| As a new kind of geological disaster, ground fissures are widely distributed in China, and definitely hinder the development of the city and daily life of the citizens. As the capital of China, Beijing is also the political economic and cultural center, where high concentrations of people live in a limited area which is filled with frequent engineering constructions. Since 1949, multiple subsidence centers have generated in urban area because of the large number of groundwater extraction. Besides, Beijing is located in the intersections of Yanshan fold(mountain area) and Huabei fault sag(plain area), with many strong earthquakes occurring in history. Therefore, Beijing is a developed area for ground fissures. With the process of urbanization and construction of metro system, metro tunnel will inevitably pass through the ground fissure areas. So, it is urgent and important to study the impact of ground fissures on metro tunnel during its construction and operation, especially in the soil and sand interbed area in Beijing. Based on the project of Beijing Subway Line 17 passing through Huangzhuang-Gaoliying ground fissure area, the main work and results of this paper are as follows:(1) The characteristics of faults along the subway line were described firstly. Then, the concomitant ground fissures of Huangzhuang-Gaoliying fracture were studied in detail on the basis of data collection and document consulting. The study showed that the activity intensity of Huangzhuang-Gaoliying fault increases and the activity time becomes new from south to north. The concomitant ground fissures are the reslut of the combination between fault and groundwater extraction.(2) Eight numerical models were established including three categories: ground fissure parallels to the subway tunnel with different distances, ground fissure intersects with the subway tunnel with different angles and the model without ground fissure just for reference. The effects of subway tunnel excavation on these different working conditions were simulated, and two special conditions were choosed for detailed analysis, including the model without ground fissure and the pratical condition of engineeringthat ground fissure is 50 m away from subway tunnel. The study showed that, the impact of ground fissure is small during the construction time of subway tunnel, and the influence of intersectional conditions is greater than the parallel conditions. The surface disturbance caused by the tunnel excavation is about 21 m, which is greater than 3 times of the tunnel diameter.(3) On the basis of the completion of tunnel excavation, the effects of ground fissure on different working conditions during operation were studied on the condition that there is a 2cm vertical dislocation on the bottom of the hanging side of ground fissure. The study found thatthe disturbance distance in hanging side caused by ground fissure movement is approximately 30 m, and 24 m in heading side. In addition, with the decreases of parallel distance and cross angle between ground fissures and subway tunnel, ground fissures activities have bigger influence on subway tunnel. When subway tunnel pass through the ground fissure site, it is the best choice to avoid intersecting with each other and the distance should be more than 30 m. If it is inevitable that the subway tunnel intersects with ground fissures, the bigger the cross angle, the more stable the tunnel support structure.(4) The simple harmonic waves with the peak acceleration of 0.2g and 0.4g were applied to the subway tunnel during the operation period, and dynamic response of the ground fissure site to the seismic load was studied. The study found that the gound fissure site has amplification effect on the seismic load, and the hanging wall of the amplification effect is greater than the footwall. |
PDF Full Text Request