Subway Open-Cut Construction Technology

With the Development of urban metro Construction, open cut construction technology is being widely used in such works. However, application of this technology is just in an initial stage in China.Beijing Metro Puhuangyu Station Project ,Northeast Ventilastion Adit was Excavated with open cut construction method. The cut depth reached 21m.A 31 stories high-rise building is located to the west side of the metro cut and the building's foundation thereat brought a great affect to the metro foundation cut construction. A symmetrical wall faces (east and west cut faces) of the metro foundation pit can not be realized and a whole upper support structure can not be formed. In addition, the high-rise building produced an uneven side pressure to the metro foundation.In the same time ,both ends of this open cut section were connected with the under-ground adit sections. The prime support structures in the open cut and underground adit will be damaged in the progress of joint area construction and a change forces therein have to be encountered. So the construction of this project is considerably difficult and it required a strict technology and quality control measures. The technical research and construction progress control are very important and application of deep open cut technology in this project is very valuable.The open cut pit is Grade I foundation pit and is located in complex geologic strata which includes silt clay, fine sand, medium-coarse sand and gravels. A strict construction method has to be design to control the sinking of surrounding strata and pipelines. A supporting system, including soil nail, pipe foundation and anchorages etc were utilized. Technical research has been applied, during construction period, to supporting system, dewatering, structure and monitoring activities, and all the technical problems for construction of such project in special geologic strata and under particular circumstance were overcome. A construction technology suitable for urban metro open cut dewatering, support and structure was formed.