The overburden deformation and damage that were caused by subway tunnel construction in a hard rock region were studied systematically. In this paper, the lithologic characteristics of the strata in the region are analyzed. The overburden deformation and damage characteristics caused by the drilling and blasting method (mine method) are presented. The crack evolution law and scaling law in the overburden are revealed. The corresponding relation between ground subsidence and the crack evolution scaling law is established. Then, these results are used to analyze and predict the ground subsidence. The damage characteristics and laws of the building on the ground that were caused by the ground subsidence are analyzed. The quality of the existing buildings in the area and their ability to withstand deformation are also evaluated. The settlement control criterion is established scientifically. Countermeasures are given that are designed to reduce the damage to the buildings.

1 Introduction

With the rapid growth of the economy and the scale of the increase in construction in the city, the problem of traffic congestion that is common in Beijing, Shanghai and other big cities has spread to other cities such as Qingdao and Dalian. Qingdao is one of the main cities on China's eastern coast and is also an important port and tourist city. The city has a total area of 10,654 square kilometers and a total population of about 2,760,000 (as of the end of 2007). With the implementation of the strategy of "Protection along the Bay, Development around the Bay", Qingdao is facing a renewed acceleration in the expansion of city and a significant increase in the size of the population, which has resulted in more serious urban road traffic problems. Therefore, the construction of Subway Line No. 3, which is about 24.9 km long, was initiated in Qingdao in 2009.

Subway Line No. 3 is mainly being constructed using mining method. The buried depth, which is generally 16 to 25 m, is relatively shallow. The formation is mainly hard rock (granite) and the geological conditions are complex and varied. The time span of the construction is long. The construction of the subway tunnel can cause damage to the environment, including to the surrounding rock mass, overburden and surface deformation, displacement, settlement, collapse, etc. The buildings (or structures) in the area, underground pipelines, various facilities and city roads that are along the line may be subject to varying degrees of damage. In particular, damage to the buildings in the area will be intensive. The construction period is long. The foundations and structures are of various types. Some of the buildings already have some structural problems that affect their safe use because of disrepair, some alteration by the residents, coastal erosion, etc. The construction of a subway tunnel under these buildings and other structures will damage them unless effective protection measures are implemented. Therefore, finding a way to avoid or at least reduce the damage to the buildings, guarantee the progress of the construction and control the construction risks has become an urgent problem that needs to be solved in the process of the construction of the subway tunnel. Therefore, conducting research on the overburden deformation, ground subsidence, damage characteristics and mechanisms that are caused by land subsidence is very useful. These as well as effective prevention and control measures are presented in the paper.

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