With the acceleration of urbanization in China, the pressure of urban traffic is further highlighted. At present, underground rail transit has become the mainstream direction of urban traffic development. Due to the particularity of underground rail transit, the safety risk management of its construction process has attracted much attention from all walks of life. At present, Beijing Metro Lines 4, 5 and 9, the Olympic branch line, Dongzhimen-Capital Airport Line and Yizhuang Line are all under construction.
Characteristics of underground rail transit engineering Underground engineering has the following characteristics: great concealment. The operation is cyclic. The workspace is limited. During dynamic construction, the mechanical state changes, and so do the mechanical and physical properties of surrounding rock. The working environment is bad. At the same time, underground engineering has a great influence on the surrounding environment, which will cause vibration, ground subsidence, noise and changes in groundwater conditions.
Urban rail transit has several remarkable characteristics, namely, the surrounding environment is complex, there are many buildings and underground pipelines, and the requirements for construction deformation control are high; Engineering geology and hydrogeology are complex, with many uncertain factors; There are many structural forms, many cross-conversions of construction methods, and the construction is difficult. Time limit for a project pressure, etc. These characteristics are concentrated in the high risk of the project. In order to complete the construction task safely, with good quality and quantity, it is necessary to systematically manage the risk and safety of the project.
The main contents of project risk management include: risk identification, estimation, evaluation, countermeasure monitoring, etc. First of all, we should identify the risk factors, understand and determine which risk factors may exist in the project, what impact these risk factors will bring to the project, and what are the specific reasons. At the same time, combined with the estimation of risk degree, we can know the main risk factors of the project. Secondly, according to the probability of possible risks, the possibility of increasing the difficulty of the project, the loss of personnel and property, the social impact and the impact on the construction period, etc.
Do basic work well and effectively prevent risks. After correctly identifying the risk factors in all aspects of the project, take measures to avoid and prevent risks from the scheme design.
First of all, on the basis of reviewing the construction drawings and methods, according to the surrounding environment, identify and study all kinds of risk points in the construction of this bid section, make qualitative evaluation and classification, formulate corresponding emergency plans, and do a good job in dynamic risk management of the project.
Dynamic monitoring of risk points identified in construction is an important content of subsequent risk management. Through dynamic management, the information transmission in construction management is standardized, and the risk awareness and scientific management awareness of all parties involved in construction, especially the construction unit, are enhanced. Dynamic management of major risk points with the construction unit as the main body mainly includes preventive preparation in advance, process monitoring and control, and information management of known and predictable risk points above AA in different construction stages.
For major risk points, the following preparations should be made in advance:
1. Preparation and approval of special plans and emergency plans for major risk points The construction unit shall dynamically identify risk points according to different construction stages, and must prepare detailed special construction plans for known and foreseeable major risk points. Planned materials, quantity and specifications of machines and tools, personnel preparation, water and electricity preparation, information contact, etc. The risk points that need to be passed should be clearly defined. The scheme should be demonstrated by enterprises or external experts one month before the risk point and submitted to the chief supervision engineer for approval. At the same time, in order to strengthen the timely control of risk points, the construction unit should comprehensively count and sort out the basic situation of risk points and actively make preparations in all aspects.
2. The external coordination preparation of major risk points, and the contact and coordination between relevant property units and transportation and municipal departments should be done 15 days in advance, so as to gain the understanding and support of relevant units and make full preparations and cooperation.
3. Full participation in dynamic risk management should establish a training and disclosure mechanism for dynamic management of major risk points to ensure full participation in dynamic risk management. According to the identified major risk points and special construction schemes, the chief engineer of the construction unit must be responsible for organizing the management personnel above the section chief and team leader of the unit to carry out training, education and technical disclosure on risk management procedures and special schemes. The section chief and team leader shall organize the training of on-site construction operators. Training should be recorded and written disclosure should be clear.
4. Appropriate risk points, process monitoring and information feedback in the process of risk point construction, measures should be adjusted in time according to engineering characteristics, corresponding early warning values and replacement values should be formulated according to standards, and construction should be guided strictly by monitoring and measurement data. When the warning value is reached, the construction unit must report it step by step according to the procedure and immediately prepare to start the emergency plan. Risk points in the process of implementation (such as underground construction crossing bridge piles, pipelines, building foundation side, tunnel face seepage, serious local collapse, etc.). ), strictly implement the established scheme and measures, strengthen the quality control of each process, and ensure the safety of process T, so as to ensure the safety of the project. Therefore, the supervision unit should strictly monitor the scheme, conduct special research with all parties in time, and solve practical problems in construction.
5. Establish dynamic management files of risk points. The dynamic management files of risk points should include the following contents: the preparation of prevention and control plans and emergency plans for major risk points, including the identification of major risk points in different construction stages, special plans and emergency plans, as well as the implementation procedures, organizations, materials and equipment, and the contact information of relevant units and personnel. The approval record of the scheme; Preparation records before the implementation of risk points. Records of the implementation process of risk points. Summary of experiences and lessons after all risk points are avoided, including: surrounding environment of risk points, main construction methods (main technical parameters and main materials should be summarized in detail), time taken for avoidance, monitoring and measurement data and other relevant data, construction technical measures and scheme implementation during risk transfer, etc.
Brief Introduction to the Project of Bid Section 3 of Beijing Metro 10 Line This paper briefly introduces the dynamic risk management of Su Huang Section of Bid Section 3 of Beijing Metro 10 Line.
The third contract section of the civil construction (the third batch) of the first phase of Beijing Metro 10 Line: suzhoujie station to Huang Zhuang Station, suzhoujie station in the west and Huang Zhuang Station in the east, including two shafts, two connecting passages and the connecting line between 10 Line and Line 4. The designed mileage of this section is k1602./kloc-0 ~ k2360.92, and the total length is 758.82m 10 and the designed mileage of Line 4 is l100316.948 ~ l/kloc-. The top of the tunnel is covered with soil from west to east 14.9 ~ 7.0m, and the excavation method is mainly adopted. The tunnel passes through Haidian South Road, and the route passes through commercial, cultural and medical areas, with concentrated passenger flow and heavy ground traffic. There are as many underground pipelines as 10, and the buried depth is relatively shallow. From top to bottom, there are artificial accumulation layers and Quaternary sediments. Groundwater in the tunnel crossing range includes upper stagnant water, interlayer diving, diving and confined water. Tunnel construction methods include: middle hole method, short step method, CRD method and double-side heading method.
According to the characteristics, different construction stages, different construction sites, construction technology, engineering geology and hydrogeological conditions of interval excavation in this project, identify risk points and determine the possible hazards caused by the above risk points in this project:
1) Tunnel collapse and roof fall.
2) Sand gushing and water gushing in the tunnel.
3) The power pipe trench cracks and collapses;
4) The water supply pipeline is cracked.
5) The rainwater (sewage) pipe cracks, water gushes out and mud gushes out;
6) pavement subsidence, cracking and uplift;
7) Bid gas leakage.
8) The power line and telecommunication line are broken and disconnected.
Therefore, this project mainly adopts the following measures:
1 Establishment of emergency rescue organization In order to ensure construction safety, in case of danger, timely and effective rescue can be obtained, and the danger can be controlled to a minimum. Set up an emergency rescue leading group. After the dangerous situation occurs, it should be reported according to the procedure. First, the monitor on duty and the technical personnel on duty report to the management department (leader and deputy leader of the emergency rescue team) and the site supervisor, and then the management department (leader and deputy leader of the emergency rescue team) informs all members of the emergency rescue team. After a brief analysis, report it according to the predetermined procedure, and the reporting personnel have a specific division of labor.
2. Prepare emergency relief materials. At ordinary times, raincoats, flashlights, square timber, woven bags, straw bags, I-beams, steel pipes, steel plates, water pipes, gas masks and other emergency supplies, generators, pumps and other equipment should be placed at a distance of 15m from the excavation face; Prepare 30m3 3-5cm gravel for each well area. Materials should be classified and neatly stacked, clearly marked, and special materials should be used. Materials, components and equipment used shall conform to the provisions and design requirements of national and industry standards, and shall have factory certificates and quality certificates. If there is any reduction or damage during construction, it should be replaced and supplemented in time. At the same time, the Equipment Department is responsible for daily checking the integrity of emergency materials and equipment.
3. Formulate prevention and control measures and emergency plans for major risk points. From section E to section F and the transition section of section F, the buried depth of tunnel roof is 6.2m and 6.7m respectively, and the excavation span is 17.4m and 16.5m respectively. Because the crossing stratum is mainly silty clay layer, silty soil layer, fine medium sand and pebble layer, the stratum has poor self-stabilization ability and is easy to collapse. During the construction period, the monitoring and measurement work must be strengthened, and the problems found should be solved in time.
This paper briefly introduces the emergency plan for collapse and roof fall in the construction of large-section shallow-buried underground excavation;
1. In the process of excavation, the principles of "pipe entry, strict grouting, short excavation, strong support, quick closure and diligent measurement" must be strictly followed to control the surface subsidence.
2. The tunnel in this section adopts "advanced large pipe shed and advanced small pipe" for pre-grouting to reinforce the stratum. Double-side heading method (9 heading pits) is adopted for excavation, and temporary I-beams are added to the left and right heading pits. Each pilot tunnel is excavated in an arc shape, leaving core soil, strictly controlling the stagger distance of the upper, lower, left and right caverns, excavating footage every cycle, closing the inverted arch in time after excavation, closing the tunnel face when necessary, thickening the initial alkali spraying thickness, and changing the steel bar grille into the I-beam grille to reduce the connection time of each process.
3. Strengthen the advance geological forecast, explore first and then dig, detect 2 times the excavation footage in advance, find out the soil and water content ahead, and guide the construction.
4. Backfilling grouting shall be carried out in time after initial support. Grouting should be carried out in strict accordance with the grouting construction technology after initial support, and grouting parameters should be controlled to ensure grouting effect.
5. The surface monitoring points in this section should be properly encrypted to strengthen the monitoring of ground settlement, tunnel clearance convergence and vault settlement. If the convergence value and vault settlement value are abnormal, feedback should be given immediately to guide the construction.
6. Send special road patrol personnel to strengthen the road patrol, and report the problems in time.
Concluding remarks
In a specific project, it may be a collection of various risks. Correct risk identification, avoidance and prevention, determination of feasible schemes, strengthening management, and close cooperation of all parties in the project are the keys to do a good job in risk management of underground rail transit projects. At present, the Su Huang section of 10 line has passed the above-mentioned risk points safely, and the section runs smoothly, entering the second lining construction stage. All aspects of work have been effectively controlled, and no engineering accidents and accidents endangering public safety have occurred. This shows that the operation of risk safety management system is effective, scientific and feasible, and can meet the needs of complex construction management of subway.
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