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1.前言 地下铁道东叶高速线的习志野台隧道,是在市区下面进行挖掘的典型的城市隧道,其中大部分区段采用新奥法施工。 被开挖的地层主要是称为成田砂层的半固结砂层。在交通十分繁忙的市区和住宅密集的地区下面施工,覆盖层厚度一般为5～12m,施工中的重要课题就是如何控制开挖中出现的地表下沉现象。另外,成田砂层的均等系数在2左右,细颗粒成分少,地下水位在隧道拱腰部位,很有可能产生流砂现象,所以在施工中必须处理好地下水。
1. Introduction The Nyohitsukai Tunnel on the Higashiyama Expressway of the Subway is a typical urban tunnel for excavation under the urban area. Most of the sections are constructed using the new Austrian law. The excavated strata are primarily semi-consolidated sand layers known as Narita Sand. In the busy traffic area and densely populated residential areas under construction, the thickness of the coating is generally 5 ~ 12m, the construction of an important issue is how to control the emergence of surface subsidence phenomenon. In addition, the equivalent coefficient of sand in Narita is about 2, with less fine particles and groundwater level in the arched part of the tunnel, which may result in quicksand, so groundwater must be properly handled during construction.