Monitoring requirements for foundation pits

Monitoring items

4.1 General provisions

4.1.1 On-site monitoring of foundation pit projects should adopt a method that combines instrument monitoring and patrol inspection.

4.1.2 The objects of on-site monitoring of foundation pit projects include: 1. Supporting structure; 2. Relevant natural environment; 3. Construction conditions; 4. Groundwater conditions; 5. Bottom of foundation pit and surrounding soil; 6. Surrounding areas Buildings (structures); 7 Surrounding underground pipelines and underground facilities; 8 Surrounding important roads; 9 Other objects that should be monitored.

4.1.3 Monitoring projects for foundation pit projects should focus on key parts, achieve key observations, and support projects to form an effective and complete monitoring system. Monitoring projects should also be matched with the foundation pit engineering design plan and construction conditions.

4.2 Instrument monitoring

4.2.1 Instrument monitoring items for foundation pit engineering should be selected according to Table 4.2.1.

4.2.2 When there are subways, tunnels or other buildings and facilities that have special requirements for displacement (settlement) around the foundation pit, the specific monitoring items should be determined in consultation with the relevant departments or units. .

4.3 Inspection and Inspection

4.3.1 During the entire construction period of the foundation pit project, dedicated personnel should conduct inspections every day.

4.3.2 The inspection of foundation pit projects should include the following main contents: 1. Supporting structure (1) Forming quality of the supporting structure; (2) Whether there are cracks in crown beams, supports, and purlins; ( 3) Whether there is any major deformation of supports and columns; (4) Whether the water-stop curtain is cracked or leaking; (5) Whether the soil behind the wall is subsidence, cracks or slipping; (6) Whether there is soil intrusion in the foundation pit, Quicksand, piping. 2 Construction conditions (1) Whether there is any difference between the soil quality exposed after excavation and the geotechnical survey report; (2) Whether the length and layer thickness of foundation pit excavation are consistent with the design requirements, and whether they are over-long or over-deep Excavation; (3) Whether the surface water and groundwater discharge conditions of the site are normal, and whether the foundation pit precipitation and recharge facilities are operating normally; (4) The ground loading conditions around the foundation pit, and whether there is any excessive loading. 3. Environment around the foundation pit (1) Whether the underground pipelines are damaged or leaking; (2) Whether there are cracks in the surrounding buildings (structures); (3) Whether there are cracks or subsidence in the surrounding roads (ground); (4) Neighboring areas Construction status of foundation pits and buildings (structures). 4. Monitoring facilities: (1) The integrity of reference points and measuring points; (2) Whether there are obstacles that affect the observation work; (3) The integrity and protection of monitoring components. 5. Other inspection contents determined based on design requirements or local experience.

4.3.4 The inspection method of inspection is mainly visual inspection, which can be supplemented by hammers, drills, measuring sticks, magnifying glasses and other tools, as well as video and photography equipment.

4.3.5 Patrol inspections should record in detail the inspections of natural conditions, supporting structures, construction conditions, surrounding environment, monitoring facilities, etc. If any abnormality is found, the client and relevant units should be notified promptly.

4.3.6 Inspection inspection records should be compiled in a timely manner and analyzed comprehensively with instrument monitoring data.

Monitoring point layout

5.1 General provisions

5.1.1 The layout of foundation pit project monitoring points should reflect the actual status and changes of the monitoring objects to the greatest extent trends and should meet monitoring requirements.

5.1.2 The layout of foundation pit engineering monitoring points should not hinder the normal work of the monitoring objects and minimize the adverse impact on construction operations.

5.1.3 Monitoring signs should be stable, obvious, and structurally reasonable, and the location of monitoring points should avoid obstacles to facilitate observation.

5.1.4 Monitoring points should be appropriately encrypted in representative parts where the internal force and deformation of the monitored object change greatly and in surrounding key monitoring parts.

5.1.5 The protection of monitoring points should be strengthened, and protective devices or protective facilities for monitoring points should be installed when necessary.

5.2 Foundation pit and supporting structure

5.2.1 The horizontal and vertical displacement monitoring points at the top of the foundation pit slope should be arranged along the periphery of the foundation pit. Monitoring points should be arranged at the sun corners. The distance between monitoring points should not be greater than 20m, and the number of monitoring points on each side should not be less than 3. The monitoring point should be set on the top of the foundation pit slope.

5.2.2 The horizontal and vertical displacement monitoring points at the top of the retaining wall should be arranged along the perimeter of the retaining wall, and monitoring points should be arranged in the middle and sunny corners of the perimeter of the retaining wall. The distance between monitoring points should not be greater than 20m, and the number of monitoring points on each side should not be less than 3. Monitoring points should be set up on crown beams.

5.2.3 Deep horizontal displacement monitoring holes should be arranged at the center and representative locations around the foundation pit slope and retaining wall. The number and spacing will depend on the specific situation, but each side should be at least Set up 1 monitoring hole. When using an inclinometer to observe deep horizontal displacement, the depth of the inclinometer tube installed in the retaining wall should not be less than the soil penetration depth of the retaining wall; the inclinometer tube installed in the soil should ensure sufficient penetration depth to ensure that the pipe end Embedded in stable soil.

5.2.4 The internal force monitoring points of the retaining wall should be arranged in representative parts with large stress and deformation. The number and horizontal spacing of monitoring points will depend on the specific situation, but at least one should be set on each side. 1 monitoring point. Monitoring points in the vertical direction should be arranged at locations with large bending moments, and the spacing between monitoring points should be 3~5m.

5.2.5 The layout of support internal force monitoring points should meet the following requirements: 1. Monitoring points should be set on rods with large support internal forces or that play a key role in the entire support system; 2. There should be no less than 3 internal force monitoring points, and the positions of the monitoring points of each support should be consistent in the vertical direction; 3. The monitoring section of the steel support should be arranged at 1/3 of the support length or at the end of the support according to the testing instrument. The monitoring section of the reinforced concrete support should be arranged at 1/3 of the support length; 4. The number and arrangement of sensors in each monitoring point section should meet different sensor testing requirements.

5.2.6 The vertical displacement monitoring points of columns should be arranged in the middle of the foundation pit, at the intersection of multiple supports, under the construction trestle, and on the columns in places with complex geological conditions. The monitoring points should not be less than the total root of the column. 10% of the number, the number of foundation pits constructed by the reverse method should not be less than 20%, and should not be less than 5.

5.2.7 The tension monitoring point of the anchor bolt should be selected at a representative location that is subject to greater stress. Monitoring points should be arranged at the mid-span of each side of the foundation pit and in areas with complex geological conditions. The number of tension monitoring points for anchor rods on each layer should be 1 to 3% of the total number of anchor rods on that layer, and should not be less than 3. The vertical position of the monitoring points on each floor should be consistent. The test point on each pole should be set near the anchor head.

5.2.8 The tension monitoring points of soil nails should be arranged along the periphery of the foundation pit. Monitoring points should be arranged in the middle and sunny corners of the periphery of the foundation pit. The horizontal spacing between monitoring points should not be greater than 30m, and the number of monitoring points on each floor should not be less than 3. The vertical positions of monitoring points on each floor should be consistent. The test points on each rod should be set at representative locations for stress and deformation.

5.2.9 The monitoring points for the uplift at the bottom of the foundation pit should meet the following requirements: 1. The monitoring points should be arranged in longitudinal or transverse sections. The section should be selected in the center of the foundation pit, about 1/4 of the distance from the bottom of the pit. Bottom width and other locations that can reflect deformation characteristics. The quantity should not be less than 2. When there are multiple monitoring sections longitudinally or transversely, the spacing should be 20 to 50m, and the lower part should be dense. 2. The lateral spacing of monitoring points on the same section should be 10~20m, and the number should not be less than 3. 3. When laying out according to the distribution of soil layers, at least one measuring point should be arranged in each layer and arranged in the middle of each layer of soil.

5.2.10 The pore water pressure monitoring points should be arranged in the foundation pit where the stress and deformation are large or representative. The vertical arrangement of monitoring points should be arranged according to the distribution of soil layers within the depth range affected by water pressure changes. The vertical spacing of monitoring points is generally 2~5m, and should not be less than 3.

5.2.11 The arrangement of groundwater level monitoring points in the foundation pit should meet the following requirements: 1 When deep well dewatering is used, the water level monitoring point should be arranged in the center of the foundation pit and in the middle of two adjacent dewatering wells; When using light well points or jet well points for dewatering, the water level monitoring points should be arranged in the center and surrounding corners of the foundation pit. The number of monitoring points is determined according to the specific situation; 2. The buried depth of the water level monitoring pipe (the elevation of the bottom of the pipe) should be at the lowest designed 3~5m below the water level. For foundation pit projects that need to reduce the level of pressurized water, the burial depth of the water level monitoring pipe should meet the dewatering design requirements. 3. Water level monitoring points should be arranged along the periphery of the foundation pit, the periphery of the protected objects (such as buildings, underground pipelines, etc.) or between them. The spacing between monitoring points should be 20~50m. Water level monitoring points should be arranged in adjacent buildings (structures), important underground pipelines or in densely populated areas of pipelines; if there is a water-stop curtain, it should be arranged about 2m outside the water-stop curtain. 4. The observation well of the recharge well point should be set between the recharge well point and the protected object.

5.3 Surrounding environment

5.3.1 Buildings (structures), underground pipelines, etc. that need to be protected within a range of 1 to 3 times the excavation depth beyond the edge of the foundation pit should be used as Monitoring objects. If necessary, the scope of monitoring should be expanded.

5.3.2 The layout of monitoring points located within the safety protection zone of important protection objects (such as subways, upstream water diversion, combined sewage, etc.) should still meet the technical requirements of relevant departments.

5.3.3 The layout of vertical displacement monitoring points of buildings (structures) should meet the following requirements: 1. Every 10~15m at the four corners of the building (structure) or along the outer wall or every 2~ 3 pillar foundations, and no less than 3 monitoring points on each side; 2 The boundary between different foundations or foundations; 3 The boundary between different structures of a building (structure); 4 Deformation joints, seismic joints or serious cracks Both sides; 5 Both sides of the intersection between new and old buildings or high and low buildings; 6 The symmetrical parts of the basic axis of tall structures such as chimneys, water towers and large storage tanks, each structure must not be less than 4 points.

5.3.4 The horizontal displacement monitoring points of buildings (structures) should be arranged at the corners, column bases and both ends of cracks in the building. There should be no less than 3 monitoring points on each side of the wall. .

5.3.5 The tilt monitoring points of buildings (structures) should meet the following requirements: 1 Monitoring points should be arranged at the corners of buildings (structures), load-bearing columns or on both sides of deformation joints or seismic joints. on the wall; 2. The monitoring points should be arranged correspondingly along the top and bottom of the main body, and the upper and lower monitoring points should be arranged on the same vertical line; 3. When using the plumb bob observation method or the laser plumbometer observation method, it should be ensured that the upper and lower monitoring points There are certain visibility conditions between the measuring points.

5.3.6 The crack monitoring points of buildings (structures) should be arranged with representative cracks. When new cracks or existing cracks are found to be increasing during foundation pit construction, they should be Set up additional monitoring points in a timely manner. At least 2 sets of measuring points should be set up for each crack. Measuring points should be set at the widest part of the crack and at the end of the crack.

5.3.7 The layout of underground pipeline monitoring points should meet the following requirements: 1 The setting of monitoring points should be determined based on the year, type, material, size and current situation of the pipeline; 2 The monitoring points should be arranged at the end of the pipeline For nodes, corner points and parts with large deformation curvature, the plane spacing between monitoring points should be 15~25m, and should be extended to 20m outside the foundation pit; 3. Direct monitoring points should be set up for pressure pipelines such as water supply, gas, and heating. Direct monitoring points should be set on the pipeline, and pipeline equipment such as valve switches, air extraction holes, and inspection wells can also be used as monitoring points; 4. In areas where direct monitoring points cannot be buried, monitoring points can be set up using the buried casing method, or The analog measuring point sets the monitoring point in the soil close to the buried depth of the pipeline.

5.3.8 The layout range of vertical settlement monitoring points on the surface around the foundation pit should be 1 to 3 times the depth of the foundation pit. The monitoring profile should be located in the middle of the pit edge or other representative parts, and Perpendicular to the edge of the pit, the number of monitoring sections is determined based on specific circumstances. The number of monitoring points on each monitoring section should not be less than 5.

5.3.9 Monitoring holes for vertical displacement of soil layering should be arranged in representative locations, the number shall be determined according to the specific situation, and a monitoring profile shall be formed. The measuring points of the same monitoring hole should be arranged vertically in each layer of soil. The number and depth should be determined according to the specific situation, and should be appropriately densed in thicker soil layers.

Monitoring methods and accuracy requirements

6.1 General provisions

6.1.1 The selection of monitoring methods should be based on the foundation pit grade, accuracy requirements, design requirements, and site conditions , regional experience and method applicability and other factors are comprehensively determined, and the monitoring method should be reasonable and easy to implement.

6.1.2 Deformation measurement points are divided into reference points, working base points and deformation monitoring points. Its layout should meet the following requirements: 1. Each foundation pit project should have at least 3 stable and reliable points as reference points; 2. The working base point should be selected at a stable location. When the visibility conditions are good or there are few observation items, the working base point may not be set and the deformation monitoring point can be measured directly on the datum point; 3. During the construction period, effective measures should be taken to ensure the normal use of the datum point and the working base point; 4. Monitoring During this period, the stability of the working base point should be checked regularly.

6.1.3 Monitoring instruments, equipment and monitoring components should meet the following requirements: 1. Meet the requirements for observation accuracy and range; 2. Have good stability and reliability; 3. Be calibrated or calibrated and checked. The records and calibration data are complete and within the specified calibration validity period;

6.1.4 For the same monitoring item, monitoring should meet the following requirements: 1. Use the same observation route and observation method; 2. Use the same monitoring instrument and equipment; 3. Fixed observation personnel; 4. Working under basically the same environment and conditions.

6.1.5 During the monitoring process, the maintenance, regular testing and inspection of monitoring components should be strengthened; the protection of monitoring instruments should be strengthened to prevent damage.

6.1.6 The initial value of the monitoring item should be the average of the stable values ??observed at least three times in advance.

6.1.7 In addition to using various foundation pit engineering monitoring methods specified in this specification, other methods that can meet the accuracy requirements specified in this specification may also be used.

6.2 Horizontal Displacement Monitoring

6.2.1 When measuring the horizontal displacement in a specific direction, the sight line method, small angle method, throwing point method, etc. can be used; the monitoring point can be measured in any direction The distribution of monitoring points can be visualized when the horizontal displacement is measured, and the forward intersection method, free station method, polar coordinate method, etc. can be used; when the reference point is far away from the foundation pit, the GPS measurement method or the triangle, three sides, and corners can be used A comprehensive measurement method that combines measurement with the baseline method.

6.2.2 Horizontal displacement monitoring reference points should be buried in a stable area that is not affected by construction beyond 3 times the excavation depth of the foundation pit, or use existing stable construction control points, and should not be buried in low-lying areas Within the scope affected by water accumulation, subsidence, frost heaving, expansion and contraction, etc.; the reference points shall be buried in accordance with relevant measurement specifications and procedures. Observation piers with forced alignment should be set up; precise optical alignment devices should be used, and the alignment error should not be greater than 0.5mm.

6.2.3 The monitoring accuracy of the horizontal displacement of the top of the retaining wall (slope) of the foundation pit should be determined according to Table 6.2.3 based on the alarm value of the horizontal displacement of the top of the retaining wall (slope).

6.2.4 The horizontal displacement monitoring accuracy of underground pipelines should not be less than 1.5mm.

6.2.5 The horizontal displacement monitoring accuracy of other surrounding environments of foundation pits (such as underground facilities, roads, etc.) should comply with relevant specifications, procedures, etc.

6.3 Vertical displacement monitoring

6.3.1 Vertical displacement monitoring can use geometric leveling or hydrostatic leveling methods.

6.3.2 The uplift (rebound) of the pit bottom should be monitored by setting rebound monitoring marks, using geometric levels and using auxiliary equipment to transmit the elevation. The metal rods or steel rulers that transmit the elevation should be temperature-controlled. , ruler length and tension and other items are corrected.

6.3.3 The vertical displacement monitoring accuracy of the top of the foundation pit retaining wall (slope), the surface behind the wall and the columns should be determined according to Table 6.3.3 based on the vertical displacement alarm value.

6.3.4 The vertical displacement monitoring accuracy of underground pipelines should not be less than 0.5mm.

6.3.5 The vertical displacement monitoring accuracy of other surrounding environments of foundation pits (such as underground facilities, roads, etc.) should comply with relevant specifications and procedures.

6.3.6 The monitoring accuracy of pit bottom bulge (rebound) should not be less than 1mm.

6.3.7 The technical requirements for geometric leveling observation at each level should comply with the requirements in Table 6.3.7.

6.3.8 The horizontal datum points should be evenly buried, and the number should not be less than 3 points. The requirements for the burial location and method are the same as 6.2.2.

6.3.9 Each monitoring point and the leveling reference point or working base point should form a closed loop or follow a leveling route.

6.4 Monitoring of deep horizontal displacement

6.4.1 The monitoring of deep horizontal displacement of the retaining wall or the soil around the pit should be based on inclinometers pre-embedded in the wall or soil. Tube, a method of observing horizontal displacement at each depth through an inclinometer.

6.4.2 The system accuracy of the inclinometer should not be less than 0.25mm/m, and the resolution should not be less than 0.02mm/500mm

6.4.3 The inclinometer should be in the foundation pit It should be buried 1 week before excavation. The following requirements should be met during burial: 1. The quality of the inclinometer pipe should be checked before burying. When connecting the inclinometer pipe, it should be ensured that the guide grooves of the upper and lower pipe sections are aligned with each other smoothly. The joints should be sealed and Pay attention to ensure that the pipe mouth is capped; 2. The length of the inclinometer pipe should be consistent with the depth of the retaining wall or not less than the depth of the soil layer being monitored; when the lower pipe end is used as the displacement reference point, it should be ensured that the inclinometer pipe enters the stable soil layer 2~3m; the gap between the inclinometer tube and the borehole should be filled densely; 3. The inclinometer tube should be kept vertical without twisting when buried, and the direction of one set of guide grooves should be consistent with the direction of the required measurement.

6.4.4 The inclinometer should be lowered into the bottom of the inclinometer tube for 5 to 10 minutes, and the measurement should be performed after the probe is close to the temperature inside the tube. For each monitoring direction, two forward and reverse measurements should be made.

6.4.5 When the upper nozzle is used as the starting point for deep horizontal displacement, the change in coordinates of the nozzle should be measured and corrected for each monitoring.

6.5 Tilt Monitoring

6.5.1 Building tilt monitoring should measure the horizontal displacement and height difference of the top of the monitored object relative to the bottom, and record and calculate the inclination and inclination of the monitored object respectively. direction and tilt rate.

6.5.2 The point projection method, horizontal angle method, front intersection method, normal vertical line method, differential settlement method, etc. should be selected according to different on-site observation conditions and requirements.

6.5.3 The accuracy of building tilt monitoring should comply with the relevant provisions of the "Engineering Measurement Specifications" (GB50026) and "Building Deformation Measurement Regulations" (JGJ/T8).

6.6 Crack monitoring

6.6.1 Crack monitoring should include the location, direction, length, width and degree of change of cracks, and if necessary, depth. The number of cracks to be monitored is determined as needed, and major or changing cracks should be monitored.

6.6.2 The following methods can be used to monitor cracks: 1. To monitor the width of cracks, you can stick gypsum cakes, draw parallel lines, or bury metal signs on both sides of the cracks, and use micrometers or vernier calipers to directly measure them. Methods; crack meter, paste installation dial indicator method, photographic measurement and other methods can also be used. 2. For crack depth measurement, when the crack depth is small, the chisel method and single-surface contact ultrasonic method should be used for monitoring; for cracks with larger depth, the ultrasonic method should be used for monitoring.

6.6.3 Before excavation of the foundation pit, the distribution position and number of existing cracks in the monitoring object should be recorded, and their direction, length, width and depth should be measured. The signs should be clear enough for measurement. end or center.

6.6.4 The crack width monitoring accuracy should not be less than 0.1mm, and the length and depth monitoring accuracy should not be less than 1mm.

6.7 Monitoring of internal forces of supporting structures

6.7.1 Changes in internal forces of supporting structures during foundation pit excavation can be measured by installing strain gauges or stress gauges inside or on the surface of the structure .

6.7.2 For reinforced concrete supports, steel stress gauges (rebar gauges) or concrete strain gauges should be used for measurement; for steel structure supports, axial force meters should be used for measurement.

6.7.3 The internal forces of retaining walls, piles and purlins should be measured by pre-embedding steel stress gauges welded to the main bars when the retaining walls and pile reinforcements are being made.

6.7.4 The monitoring value of the internal force of the supporting structure should consider the influence of temperature changes. For reinforced concrete supports, the influence of concrete shrinkage, creep and crack development should also be considered.

6.7.5 The measuring range of the stress gauge or strain gauge should be 1.2 times the maximum design value, the resolution should not be less than 0.2%F·S, and the accuracy should not be less than 0.5%F·S.

6.7.6 The internal force monitoring components of retaining walls, piles, purlins, etc. should be buried during the construction of corresponding processes and obtain stable initial values ??before excavation.

6.8 Earth pressure monitoring

6.8.1 Earth pressure should be measured using an earth pressure meter.

6.8.2 The measuring range of the earth pressure gauge should meet the requirements of the measured pressure. The upper limit can be 1.2 times the maximum design pressure. The accuracy should not be less than 0.5% F·S, and the resolution should not be less than 0.2%. F·S.

6.8.3 The earth pressure gauge can be buried or boundary type (contact type). The following requirements should be met when burying: 1. The stress surface should be perpendicular to the direction of the pressure to be monitored and close to the object to be monitored; 2. Earth pressure film protection measures should be taken during the burying process; 3. When burying using the drilling method, the backfill should be even and dense. , and the backfill material should be consistent with the surrounding rock and soil. 4. Keep complete burial records.

6.8.4 The earth pressure gauge should be inspected and tested immediately after it is buried. It should be monitored for at least one week and a stable initial value should be obtained before excavation of the foundation pit.

6.9 Pore water pressure monitoring

6.9.1 Pore water pressure should be measured by burying steel string type, strain gauge and other pore water pressure gauges, and using frequency meters or strain gauges.

6.9.2 The pore water pressure gauge should meet the following requirements: the measuring range should meet the requirements of the measured pressure range, which can be 1.2 times the sum of the hydrostatic pressure and excess pore water pressure; the accuracy should not be less than 0.5%F ·S, the resolution should not be lower than 0.2%F·S.

6.9.3 The pore water pressure gauge can be buried using the pressing method, drilling method, etc.

6.9.4 The pore water pressure gauge should be buried 2 to 3 weeks in advance. The following requirements should be met before burial: 1. The pore water pressure gauge should be soaked and saturated to eliminate air bubbles in the permeable stone; 2. Check the accuracy data, record the probe number, and take the initial reading.

6.9.5 Use the drilling method to bury the pore water pressure meter. The diameter of the hole should be 110~130mm. It is not suitable to use mud to protect the wall. The hole should be round, straight and clean; the sealing material should be 10~20mm in diameter. dry bentonite balls

6.9.6 The initial value of the pore water pressure gauge should be measured after it is buried, and it should be measured daily for more than 1 week to obtain a stable initial value.

6.9.7 The groundwater level near the location where the pore water pressure gauge is buried should be measured while monitoring the pore water pressure.

6.10 Groundwater level monitoring

6.10.1 Groundwater level monitoring should be carried out by setting up a water level pipe in the hole and using water level meters and other methods for measurement.

6.10.2 The accuracy of groundwater level monitoring should not be less than 10mm.

6.10.3 The water level observation wells to test the precipitation effect should be arranged in the precipitation area. When using light well point tubes for dewatering, they can be arranged on both sides of the main pipe. When using deep wells for dewatering, they should be arranged between two deep wells. time, the depth of the water level hole should be 2~3m below the lowest design water level.

6.10.4 The submersible water level pipe should be buried before foundation pit construction, and the length of the filter pipe should meet the measurement requirements; effective water isolation should be adopted between the measured aquifer and other aquifers during pressurized water level monitoring. measure.

6.10.5 After the water level pipe is buried, the water level should be continuously observed every day and a stable initial value should be obtained.

6.11 Anchor tension monitoring

6.11.1 A special anchor dynamometer should be used to measure the anchor tension. Rebar stress gauges or strain gauges can be used for steel anchors. When using steel tendons, the stress on each steel bar should be monitored individually.

6.11.2 The measuring range of the anchor axial force gauge, steel stress gauge and strain gauge should be 1.2 times the designed maximum tension value, the measurement accuracy should not be less than 0.5% F·S, and the resolution should not be low At 0.2%F·S.

6.11.3 The stress gauge or strain gauge should obtain a stable initial value before the anchor is locked.

6.12 Monitoring of layered vertical displacement of soil outside the pit

6.12.1 The layered vertical displacement of soil outside the pit can be measured by burying layered settlement magnetic rings or deep settlement markers. Measurement is carried out using a layered sedimentation meter combined with a level measurement method.

6.12.2 Stratified vertical displacement markers should be buried in advance. The settlement magnetic ring can be positioned and buried through drilling and layered settlement pipes.

6.12.3 The initial value of the vertical displacement of the soil layer should be established after the vertical displacement mark of the layer has been buried and stabilized. The stabilization time should not be less than 1 week and a stable initial value should be obtained; monitoring accuracy It should not be lower than 1mm.

6.12.4 Each measurement should be repeated twice, and the error between the two times should not be greater than 1mm.

6.12.5 When using the layered sedimentation meter method for monitoring, the elevation of the pipe mouth should be measured for each monitoring, and the elevation of each monitoring point in the measuring pipe should be converted based on the height of the pipe mouth.

7.0.1 The monitoring frequency of foundation pit engineering should be based on the principle that it can systematically reflect the important change process of the measured items of the monitoring object without missing the moment of change.

7.0.2 Foundation pit engineering monitoring work should be carried out throughout the entire process of foundation pit engineering and underground engineering construction. Monitoring work should generally start before the construction of the foundation pit project and continue until the underground project is completed. Monitoring of the surrounding environment with special requirements should be continued as necessary until the deformation becomes stable before it can be ended.

7.0.3 The monitoring frequency of monitoring items should take into account the grade of the foundation pit project, the different construction stages of the foundation pit and underground engineering, and changes in the surrounding environment and natural conditions. When the monitoring value is relatively stable, the monitoring frequency can be appropriately reduced. For items that should be measured, in the absence of data anomalies and signs of accidents, the frequency of instrument monitoring after excavation can be determined by referring to Table 7.0.3.

7.0.4 When one of the following situations occurs, monitoring should be strengthened, the frequency of monitoring should be increased, and the monitoring results should be reported to the client and relevant units in a timely manner: 1. The monitoring data reaches the alarm value; 2. The monitoring data changes. The amount is larger or the speed is accelerated; 3. There are unfavorable geological conditions that were not discovered during the survey; 4. The construction is not according to the design, such as ultra-deep and ultra-long excavation or failure to add supports in time; 5. A large amount of water accumulation and long lengths in and around the foundation pit. Continuous rainfall and leakage in municipal pipelines; 6. The ground load near the foundation pit suddenly increases or exceeds the design limit; 7. Cracks occur in the supporting structure; 8. Sudden large settlement or serious cracking occurs in the surrounding ground; 9. Neighboring Sudden large settlement, uneven settlement or severe cracking of buildings (structures); 10. Piping, leakage or quicksand at the bottom of the foundation pit, slope or supporting structure; 11. Reconstruction after an accident in the foundation pit project Organize construction; 12. Other abnormal situations that affect the safety of the foundation pit and surrounding environment occur.

7.0.5 When there are signs of dangerous accidents, real-time tracking and monitoring should be carried out. 8.0.1 The monitoring alarm values ??of foundation pit projects should comply with the design limits of foundation pit projects, the design requirements of underground main structures, and the control requirements of monitoring objects. The foundation pit engineering monitoring alarm value is determined by the foundation pit engineering designer.

8.0.2 The monitoring alarm value of foundation pit engineering should be controlled by the cumulative change amount and change rate value of the monitoring item.

8.0.3 The ground displacement inside and outside the foundation pit caused by the construction of retaining walls, excavation of foundation pits and precipitation should be controlled according to the following conditions: 1. It shall not cause instability of the foundation pit; 2. It shall not affect the underground structure. The size, shape and normal construction of underground projects; 3 The deformation caused by the surrounding existing buildings (structures) shall not exceed the requirements of relevant technical specifications; 4 It shall not affect the normal use of surrounding roads, underground pipelines, etc.; 5 Technology that meets the special environment Require.

8.0.4 The monitoring alarm values ??for foundation pits and supporting structures should be determined based on the monitoring items, the characteristics of the supporting structures and the level of the foundation pit. Please refer to Table 8.0.4.

Note: 1.h - Design excavation depth of foundation pit; f - Design limit value. 2. The cumulative value takes the smaller value of the absolute value and the relative foundation pit depth (h) control value. 3. When the change rate of the monitored item exceeds 50% of the alarm value for 3 consecutive days, an alarm should be issued.

8.0.5 The limits of surrounding environment monitoring alarm values ??should be determined according to the requirements of the competent department. If there are no specific regulations, they can be determined by referring to Table 8.0.5.

8.0.6 The alarm value of surrounding buildings (structures) should be determined based on the observation of cracks in the building (structure), and the original deformation of the building (structure) and the damage caused by the excavation of the foundation pit should be taken into consideration. Overlay of additional deformations.

8.0.7 When one of the following situations occurs, the police must be called immediately; if the situation is serious, construction should be stopped immediately, and emergency measures should be taken for the foundation pit supporting structure and surrounding protection objects. 1 When the monitoring data reaches the alarm value; 2 Abnormal displacement of the foundation pit supporting structure or surrounding soil occurs, or leakage, quicksand, piping, uplift or collapse occurs in the foundation pit; 3 Supports or anchors of the foundation pit supporting structure The system shows signs of excessive deformation, buckling, fracture, relaxation or pull-out; 4. Structural parts of surrounding buildings (structures) and surrounding ground may develop deformation cracks or serious sudden cracks; 5. According to local engineering Judgment based on experience, there are other situations where the police must be called. 9.0.1 Monitoring analysts should have comprehensive knowledge of geotechnical engineering and structural engineering, have engineering practical experience in design, construction, measurement, etc., have high comprehensive analysis capabilities, and be able to make correct judgments and accurate expressions, and provide high-quality results in a timely manner. Comprehensive analysis report.

9.0.2 On-site testers should be responsible for the authenticity of monitoring data, monitoring analysts should be responsible for the reliability of monitoring reports, and monitoring units should be responsible for the monitoring quality of the entire project. Monitoring records and monitoring technical results should be signed by the person in charge, and monitoring technical results should be stamped with an achievement seal.

9.0.3 On-site monitoring data should meet the following requirements: 1. Use formal monitoring record forms; 2. Monitoring records should have corresponding descriptions of working conditions; 3. Monitoring data should be organized in a timely manner; 4. Review of monitoring data Changes and developments should be analyzed and reviewed in a timely manner.

9.0.4 Field observation values ??and note items must be recorded directly in the observation record form on site.

Any original records must not be altered, forged or copied, and must be signed by the testing and recording personnel.

9.0.5 If there is an abnormality in the observation data, the reasons should be analyzed in time and retested if necessary

9.0.6 When analyzing the data of the monitoring project, the monitoring data of other related projects should be combined with the The natural environment, construction conditions and other conditions as well as past data are carried out, their development trends are considered, and forecasts are made.

9.0.7 Technical results should include daily reports, periodic reports, and summary reports. The content provided for technical achievements should be true, accurate, and complete, and should be expressed in the form of a combination of document descriptions and drawings using changing curves or graphics. Technical results should be submitted on time.

9.0.8 Professional software should be used for monitoring data processing and information feedback. The functions and parameters of professional software should comply with the relevant provisions of this specification, and should integrate data collection, processing, analysis, query and management. ization and visualization of monitoring results.

9.0.9 Observation records, calculation data and technical results of foundation pit engineering monitoring should be organized and archived.

9.0.10 The daily report should include the following contents: 1. The weather conditions of the day and the working conditions of the construction site; 2. The current test value, single change value, change rate and each monitoring point of the instrument monitoring project. Cumulative values, etc., and draw relevant curves when necessary; 3. Records of inspections; 4. There should be judgmental conclusions about whether monitoring items are normal or abnormal; 5. Monitoring points that reach or exceed the monitoring alarm value should have alarm signs with reasons. Analysis and suggestions; 6. Abnormalities found during inspections should be described in detail, dangerous situations should be marked with alarms, and there should be cause analysis and suggestions; 7. Other relevant instructions. The daily report should adopt the format of Appendix A ~ Appendix G of this specification.

9.0.11 The periodic monitoring report should include the following contents: 1. Overview of the corresponding engineering, meteorological and surrounding environment during the monitoring period; 2. The layout of monitoring items and measuring points during the monitoring period; 3. Each item Collection and statistics of monitoring data and process curve of monitoring results; 4. Change analysis, evaluation and development prediction of monitoring values ??of each monitoring project; 5. Relevant design and construction suggestions.

9.0.12 The content of the foundation pit project monitoring summary report should include: 1. Project overview; 2. Monitoring basis; 3. Monitoring items; 4. Measuring point layout; 5. Monitoring equipment and monitoring methods; 6. Monitoring frequency; 7 Monitoring alarm values; 8 Analysis and overall review of the development and changes of each monitoring project throughout the entire process; 9 Conclusions and suggestions on monitoring work.

9.0.13 The summary report should indicate the name of the project, the monitoring unit, and the start and end dates of the entire monitoring work. It should also have the seal of the monitoring unit and the signatures of the project leader, the unit's technical leader, and the enterprise's administrative leader.