First, the process principle
DTH drill is used to drill holes in bedrock. By setting anti-floating anchor rods, the foundation of a building or structure is connected with the bedrock as a whole and works together as a part of the foundation or superstructure, so that the foundation can effectively resist the buoyancy of groundwater.
Second, the scope of application
The structure is large, the groundwater level is shallow, the foundation is buried deeply, the number of buildings is small, and the weight of the structure itself can not meet the anti-floating construction of structures or structures that resist the buoyancy of groundwater.
Third, the process flow and operation points
1, process
Anchor rod fabrication and foundation test → anchor rod positioning and pay-off → drilling rig in place → connecting drill rod → correcting hole position → adjusting angle → opening air source for drilling → repeatedly lifting drill rod → cleaning (wind slag discharge) → drilling to design depth → anchor rod installation → pressure grouting → secondary grouting → maintenance → anchor rod test acceptance.
2. Key points of operation
2. 1 anchor manufacturing and basic test
(1) The anchor adopts HRB400 steel bar 3φ25 ring combination, and the fixed steel bar adopts ring 1φ28, and every 1.5m increases 1 section, and it is welded with 3φ25 steel bar for firm positioning.
(2) Before the formal construction of anchorage, the basic test of anchorage should be carried out first. The geological conditions, anchor material and construction technology of anchor foundation test should be consistent with engineering anchor. The maximum test load in foundation test should not exceed 0.9 times of the standard value of anchor bearing capacity. The main purpose of foundation test is to determine the characteristic value of bond strength between anchor body and geotechnical layer, the design parameters and construction technology of anchor rod. The number of each test anchor should not be less than 3. Cyclic loading and unloading method should be adopted in the basic test of anchor rod. The basic test points of anchor bolts shall be implemented according to Appendix C.2 of Technical Specification for Building Slope Engineering (GB50330-20 13).
2.2 Anchor positioning and setting-out: firstly, according to the design drawings, use theodolite or total station to measure the hole position of anti-floating anchor in each construction area, and mark and number it with wooden stakes or steel bars. The allowable deviation of anchor hole position is ≤ 50 mm.
2.3 Rig positioning: After measuring and releasing the anchor hole position, the rig can be positioned. Stabilize the drilling rig with wooden Fang to ensure that the drilling rig will not shake greatly during drilling, which will affect the hole-forming quality. Adjust the verticality of drill pipe with compass or messenger wire method. The verticality shall be ≤ 65438 0%, and the drill bit shall be aimed at the anchor hole to be constructed. Drilling can only be started after the management sign to confirm the hole location.
2.4 correction drilling: the diameter of the anchor hole is 150mm, and the deviation of the hole position is not more than 50mm ... Combined with the actual situation, the construction personnel should always pay attention to the change of slurry returning in the hole during the hole-forming process, and adjust the construction technology to ensure the smooth hole-forming. The hole-forming depth is generally required to be 20 ~ 30cm deeper than the design depth. In case of hole collapse during drilling, mud circulation can be used to protect the wall and form holes. When drilling into the rock stratum, managers should confirm and carefully record the upper elevation, lower elevation and total depth of the rock stratum. Each anchor must record the original borehole in detail.
2.5 hole cleaning: use mud to clean the hole first, then use BM- 150 pressure pump to clean the hole and discharge the sediment in the hole until the hole is clean and there is no large amount of sediment. Note that the hole cleaning time should not be too long to prevent the hole collapse from affecting the grouting quality.
2.6 Anchoring:
1) Before anchoring, check whether the grouting pipe is cracked or blocked, and whether the joint is firm, so as to prevent cracking and slurry leakage when the pressure increases;
2) Tie a 30mm grouting pipe on the anchor, which is moderately elastic and easy to pull out after grouting. The lower end of grouting pipe is generally shorter than the lower end of anchor body 150mm, and the nozzle at the lower end is temporarily closed with adhesive tape or cement bag to prevent the mud in the hole from blocking the grouting nozzle during anchoring;
3) Use tower crane or drilling rig to lift the anchor rod and grouting pipe together and put them into the hole. When placing, the anchor rod should be prevented from twisting, bending and parts loosening. In the process of anchoring, if the rod body can't reach the bottom of the hole, it should be pulled out and scanned again with a drill before anchoring;
4) After the anchor body is lowered to the hole position, the top elevation shall be measured to ensure the overall smoothness.
2.7 Pressure grouting: Grouting is an important working procedure of anchor construction, which must be carried out seriously, and relevant data should be recorded completely. The role of grouting: filling the pores in the soil layer to form the anchor body, preventing the corrosion of the anchor rod and forming the pull-out resistance of the anchor rod.
After the anchor rod is cleaned, grouting pump can be used for grouting, and the bottom of the hole is used for grouting.
Grouting material and mixture ratio: the grouting slurry is cement slurry with water cement ratio of 0.5, and ordinary portland cement with strength grade of 42.5MPa is selected, but high alumina cement is not applicable. The cement slurry should have enough fluidity to be pumped. In order to prevent the cement slurry from bleeding and drying shrinkage and reduce the water-cement ratio, FDN-5 superplasticizer, which is 5‰ of the cement weight, can be added to ensure the fluidity and strength of the cement slurry.
When grouting pump is used for grouting, a 30mm PVC pipe or hose is used as a conduit, one end of which is connected with grouting pump, and the other end is sent to the bottom of the hole together with the anchor rod. The distance between the end of grouting pipe and the bottom of the hole should be 150mm, and the grouting pressure should be 0.4 ~ 0.6 MPa. With the grouting, when the slurry overflows from the orifice, the grouting pipe can be gradually pulled out, but the nozzle should always be buried in the slurry until the orifice, so that all the water and air in the hole can be squeezed out of the hole to ensure the grouting quality. Mud should be prepared in strict accordance with the design mixture ratio and stirred evenly, and can only be pumped after sieving. Grouting shall be continuous and used up before initial setting.
Due to the shrinkage of the slurry during solidification, the slurry level falls back and must be replenished in time. After grouting, the anchor head should be temporarily supported to ensure that the anchor is in the center of the hole.
If the delay time during grouting is too long and exceeds the initial setting time of mud, the borehole should be cleaned and grouted again. Detailed and complete construction records should be made during grouting.
After grouting, the anchor body shall not bear external force or move before the strength of grout fails to meet the design requirements.
2.8 anchorage acceptance test
Anchor acceptance After the grouting strength of the anchor body reaches 90% of the design strength, the anchor acceptance test can be carried out. The purpose of anchor acceptance test is to check whether the construction quality meets the design requirements. The number of acceptance test anchors shall be 5% of the total number of each type of anchors (3% of the total number when the free section is located in Class I, II or III rocks) and shall not be less than 5. The anchor rod for acceptance test shall be randomly sampled. The quality supervisor, supervisor, owner or design unit should also take samples for acceptance test of the bolts with quality doubts. When the anchor rod is unqualified, it shall be re-sampled according to 30% of the total anchor rod; If there are unqualified anchors, check them all. The total deformation of anchor should meet the design allowable value, which is basically consistent with the regional experience.
Fourth, materials and equipment.
1, material
1. 1 The material of anchor rod body mainly adopts threaded steel bars above HRB335 level. The anti-corrosion material of anchor rod should not react chemically with the rod body, and it will not be damaged during the construction process or the design and use of the main structure.
1.2 M30 cement mortar (water cement ratio is 0.5) is used for the anchor body, tap water and ordinary portland cement are required for the cement mortar, and medium sand is used for the fine aggregate, with sand content (weight) not greater than 3%. Grouting pressure of anchor hole is about 0.5MPa, and sand and cement must be retested in advance, and can only be used after inspection. When fine stone concrete is used as grouting material, the strength grade of concrete should not be lower than C30, and the maximum particle size of stones should not be greater than15 mm. ..
Step 2 equip
Verb (abbreviation of verb) quality management
1, quality control
2. The number of anchors in the acceptance test should meet the design requirements. When there is no requirement in the design, it should not be less than 5% of the total number of anchors, and should not be less than 3. The maximum test load of the permanent anti-floating anchor is 1.5 times the axial tension of the anchor, and the acceptance test should be loaded in stages. The initial load should be 0. 10 times of the designed axial tension value of the anchor, and the graded loading value should be 0.50, 0.75, 1.00, 1.20 and 65438+ of the designed axial tension value of the anchor. Each level of load should be stable for 5~ 10min, and the displacement increment should be recorded. The last level of load should be kept at 10min.
3. Anti-seepage measures for anti-floating anchor joint
3. 1 When pouring anchor cushion, reserve a groove with a side length of 500mm×500mm×250mm.
3.2 The anti-floating anchor rod of basement floor adopts ribbed steel bar with a diameter of 25mm, and a φ 6 positioning steel bar with the same length as the aperture is welded at the upper and lower ends of the anchor rod 20cm away from the rock stratum, so as to ensure that the anchor rod can be placed in the middle of fine stone concrete and facilitate concrete pouring. The fine stone concrete filled in the reserved slot of anchor drilling adopts impervious concrete and retains the specimen, and its impermeability and strength grade are the same as those of foundation concrete.
3.3 Use polyurethane waterproof coating to block the bolt hole, and turn it up 250mm along the bolt. After the construction of the secondary polyurethane waterproof coating is completed and the coating is cured, a layer of waterproof coiled material is laid on the anchor rod, and the coiled material is cut into a cross at the anchor rod to pass through. The normal waterproof construction in the basement will return to the anchor rod for 20 mm After the waterproof layer construction is completed, the convergent position of waterproof coiled material around the anchor rod will be closed with polyurethane waterproof coating, and then the waterproof ring will be tightened with water expansion to prevent the subsequent process from being damaged.
4, anti-floating anchor anti-corrosion measures
All steel bars in pull-out anchor bars shall be derusted by hand, with the derusting grade of St2.5, and the steel bars shall be galvanized, and the coating thickness shall not be less than 35 microns. ..
Benefit analysis of intransitive verbs
1, this construction method is low in labor intensity, safe in construction and simple in operation, especially suitable for the construction environment limited by the site, which effectively reduces the investment of mechanical equipment, accelerates the construction efficiency of the anchor rod in the rock mass, shortens the construction period and ensures the pull-out requirements of the rod body. According to different rock conditions, choosing different drilling rigs and supporting construction anchors such as air compressors, drill pipes and drilling tools can meet the requirements of permanent uplift of buildings.
2. Anti-floating anchor construction technology replaces the traditional pile foundation construction technology, saving resources and reducing costs. As an anti-floating measure, anchor fully embodies the concept of green building, and it is an anti-floating measure that adapts to local conditions and meets the requirements of "saving water, energy, land and materials". Compared with other schemes, it has great cost and environmental protection advantages.
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