Supporting and retaining structure of miniature steel pipe piles and high-pressure jet grouting pre-stressed anchor cables

Abstract

The utility model relates to a supporting and retaining structure of a miniature steel pipe pile and a high-pressure jet grouting pre-stressed anchor cable. The supporting and retaining structure is formed by connecting the miniature steel pipe pile and the high-pressure jet grouting pre-stressed anchor cable together. The miniature steel pipe piles are grouped piles arranged in a matrix mode. Each miniature steel pipe pile comprises a miniature steel pipe and a leakage-proof sleeve pile, wherein the miniature steel pipe is internally filled with a cement paste filling body and externally wrapped with a cement paste protection layer, and the leakage-proof sleeve pile is formed through jet grouting treatment. Pile caps are arranged at the tops of the micro steel pipe piles, and crown beams are arranged on the pile caps; the high-pressure jet grouting pre-stressed anchor cable comprises a steel strand, an anchor cable free section and an anchor cable anchoring section. An anchoring section expanding head formed by a high-pressure jet grouting method is arranged at the end part of the anchor cable anchoring section; an anchor head is arranged at the front end of the steel strand and is fixed on the crown beam; the incident angle of the high-pressure jet grouting pre-stressed anchor cable is 30 degrees. According to the utility model, the direct contact between the steel pipe and the soil body can be avoided, the anti-sliding force requirement of the landslide can be met, the on-site construction by using large-scale mechanical equipment is avoided, and the purposes of low cost and high benefit are realized.

Description

Technical Field

[0001] The utility model relates to the technical field of landslide support, in particular to a retaining structure of micro steel pipe piles + high-pressure rotary jet prestressed anchor cables. Background Art

[0002] Loess mudstone landslides are loess landslides that occur in the Loess Plateau. They are one of the most widespread and frequent landslide types in the Loess Plateau. Loess-mudstone contact landslides are mostly developed in loess slopes with gentle slopes. The landslide slope is gentle and the sliding potential energy is small, which makes the landslide body more likely to undergo slow creep deformation when subjected to external forces, and has a certain creep property.

[0003] Due to the long-term creep characteristics of the landslide body, traditional landslide support methods, such as pile support structures made of reinforced concrete materials, are difficult to achieve ideal support effects. The construction material of reinforced concrete piles is reinforced concrete, which is expensive and has a large difference from the original soil characteristics in the area. The use of materials is not environmentally friendly. On the other hand, the landslide soil is fragile and the internal structure of the soil is unstable. Large-scale machinery and equipment are difficult to operate on landslides that have been creeping for a long time. Large-scale machinery operating on the landslide body may cause artificial sliding damage to the landslide body. At the same time, the low efficiency of manual operation poses a great safety risk. During the construction of reinforced concrete piles, large machinery is required to hoist steel cages and pour a large amount of concrete. Therefore, traditional reinforced concrete piles are not suitable for the treatment of such landslides.

[0004] At present, micro steel pipe piles, as a small-diameter and high-strength pile, can provide a certain amount of anti-sliding force in landslide support projects, and the pile body has high shear strength and is not easy to deform due to the steel pipe material. However, there are several problems with the existing micro steel pipe piles in engineering applications: ① Since the micro steel pipe piles will be buried in a complex underground environment in the project, the steel is susceptible to severe erosion by corrosive salts in the soil. If there are no appropriate anti-corrosion protection measures for the micro steel pipe piles, it will directly affect the service life and support effect of the steel pipe piles; ② The anti-sliding force provided by the micro steel pipe pile as a support means is limited, and it is difficult to compete with the sliding force generated by multi-level loess mudstone creep landslides. Therefore, it is particularly important to properly solve the problems of insufficient durability and anti-sliding force of micro steel pipe piles during application. Utility Model Content

[0005] The technical problem to be solved by the utility model is to provide a retaining structure of micro steel pipe piles + high-pressure rotary spray prestressed anchor cables which can avoid direct contact between steel pipes and soil and meet the requirements of landslide resistance, avoid the use of large-scale mechanical equipment in on-site construction and achieve low cost and high efficiency.

[0006] In order to solve the above problems, the utility model discloses a retaining structure of micro steel pipe piles + high-pressure rotary grouting prestressed anchor cables, which is characterized in that: the retaining structure is connected by micro steel pipe piles and high-pressure rotary grouting prestressed anchor cables; the micro steel pipe piles are 3*3 matrix-arranged pile groups, wherein a single micro steel pipe pile comprises a micro steel pipe with a cement slurry filling body filled inside, a cement slurry protective layer wrapped outside, and a leak-proof sleeve pile formed by rotary grouting; the micro steel pipe passes through 2 leakage layers in turn; the leak-proof sleeve pile is arranged within a depth range of 1 meter above and below the leakage layer; the micro steel pipe and the leak-proof sleeve pile The piles are connected to each other, and the connection strength comes from the bonding strength between the anti-leakage piles generated after high-pressure grouting of cement slurry; a pile cap is provided on the top of the micro steel pipe pile, and a crown beam is provided on the pile cap; the high-pressure rotary spraying prestressed anchor cable comprises a steel strand, an anchor cable free section at the front of the steel strand that is not wrapped by the grouting body, and an anchor cable anchoring section installed at the rear of the steel strand; an anchor cable anchoring section enlarged head formed by high-pressure rotary spraying grouting is provided at the end of the anchor cable anchoring section; an anchor head is provided at the front end of the steel strand, and the anchor head is fixed on the crown beam; the incident angle of the high-pressure rotary spraying prestressed anchor cable is 30°.

[0007] The micro steel pipe is formed by splicing a plurality of steel casings with a length of 1 m through their own threaded connection method, and the number of the steel casings is determined according to the actual pile length.

[0008] The diameter of the micro steel pipe pile is 170 mm to 350 mm; the diameter of the micro steel pipe is 150 mm to 300 mm, and is smaller than the diameter of the micro steel pipe pile; the thickness of the cement slurry protective layer is 20 mm to 50 mm.

[0009] The leak-proof sleeve pile is a hollow cylindrical hole formed by high-pressure rotary jetting of mud on the hole wall after drilling by a drilling rig. Its height is the same as that of the micro steel pipe pile, and its diameter is slightly larger than that of the micro steel pipe pile. It is located on the side wall of the soil through which the pile is inserted.

[0010] The steel strands are composed of at least 4 bundles of high-strength, low-relaxation steel strands with a diameter of 15.7 mm and a tensile strength of 1860 MPa.

[0011] The micro steel pipe pile is buried underground, and the height difference between the pile top and the ground is 90-110 cm.

[0012] Compared with the prior art, the utility model has the following advantages:

[0013] 1. The use of micro steel pipe piles instead of ordinary reinforced concrete piles in the utility model effectively avoids the problem of large machinery and equipment being unable to enter the site, greatly reduces the project cost, improves construction safety, and meets the requirements of environmentally friendly construction.

[0014] 2. The utility model adopts a high-pressure circulating grouting design, in which a cement slurry filling body is filled inside the micro steel pipe, and a cement slurry protective layer is wrapped outside to form a mud wall, thereby avoiding direct contact between the micro steel pipe and the soil and being eroded by corrosive salts, thereby improving the durability of the micro steel pipe pile.

[0015] 3. The utility model is provided with leak-proof sleeve piles, which successfully solves the problems of mud seepage and leakage along the stratum interface during the mud circulation when drilling and lowering micro steel pipes and the pile grouting process for projects with stratum interfaces in underground soil.

[0016] 4. The retaining structure combining micro steel pipe piles with high-pressure rotary jet prestressed anchor cables in the utility model not only meets the requirements of multi-level creep landslides for structural anti-sliding force, but also greatly curbs the tendency of this type of landslide to creep and slide along the fragile sliding belt surface for a long time.

[0017] 5. The utility model has strong engineering practical value and important social and economic benefits in similar multi-stage creep loess-mudstone landslide control projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The specific implementation of the utility model is further described in detail below with reference to the accompanying drawings.

[0019] Figure 1 This is the original stratum profile of the multi-stage creep loess-mudstone landslide of the utility model.

[0020] Figure 2 This is a cross-sectional view of the micro steel pipe pile + high-pressure rotary jet prestressed anchor cable structure arrangement of the utility model.

[0021] Figure 3 This is a plan view of the retaining structure of the utility model.

[0022] Figure 4 It is a schematic diagram of the structure of a micro steel pipe pile group of the utility model.

[0023] Figure 5 This is a schematic diagram of the micro steel pipe pile + high-pressure rotary jet prestressed anchor cable structure of the utility model.

[0024] Figure 6 This is a diagram showing the effect of the leak-proof sleeve pile jet grouting treatment of the utility model.

[0025] Figure 7 This is a schematic diagram of mud circulation for a single micro steel pipe pile of the utility model.

[0026] In the figure: 1—plain fill layer, 2—silt layer, 3—conglomerate layer, 4—loess-mudstone sliding zone layer, 5—mudstone layer, 6—original landslide terrace slope line, 7—micro steel pipe, 8—micro steel pipe pile, 9—pile cap, 10—crown beam, 11—anchor head, 12—cement slurry filling body, 13—cement slurry protective layer, 14—leakage-proof sleeve pile, 15—slurry flow direction, 16—steel strand, 17—anchor cable free section, 18—anchor cable anchoring section, 19—anchor section enlarged head, 20—existing slope foot retaining structure, 21—building, 22—reinforced concrete pile row retaining structure, 23—micro steel pipe pile + high-pressure rotary spray prestressed anchor cable retaining structure. DETAILED DESCRIPTION

[0027] Figure 1 The original stratigraphic profile of the multi-stage creep loess-mudstone landslide is shown in Figure 1. The main difference between this type of landslide and the ordinary landslide is that the slope foot angle of the original landslide terrace slope line 6 is relatively gentle, and there is a long-term creeping sliding characteristic. Although there is a reinforced concrete pile support structure 22 at the slope foot for preliminary support, the anti-sliding force it provides is far from enough to resist the sliding force generated by the overall creep landslide under the influence of bad weather, and there is a great safety hazard for the existing buildings 21 at the slope foot. Therefore, the support structure described in the utility model is applied to the loess mudstone multi-stage creep landslide.

[0028] like Figure 2 As shown in the figure, after the loess mudstone multi-level creep landslide terrace slope line 6 is initially leveled, a micro steel pipe pile + high pressure rotary grouting prestressed anchor cable retaining structure 23 is constructed at the front edge of each terrace to increase the anti-sliding force and supplement the anti-sliding force generated by the existing slope foot retaining structure 20 to stabilize the creep deformation of each terrace. The overall layout plan of the micro steel pipe pile + high pressure rotary grouting prestressed anchor cable retaining structure 23 is shown in the figure. Figure 3 shown.

[0029] like Figures 4 to 6As shown, a retaining structure of micro steel pipe piles + high-pressure rotary jet prestressed anchor cables is connected by micro steel pipe piles 8 and high-pressure rotary jet prestressed anchor cables. The micro steel pipe piles 8 are a group of piles arranged in a 3*3 matrix, wherein a single micro steel pipe pile includes a micro steel pipe 7 with a cement slurry filling body 12 filled inside and a cement slurry protective layer 13 wrapped outside, and a leak-proof sleeve pile 14 formed by rotary jet treatment to prevent leakage caused by excessive pores and cracks in the stratum or water seepage in the rock mass; the micro steel pipe 7 passes through each leaking layer 2 in turn; the leak-proof sleeve pile 14 is arranged within a depth range of 1 meter above and below the leaking layer; the micro steel pipe 7 and the leak-proof sleeve pile 14 are interconnected, and the connection strength comes from the high-pressure grouting of cement slurry. The generated bonding strength between the micro steel pipe pile 8 and the leak-proof sleeve pile 14; a pile cap 9 is provided on the top of the micro steel pipe pile 8, and a crown beam 10 is provided on the pile cap 9; the high-pressure rotary grouting prestressed anchor cable includes a steel strand 16, an anchor cable free section 17 at the front of the steel strand 16 that is not wrapped by the grouting body, and an anchor cable anchoring section 18 installed at the rear of the steel strand 16; an anchor cable anchoring section enlarged head 19 formed by a high-pressure rotary grouting method is provided at the end of the anchor cable anchoring section 18; an anchor head 11 is provided at the front end of the steel strand 16, and the anchor head 11 is fixed on the crown beam 10; the incident angle of the high-pressure rotary grouting prestressed anchor cable is 30°.

[0030] Wherein: the micro steel pipe 7 is formed by splicing a plurality of steel casing pipes with a length of 1 m through their own threaded connection method, and the number of the steel casing pipes is determined according to the actual pile length.

[0031] The diameter of the micro steel pipe pile 8 is 170mm~350mm; the diameter of the micro steel pipe 7 is 150mm~300mm, which is smaller than the diameter of the micro steel pipe pile 8; the thickness of the cement slurry protective layer 13 is 20mm~50mm. In actual projects, the thickness of the cement slurry protective layer 13 and the diameter of the micro steel pipe 7 are determined according to needs. The slurry used for the cement slurry filling body 12 and the cement slurry protective layer 13 is a cement slurry formed by mixing and stirring a pore grouting agent, cement, and water in proportion. The specific mix ratio is determined according to the required strength of the actual project, and the mix ratio of cement, pore grouting agent, and water is calculated to guide the construction. The slurry flow direction 15 of the cement slurry filling body 12 and the cement slurry protective layer 13 is as shown in Figure 7 shown.

[0032] The leak-proof sleeve pile 14 is a hollow cylindrical hole formed by high-pressure rotary spraying of mud on the hole wall after drilling by a drilling rig. Its height is the same as that of the micro steel pipe pile 8, and its diameter is slightly larger than that of the micro steel pipe pile 8. It is located on the side wall of the soil through which the pile is inserted.

[0033] The steel strand 16 is composed of at least 4 bundles of high-strength, low-relaxation steel strands with a diameter of 15.7 mm and a tensile strength of 1860 MPa. The specific required number and diameter are based on the actual calculated area. The applied prestress value should be controlled between 0.6 and 0.7 times the ultimate tensile strength of the steel strand. The engineering value is determined based on the actual calculation results.

[0034] The micro steel pipe pile 8 is buried underground, and the height difference between the pile top and the ground is 90-110 cm. Preferably, the pile top is located 100 cm below the ground surface, and the distance of 100 cm between the pile top and the ground surface is used for the construction preparation of the pile cap of a single group of micro steel pipe piles.

[0035] The overall length of the anchor cable is determined according to the actual drilling depth of the loess-mudstone sliding zone layer 4 at each drilling point, ensuring that the anchor section enlarged head 19 just passes through the fragile sliding zone soil layer to play an anchoring role. The specific length ratio of the anchor section and the free section under each pile needs to be calculated based on specific calculations. The anchor section enlarged head 19 formed after part of the high-pressure rotary grouting is connected to the lower structure of the micro steel pipe pile 8. The connection method is only a small part of the connection formed after the cement slurry infiltrates the soil around the micro steel pipe pile 8, and the connection strength is only the bonding strength of the cement slurry infiltrating the soil.

[0036] When grouting the free section 17 of the anchor cable, the grouting speed should be controlled at 10-15 mm / min, and the pressure gauge indication value should not be lower than 25 MPa.

[0037] During the grouting operation of the anchor cable anchoring section 18 and the anchoring section enlarged head 19, the grouting pressure value should be controlled at 25-30 MPa, and the nozzle retreat speed should be controlled at 8-10 mm / min.

[0038] The grouting material used in the construction of high-pressure jet grouting prestressed anchor cables is ordinary Portland cement, and the water-cement ratio is controlled between 0.45:1 and 0.55. The strength of the grouting body is not less than 30MPa. During the grouting process, ensure that the grouting slurry is stirred evenly and used immediately after stirring to prevent stones and debris from mixing into the slurry.

[0039] The leakage slurry layer described in the utility model is located at the interface between different soil strata. Since there are a large number of pores in the interface between strata of different soil types, a large amount of slurry seeps into the stratum when cement slurry is injected, resulting in a decrease in grouting pressure and a significant increase in material loss during cement slurry filling.

[0040] The utility model combines the supporting advantages of micro steel pipe piles and high pressure rotary jet prestressed anchor cables. On the one hand, micro steel pipe piles are driven into the front edge of each creep landslide body to improve the overall anti-sliding force of the upper soil. On the other hand, the expanded head of the anchoring section of the high pressure rotary jet prestressed anchor cable is deeply embedded in the loess-mudstone sliding zone soil layer to prevent the sliding zone soil from creeping and sliding again after being saturated by rainwater infiltration. The two parts of the structure are connected as a whole through the crown beam at the top of the micro steel pipe pile, which greatly increases the overall anti-sliding effect of the landslide.

[0041] The construction method of the micro steel pipe pile + high-pressure rotary grouting prestressed anchor cable retaining structure comprises the following steps:

[0042] ⑴ Geological survey: Through geological survey and drilling exploration, the overall stratigraphic distribution type, depth, characteristics and change patterns of the landslide are determined.

[0043] (2) Design of micro steel pipe piles 8: According to the engineering design data and geological survey report, the specific location of the micro steel pipe piles 8 is determined by surveying and laying out, and it is clear that the body of each micro steel pipe pile 8 should be 3 to 5 meters below the sliding soil layer, so as to determine the length, pile diameter and soil environment of each micro steel pipe pile 8, and select the strength of the cement paste; first, the landslide slope is artificially leveled according to the stepped terrace form in the design of the treatment plan, and then the micro steel pipe piles 8 are arranged at the front edge of each terraced cultivated land to provide great anti-slip force for this layer of terraces.

[0044] ⑶ Design specific parameters such as size and reinforcement of pile cap 9 and cap beam 10.

[0045] ⑷ Design of high-pressure rotary grouting prestressed anchor cable: Calculate the relationship between sliding force and anti-sliding force based on the landslide parameters obtained from geological survey, calculate the size of prestress required to be applied by high-pressure rotary grouting prestressed anchor cable on each level of creep landslide, as well as the length of the free section and anchoring section, and determine specific parameters such as the anchor cable incident angle and enlarged head diameter.

[0046] ⑸ Formulate a construction plan: According to the survey data, in order to solve the problems of corrosion resistance of micro steel pipe piles 8 and insufficient anti-sliding force of the overall structure, the construction can be divided into two parts: micro steel pipe piles 8 and high-pressure rotary spray prestressed anchor cables.

[0047] ① The pile forming process of the micro steel pipe pile 8: The mud and cement slurry in the micro steel pipe pile 8 are continuously returned from the bottom of the pile along the outer side of the micro steel pipe 7 to the ground, so as to achieve the mud wall protection effect and realize the pouring of the steel casing cement slurry filling body 12 and the cement slurry protective layer 13; at the same time, the leakage-proof casing pile 14 solution is adopted to solve the leakage problem at the stratum interface faced in the pile forming grouting process.

[0048] Step 1: Before the formal start of construction, according to the engineering design data and geological survey report, the slope line 6 of the landslide terrace is partially leveled to make each level of the slope relatively gentle, and the depth range of the soil layer required for jet grouting treatment is determined.

[0049] Step 2: Move the drilling rig to the designed hole position and adopt the jet grouting method. Start the drilling rig and drill to 1m below the bottom of the deepest stratum interface within the designed pile length. While drilling, you can prepare the jet grout: first calculate the amount of cement and water according to the water-cement ratio required for the project, add water first, then pour in cement and stir it with a grout mixer for 10min to 20min. After stirring, put the slurry into the grout bucket for standby use.

[0050] Step 3: After the reserve slurry is pressurized by a high-pressure pump, it is sent to the drilling rig through a high-pressure pipe for rotary jetting. In order to fully consider the errors existing in geological survey and the construction quality, the thickness of the stratum interface of the leaking slurry layer should be corrected, that is, uniform rotary jetting is carried out in the depth range from 1m below the bottom design elevation of the stratum interface layer to 1m above the top design elevation of the layer, and maintenance is carried out.

[0051] Step 4: During the maintenance of the anti-leakage sleeve pile 14, the micro steel pipe pile 8 is poured with cement slurry. The preparation is carried out on-site. The cement slurry is mostly made of bentonite, which is divided into three types: sodium-based soil, calcium-based soil and lithium-based soil. In actual projects, the type of bentonite is appropriately selected based on the principle of economy, and the mass ratio of cement, soil and water is controlled to be 1:2.5:1.

[0052] Step 5: One hour before the first steel casing is drilled to the bottom of the pile, prepare the cement paste according to the calculated mix ratio and required amount of cement, hole grouting agent and water; the mixing order of cement paste is as follows: ⅰ first add all the materials required for mixing; ⅱ start the grout mixer; ⅲ evenly add all the hole grouting agent; ⅳ evenly add all the cement; ⅴ continue to stir for 2 minutes. After stirring evenly, immediately put the cement paste into the grouting bucket, and the cement paste should be continuously stirred in the grouting bucket to ensure the fluidity of the cement paste.

[0053] Step 6: The drilling rig is moved to the drilled hole position for the second time to start the secondary drilling work, and the steel casing is drilled synchronously; at the same time, the mud is pressurized by the high-pressure pump, and then sent to the drilling rig through the high-pressure grouting pipe and enters the micro steel pipe 7. At this time, the high pressure causes the mud in the micro steel pipe 7 to continuously flow back from the bottom of the pile along the outside of the micro steel pipe 7 to the ground, so that the outside of the micro steel pipe 7 is wrapped with mud; by increasing the grouting pressure, the mud is wrapped as much as possible for every gap inside and outside the micro steel pipe pile 8. Continue to apply high pressure to cause the cement slurry in the micro steel pipe 7 to continuously flow back from the bottom of the pile along the outside of the micro steel pipe 7 to the designed elevation of the pile top. When the mud at the pile top elevation outside the micro steel pipe 7 has all flowed out and the returned slurry is cement slurry, slowly pull out the drilling rig grouting pipe, fill the micro steel pipe 7 with cement slurry, and then perform grouting operations on the outside of the micro steel pipe 7 to ensure that the inside and outside of the micro steel pipe 7 are completely wrapped with cement slurry.

[0054] Step 7: After the grouting operation is completed, all the cement slurry in the drilling rig and high-pressure pipe should be removed to prevent the remaining cement slurry from clogging the pipeline, and the mud diversion groove should be backfilled and the drilling rig should be moved to the next pile position.

[0055] Step 8: After all the micro steel pipe piles 8 are constructed and maintained, the construction of the pile cap 9 and the crown beam 10 of the individual pile groups begins. The specific steps are as follows: determine the position and elevation of the pile cap 9 and the crown beam 10 support according to the construction design plan, excavate the micro steel pipe pile group that has completed the cement slurry pouring to 100 cm below the ground surface, the excavation surface size is the design size of the pile cap 9, and the support is pre-buried and fixed in the notch after excavation; make the pile cap 9 and the crown beam 10 template according to the design requirements, and cut, splice and strengthen the template; according to the design requirements, process and install the steel bars, and pay attention to the correct position and spacing during installation; finally, pour concrete, mix the concrete according to the predetermined mix ratio, and pump or manually pour it into the crown beam 10 template, connect the single group of 3*3 micro steel pipe piles through the same pile cap 9 combination, vibrate to eliminate gaps during pouring, and perform maintenance in time to prevent cracks and cracks; after the concrete hardens, remove the mold according to the maintenance period requirements, and perform appropriate maintenance.

[0056] ② Construction technology of high-pressure rotary jet prestressed anchor cable: Use multi-stage enlarged head prestressed anchor cable technology to enhance the anchoring effect of high-pressure rotary jet prestressed anchor cable, and use it in combination with the micro steel pipe pile 8 through the pile cap 9 and the crown beam 10. Note that the anchor cable should not pass through the formed micro steel pipe pile 8 during the hole forming process to avoid damage to the micro steel pipe pile 8; the grouting pressure should be slightly increased during high-pressure rotary jet grouting so that the enlarged head part of the anchoring section of the high-pressure rotary jet prestressed anchor cable is partially connected to the lower part of the micro steel pipe pile 8.

[0057] Step 1: Prestressed anchor cables used for off-site prefabrication construction, the prestressed anchor cables comprising an anchor plate, three steel strands and an extrusion anchor matched with the steel strands for fixing one end of the steel strand on the anchor plate.

[0058] Step 2: According to the elevation and horizontal spacing requirements in the construction design plan, the anchor hole positions are located and marked on the crown beam 10 of the pile cap 9 at the top of the micro steel pipe pile 8.

[0059] Step 3: Place the drilling rig at the designed position, align the front end of the drilling rig drill bit with the marked anchor hole position and drill. The drilling rig first passes through the completed micro steel pipe pile 8 pile cap 9 and crown beam 10, and then passes through the landslide slope soil; the drilling rig drills to the designed free section depth, and the prestressed anchor cable enters the hole with the drill bit during the drilling process. When drilling the free end, avoid contact with the steel bars in the pile cap 9 and crown beam 10, and drill one hole at a time when drilling the free section.

[0060] Step 4: After the free section hole reaches the designed depth, the drill bit rotates and drills, and the high-pressure cement slurry injected by the high-pressure pump passes through the cement slurry channel of the drill rod and the drill bit and rotates and sprays outward from each nozzle of the drill bit. The high-pressure cement slurry jet cuts the surrounding soil and stirs and mixes to form an anchoring section with a diameter larger than the free section. When grouting the anchoring section, the cement slurry injection pressure is not less than 20MPa, and the drilling or lifting speed is 0.25m / min.

[0061] Step 5: After the anchoring section reaches the designed length, increase the grouting pump pressure and reduce the drilling speed. Use a two-in, two-out, four-times jetting process to form the anchor body of the anchoring section enlarged head. This "two-in, two-out, four-times jetting" process can ensure that the grouting in the anchor hole is sufficient and uniform, and improve the reinforcement effect and bearing capacity of the anchor. At the same time, by observing and adjusting the grouting parameters, the grouting effect can be accurately controlled to ensure the quality of the project. When constructing the enlarged head, the grouting pump pressure is 25MPa, the drilling speed is 0.15m / min, and the grouting volume of the enlarged head is more than twice that of the anchoring section. It should be pointed out that when forming the enlarged head, the two-in, two-out, four-times jetting process specifically refers to the four jetting operations performed by high-pressure rotary spraying equipment during the formation and reinforcement of the anchor hole. These four injection operations can be divided into two grouting operations (i.e. grouting) and two grouting operations (i.e. grouting); respectively, the first grouting operation: injecting the prepared cement slurry into the anchor hole through the high-pressure rotary jet equipment, and using the rotation and propulsion of the rotary jet drill to fully mix the cement slurry with the hole wall soil; the second grouting operation: on the basis of the first grouting operation, injecting cement slurry again to further reinforce the hole wall soil. After the two grouting operations, two grouting operations will be performed. The first grouting operation: the excess cement slurry in the hole and the slurry mixed with the soil are discharged through the high-pressure rotary jet equipment, and the state of the discharged slurry is observed to judge the grouting effect; the second grouting operation: after the first grouting operation, the slurry in the hole is discharged again to ensure that the slurry in the hole is fully discharged to avoid affecting the subsequent operations. The above operations can ensure that the grouting in the anchor hole is sufficient and uniform, and achieve the expected reinforcement effect.

[0062] Step 6: Drill bit and drill rod withdraw and repeat grouting: After the construction of the enlarged head anchoring section is completed, the drill rod and drill bit are rotated and withdrawn while repeating the grouting. The anchor plate of the prestressed anchor cable, the extrusion anchor and a section of the steel hinge wire remain in the cement slurry soil mixture.

[0063] Step 7: After the rotary jet mixing pile body composed of prestressed anchor cable and cement slurry soil mixture has been cured for 7 days, the protruding end of the prestressed anchor cable steel hinge wire is tensioned and locked. After locking, the remaining anchor bars are cut mechanically and 5 to 10 cm of exposed anchor bars are left to prevent slipping.

[0064] Step 8: Finally, fill all gaps with cement slurry and seal the anchors according to the design requirements.

[0065] Example:

[0066] A multi-level creep loess mudstone landslide disaster occurred in a county in Longnan City, Gansu Province. The geomorphic unit in the area is low and medium mountains, with high terrain in the west and low terrain in the east, high terrain in the north and low terrain in the south. The overall slope of the site is relatively gentle, with a slope of 8~15° and an altitude of 1020∼1100m. The landslide area is terraced farmland with a gentle slope. The steps at the front edge of the terrace are nearly vertical, and the step height is generally between 1~3m. A substation was built at the foot of the landslide, and the reinforced concrete pile support structure at the foot of the slope had large deformation and cracks. According to the on-site investigation of the engineer, the support structure could not play an effective long-term support effect. Therefore, according to the requirements of post-disaster prevention and control construction, the multi-level creep loess mudstone landslide needs to be managed with secondary slope support engineering to control the creep trend of the landslide, increase the overall stability of the landslide, and prevent the loess mudstone contact surface layer from causing binary landslides between loess mudstone layers due to long-term creep and rainfall infiltration, and avoid damage to the substation facilities at the foot of the landslide. The landslide surface originally belonged to terraced farmland. According to construction requirements, after the landslide control is completed, the terraced farmland will continue to be used as a crop production site for the surrounding villagers to produce and work. It is now necessary to carry out secondary management of the multi-level creep loess mudstone landslide. After comprehensive comparison of multiple plans, it was decided to adopt the landslide support technology of micro steel pipe piles + high-pressure rotary spraying prestressed anchor cables. The specific construction process is as follows:

[0067] (1) Geological survey: According to the previous geological survey report, the geomorphic unit of the multi-level creep loess mudstone landslide survey area is low and medium mountain, with high terrain in the west and low terrain in the east, high terrain in the north and low terrain in the south. The overall slope of the site is relatively gentle, with a slope of 8~15°. According to the regional geological data combined with the drilling and exploration well data of this project, the survey area of ​​this project is overlying the Quaternary wind-accumulated and slope-accumulated silt, and the underlying Tertiary mudstone or conglomerate. From top to bottom, they are plain fill layer 1, silt layer 2, conglomerate layer 3, and mudstone layer 5.

[0068] The soil of the plain fill layer 1 is gray-black and brick-red, mainly composed of silty clay, mixed with a small amount of broken bricks, ginger stones and roots. The soil is uneven and was filled during the construction of the substation. The filling time is 1-3 years and the layer thickness is generally 3.5m-4.5m.

[0069] The soil of silt layer 2 is grayish yellow, brownish yellow, wet, slightly dense to medium dense, mainly composed of quartz and mica fragments, with low toughness, smooth cross section and uniform soil. The thickness of this layer is generally 1.0-4.5m.

[0070] The soil of conglomerate layer 3 is brown-red and variegated, mainly composed of quartzite, granite, sandstone, etc. The particles are uneven, with a particle size of about 2-45mm, mud cementation, gravel structure, layered structure, the core is scattered, easy to break by hand, and completely weathered. The layer thickness is generally 4.1-5.0m.

[0071] The soil of mudstone layer 5 is brown-red, with mud cementation, mud structure, and layered structure. The main mineral components are clay minerals. The rock properties are swelling, the hammer sound is dull, and it is easy to break by hand. There are a small amount of small gravels in some parts, and the core is columnar. This layer has not been exposed.

[0072] According to the survey site, the groundwater type is mainly stagnant water above the bedrock surface, which is replenished by atmospheric precipitation, flows down along the mountain in the silty clay layer, and is discharged into the bottom gully. According to multiple water level measurements in the borehole, the stable groundwater level in the survey site is 2.8-6.4m.

[0073] (2) Design of micro steel pipe pile 8: Based on geological survey reports and other information, taking the first-level terraced farmland support structure from the high-altitude area to the low-altitude area as an example, the length of the micro steel pipe pile 8 of the support structure is determined to be 9m. The micro steel pipe pile 8 is designed to have a hole diameter of φ198mm, with a built-in φ168mm steel pipe. The steel pipe is made of geological pipe material DZ40 for drilling, with a yield strength of 400MPa and a wall thickness of δ=8mm. The micro steel pipe pile 8 enters the mudstone layer to a depth of 2m, and M50 cement slurry is poured into the micro steel pipe pile 8.

[0074] (3) Design of pile cap 9 and cap beam 10: Pile cap 9 adopts the dimensions of 800mm×800mm×100mm (length×width×height), cap beam 10 adopts the dimensions of 1200cm×50cm (length×height), cast with C30 concrete, and built-in structural stirrups And adopt double-limb hoop binding method.

[0075] (4) Design of high-pressure rotary jet prestressed anchor cable: The total length of the high-pressure rotary jet prestressed anchor cable is 14 m, of which the free section is 6 m and the anchor section is 8 m. In the 8 m anchor section, 4 m is the length of the enlarged head anchor body, with a determined diameter of 1000 mm; 4 m is the length of the ordinary anchor body, with a determined diameter of 50 mm.

[0076] (5) Formulate a plan: According to the survey data and the analysis of the causes of the landslide, the loess on the upper part of the landslide has good permeability, and the slope surface is similar to a multi-level terrace. When it rains, a large amount of rainwater infiltrates. Due to the poor permeability of mudstone, the infiltrated rainwater and groundwater tend to gather near the contact surface between mudstone and loess and its low-lying parts, making the loess contact surface (belt) above the impermeable layer of the loess landslide in an over-wet, soft plastic-saturated state for a long time, forming a weak sliding belt soil layer. The landslide is in a state of creep and slow sliding along this weak surface for a long time. In order to achieve the ideal support effect, a support structure of micro steel pipe piles + high-pressure rotary jet prestressed anchor cables is used, which includes the following steps:

[0077] [1] Piling technology of micro steel pipe pile 8:

[0078] Step 1: According to the engineering design data and the geological survey report, determine the soil layer depth range required for the rotary jet grouting to form the leak-proof sleeve pile 14, which is 4m~6m and 9m~11m respectively.

[0079] Step 2: Move the drilling rig to the designed hole position and adopt the rotary jet pile construction method. Start the drilling rig and drill to the designed elevation of the leak-proof sleeve pile 14. While drilling, the rotary jet slurry can be prepared: ordinary silicate cement is used for cement, and the water-cement ratio is determined to be 1:1. First add water and then pour in cement and stir it through a slurry mixer for 10min to 20min. After stirring, put the slurry into a slurry bucket for standby use.

[0080] Step 3: After the spare slurry is pressurized by a high-pressure pump, it is sent to the drilling rig through a high-pressure pipe for rotary spraying; in order to fully consider the errors existing in geological survey and the construction quality, the thickness of the leaking slurry layer should be corrected, that is, the slurry should be evenly rotary sprayed from the depth range of -4.0m to -6.0m and -9.0m to -11.0m at elevations and maintained for 7 days.

[0081] Step 4: During the maintenance of the leak-proof sleeve piles 14, the micro steel pipe piles 8 are poured with cement slurry. The preparation is carried out on-site. The cement slurry slurry material is mostly bentonite, which is divided into three types: sodium-based soil, calcium-based soil and lithium-based soil. In this project, calcium-based soil is used as the cement slurry slurry material, and the mass ratio of cement, soil and water is controlled to be 1:2.5:1.

[0082] Step 5: The drilling rig moves to the designed hole position and starts drilling, and the steel casing is drilled synchronously; at the same time, the mud is pressurized by the high-pressure pump, sent to the drilling rig through the high-pressure pipe and enters the micro steel pipe 7. At this time, the high pressure causes the mud in the micro steel pipe 7 to continuously flow back from the bottom of the pile along the outside of the micro steel pipe 7 to the ground, so that the outside of the micro steel pipe 7 is wrapped by mud. According to the principle of mud wall protection, the occurrence of hole collapse and steel pipe locking can be prevented.

[0083] Step 6: One hour before the first steel casing is drilled to the bottom of the pile, prepare cement slurry; the water-to-cement ratio is 0.31, where the cement is a mixture of cement and hole grouting agent, and the ratio of cement to hole grouting agent is about 10:1; based on the mix ratio of M50 cement slurry, calculate the relative amounts of cement, hole grouting agent and water, and the materials contained in 1000kg of cement slurry are calculated as follows: 694.5kg of cement, 62.5kg of hole grouting agent, and 243kg of water. Therefore, the mix ratio preliminarily calculated by the mass method is: cement: hole grouting agent: water = 1:0.09:0.35; that is, during actual construction, the mortar machine feeds 350kg of cement, 31.5kg of hole grouting agent, and 122.5L of water at one time; use a slurry mixer to mix all the materials, first add water and then add solid materials evenly while stirring, and continue mixing for 120s after all materials have been added. After ensuring that the total mixing time is not less than 240s, put the evenly mixed cement slurry into the slurry barrel and continue stirring to maintain the fluidity of the cement slurry.

[0084] Step 7: After the first steel casing is drilled to the pile bottom elevation, the cement slurry is immediately pressurized by a high-pressure pump through a grouting pipe, and then sent to the drilling rig through a high-pressure pipe and enters the micro steel pipe 7. At the same time, the high pressure causes the cement slurry in the micro steel pipe 7 to continuously flow back from the pile bottom along the outside of the micro steel pipe 7 to the pile top design elevation. When the mud at the pile top elevation outside the micro steel pipe 7 has all flowed out and the returned slurry is cement slurry, the drilling rig grouting pipe is slowly pulled out, and the micro steel pipe 7 is filled with cement slurry, and then the outside of the micro steel pipe 7 is grouting to ensure that the outside of the micro steel pipe 7 is completely wrapped with cement slurry.

[0085] Step 8: After the grouting operation is completed, all the cement slurry in the drilling rig and high-pressure pipe should be removed to prevent the remaining cement slurry from clogging the pipeline, and the mud diversion groove should be backfilled and the drilling rig should be moved to the next pile position.

[0086] Step 9: After all micro steel pipe piles 8 are constructed and maintained, the construction of the pile cap 9 and the crown beam 10 of the single micro steel pipe pile group begins. The pile cap 9 adopts the size of 800mm×800mm×100mm (length×width×height), and the crown beam 10 adopts the size of 1200cm×50cm (length×height). C30 concrete is poured, and structural stirrups are built in. The double-leg hoop binding method is adopted. According to the construction design plan, the position and elevation of the crown beam support are determined. The micro steel pipe pile group that has completed cement slurry pouring is excavated to 100cm below the surface. The excavation surface size is the design size of the pile cap 9. The pile cap 9 and the crown beam support are embedded and fixed in the notch after excavation; the templates of the pile cap 9 and the crown beam 10 are made according to the design requirements, and the templates are cut, spliced ​​and strengthened; according to the design requirements, the steel bars are processed and installed, and the correct position and spacing are paid attention to during installation; finally, the concrete is poured. The concrete used is mixed according to the C30 concrete standard mix ratio of cement: sand: gravel of 0.38:1:1.11:2.72, and is pumped or manually poured into the pile cap 9 and crown beam 10 templates. At the same time, it is vibrated to eliminate gaps and timely maintenance is carried out to prevent cracks and cracks; after the concrete hardens, the template is removed after 7 days of maintenance, and appropriate maintenance is carried out.

[0087] [2] High-pressure jet grouting prestressed anchor cable construction technology:

[0088] Step 1: The prestressed anchor cables used in off-site prefabrication construction actually use an anchor plate model of M16 with dimensions of 138mm×138mm×65mm and an anchor plate aperture of 18mm. Four steel strands with a diameter of 15.7mm and a tensile strength of 1860MPa are used. In addition, supporting equipment for the steel strands is used, such as an extrusion anchor used to fix one end of the steel strand to the anchor plate.

[0089] Step 2: Locate and mark the anchor holes on the top pile cap 9 and the crown beam 10 of the micro steel pipe pile 8 according to the elevation and horizontal spacing requirements in the construction design plan.

[0090] Step 3: Place the drill rig in the set position, align the front end of the drill bit with the marked anchor hole and drill until the set free section depth is reached. During the drilling process, the prestressed anchor cable enters the hole along with the drill bit.

[0091] Step 4: After the free section hole reaches 6m, the drill bit rotates and drills, and the high-pressure cement slurry injected by the high-pressure pump passes through the cement slurry channel of the drill rod and the drill bit and then rotates and sprays outward from each nozzle of the drill bit. The high-pressure cement slurry jet cuts the surrounding soil and stirs and mixes, forming a common anchoring section with a diameter of 50mm;

[0092] Step 5: After the anchoring section reaches 4m, increase the grouting pump pressure and reduce the drilling speed. Use a two-in, two-out, four-time injection process to form an enlarged head anchor body with an anchoring section length of 4m and a diameter of 1000mm, and connect it to the bottom of the micro steel pipe pile 8 through high-pressure rotary spraying. This "two-in, two-out, four-time injection" process can ensure that the grouting in the anchor hole is sufficient and uniform, and improve the reinforcement effect and bearing capacity of the anchor. At the same time, by observing and adjusting the grouting parameters, the grouting effect can be accurately controlled to ensure the quality of the project.

[0093] Step 6: After the enlarged head is constructed, the drill rod and drill bit are rotated and withdrawn while repeating the grouting. The anchor plate of the prestressed anchor cable, the extrusion anchor and a section of the steel hinge wire remain in the cement slurry soil mixture.

[0094] Step 7: After the rotary jet mixing pile body composed of prestressed anchor cable and cement slurry soil mixture has been cured for 7 days, the protruding end of the steel hinge wire of the prestressed anchor cable is tensioned and locked. The actual prestress value of the anchor cable set in this project is 1100MPa, and the tension control error should be controlled within ±5% of the prestressed strength. After locking, the remaining anchor bars are cut mechanically and 5 to 10 cm of exposed anchor bars are left to prevent slipping; finally, the gaps in each part are filled with cement slurry and the anchors are sealed according to the design requirements.

[0095] Step 8: Repeat the above construction steps until all anchor cables are constructed and then conduct quality inspection.

Claims

1. A retaining structure of micro steel pipe pile + high pressure rotary grouting prestressed anchor cable, characterized in that: The retaining structure is connected together by micro steel pipe piles (8) and high-pressure rotary grouting prestressed anchor cables; the micro steel pipe piles (8) are a group of piles arranged in a 3*3 matrix, wherein a single micro steel pipe pile comprises a micro steel pipe (7) filled with a cement slurry filling body (12) on the inside, a cement slurry protective layer (13) wrapped on the outside, and a leak-proof sleeve pile (14) formed by rotary grouting; the micro steel pipe (7) passes through two leakage slurry layers in sequence; the leak-proof sleeve pile (14) is arranged within a depth range of 1 meter above and below the leakage slurry layer; the micro steel pipe (7) and the leak-proof sleeve pile (14) are connected to each other, and the connection strength is generated by the high-pressure grouting of cement slurry and the leak-proof sleeve pile (14). 14); the top of the micro steel pipe pile (8) is provided with a pile cap (9), and the pile cap (9) is provided with a crown beam (10); the high-pressure rotary grouting prestressed anchor cable comprises a steel strand (16), an anchor cable free section (17) at the front of the steel strand (16) not wrapped by the grouting body, and an anchor cable anchoring section (18) installed at the rear of the steel strand (16); the end of the anchor cable anchoring section (18) is provided with an anchoring section enlargement head (19) formed by a high-pressure rotary grouting method; the front end of the steel strand (16) is provided with an anchor head (11), and the anchor head (11) is fixed on the crown beam (10); the incident angle of the high-pressure rotary grouting prestressed anchor cable is 30°.

2. A retaining structure of micro steel pipe pile + high pressure rotary grouting prestressed anchor cable as claimed in claim 1, characterized in that: The micro steel pipe (7) is formed by splicing a plurality of steel casing pipes with a length of 1 m through their own threaded connection method, and the number of the steel casing pipes is determined according to the actual pile length.

3. A retaining structure of micro steel pipe pile + high pressure rotary grouting prestressed anchor cable as claimed in claim 1, characterized in that: The diameter of the micro steel pipe pile (8) is 170 mm to 350 mm; the diameter of the micro steel pipe (7) is 150 mm to 300 mm, and is smaller than the diameter of the micro steel pipe pile (8); and the thickness of the cement slurry protective layer (13) is 20 mm to 50 mm.

4. A retaining structure of micro steel pipe pile + high pressure rotary grouting prestressed anchor cable as claimed in claim 1, characterized in that: The leak-proof sleeve pile (14) is a hollow cylindrical hole formed by high-pressure rotary jetting mud wall protection on the hole wall after drilling by a drilling rig. Its height is the same as that of the micro steel pipe pile (8), its diameter is slightly larger than that of the micro steel pipe pile (8), and it is arranged on the side wall of the soil through which the pile is inserted.

5. The retaining structure of micro steel pipe pile + high pressure rotary grouting prestressed anchor cable as claimed in claim 1, characterized in that: The steel strands (16) are composed of at least four bundles of high-strength, low-relaxation steel strands with a diameter of 15.7 mm and a tensile strength of 1860 MPa.

6. The retaining structure of micro steel pipe pile + high pressure rotary grouting prestressed anchor cable as claimed in claim 1, characterized in that: The micro steel pipe pile (8) is buried underground, and the height difference between the pile top and the ground is 90-110 cm.

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