HG/T 20578-1995 Technical specification for strengthening soft soil foundation by vacuum preloading method
Some standard content:
Industry Standard of the People's Republic of China
Construction of Vacuum Preloading Method to Reinforce Soft Soil Foundation
Technical Regulations
HG/T20578-95
Editor: First Survey and Design Institute of the Ministry of Chemical Industry Approved by: Ministry of Chemical Industry
Effective Date: May 1, 1996 Engineering Construction Standard Editing Center of the Ministry of Chemical Industry
1996 Beijing
Standard Approved by m.bzsoso.cn All kinds of standards industry information are free to download 1 General Principles
1.0.1 Vacuum preloading is an effective method to reinforce soft soil foundation, with the characteristics of low cost, good effect and short construction period. It has been widely used in coastal areas. In order to standardize construction, improve the success rate, facilitate supervision and inspection and summarize and develop this technology, this regulation is specially formulated. 1.0.2 Vacuum preloading method is suitable for the reinforcement of silt, silty soil, backfill and other soft soil foundations.
1.0.3 This method is not suitable for reinforced soil covered with backfill soil or hard plastic clay layer with a thickness of more than 5m.
1.0.4 When there is a sand layer in the reinforced soil, the water and air connection inside and outside the reinforced area should be cut off, otherwise it is not suitable for use.
Standard Technical Network.boso.cm2 Project Preparation and Construction
2.1 Preliminary Work
2.1.1 The layout and positioning of the reinforcement area boundary should be carried out according to the design drawings, with an allowable deviation of 10cm; remove debris and accumulated water in the reinforcement area, level the site, and the allowable height difference of the site is not more than 25cm. 2.1.2 Setting of settlement mark and foundation soil testing. Before setting up sand wells (or plastic boards) and laying sand cushions, the ground settlement markers should be set up, the foundation soil should be drilled and sampled, in-situ tests (cross plates, lateral pressure tests, static penetration tests, load tests, etc.) should be carried out, and data should be obtained. 2.1.3 Water and electricity systems
2.1.3.1 Water system
(1) Water supply system
Tap water should be used. When it is difficult to use tap water, other water sources such as ponds, seas, rivers, lakes, etc. can also be used. However, the water quality should be less corrosive and have fewer impurities. In winter, water supply pipes should be protected from cold or buried below the maximum freezing depth.
(2) Drainage system
Open ditches or submersible pumps can be used for drainage. However, the water should be discharged into the cofferdam on the sealing membrane or far away from the reinforcement area.
2.1.3.2 The power supply system
should ensure the safe and normal operation of the drilling machine and jet pump, as well as the normal use of ancillary facilities such as lighting and living.
2.2 Sand cushion and sand well (plastic board) construction
2.2.1 Sand cushion construction
2.2.1.1 Sand should be medium-coarse sand, and the content of impurities such as mud should be less than 5%. It is strictly forbidden to mix sharp stones, ironware and other sharp objects in the sand, and they must be removed after discovery. Dry sand should be used for winter construction. 2.2.1.2 The laying of the sand cushion should be carried out in two times. Before the sand well (plastic board) is set, a 10cm sand cushion should be laid on the ground, and the remaining part should be laid after the sand well (plastic board) is set. 2.2.1.3 The laying thickness of the sand cushion is 20~30cm, and the allowable deviation is ±h/10 (h is the designed sand cushion thickness). During inspection, one inspection point is required for every 100 square meters. The laying range of the sand cushion layer is the entire reinforcement area. 2.
Standard technology network.bzbeo.comCustomer standard industry data free download 2.2.1.4 When the surface layer of the reinforcement area is very soft and cannot withstand the construction of personnel and machinery, 1 to 2 layers of thorns or other artificial woven fabrics should be laid on the surface layer before laying the sand cushion layer, and they should be tied together with iron wire. The overlap length should be 20cm. If the thorns or woven fabrics are easy to rot, they should be removed after the vacuum preloading construction is completed.
2.2.1, 5 The construction method of the sand cushion layer can adopt mechanical construction method and manual laying method. 2.2.2 Bag sand well (plastic board) construction
2.2.2.1 Construction machinery is divided into crawler type, pontoon type, track type, walking type, etc. according to the travel mode, and the casing drive mode is mostly vibration type. It can be selected according to geological conditions and technical requirements. 2.2.2.2 The sand bags used for bagged sand wells should be made of materials with strong tensile strength, strong corrosion resistance and UV resistance, good water permeability, and no exposed sand particles. Gunny cloth and polypropylene woven bags are preferred. 2.2.2.3 The diameter of the sand bag should be 7~10cm, the sand filling rate should be greater than 95%, and the quality of the sand material should not be lower than the sand material used in the sand cushion layer.
2.2.2.4 The plane position allowable deviation of the sand well (plastic board) construction should be ±20cm (underwater) and ±10cm (land). The bottom elevation should meet the design requirements, the top should be 20~40cm higher than the sand cushion layer, and the verticality allowable deviation is ±1.5cm/m. When encountering boulders, boulders, etc., it is difficult to drill holes in situ, they should be moved and supplemented, and the displacement distance shall not be greater than 30% of the sand well spacing. 2.2.2.5 When sandbags are put into the casing of the machine, kinking, breaking and other phenomena are strictly prohibited; if it is found that the sandbags are not full after construction, sand must be added to connect with the sand cushion layer. 2.2.2.6 Pile shoes should be used to fix the plastic board to the predetermined depth. At present, there are four types of pile shoes: concrete type, triangle iron type, steel plate type and steel bar type, which can be selected according to geological conditions. 2.2.2.7 Sandbags (plastic boards) that are higher than the sand cushion layer should be buried in the middle of the sand cushion layer and must not touch the mud surface below or expose the sand surface above.
2.2.2.8 During winter construction, anti-freezing and anti-breaking measures should be taken for sandbags (plastic boards). 2.3 Pre-pressing installation
2.3.1 Processing and transportation of sealing film
2.3.1.1 The sealing film should be polyvinyl chloride and polyethylene film with a thickness of 0.12~0.17mm. Its shape after processing must be consistent with the reinforcement area. The area of the film after processing shall not be less than the design area. The length of each side of the sealing film shall be 3~4m longer than the corresponding side of the reinforcement area. 2.3.1.2 The film processing can be done by heat treatment. It is strictly forbidden to have hot penetration, loose heat sealing, and cross heat sealing seams. If holes are found in the raw material film, they should be repaired in time. After the heat sealing is completed, it should be inspected by the user. ·3·
Standard Technology Network wm.bzcoso.om2.3.1.3 Each reinforcement area can use 2~3 layers of sealing film, and the specific number of layers can be determined according to the performance of the sealing film. 2.3.1.4 Before transportation, the processed film should be gathered in the direction perpendicular to the heat sealing seam and should not be rolled into a roll. The radius of the bend shall not be less than 1m. During transportation, it should be handled with care and should not be dragged or pulled. Pads or canvas should be laid in advance in the transport compartment to protect the sealing film for safe transportation. 2.3.2 Processing and laying of filter tubes
2.3.2.1 The material of the filter tube can be 460Φ70mm iron pipe or hard plastic pipe. After punching and processing the outer filter layer, it should only be permeable to water and air but not sand. 2.3.2.2 The location of the filter tube should be laid out and positioned by the surveyor according to the design drawings. The filter tube can be connected with a hose about 30cm long. The length of the hose inserted into the filter tube should be 10cm, and then tied with lead wire. The lead wire knot is strictly prohibited to face upwards.
2.3.2.3 The filter tube should be buried in the middle of the sand cushion layer, and the distance from the mud surface and the top surface of the sand cushion layer should be greater than 5cm. The filter tube must be filled with sand around it, and it is strictly prohibited to fill it in the air. 2.3.2.4 After the filtration tube is buried, the sand surface should be leveled and debris such as stones and rubble should be removed. 2.3.3 The vacuum device should preferably be a jet vacuum device (jet pump). A test pump should be tested before leaving the factory. The test pump operation should form a vacuum pressure of 0.096MPa, otherwise it is a defective product. 2.3.4 Sealing ditch and cofferdam
2.3.4.1 The excavation of the sealing ditch should be carried out along the boundary of the reinforcement area. Its depth should reach the groundwater and cut off the permeable layer. The inner and outer slopes should be smooth and free of sand. The width of the ditch bottom should be more than 0.4m to ensure that the sealing membrane is in full contact with the clay at the bottom of the ditch to meet the sealing requirements. 2.3.4.2 The backfill material of the sealing ditch should be pure clay without impurities. When backfilling, the backfill material should be prevented from directly hitting the sealing membrane to avoid breaking and leaking; when backfilling, it should be compacted in layers. 2.3.4.3 The weir should be built across the outer edge of the sealing ditch, and the soil should be compacted in layers or filled with straw bags.
2.3.5 Before laying the membrane, the membrane outlet elbow should be connected to the filter tube and the sand should be compacted. The outlet pressure plate should be flush with the surface of the sand cushion layer, and the lower rubber gasket should be placed. After the membrane is laid, the membrane should be cut along the outlet elbow, and then the upper rubber gasket and the upper pressure plate should be placed. Grease should be evenly applied in between, and finally the two nuts should be tightened. Sand is strictly prohibited between the rubber gasket and the membrane.
2.3.6 Fabrication and burial of vacuum pressure probe The vacuum pressure probe can be a small filter tube, which is connected to the vacuum pressure gauge outside the membrane with a soft plastic tube.
The probe should be buried in the sand cushion layer, and the plastic hose should be led out through the bottom of the sealing membrane trench. 2.3.7 Laying of sealing membrane
Standard control network mm.baoso.ca2.3.7.1 When laying, it should be extended from the upwind direction to the downwind direction first, and the remaining volume around the reinforcement area should be basically the same. Construction workers should wear soft-soled shoes to apply the membrane, and it is strictly forbidden to wear spiked shoes to apply the membrane. Each layer should be checked by a special person, and if there are holes, they should be patched in time. The membrane should be laid flat on the inside of the sealing ditch. If the film is too long, it can be folded at the bottom of the ditch, and it should not be laid on the outer slope. 2.3.7.2 For areas with a large clay content, high water content, and a very shallow groundwater level in the foundation soil, the flat membrane process can be used, but the sand and other debris on the ground must be cleaned up. 2.3.7.3 The time for laying the membrane should be during the day. When the wind force is greater than level 5, it is not suitable to lay the membrane. 2.3.8 The pipes on the membrane can be iron pipes and rubber hoses. Rubber hoses are commonly used. After the installation is completed, it is advisable to place a support every 4m.
2.3.9 The jet pump should be tested once before installation. If the vacuum pressure does not reach 0.09MPa, it should be repaired until it reaches the requirement. When installing, place them neatly. If necessary, the jet pump can be placed on the soil platform, and then the power supply is turned on.
2.3.10 The exposed parts such as the jet pump and the pipes on the membrane should be well protected against corrosion and rust. Cold protection should be done in winter.
2.3.11 After the sealing membrane is laid, the ground settlement observation plate can be placed on the membrane, and its specific position should comply with the design drawings.
2.4, vacuum test
Before covering with water, vacuum test should be carried out, and the operation of each jet pump and the sealing of the membrane should be carefully checked. If any problems are found, they should be dealt with in time. The vacuum test should be 7 to 10 times, and the vacuum pressure under the membrane should reach 0.06 to 0.08MPa; if it is lower than this value, it is abnormal, and the cause should be found and dealt with in time. At the beginning of the test pumping, the parameters such as vacuum pressure and settlement should be observed. 2.5 Normal vacuum pumping
2.5.1 After the test pumping meets the requirements, water can be covered and the normal vacuum pumping stage can be started. This stage is the main stage of vacuum preloading and strengthening the foundation, which can last for 2 to 5 months. 2.5.2 The thickness of water covering should be 20 to 40 cm. After water covering, the vacuum pressure under the membrane should gradually stabilize at more than 0.08 MPa.
Standard according to the network mm.baoso.ca3 Construction monitoring and project acceptance
3.1 Construction monitoring
3.1.1 Preloading parameters include pore water pressure value, vacuum pressure value, ground settlement, deep settlement, horizontal displacement, etc. Usually only vacuum pressure value and ground settlement are observed. 3.1.2 Vacuum pressure observation every 2 to 4 hours. If the vacuum pressure drops, the cause should be found immediately and handled in time.
3.1.3. Settlement Observation
3.1.3.1 Observation should be carried out at a fixed point, at a fixed time, and by a designated person. The position of the settlement mark should correspond to that before and after film laying. Before film laying, observation should be carried out every two days; after film laying, observation should be carried out every 24 hours within the first 10 days and nights of vacuuming, and every 48 hours thereafter.
3.1.3.2 Before the construction of the sand well (plastic board), the ground elevation map within the 7m range of the reinforced area after leveling and the surrounding extension should be measured and drawn into a topographic map; after vacuum preloading is completed, the ground elevation within the above range should be re-measured and drawn into a map, and the settlement cross-section diagram in the longitudinal and transverse directions should be measured at the same time. 3.1.3.3 The observation data should be complete, accurate, and realistic, and the settlement and time relationship curve should be drawn in a timely manner. For abnormal values, re-observation should be carried out, and each closing error should meet the requirements of relevant specifications.
3.2 Project Acceptance
3.2.1 When the measured ground settlement for four consecutive days and nights is less than 2mm/d or the foundation consolidation degree has reached the design requirements, the preloading can be terminated after acceptance by Party A. 3.2.2 After the termination of preloading, the site should be leveled. All equipment and pipes used should be dismantled and repaired. 3.2.3 After the preloading is completed, the preloading effect should be tested and a completion report should be submitted. The testing method should be consistent with the foundation soil testing method in the previous work. The testing position should be near 1m of the origin. The test results should be organized into a map to visually compare the foundation reinforcement effect. .6.
Standard switching network oburounicom observer
Observation time
(year month day time)
Appendix A Vacuum pressure field record table
Vacuum on the pump
Vacuum under the membrane
Is there any abnormal phenomenon
Pressure (MPa) Pressure (MPa) Pump operation Jet box water sealing membrane standard control room m.b28oso.cm preparation
Verifier:
Appendix B
First time
Second time
Average value
Daily settlement
Total settlement
Third time
Second time
Average value
Daily settlement
Total settlement
First time
Second time
Average value
Daily settlement
Total settlement
Vacuum preloading settlement observation record
Observer:
Standard loss according to the website wm.b2st8o.com Standard industry information free download Project name
Date of burial
Physical location
Measurement range
Calibration:
Appendix C Earth pressure observation record table
Project number
Manufacturer number
Sensitivity
Indication value
Average value
Pressure value
Record:
Standard control network.baoso.cm. Preparation
Instrument number:
Recorder:
|Appendix D Original record of pore water pressure measurement
Factor fo
Average value
Absolute pore pressure
·10·
Excess pore pressure
Proofreader:
Standard Technology Network.b2DBocom
Project name
Verification:
On-site water level dynamic observation record table
Appendix E
Record:
Standard Technology Network.buso80(comAll kinds of standard industry information free download2 Before the construction of sand well (plastic board), the ground elevation map within the 7m range of the reinforced area and the surrounding area after leveling should be measured and drawn into a topographic map; after the vacuum preloading is completed, the ground elevation within the above range should be re-measured and drawn into a map, and the settlement cross-section diagrams in the longitudinal and transverse directions should be measured at the same time. 3.1.3.3 The observation data should be complete, accurate, and realistic, and the settlement and time relationship curve should be made in time. For abnormal values, they should be re-observed once, and each closing error should meet the requirements of relevant specifications.
3.2 Project acceptance
3.2.1 When the measured ground settlement for four consecutive days and nights is less than 2mm/d or the foundation consolidation degree has reached the design requirements, the preloading can be terminated after acceptance by Party A. 3.2.2 After the preloading is terminated, the site should be leveled. All equipment and pipes used should be dismantled and repaired. 3.2.3 After the preloading is completed, the preloading effect should be tested and the completion report should be submitted. The detection method should be consistent with the foundation soil test method in the previous work. The detection position should be 1m near the origin. The test results should be organized into a map to visually compare the foundation reinforcement effect. .6.
Standard switching network oburounicom Observer
Observation time
(year month day time)
Appendix A Vacuum pressure field record table
Vacuum on the pump
Vacuum under the membrane
Is there any abnormal phenomenon
Pressure (MPa) Pressure (MPa) Pump operation Jet box water sealing membrane standard control room m.b28oso.cm Preparation
Verifier:
Appendix B
First time
Second time
Average value
Daily settlement
Total settlement
Third time
Second time
Average value
Daily settlement
Total settlement
First timeWww.bzxZ.net
Second time
Average value
Daily settlement
Total settlement
Vacuum preloading settlement observation record
Observer:
Standard loss according to the website wm.b2st8o.com Standard industry information free download Project name
Date of burial
Physical location
Measurement range
Calibration:
Appendix C Earth pressure observation record table
Project number
Manufacturer number
Sensitivity
Indication value
Average value
Pressure value
Record:
Standard control network.baoso.cm. Preparation
Instrument number:
Recorder:
|Appendix D Original record of pore water pressure measurement
Factor fo
Average value
Absolute pore pressure
·10·
Excess pore pressure
Proofreader:
Standard Technology Network.b2DBocom
Project name
Verification:
On-site water level dynamic observation record table
Appendix E
Record:
Standard Technology Network.buso80(comAll kinds of standard industry information free download2 Before the construction of sand well (plastic board), the ground elevation map within the 7m range of the reinforced area and the surrounding area after leveling should be measured and drawn into a topographic map; after the vacuum preloading is completed, the ground elevation within the above range should be re-measured and drawn into a map, and the settlement cross-section diagrams in the longitudinal and transverse directions should be measured at the same time. 3.1.3.3 The observation data should be complete, accurate, and realistic, and the settlement and time relationship curve should be made in time. For abnormal values, they should be re-observed once, and each closing error should meet the requirements of relevant specifications.
3.2 Project acceptance
3.2.1 When the measured ground settlement for four consecutive days and nights is less than 2mm/d or the foundation consolidation degree has reached the design requirements, the preloading can be terminated after acceptance by Party A. 3.2.2 After the preloading is terminated, the site should be leveled. All equipment and pipes used should be dismantled and repaired. 3.2.3 After the preloading is completed, the preloading effect should be tested and the completion report should be submitted. The detection method should be consistent with the foundation soil test method in the previous work. The detection position should be near 1m of the origin. The test results should be organized into a map to visually compare the foundation reinforcement effect. .6.
Standard switching network oburounicom Observer
Observation time
(year month day time)
Appendix A Vacuum pressure field record table
Vacuum on the pump
Vacuum under the membrane
Is there any abnormal phenomenon
Pressure (MPa) Pressure (MPa) Pump operation Jet box water sealing membrane standard control room m.b28oso.cm Preparation
Verifier:
Appendix B
First time
Second time
Average value
Daily settlement
Total settlement
Third time
Second time
Average value
Daily settlement
Total settlement
First time
Second time
Average value
Daily settlement
Total settlement
Vacuum preloading settlement observation record
Observer:
Standard loss according to the website wm.b2st8o.com Standard industry information free download Project name
Date of burial
Physical location
Measurement range
Calibration:
Appendix C Earth pressure observation record table
Project number
Manufacturer number
Sensitivity
Indication value
Average value
Pressure value
Record:
Standard control network.baoso.cm. Preparation
Instrument number:
Recorder:
|Appendix D Original record of pore water pressure measurement
Factor fo
Average value
Absolute pore pressure
·10·
Excess pore pressure
Proofreader:
Standard Technology Network.b2DBocom
Project name
Verification:
On-site water level dynamic observation record table
Appendix E
Record:
Standard Technology Network.buso80(comAll kinds of standard industry information free download
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