Second, combined with case analysis
1. Engineering overview
Zhuhu Tunnel is one of the key control projects in the Tai-Gan section of Jiangxi-Guangdong Expressway. The pile number is k196+569-k196+720, the total length is 15 1m, and the axial distance between the left and right tunnels is11.5m..
The inner contour of Zhuhu Tunnel is an arc-shaped wall semicircle arch with an arch radius of 5.71m. The width of the middle wall of the multi-arch tunnel is 1.8m, the clear width of a single tunnel is 10.25m, and the maximum total excavation width is 25.22m.
General situation of construction
(1) construction process
Middle pilot tunnel excavation support, partition wall construction, left pilot tunnel excavation support, left tunnel upper half excavation support, left tunnel lower half excavation support and secondary lining construction, left tunnel inverted arch construction, right pilot tunnel excavation support, right tunnel upper half excavation support, right tunnel lower half excavation support and secondary lining construction, right tunnel inverted arch construction. It is feasible to construct according to this technology, but the construction period is long.
(2) Monitoring quantity control
Monitoring and measurement of Zhuhu Tunnel can be divided into mandatory and optional items. The necessary items are observation of geology and supporting conditions, clearance convergence and vault subsidence. The selected items include axial force of anchor rod, internal displacement of surrounding rock, stress of supporting lining, supporting pressure of surrounding rock and interlayer, and surface settlement. Through monitoring and measurement, the changes and laws of mechanical form of surrounding rock and working state of support are mastered.
economic analysis
Two side wall pilot tunnels were cancelled, but the construction progress was accelerated, and the construction period was shortened from the expected 24 months to 17 months, five months ahead of schedule. At the same time, the project investment is greatly saved, and the temporary support amount of the side wall pilot tunnel is saved. The total cost saving is 1506896 yuan,
Third, the significance and content of construction monitoring of multi-arch tunnel
1. The significance of tunnel construction monitoring
Tunnel site monitoring and measurement is one of the core technologies in the design and construction of NATM composite lining, and it is also one of the important components of tunnel information design. Pre-design the cofferdam deformation of tunnel section, and grasp the extremely stable degree of the mechanical dynamics of surrounding rock and support in the construction process through the construction site monitoring, so as to ensure the construction safety, provide information basis for evaluating and modifying the initial support parameters, mechanical analysis and secondary lining time, and accumulate data to provide analogy basis for future design, ensure the tunnel safety, achieve the purpose of tunnel construction safety and save engineering investment.
Through the measurement of peripheral convergence, it provides a basis for the stability analysis of tunnel supporting structure. By calculating the peripheral convergence displacement rate, the final displacement value is predicted, and the best time for secondary lining pouring is selected. It provides reference for the optimization of tunnel construction technology and supporting lining parameters. Peripheral displacement is the most intuitive response to the change of stress state of tunnel surrounding rock, and measuring peripheral displacement can provide reliable information for judging the stability of tunnel space. According to the displacement velocity, the stability degree of tunnel surrounding rock is judged, which provides a reasonable supporting opportunity for secondary lining. Judge the design and construction of initial support: guide the design and construction with the rationality of method selection; Measure the overbreak and underbreak to determine the excavation quality and guide the construction.
2. The content of tunnel construction monitoring
In order to ensure the safe and reliable information of the tunnel, provide reference for similar projects, and provide the original basis for further theoretical research, this tunnel construction monitoring is carried out in full accordance with People's Republic of China (PRC) * * and national industry standards "Code for Design of Highway Tunnels" and "Technical Code for Construction of Highway Tunnels".
The main contents of geological monitoring include: observing and describing the surrounding rock geology, groundwater and lining support of the tunnel. Specifically, there are surrounding rock lithology, geological structure, structural characteristics of rock mass, deformation and failure of support, groundwater and so on. For the lithology of surrounding rock, it is necessary to record and describe the lithology in detail during excavation. For geological structures, it is necessary to accurately measure the occurrence of strata, record the occurrence, spacing, width, ductility, connectivity, fluctuation, filling and groundwater exposure of structural planes, and draw a sketch. As for the structural characteristics of rock mass, the structural types of rock mass should be divided according to the structural plane and its combination characteristics from the perspective of rock mass mechanics. For support deformation and failure, all kinds of support deformation and failure linearity of surrounding rock during construction should be recorded, and its occurrence law and control factors should be analyzed. For groundwater, it is necessary to monitor the leakage situation, leakage location and flow rate of groundwater.
Four, tunnel construction monitoring methods and measures
1. Preview method
(1) convergence meter monitoring
For the measurement of surrounding conditions, convergence meter or high-precision total station is usually used for data acquisition. Suggestions on the use of the convergence meter are as follows: take off several thin sections at the front end of a long fishing rod, process them with iron wire with appropriate thickness, fix a small hook at the top of the fishing rod, and then fix a similar hook near the hook of the convergence meter, which will be marked as hook B. When using, hang hook A on hook B, and then extend the fishing rod, so that the convergence meter can be hung on a high place conveniently.
(2) Landmark settlement monitoring
Drill (or dig) a hole with a depth of 20 ~ 50 cm on the surface of the earth, and put steel bars vertically. Cement mortar can be filled between the steel bar and the hole wall. The head of steel bar shall be polished smoothly and exposed to the ground about 1cm, and the measuring points shall be marked with red paint. The elevation of the measuring point is measured by the leveling point, and the surface subsidence value can be calculated by calculating the change value of the elevation of the measuring point before and after the surface subsidence.
(3) Monitoring of vault subsidence
Vault subsidence is mainly used to confirm the stability of surrounding rock. Three self-made steel bar embedded parts are buried at equal intervals in the arch of each measuring section. Before embedding, drill holes in the parts to be measured with a small drill, then put the embedded parts in, and fill them with concrete, and then measure them after the concrete is solidified. When measuring, it is necessary to use a steel tape with a suitable length, and the end of the ruler is connected with a self-made hook. Hang it on the measuring point, put the ruler down vertically, and measure it with a level after it is stable.
Monitoring measures
(1) adopts the method of field investigation.
The geological theory of advanced geological prediction is applied to analyze and determine the nature, type, genetic characteristics, approximate location, approximate scale, possible geological disasters and their influence on tunnel construction. Adopt the following analysis methods and steps: be familiar with survey and design documents, materials and drawings. Its purpose is to have a basic understanding and macro grasp of the geological environment in which the whole tunnel is located. Make a supplementary survey of the ground geology. Its purpose is to verify the geological conditions of the tunnel and determine the key sections and key problems of the tunnel's advanced geological prediction. In-depth investigation of tunnel geological conditions, delineation of stratum exposure position, measurement of lithologic occurrence, determination of fault occurrence, statistics of joint and fissure development, determination of adverse geological impact, and understanding of special rock and soil distribution characteristics. On the topographic map, we can know whether the understanding of geological conditions in the design documents is correct and whether the determination of surrounding rock grade is appropriate, and compile long-term geological forecast reports to guide the implementation of short-term geological forecast more pertinently.
(2) Do a good job of information feedback.
Through on-site geological survey, comprehensively grasp the geological conditions along the tunnel, and analyze the possibility of the tunnel passing through bad geological bodies; Statistics of joint and fissure development, determination of adverse geological processes, and understanding of special rock and soil distribution characteristics; Check whether the understanding of geological conditions in the design documents is correct and whether the judgment of surrounding rock level is appropriate; Compile a long-term geological forecast report to guide the short-term geological forecast to be implemented more pertinently.
Monitoring data should be sorted out and analyzed in time. Under normal circumstances, it should be reported once a week, and under special circumstances, it should be reported once a day. The monitoring report shall include the stage deformation value, deformation rate and accumulated value, and draw the curve of settlement tank and time (or time history) curve. , the necessary regression analysis, and evaluate the monitoring results. The monitoring data will be recorded into the safety monitoring (surrounding rock measurement) subsystem of the railway construction project management information system of Guiguang Company in time.
(3) Do a good job in quality inspection.
The monitoring management and monitoring implementation plan will be included in the construction production plan as an important construction process to ensure that there is a certain time and space for monitoring. Each construction unit shall form a special monitoring team composed of engineering technology management center to be responsible for monitoring.
Make feasible monitoring implementation plan and corresponding protection measures for measuring points, and incorporate them into the construction schedule control plan of the project. Construction monitoring is closely combined with construction steps, monitoring the influence of each construction step on the surrounding environment, surrounding rock, supporting structure and deformation, and optimizing the construction scheme accordingly.
Actively cooperate with the supervision design unit to inspect, supervise and guide the monitoring work, reflect the situation and problems to the supervision design unit in time, and provide relevant and reliable data records. After the completion of the project, the monitoring and analysis general report of this bid will be sorted out according to the monitoring data and included in the completion data. Measurement project personnel should be relatively fixed to ensure the continuity of data. Measuring instruments should be used by special personnel, maintained by professional institutions and calibrated by professional institutions. Measuring equipment, components, etc. They are calibrated before use and can only be used if they are qualified. After the test, check the instruments, do a good job of maintenance and storage, and timely sort out the data and feedback information.
In tunnel construction, the monitoring link is helpful to improve the quality of the project and prevent the project from collapsing. Therefore, according to the specific construction situation, it is very important to make clear the monitoring purpose and content, and do a good job in related monitoring. Through the writing of this article, I hope that related projects can be strictly monitored in the future construction process to ensure good quality.
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