越江公路盾构隧道浅埋段地温场演化趋势模拟分析

Simulation Analysis of Geothermal Field Variation Tendencies around Shallow Sections of Cross-river Road Shield Tunnels

越江公路盾构隧道浅埋段地温场演化将影响隧道穿越的江滩区域的工程地质条件。基于有限差分法建立了南京长江隧道的数值模型,分别将实测地表温度和管片内侧温度作为地层外部交变热源与内部交变热源,对隧道浅埋段典型断面地温场的演化过程进行了模拟分析。结果表明:隧道与土体间的热交换作用使隧道周围的初始恒温地层转变为年变温地层。在高温期,隧道向周围土体传热;在低温期传热方向相反。隧道周围及两孔间存在显著变温区,其最大温升值达7.14℃,年波动最大峰谷值接近10℃。该显著变温区位于距隧道外壁5m以及两孔之间的区域。其地温场在隧道运营20a后可达到初步稳定。建立了该显著变温区内地温场的年际波动模型,据此可估算出隧道周围土体不同距离处的年际温度值,该模型可为火灾等极端传热条件下估算隧道浅埋段地温场提供初始值。

The geothermal field variation around the shallow section of cross-river highway shield tunnels will influence the engineering geological condition of the river beach where the tunnel has gone through.A case study on Nanjing Yangtze River tunnel is proposed in this paper with developing the numerical models using finite difference method.The measured ground surface temperature and inner segment temperature are employed as external alternating heat source and internal alternating heat source,respectively.The variation process of the typical shallow-buried section of the tunnel is then simulated and analyzed.The results show that the initial temperature-constant geothermal field is transferred to daily temperature-variation one owing to the heat transferring effects.The heat transferrs from the tunnels to the soil mass around in high air temperature period and vice versa in low air temperature period.An obvious varying temperature zone is discovered.Its highest temperature increase reaches 7.14℃,and the highest peak-to-valley value of temperature fluctuation approaches 10℃.This zone is located within the distance of 5mto tunnel exterior and ranges between the two tunnels.The distribution characteristics of geothermal field will be preliminarily stable after 20 years of tunnel operation.In addition,an annual fluctuation model for geothermal field in relative high temperature zone is developed,which could be employed to calculate the temperature around the tunnels with different distances in different times.The model can be used to estimate the initial temperature value around the shallow section of the tunnel under the extreme heat transfer conditions like fires.