Research On The Key Technologies Of Deformation Control Under Construction Disturbance Conditions And Its Application To Subway Crossing Above Existing Subway At Close Range

In order to improve the worst traffic condition of the cities in our country, developing the subway is a major strategic decision to solve traffic problems in large cities. Duing the subway construction, it unavoidably happens that some newly built subway lines or the municipal pipelines will pass through an existing subway line. Besides, metro construction is always of the complicated construction conditions, large span, temporary support, frequent construction methods exchange, and obvious excavation time-space effects . Consequently, the subway construction crossing an existing subway line at close range is a project which is a very difficult and complex technology, with a lot of risks. In the construction of the metro, these safety problems which cover a wide range of underground structure, many surface objects and surroundings, are not only inevitable , but also increasing . Consequently, some construction methods and auxiliary methods for minimizing the bad effect on existing lines to large extent ,should be adopted at present in underground construction crossing existing subway lines at close range, and it is a very important technical problem to be solved immediately.Based on the background of the No.10 line crossing the existing No.1 line of Beijing metro at close range, the key technology and its application in deformantion control for underground construction crossing existing subway lines at close range are studied by combunation of field investigation, lab tests, numerical simulation, theoretical analysis and field monitoring. The main conclusion of the present study are as follows:1. On the basis of engineering geological conditions and the technical difficulties, the reasonable technology schemes subjecting to the deformanon control are put forward. namely in view of actual project, the author first put forward the comprehensive measures to reduce the disturbance effect centering on the deformation of the existing subway, firstly construct ing the gate type wall for grouting using sleevet-grouting technique, which has good strata strengthening and antiwater effect. And then, the construction methods such as from top-to-bottom bench excavation in cross-section, pilot heading advanced excavation and supporting along the longitudinal section are conducted under the protection of the gate type wall, and the measured data from monitoring were applied to confirm design assumption and optimize construction schemes.2. A 3-D calculation lmodel of considering stratum-structure was built by using FLAC3D , the visual numerical simulation analysis of the construction process of the underground engineering crossing existing subway lines at close range is studied considering the time-space-construction, including from top-to-bottom bench excavation in cross-section, pilot heading advanced excavation and supporting along the longitudinal section. Besides, the deformation and stress characteristics of the gate type wall for grouting using sleevet-grouting technique, and the auxiliary measures of pre-grouting for the excavation section, and foot bolts with pre-grouting, are analysed. The above results have important theoretical meaning for guiding the practice of grouting and supporting of tunnels to meet the requirements and control deformation of the existing tunnels structures.3. In view of the deficiencies existing in the double-curve model and grey model, based on them, a new combined weighting model of the subsidence for the excavation tunnel crossing below the existing subway line is built on the condition of the minimal absolute values of errors, in which the weighting average is calculated with MATLAB. The engineering measurement results show that the predictive error with combined weighting model is reduced, and the satisfactory results are obtained. A new method for predicting subsidence deformation of the subgrade is provided.By implementing these above technical schemes, the subsidence deformation curves of the north line and the south line subgrade in existing subway line are gradually convergent, and the ultimate subsidence deformation can meet the requirements control deformation of the existing tunnels structures. Engineering practice shows that the construction of No.10 line crossing the existing No.1 line of Beijing metro at close range is successful, and the good technological social benefits are obtained, and it is of important theoretical meaning to guide the practice in the similar engineering.