Key points of subway engineering monitoring, measurement and supervision
8.1 Overview.
8.1.1. The purpose of monitoring and measurement.
The main points are: firstly, to grasp the dynamics of the surrounding rock, supporting structure and surrounding environment, and to use the monitoring results to provide a reference for design and construction. Secondly, the monitoring data is analyzed and processed and the necessary calculations and judgments are carried out and fed back in order to provide reliable information for engineering and environmental safety. Finally, the data and experience are accumulated to provide an analogy basis for similar projects in the future.
8.1.2. Characteristics of underground engineering construction monitoring.
The external force is not clear: underground engineering is in a complex and changeable rock and soil body as a structure, and the force exerted by different types of rock and soil mass and groundwater state on the structure is different
The stress state is changeable: in the process of underground engineering construction, there is a characteristic of change in the stress state from beginning to end, before the excavation of underground engineering, the rock and soil mass is in a state of equilibrium, and the balance is broken after excavation, and it is in dynamic change, and the supporting structure and the surrounding soil have been in flux.
8.1.3. The significance of monitoring work in the construction of subway projects.
The actual situation of the calculation of the stressed earth pressure of the supporting structure is quite different from the theoretical calculationThe calculation index of soil and water pressure has a large randomness;The construction period is long, and it needs to experience many disadvantages such as surrounding loading, vibration, rain, and improper construction in winter, and the randomness of the safety degree is large, and the accident occurs suddenly. Therefore, in view of these factors, it is of great significance to carry out information construction and implement monitoring.
8.2 Monitoring and measurement items and methods.
8.2.1. The main monitoring and measurement items of the subway project.
The main adaptation is the subway construction project in the Beijing area).
It mainly monitors the surrounding environment and the civil construction enclosure (support) system. Surrounding environment monitoring, mainly roads and ground.
Surface settlement, ground building (structure) settlement, inclination and cracks, underground pipeline settlement, bridge settlement, groundwater level, vertical displacement of soil in the ground, horizontal displacement of soil in the ground, etc.;The monitoring of the civil construction enclosure (support) system mainly includes the subsidence and horizontal convergence of the tunnel vault, the displacement of the pile top, the internal force of the lining structure, the internal force of the temporary support, and the earth pressure behind the wall. The monitoring and measurement items are divided into deformation and stress monitoring, the deformation monitoring instruments mainly use total stations, levels and inclinometers, etc., and the stress monitoring instruments mainly use strain gauges and steel bar meters. All kinds of observation points should be arranged on the same monitoring surface as much as possible, so that the monitoring data can be transmitted accurately and ensure the reliability of the monitoring results.
8.2.2. Control the requirements for the monitoring scope.
The monitoring range of building (structure) settlement and inclination monitoring project is generally selected for 1 5 2 oh (h is the excavation depth of the foundation pit or the buried depth of the tunnel) on both sides of the foundation pit or tunnel.
The underground pipeline only monitors the settlement and differential settlement of sewage, rainwater, water supply, gas and other pipelines, and the monitoring range is generally selected from the foundation pit or tunnel on both sides of the 1 0h range.
The monitoring range of road and surface settlement is generally 1 oh on each side of the foundation pit or tunnel.
The monitoring scope of the subway section structure is generally within 30m on each side of the outer edge of the subway structure, but in the construction section of the subway station, the monitoring scope should be appropriately increased according to the surrounding environment of the station and the situation of the building (structure).
The monitoring frequency should be closely coordinated with the construction progress, and the corresponding monitoring frequency should be formulated for different construction methods and different construction steps.
The initial value of the measurement point should be measured and read after the measurement point is stable, and the average value of the three observations should be taken as the initial observation value.
The monitoring instruments and components used in monitoring should meet the requirements of various monitoring work.
8.2.3. Key points of foundation pit monitoring, measurement and supervision of open cut method.
The purpose of open-cut foundation pit monitoring and measurement is to comprehensively monitor the dynamic changes of the enclosure structure, the stress and displacement of the surrounding environment with the help of instruments and equipment during the excavation of the foundation pit. The construction monitoring content is similar to that of general urban deep foundation pit engineering, including the monitoring of the enclosure structure and the deformation control monitoring of the surrounding existing buildings.
Control the stability of the soil around the foundation pit, and no soil sliding failure will occur.
The strength of the supporting structure meets the design requirements of the strength of the components.
The displacement of the stratum caused by the excavation of the foundation pit and the ground deformation caused by the change of groundwater shall not exceed the allowable deformation value of the buildings and underground facilities around the foundation pit.
Cut-and-cover station monitoring projects, instruments and purposes.
8.2.4. Cover excavation method foundation pit monitoring and measurement.
The principle of environmental monitoring and distribution around the station of the open (cover) excavation method.
The principle of monitoring and distribution of the enclosure structure system by the open (cover) excavation method.
8.2.5. Monitoring and measurement of dark excavation method.
In the process of underground excavation construction, the deformation and loosening of the surrounding rock (stratum) may be transmitted to the surface, affecting the safety of surface buildings (structures), pipelines, bridges, etc., therefore, in addition to the monitoring of the surrounding rock (strata) and supporting structures, it is also necessary to observe the deformation of the surface and ground buildings (structures) and pipelines.
Shaft inspection item list
8.2.5.1. Key points of monitoring, measurement and control of the hidden excavation section:
Observation of geology and support conditions: record and observe the excavation, support footage and working conditions, record and map the geology of the tunnel face profile, hydrogeological state and support thickness, cracking or extrusion damage, etc., and draw the longitudinal engineering geology and hydrology of the cavern on a weekly basis.
Geological profile: Observe and record the undesirable deformation, cracking and damage and water leakage of buried objects in the ground.
Horizontal convergence displacement of headroom: A headroom convergence monitoring section is set every 5m in the monitoring section;Each convergence monitoring section is provided with two horizontal measuring lines, which are respectively located at the arch line on both sides of the upper half section, using ball club type embedded parts, and the end is welded to the grid or the longitudinal connection steel bar head of the grid, and the rod thread or ball should be wrapped and protected, and the convergence meter is used for monitoring. Observe the time until the deformation of the cavern stabilizes.
Measurement of vault sinking and floor uplift. The observation section and the clearance convergence monitoring section are arranged in the same section, that is, there is a monitoring section every 5m in the longitudinal direction of the cavern. Each monitoring section is provided with one vault settlement observation point at the vault, which is located at the intersection of the tunnel centerline and the vault, and is measured by the level method by precision level and indium steel ruler.
The floor uplift mainly refers to the release of in-situ stress caused by the excavation of the soil body of the cavern, and the ground pressure of the aquifer in the foundation pit and the soil on it is not enough to offset the confined head, resulting in a sudden surge of confined water and the uplift of the soil layer at the bottom of the cavern. A monitoring section is set up every 5m longitudinally along the longitudinal direction of the tunnel, and each section is provided with a measuring point at the bottom of the inverted arch, which is located at the intersection of the center line of the tunnel and the inverted arch, and the level method is measured by precision level and indium steel ruler.
Surface subsidence: A surface subsidence monitoring section is set every 5m, and according to the general law of land subsidence, the measurement point in the middle of the monitoring section is densely arranged and the outer side is thin. For the hardened pavement, use the air drill to drill holes, cement slurry to bury the reinforcement measuring pile, for the unhardened pavement or other parts, use the pit digging method to bury the reinforcement measuring pile, fix it with cement slurry, and expose the ground end to grind round. Leveling measurement is carried out using a precision level and a steel ruler.
Pipeline monitoring: The underground pipeline measurement points are mainly laid on the gas pipelines, water supply pipelines, sewage pipelines, large rainwater pipes and power ditches, and the relative position relationship between the underground pipelines and the tunnel should be considered when the measurement points are arranged.
The pipeline with inspection wells should be opened to directly lay the monitoring point on the pipeline or pipeline carrierPipelines without inspection wells but with excavation conditions should be excavated and exposed, and observation points should be directly laid on the pipelinesPipelines without inspection wells and excavation conditions can be buried with indirect observation points on the corresponding surface. The setting of the pipeline settlement observation point can be based on the site conditions, and the hoop type or sleeve type is adopted. There should be a minimum of 3 5 measuring points on each monitored pipeline.
Measurement of vertical displacement of soil layering: It can understand the disturbance of underground excavation construction to the surrounding soil, find out the change law, and provide a reliable basis for decision-making and control of settlement technical construction.
Monitoring of the horizontal displacement of foundation pit retaining piles and soil. It can grasp the movement law of soil and the impact of soil on the ground, and study the construction measures to reduce construction disturbances to protect the ground buildings and underground pipelines.
8.2.6. Monitoring and measurement of shield method.
8.2.6.1. Key points of monitoring, measurement and control of shield method:
The deformation of the stratum caused by the propulsion of the shield can be analyzed by the lateral and longitudinal settlement of the ground surface. Most of the studies on transverse settlement troughs are based on the empirical formula of PECK or the settlement distribution based on the stochastic medium theory.
The longitudinal settlement of the ground surface caused by shield construction is generally divided into four stages: early deformation, settlement when the shield passes, deformation after the shield tail and lining are separated, and subsequent settlement.
Before the shield reaches the observation point, the ground surface ahead will sink or heave due to the jacking speed or the amount of excavation.
The settlement generated at the stage from the time the shield excavation face reaches directly below the observation point to the time when the shield tail is about to break away from the point is the settlement when the shield passes.
The main reason for this part of the subsidence is that the friction of the shield shell on the soil destroys the structural strength of the soil, reduces the modulus of the soil, and causes the soil to produce extrusion and shear deformation, thereby causing the formation settlement.
After the shield tail is separated from the segment lining, the grouting is used to make up for the void of the shield tail, and when the grouting is not enough or the grouting filling rate is insufficient, the formation settlement will be produced due to the formation lossConversely, when the grouting is excessive, it will cause the formation to uplift.
The subsequent settlement stage refers to the part of the formation that subsidence occurs after the end of grouting and is mainly due to the consolidation, deformation and creep of the soil. The excess pore water pressure of the formation gradually dissipates, and the soil produces consolidation and deformation, so that the surface consolidates and settles.
Creep deformation includes creep deformation of soil and creep deformation of segments.
8.2.6.2. Tunnel monitoring projects, instruments and purposes of shield method
8.2.6.3. Tunnel measurement point layout and monitoring frequency in the shield method
8.3. Monitoring information of the supervision unit.
Taking the Beijing subway project as an example, the monitoring information of the supervision unit refers to various inspection information, including: surrounding environment inspection information, support system inspection information, excavation face inspection information, construction technology equipment inspection information, construction organization management and operation status inspection information.
In addition to the information reporting content of monitoring and early warning of the supervision unit, it also includes comprehensive early warning information, risk transaction processing information (including treatment plans, projects, results and change trends, etc.), risk treatment suggestion information, etc.
Content requirements for monitoring and early warning information reporting by the supervision unit:
*: Including the surrounding environment inspection information, support system inspection information, excavation face inspection information and its early warning recommendation information (on the basis of the verification of the information submitted by the construction unit), and the construction process equipment inspection information, construction organization management and operation status inspection information submitted (fill in after their own inspection).
Early warning report: The content of the report mainly includes the risk time, place, risk profile, preliminary analysis of the causes, change trends, risk treatment suggestions, etc. Among them, when the express report is sent to the construction unit, it should also issue a potential safety hazard report, rectification notice, stoppage order and other early treatment methods according to the early warning level.
Weekly and monthly reports: The content should mainly include the abnormal situation of the safety inspection in the past week and the past month, the situation of the weekly and monthly regular meeting of the supervision, the risk early warning, the implementation of feedback and the handling of risk affairs, the effect, the change trend, the existing problems, and the next risk treatment suggestions.
8.4. Information management and feedback of the monitoring unit.
8.4.1. Monitoring information of the monitoring unit.
Including monitoring data and inspection information, inspection information includes surrounding environment inspection information, supporting structure inspection information, excavation face inspection information, etc. As a supervisor, you need to master its information process and feedback mechanism.
8.4.2. Monitor the processing and management of measurement data.
Monitoring and measurement data are processed and managed by the computer, and after obtaining various monitoring data, it needs to be processed in a timely manner, drawing various types of curves and graphs, regression analysis of the monitoring results, the final displacement value, the safety of the structure, and the determination of engineering and technical measures. The monitoring results of each measurement point should be based on the management benchmark and displacement change rate (mm) d and other comprehensive judgment of the safety status of the structure and building, and the preparation of daily, weekly and monthly summary reports, timely feedback and guidance of construction, adjustment of construction parameters, to achieve the purpose of safe, fast and efficient construction.
8.4.3. The form and content of information feedback.
The monitoring information feedback results report of the monitoring unit is divided into **, weekly report, and summary report. The results report should include the general situation of the project, the construction progress, the monitoring method, the monitoring time, the monitoring frequency, the use of instruments, the specification, etc., list the monitoring value, the cumulative deformation value, the deformation rate, the deformation curve, etc., and put forward conclusive opinions based on the monitoring results.
After the completion of each observation and calculation, the calculation results shall be immediately reported in writing to the construction unit, supervision unit and other relevant departments.
Taking the Beijing subway project as an example, the monitoring and forecast information of the third-party monitoring unit is as follows:
Form of submission. 3. Early warning, express report, weekly and monthly report.
Contents: **All monitoring data, patrol information and early warning suggestion information of the day;
Early warning report: When it is judged that the project risk may reach the red comprehensive warning state or a major emergency risk event occurs, the express report should be carried out, and the content of the report mainly includes the risk time, place, risk profile, preliminary analysis of the causes, change trend, risk treatment suggestions, etc.;The early warning express should be a comprehensive early warning express report based on the monitoring and early warning suggestion information submitted by the construction unit and the supervision unit.
Weekly and monthly reports: The content includes the data of the third-party monitoring and construction unit and the supervision unit in the past week and month, the summary and analysis of inspection information and its abnormal conditions, risk early warning and safety evaluation, the implementation of feedback, monitoring and tracking, and suggestions for the next step of risk treatment.
Alarm system: According to the monitoring and measurement control index value determined in the design stage, the early warning status of the monitoring point in the construction process is divided into different levels from small to large according to the severity, such as Beijing Metro is divided into **, which are yellow monitoring and early warning, orange monitoring and early warning and red monitoring and early warning.
Yellow monitoring and warning: when the "dual control" indicators (change amount and change rate) exceed 70 of the monitoring and measurement control value, or when one of the dual control indicators exceeds 85 of the monitoring and measurement control value. The construction unit shall strengthen the organizational analysis, the technical person in charge of the project shall preside over and organize the risk treatment, and the professional person in charge of the design unit, the project director and the engineer of the project, the project leader of the third-party monitoring unit and the monitoring sub-center shall participate in the formulation of the risk treatment plan and the supervision and management of the risk treatment processConstruction units, supervision units, and third-party monitoring units have strengthened monitoring and inspections, and monitoring sub-centers have monitored and tracked.
Orange monitoring warning: when the "dual control" indicators exceed 85 of the monitoring and measurement control value, or when one of the dual control indicators exceeds the monitoring and measurement control value.
The construction unit shall organize a four-party meeting, the construction project manager shall preside over and organize the risk treatment, and the project leader of the design unit and the survey unit, the chief engineer of the supervision unit, the technical person in charge of the third-party monitoring unit and the relevant leaders of the construction unit shall participate in the formulation of the risk treatment plan and the supervision and management of the risk treatment processThe monitoring sub-center strengthens monitoring and tracking, and the construction unit strengthens supervision and coordination and handling.
Red monitoring and early warning: When the "dual control" indicators exceed the monitoring and measurement control value, or the measured change rate increases sharply. The construction unit shall organize expert demonstration, enable the emergency plan, the construction unit supervisor leader presides over and organizes risk treatment, the chief engineer, the technical person in charge of the design and survey unit and the technical person in charge of the third-party monitoring unit, the monitoring center, and the leaders of the construction unit participate in the formulation of the risk management plan and the supervision and management of the risk treatment process, and the competent leadership of the construction unit and relevant departments supervise and coordinate the processing, and the monitoring center strengthens monitoring and tracking.
8.5. Key points of monitoring and measurement.
8.5.1. Monitor the content.
The monitoring of field and internal work should be strengthened in accordance with the mandatory provisions and standards, so as to fully grasp the situation and quality of the construction (and third-party monitoring) unit, and the whole process should be inspected and checked, and problems should be rectified in a timely manner
Observation instrument personnel and equipment: review and check whether the qualifications of the surveyors and instruments and equipment entering the site are consistent with the bidding, and the personnel and measuring instruments that cannot meet the requirements shall be replaced within a time limit, and the instruments used shall be inspected on time according to the provisions of the industry, and the instruments whose accuracy does not meet the requirements shall be stopped from being used.
Monitoring and control network: It is necessary to carry out inspections and require the measurement unit to conduct regular reviews and retests.
Settlement observation point layout and burial: important parts need to be side-stationed.
Settlement observation: The method of patrol inspection is mainly adopted.
If there is one of the following situations, the observation unit should be required to increase the observation frequency, and the supervisor needs to focus on this part:
The rate of change or cumulative change of the observed item reaches or exceeds the warning value.
The observed values suddenly increased significantly, and the sedimentation rate increased abruptly.
The monitoring personnel must be familiar with the monitoring project and its early warning, alarm and control indicators, and be able to make suggestions and opinions on the next step of construction according to the cumulative deformation and the daily deformation rate value in the latest monitoring report data.
8.5.2. Review and control points of the monitoring program.
The monitoring plan is an important document to guide the on-site construction, and the supervision unit needs to carefully review the plan and put forward review opinions, and actively participate in the expert demonstration meeting of the monitoring plan organized by the owner.
Make sure that the plan is feasible and ensure the reliability of the plan and measures.
The monitoring plan should include two parts: design description and drawings
The design description includes the general situation of the project, the basis of the monitoring design, the purpose of the monitoring, the scope of the monitoring, the monitoring object, the monitoring project, the monitoring method and the accuracy requirements, the monitoring method, and the principle of the layout of the monitoring and measurement pointsDuration and frequency of monitoring for each monitoring project;Monitoring control indicators;Monitoring considerations and other requirements;Requests for feedback;Bills of work, etc.
The drawings mainly include: general plan;Layout plan of the measurement points of each monitoring project;Layout profile of the measurement points of each monitoring project;Sample diagram of base point and measurement point.
The focus of the review is as follows:
Whether the basis for the preparation of the program is comprehensive, correct and sufficient.
Whether the location, scope and frequency of the distribution meet the specifications and design and construction requirements.
Whether the monitoring method is correct.
Verification of organizational structure and personnel. Monitor whether the organizational structure in the program is perfect, and whether the qualifications of personnel meet the relevant requirements.
The monitoring plan needs to be approved by the technical person in charge of the monitoring unit.
8.5.3. Monitoring and management of the monitoring process.
The process control is mainly carried out by means of inspection, and the supervisors should regularly and irregularly go to the site for inspection and inspection, and strengthen the inspection rate of key parts and key processes.
Check whether the monitoring unit is organized and implemented in accordance with the monitoring plan, whether the personnel and equipment are consistent with the plan, and focus on checking whether the qualifications of the personnel and the instruments have been calibrated.
Check whether the monitoring report is reported in a timely manner.
In the specific implementation, it is also necessary to pay attention to the following issues:
The position of the surface deformation measurement point should not only reflect the deformation characteristics of the monitoring object, but also facilitate the application of the instrument for observation, and be conducive to the protection of the measurement point. The buried measuring point cannot affect and hinder the normal force of the structure, and cannot weaken the stiffness and strength of the structure. When implementing a number of content tests, the arrangement of various measurement points should be organically combined in time and space, so that a monitoring part can reflect different physical changes at the same time, and find out the internal connection and change law.
According to the monitoring plan, each monitoring point is arranged in advance, so that when the monitoring work begins, the monitoring element enters a stable working state. If the measuring point is damaged during the construction process, the measuring point should be re-installed at the original location or as close to the original position as possible to ensure the continuity of the observation data of the measuring point. The shield tunnel is mainly distributed with the monitoring of the tunnel, the surface, the pipeline and the houseThe station is mainly distributed with surface deformation monitoring of pipelines, houses and foundation pits.
8.5.4. Key points for judging the monitoring data.
Monitoring data analysis and feedback can be used to correct design support parameters, guide construction, adjust construction measures, etc., which is an important part of monitoring and measurement. As a supervisor, it is necessary to understand the processing and analysis process of the monitoring data of the monitoring unit, and be able to feedback the construction according to the processing and analysis conclusions of the monitoring data.
Monitor data processing.
After the monitoring unit obtains various monitoring data, it needs to be processed in a timely manner, eliminate errors in the operation process of instruments and readings, eliminate and identify various coarse, accidental and systematic errors, avoid missed and wrong measurements, ensure the reliability and integrity of monitoring data, and use computers to sort out and preliminary qualitative analysis of monitoring and measurement data.
Draw a time curve (or scatter plot) of displacement based on the field monitoring data. In the collation of measurement data, one of the two methods of displacement-time curve and scatter plot can generally be selected. Displacement ( ) a time (t) relationship curve under the time abscissa should indicate the construction process and the distance between the excavation face and the monitoring section.
According to the -t temporal curve (or scatter plot) and spatial relationship curve drawn from the field monitoring data, the following judgments can be made:
When the displacement-time relationship tends to be flat, data processing and regression analysis should be carried out to estimate the final displacement and grasp the displacement change law.
When the displacement-time relationship curve appears to be reversed, it indicates that the surrounding rock and the support have been in an unstable state, at this time, the surrounding rock dynamics should be closely monitored, and the support should be strengthened, and the excavation should be suspended immediately if necessary, and the suspension of work should be taken to reinforce and carry out support treatment.
Monitoring data analysis.
After obtaining the monitoring data, the monitoring unit should organize and proofread it in a timely manner. All kinds of monitoring data should be drawn in time history curves, and the corresponding working condition information should be indicated.
In addition to the single analysis of each project, the comparison and comprehensive analysis of multiple items should also be carried out in the calculation and analysis of monitoring and measurement data.
When the monitoring time history curve shows a convergence trend, the appropriate function should be selected according to the curve morphology, and the regression analysis should be carried out on the monitoring results, so as to determine the scientificity and rationality of the construction plan based on the final displacement value that may occur at the measurement point and the safety of the structure.
When any kind of early warning state appears in the measured data, the monitoring team shall immediately report to the construction unit, supervision unit, construction unit and design unit, etc., or orally, and submit a written early warning report as soon as possible.
Monitoring data analysis and feedback applications.
Geological forecasting: Geological forecasting in tunnel construction is based on the engineering geology and hydrogeological conditions of the surrounding rock a few meters to tens of meters or even hundreds of meters in front of the detection or excavation work, combined with the changes in the geological conditions in the tunneling, according to the geological description, rock structure plane investigation and water inrush observation in the monitoring and measurement.
Underground pipeline: According to the construction progress, the deformation value of each measurement point is drawn into a pipeline deformation curve. That is, a scatter plot of a time curve of displacement is drawn to determine the effectiveness of construction measures;When the displacement curve tends to be flat, a suitable function can be selected for regression analysis, **The maximum settlement of the pipeline;Along the pipeline settlement groove curve, judge the construction influence range, the maximum settlement slope, the minimum curvature radius, etc.
Layered vertical displacement monitoring of soil in the ground: after each monitoring, the displacement of different depths should be plotted a time curve and a displacement relationship curve of hole depth. When the displacement rate increases suddenly, a comprehensive analysis of various monitoring information should be carried out immediately to determine what problems occur in the construction, and timely take countermeasures to ensure the safety of the construction.
Horizontal displacement monitoring of foundation pit enclosure pile and soil in the ground: after each monitoring, a displacement-time curve and a one-position displacement curve of hole depth should be drawn. When the horizontal displacement rate suddenly increases excessively is an alarm signal, after receiving the alarm signal, a comprehensive analysis of various monitoring information should be carried out immediately to judge what problems have occurred in the construction, and take countermeasures to ensure the safety of the construction in time.
Groundwater level observation: Draw the change curve of water level 1 with time and the change curve of water level with construction according to the water level change value.
Tunnel vault settlement and horizontal convergence monitoring: according to the deformation value to draw the deformation time curve diagram and the curve change diagram of the deformation excavation distance, according to different construction stages on the tunnel cross-sectional diagram, the deformation value is drawn on the distribution position in a certain proportion, and the points are connected in the form of a line to become the tunnel support deformation distribution pattern diagram. And compare with the design calculation value to verify the rationality of the design structure.
Observation of cracks in segmental structures: The monitoring of crack development usually adopts the method of direct observation, and the cracks are numbered and marked out by the reading position, and the crack width is measured by the crack observation instrument if necessary. The number and location of monitoring are determined according to the site conditions.
Horizontal support axial force: The value of the monitored horizontal support axial force is drawn into a stress change curve and reported to the engineer in charge in time. Note: The range of the axial force gauge should meet the requirements of the design axial force. Before the steel support erection that needs to be buried with the axial force meter, the axial force gauge is welded in the center of the non-afterburner end of the support, and a steel plate should be cushioned between the axial force gauge and the steel cofferdam and the steel support, so as to avoid the deformation of the cofferdam caused by the excessive axial force, resulting in the loss of the support. After supporting the force port, after the force, it can be monitored.
Determination of the stability of the surrounding rock: During tunnel construction, the displacement value or rate of the surrounding rock and the support is often used as a sign to determine the stability of the surrounding rock. If it exceeds a certain critical value, it means that the surrounding rock is unstable and needs to be strengthened to support the lining. The allowable displacement value or rate value is related to factors such as tunnel section size, burial depth, geological conditions and surface building type.
8.5.5. Problems that should be paid attention to in monitoring.
Measuring point protection issues guarantee a 100% survival rate.
Emphasis on visual observation.
Timely information feedback: monitoring reports have five forms: **, weekly, monthly, special report, and summary report, ** submitted daily, under normal circumstances, a weekly report is submitted once a week, and a monthly report is submitted once a monthIn addition, according to the requirements of the relevant parties, a special analysis report shall be made on the historical data of the measurement points involving the monitoring interval, and a summary report shall be submitted after the completion of the monitoring task.
The amount of information in the report should be abundant: **Schematic diagram of the layout of the measurement point;According to the control standard;Construction Recommendations;Trend line chart. Weekly report: project progress;Statistical analysis of data;Outlier analysis.