Model Test Of The Effect Of Land Subsidence On Subway Tunnel

Land subsidence is a local engineering geological phenomena manifested as the lower earth crust surface elevation, that because the underground loose strata’s consolidation and compression. It is mainly due to excessive extraction of groundwater. Land subsidenceand ground fissures in Xi’an have become an important geological disaster,whichhas hindered Xi’an urban construction,brought serious losses and restricted the sustainable development of Xi’an city, and will bring a serious safety hazard to present large-scale urban rail transit constructions in Xi’an. Therefore, it is very significant and valuable to study the effect of land subsidence on metro tunnel in Xi’an city.This paper firstly described the basic characteristics of land subsidence along the Xi’an Metro lines, including regional geological background, formation lithology, geological structure, neotectonic movement, earthquake and hydrogeological condition. The influence of tectonic movement, groundwater, formation and construction activities on land subsidence were analyzed. Then the Xi’an metro line3was taken as engineering research background, the basic characteristics of regional land subsidence were also analyzed. On the basis of this, using the condition of Xi’an Metro Line3across Yuhuazhai ground subsidence groove center as a prototype, through the physical model test with1:25geometric scale, the basic characteristics of structure stress-strain data, soil pressure trends, the scope and size of the tunnels and surface displacement under the two different conditions (the1st condition is metro tunnel going across the long axis of the land subsidence groove centerand the2nd condition is metro tunnel going across the outer edge of groove center) were studied.The results show that under the1st condition, tensile stress increases in the bottom of the tunnel. The soil pressure affected area at the roof and bottom of the tunnel isrespectively about1.25and1.2times of the length of the groove center long axis(D).When the land subsidencereachs120mm, the surface displacement deformation zone is up to2.25D, the maximum ground settlement(Sg) is equal to0.051times of Sw, the maximum settlement on the roof of the tunnel(Sg) is equal to0.058times of Sw. Under the2nd condition, The soil pressure affected area at the roof and bottom of the tunnel is respectively about0.75and0.8times of the length of the groove center long axis(D). When the land subsidence reachs120mm, the surface displacement deformation zone is up to1.75D, the maximum ground settlement(Sg) is equal to0.022times of Sw, the maximum settlement on the roof of the tunnel(Sg) is equal to0.027times of Sw.According to the calculation result of model test, this paper provided the scientific theoretical guidance and evidence for Xi’an metro lines design, construction and safe operation. Meanwhile, it can also provide a reference for other regions tunnels and subways construction which affected by land subsidence.