 1m at downstream, respectively. After this countermeasure was built, the water table is stabilized at the same depth as before. Therefore, the effect of engineerings for recovering groundwater system is obviously satisfactory.