Double-layer rotary jet reinforced core composite pile with bag extrusion and expansion and construction method and device thereof

Abstract

The present invention discloses a double-layer rotary jet reinforced core composite pile with a bag extrusion and expansion body and a construction method and device thereof, comprising a pile pipe, a plurality of grouting ports and lateral stirring blades arranged at the bottom of the pile pipe; a casing is arranged on the inside of the pile pipe, a first grouting part and a second grouting part are installed between the pile pipe and the casing, the first grouting part and the second grouting part are connected to the grouting port; the first grouting part and the second grouting part are fixedly connected to the pile pipe and rotatably connected to the casing; a drainage board is installed circumferentially on the inside of the casing, and an air bag is installed on the inside of the drainage board. The present invention arranges the air bag along the entire length of the pile body, so that according to the design requirements of the pile foundation bearing capacity, the entire length of the second stirring body can be extruded and expanded in combination with the construction method of the present invention, thereby increasing the pile body diameter and significantly improving the pile side interface friction resistance, thereby significantly improving the pile foundation bearing capacity. After the air bag is recovered, a reinforcing core is constructed in the center of the stirring body, which increases the strength and rigidity of the pile body and reduces the pile foundation settlement.

Description

Technical Field

[0001] The present invention relates to the technical field of composite pile foundations used in building construction, bridge construction, road construction and the like, and in particular to a double-layer rotary jet reinforced core composite pile having a bag-extrusion expansion body and a construction method and device thereof. Background Art

[0002] my country has a vast area of ​​soft soil, covering many provinces. Soft soil foundation treatment is crucial for engineering construction. Currently, flexible piles, such as cement-soil mixing piles, and rigid piles, such as concrete pipe piles and cast-in-place concrete piles, are the main methods for treating soft soil foundations in my country. Although cement-soil mixing piles are low-cost and easy to construct, they have disadvantages such as low pile strength and rigidity, low bearing capacity, and large pile foundation settlement. They are no longer able to meet the needs of reinforcing complex soft soil foundations for major projects such as high-rise buildings, high-grade highways, and railways. Although concrete piles overcome the shortcomings of cement-soil mixing piles, their cost is relatively high.

[0003] In recent years, my country has developed a reinforced-core cement-soil composite pile by inserting a concrete core into a cement-soil mixing pile. This type of pile foundation, composed of two materials of varying hardness and softness, cement-soil and the reinforced core, combines the advantages of both cement-soil and concrete piles. Furthermore, compared to using simple cement-soil mixing piles, reinforced-core cement-soil composite piles for reinforcing soft soil foundations can significantly reduce project costs. Consequently, reinforced-core cement-soil composite piles are increasingly being used in engineering projects.

[0004] However, in existing construction techniques, after cement is jet-jetted into the soil and stirred into cement-soil, a concrete core is quickly inserted into the soil while it is in a liquid or semi-liquid state. This inevitably causes the cement-soil to squeeze out of the pile top and onto the ground surface, resulting in not only a waste of cement-soil material but also environmental pollution at the construction site. Furthermore, under this construction method, the cement-soil cannot be further squeezed and diffused into the soil surrounding the pile through the insertion of the core. Therefore, while the strength and rigidity of composite piles are significantly improved after the cement hardens, significantly reducing pile foundation settlement, the interfacial friction between the cement-soil and the soil surrounding the pile is minimally improved, resulting in a minimal increase in pile foundation bearing capacity. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned strong core cement soil composite pile construction technology and provide a composite pile foundation reinforcement technology with strong bearing capacity, convenient construction and good economy.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A double-layer rotary jet reinforced core composite pile construction device with bag extrusion and expansion comprises a pile pipe, a plurality of grouting ports and lateral stirring blades are arranged at the lower part of the pile pipe, a plurality of flap pile tips are hingedly connected to the bottom of the pile pipe, and the flap pile tips are arranged along the circumference of the pile pipe; a plurality of bottom stirring blades are arranged on the outer periphery of the flap pile tip; a casing is provided on the inner side of the pile pipe, a first grouting part and a second grouting part are installed between the pile pipe and the casing, and the first grouting part and the second grouting part are connected to the grouting port; the first grouting part and the second grouting part are fixedly connected to the pile pipe and rotatably connected to the casing; a drainage board is installed circumferentially inside the casing, an air bag is installed on the inner side of the drainage board, and a pore water pressure sensor is provided at the bottom of the air bag.

[0008] As a further improvement, several first grouting bins are connected in series from top to bottom to form a first grouting piece, and several second grouting bins are connected in series from top to bottom to form a second grouting piece; the first grouting piece and the second grouting piece are arranged at intervals from each other along the circumference of the pile pipe; wherein, the first grouting bins on the same layer are connected to each other through the first connecting pipe, and the second grouting bins on the same layer are connected to each other through the second connecting pipe.

[0009] A further improvement is that the first grouting part includes a first grouting bin in the middle, a first grouting channel is formed at the bottom of the first grouting bin, and a first interface cooperating with the first grouting channel is formed at the top; the first grouting bin is opened on the side opposite to the grouting port, and a first sealing gasket is fixed on the outer periphery of the opening, and a first steel ball is installed on the side opposite to the casing of the first grouting bin; the second grouting part has the same structure as the first grouting part.

[0010] A further improvement is that the sleeve includes an end sleeve, the top of the end sleeve is threadedly connected to the top sleeve, a pressure plate is provided at the bottom of the end sleeve, a first supporting plate is formed at the bottom of the pile pipe, the first supporting plate is located below the pressure plate, and several groups of steel balls are installed between the pressure plate and the first supporting plate; a guide plate is provided on the side wall of the end sleeve to separate the first grouting part and the second grouting part, a guide groove is formed between adjacent guide plates, and the first grouting part and the second grouting part are located in the guide groove; a second supporting plate is provided on the upper part of the top sleeve, the second supporting plate is fixed with a limiting plate, a limiting groove is formed between adjacent limiting plates, a centering device located in the limiting groove is arranged on the top surface of the second supporting plate, and a third steel ball is installed at the outer end of the centering device.

[0011] A method for constructing a double-layer rotary jet reinforced core composite pile with a bag extrusion and expansion body is provided, wherein the construction is carried out using the above-mentioned double-layer rotary jet reinforced core composite pile construction device with a bag extrusion and expansion body, and specifically comprises the following steps:

[0012] Step 1. Construction preparation: Survey the physical and mechanical parameters of each soil layer and the groundwater level at the construction site, level the site, measure and stake out, and mark the foundation pile points; the physical and mechanical parameters include gravity γ, moisture content w, cohesion c, internal friction angle Elastic modulus E and Poisson's ratio μ;

[0013] Step 2: Mixing and grouting: Align the pile pipe with the foundation pile point and sink it vertically and stir the soil. After reaching the preset depth, inject the first cementitious material and mix the first cementitious material and the soil evenly. After the pile pipe continues to sink and reaches the preset depth, inject the second cementitious material and mix it evenly with the soil. The setting speed of the first cementitious material is faster than that of the second cementitious material, and the first cementitious material is above the second cementitious material.

[0014] Step 3: Bag extrusion and expansion: Before the first cementitious material is initially set, the pile pipe, the first grouting part, the second grouting part and the casing are taken out; after the first cementitious material is initially set, a first mixing body is formed, and the thickness h1 of the first mixing body is sufficient to ensure that the second cementitious material will not leak to the surface when the air bag applies the designed air pressure p0 to the second cementitious material; when the first mixing body hardens, the compressive strength f cu,1 When the second gelling material is not fractured and the second gelling material is not solidified, a designed air pressure p0 is applied in the airbag to squeeze and expand the second gelling material outward;

[0015] Step 4: Drainage and pore water pressure monitoring: Use drainage boards and water pumps to pump water while monitoring the pore water pressure of the second cementitious material and the surrounding soil;

[0016] Step 5: Depressurize the bag, recover the bag, and pour concrete: After the second cementitious material reaches the initial setting state to form a second mixing body, and the pore water pressure is released to meet the requirements, the air pressure in the bag is released, the bag and the pore water pressure sensor are recovered, leaving a hole in the second mixing body, and the mixed concrete is poured in the hole, which forms a strong core after hardening.

[0017] Further improvement, in step three,

[0018] The thickness h1 of the first stirring body satisfies the following conditions:

[0019]

[0020] The first mixing body needs to be hardened to the compressive strength f cu,1 The following conditions are met:

[0021]

[0022] Where D1 is the diameter of the airbag before expansion; D2 is the diameter of the second stirring body before expansion; f1 is the interfacial friction between the first stirring body and the surrounding soil; and p0 is the air pressure applied to the airbag.

[0023] Further improvement, the ultimate bearing capacity of the double-layer jet-jet reinforced core composite pile is P f for:

[0024]

[0025] Where h 2-i is the thickness of the i-th soil layer in the layered foundation; f 2-i is the interfacial friction between the second mixing body and the i-th soil layer, c i and are the interfacial bonding force and interfacial friction angle between the second stirring body and the i-th soil layer respectively; α i is the interface normal stress loss coefficient; D ′ 2-i is the diameter of the second mixing body in the i-th layer of soil after the airbag is pressurized and expanded, and D2 is the diameter of the second mixing body before expansion; the ultimate bearing capacity of the double-layer jet-jet reinforced core composite pile is P f Not less than the required ultimate bearing capacity.

[0026] Further improvements, D ′ 2-i The method for determining is as follows:

[0027]

[0028] Where, μ i is the Poisson's ratio of the i-th layer of soil in the layered foundation; E i is the elastic modulus of the i-th soil layer.

[0029] As a further improvement, in step 5, before releasing the air pressure to recover the airbag, the pore water pressure monitored by the pore water pressure sensor must meet the following conditions:

[0030]

[0031] Where: u w The pore water pressure is obtained by monitoring the pore water pressure sensor; h w is the water head height between the pore water pressure sensor and the groundwater level; γ w is the weight of water;

[0032] The concrete volume Q required for core pouring construction is estimated by the following formula:

[0033]

[0034] Where n is the number of soil layers that the second mixing body passes through; h 1-i is the thickness of the i-th soil layer; D ′ 1-i is the diameter of the stiffener in the i-th layer of soil after expansion,

[0035]

[0036] A double-layer rotary jet reinforced core composite pile with a bag extrusion and expansion body includes a first stirring body, and the bottom of the first stirring body is connected to a second stirring body; the first stirring body is formed by condensing a cementitious material with a fast coagulation and hardening speed, and the second stirring body is formed by condensing a cementitious material with a slow hardening speed; a reinforcement core is formed in the middle of the second stirring body and the first stirring body, wherein the diameter of the reinforcement core inside the second stirring body is larger than the diameter of the reinforcement core inside the first stirring body; the cementitious material with a fast coagulation and hardening speed is fast-hardening cement or polymer cement; the cementitious material with a slow hardening speed is slow-setting cement.

[0037] The beneficial effects of the present invention are:

[0038] 1. The present invention arranges air bags along the entire length of the pile body. In this way, according to the design requirements of the pile foundation bearing capacity, combined with the construction method of the present invention, the entire length of the second mixing body can be squeezed and expanded, thereby increasing the diameter of the pile body and significantly improving the normal stress and interface friction resistance at the pile-soil interface, thereby significantly improving the bearing capacity of the composite pile.

[0039] 2. The present invention pours concrete or other materials in the center of the first mixing body and the second mixing body, which hardens to form a strong core, thereby improving the strength and rigidity of the pile body and significantly reducing the settlement of the pile foundation.

[0040] 3. The first stirring body of the present invention is located at the top of the pile and solidifies quickly. In this way, the first stirring body can not only play a role in rapid load-bearing, but also when the air bag is used to extrude and expand the second stirring body that has not yet initially solidified, the solidified and hardened first stirring body can also play a role in sealing. In this way, the slurry of the second stirring body can be prevented from being squeezed out of the surface, thereby avoiding waste of construction materials and pollution of the construction surface environment.

[0041] 4. The present invention arranges multiple grouting parts along the bottom of the pile pipe. The grouting parts are composed of several grouting bins. The grouting parts at different positions are connected in series to form a whole, thereby ensuring that the cementitious material can be evenly injected into the soil. Combined with the stirring blades on the side of the pile pipe and the valve pile tip, the cementitious material and the soil can be evenly mixed. In addition, the grouting bins can be connected in series in various forms, thereby realizing the effects of simultaneous grouting of multiple cementitious materials, grouting of different soil layers with different cementitious materials, etc., which can not only greatly improve the bearing capacity of the pile body, but also carry out customized construction according to design requirements or site conditions to improve construction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a structural principle diagram of the composite pile construction device of the present invention.

[0043] Figure 2 This is a schematic diagram of the connections of the components at the bottom of the composite pile construction device of the present invention.

[0044] Figure 3 This is a schematic structural diagram of the first grouting member 6 of the present invention.

[0045] Figure 4 This is a cross-sectional view of the bottom position of the composite pile construction device of the present invention.

[0046] Figure 5 This is a schematic diagram of the connection between the first grouting piece 6 and the second grouting piece 7 of the present invention.

[0047] Figure 6 Schematic diagram of the arrangement of the centering device 10 of the present invention.

[0048] Figure 7 This is the shape of the second stirring body 15 after the rotary spray stirring is completed.

[0049] Figure 8 Schematic diagram of the force applied to the second stirring body 15 and its deformation before and after expansion of the second stirring body 15 according to the present invention.

[0050] Figure 9 This is the pile shape used for homogeneous foundation in the present invention.

[0051] Figure 10 This is the pile form used for layered foundations according to the present invention.

[0052] Figure 11 It is a construction flow chart of the present invention.

[0053] The labels in the figure are:

[0054] 1-pile pipe, 1a-spraying port, 1b-first support plate, 2-lateral mixing blade, 3-bottom mixing blade, 4-valve pile tip, 5-steel ball, 6-first grouting part, 6a-first sealing gasket, 6b-first steel ball, 6c-first grouting channel, 6d-first interface, 6e-first connecting pipe, 6f-first grouting pipe, 6g-first grouting chamber, 7-second grouting part, 7a-second sealing gasket, 7b-second steel ball, 7c-second grouting channel, 7d-second interface, 7e-first Second connecting pipe, 7f-second grouting pipe, 7g-second grouting chamber, 8-end sleeve, 8a-pressure plate, 8b-guide groove, 9-top sleeve, 9a-second support plate, 9b-limiting groove, 10-centering device, 10a-third steel ball, 10b-connecting rod, 11-drainage plate, 12-air bag, 13-air pipe, 14-first stirring body, 15-second stirring body, 16-strength core, 17-pore water pressure sensor, 18-stirring body before expansion, 19-air bag before expansion. DETAILED DESCRIPTION

[0055] The following further describes the embodiments of the present invention in conjunction with the accompanying drawings and examples. It should be noted that the examples do not limit the scope of protection claimed in the present invention.

[0056] Example 1

[0057] A double-layer rotary jet reinforced core composite pile construction device with bag extrusion and expansion, such as Figure 1 and Figure 2 As shown, it mainly includes a pile pipe 1 and an end sleeve 8. Three rows of spray ports 1a and three rows of lateral stirring blades 2 are set at the bottom of the pile pipe 1. Each row is evenly provided with 8 spray ports 1a. A valve pile tip 4 is hinged below the pile pipe 1. Three rows of bottom stirring blades 3 are set on the periphery of the valve pile tip 4. In this embodiment, the total outer diameter of the pile pipe 1 and the lateral stirring blades 2 is 800mm, and the inner diameter of the end sleeve 8 is 320mm. The first grouting piece 6 and the second grouting piece 7 are installed between the pile pipe 1 and the end sleeve 8. The first grouting piece 6 and the second grouting piece 7 have the same structure.

[0058] like Figure 3 As shown, the first grouting element 6 is composed of multiple first grouting bins 6g, which are connected by a first grouting channel 6c with a diameter of no less than 5 cm. First sealing gaskets 6a are installed at the contact points between the first grouting bins 6g and the inner wall of the pile pipe 1. Several groups of first steel balls 6b are evenly embedded at the contact points between the first grouting bins 6g and the end sleeve 8. All first grouting bins 6g are connected to the grouting port 1a. In this embodiment, the first grouting element 6 is composed of three first grouting bins 6g, and the diameter of the first grouting channel 6c is 6 cm.

[0059] like Figure 4 and Figure 5 As shown, in this embodiment, the four first grouting parts 6 are connected to the first connecting pipe 6e through the first top interface 6d, and the center of the first grouting chamber 6g is in the same plane as the grouting port 1a. The end sleeve 8 is threadedly connected to the top sleeve 9. A pressure plate 8a is provided at the bottom of the end sleeve 8. Several groups of steel balls 5 are fixed between the pressure plate 8a and the first support plate 1b. The side wall of the end sleeve 8 is provided with a guide groove 8b to separate the first grouting part 6 and the second grouting part 7. An air bag 12 and a drainage plate 11 are provided in the center of the end sleeve 8 and the top sleeve 9. A pore water pressure sensor 17 is provided at the bottom of the air bag 12. A second support plate 9a and a limit groove 9b are provided on the upper part of the top sleeve 9. A centering device 10 is arranged on the top surface of the second support plate 9a.

[0060] like Figure 6 As shown, third steel balls 10a are mounted on both ends of the centralizer 10, which is fixed as a whole by connecting rods 10b. There is no gap between the centralizer 10, the top sleeve 9, and the pile pipe 1. The centralizer 10 and the first and second grouting members 6 and 7 restrain the end sleeves 8 and the top sleeve 9 at the center of the pile pipe 1, thereby ensuring that the airbag 12 is centered.

[0061] Example 2

[0062] A double-layer rotary jet reinforced core composite pile with bag extrusion and expansion, including a first stirring body 14 and a second stirring body 15. In this embodiment, the diameter D2 of the first stirring body 14 and the second stirring body 15 before extrusion and expansion is 800 mm, the total length h2 of the second stirring body 15 is 10 m, the cementitious material of the first stirring body 14 is a mineral powder-based polymer with an initial setting time of 30 min, and the cementitious material of the second stirring body 15 is a slow-setting cement with an initial setting time of 240 min. The second stirring body 15 passes through three layers of soil, which are, from top to bottom: ① plain fill, thickness 3 m, elastic modulus E1 = 50 MPa, Poisson's ratio μ1 = 0.30, pile-soil interface bonding force c1 = 100 kPa, interface friction angle ② Muddy clay, thickness 5m, elastic modulus E2 = 30MPa, Poisson's ratio μ2 = 0.33, pile-soil interface bond strength c1 = 50kPa, interface friction angle ③ Fine sand, thickness 2m, elastic modulus E3 = 100MPa, Poisson's ratio μ3 = 0.30, pile-soil interface bond strength c1 = 120kPa, interface friction angle like Figure 7 As shown, the center of the first stirring body 14 and the second stirring body 15 is provided with an air bag 12 for squeezing and expanding the body along the entire length, and a drain board 11 is arranged on the periphery of the air bag 12. The drain board 11 is a plurality of flexible drain boards arranged along the circumference of the air bag or arranged as a whole. A pore water pressure sensor 17 is arranged at the bottom of the air bag 12. In this embodiment, the diameter D1 of the air bag 12 before squeezing and expanding the body is 300 mm, and the drain board 11 is a plastic drain board. After the compressive strength of the first stirring body 14 meets the requirements, the air bag 12 is used to squeeze and expand the body, and the second stirring body 15 is expanded into a cylindrical hardened body with a vertical diameter change in the soil. After the air bag 12 is recovered, the center of the second stirring body 15 is formed into a hole with a vertical diameter change. Concrete, cement mortar and other materials are poured into the hole, and a strong core 16 is formed after hardening.

[0063] The hardened first stirring body 14 acts as a plug to ensure that the slurry in the second stirring body 15 does not leak to the surface during the extrusion and expansion. To this end, the thickness of the first stirring body 14 should meet the following conditions:

[0064]

[0065] Wherein, D1 is the diameter of the airbag 12 before expansion; D2 is the diameter of the second stirring body 15 before expansion; f1 is the interfacial friction between the first stirring body 14 and the surrounding soil; and p0 is the air pressure applied to the airbag 12.

[0066] In this embodiment, the air pressure p0=0.8 MPa, the interface friction resistance f1 between the first stirring body 14 and the surrounding soil is 100 kPa, and h1 needs to be greater than 0.75 m after calculation. In this embodiment, h1 is set to 1.0 m.

[0067] The compressive strength f of the first stirring body 14 cu,1 The following conditions are met:

[0068]

[0069] Wherein, D1 is the diameter of the airbag 12 before expansion; D2 is the diameter of the second stirring body 15 before expansion; and p0 is the air pressure applied to the airbag 12.

[0070] In this embodiment, it is calculated that the first stirring body 14 needs to be hardened to a compressive strength f cu,1 The initial setting time of the retarded cement used in the second stirring body 15 is 240 minutes. After 180 minutes of stirring of the first stirring body, the second stirring body 15 has not yet reached the initial setting state. At this time, the designed air pressure p0 = 0.8 MPa is applied to the airbag 12 to squeeze and expand the second stirring body 15 outward. The compressive strength of the first stirring body 14 is 450 kPa, which meets the requirements.

[0071] like Figures 8 to 10 As shown, in the i-th layer of soil in the layered foundation, the diameter D of the second stirring body 15 after being pressurized and expanded by the air bag 12 is ′ 2-i and the diameter D of the core 16 ′ 1-i It can be estimated by the following formula:

[0072]

[0073] Where, μ i is the Poisson's ratio of the i-th layer of soil; E i is the elastic modulus of the i-th soil layer.

[0074] In this embodiment, after calculation, the diameters of the second stirring body 15 and the stiffening core 16 in each soil layer are: ① plain fill, D ′ 2-1 =806.2mm, D ′ 1-1 =316.3mm;② silty clay, D ′ 2-1 =810.6mm, D ′ 1-1 =327.3mm; ③ Fine sand, D ′ 2-1 =803.1mm, D ′ 1-1 =308.2mm.

[0075] The ultimate bearing capacity P of double-layer jet-jet reinforced core composite piles with bag extrusion and expansion fIt can be estimated by the following formula:

[0076]

[0077] Where h 2-i is the thickness of the i-th soil layer; f 2-i is the interfacial friction between the second stirring body 15 and the i-th soil layer,

[0078] c i and are the interfacial bonding force and interfacial friction angle between the second stirring body 15 and the i-th layer of soil respectively; α i is the interface normal stress loss coefficient.

[0079] In this embodiment, the interface normal stress loss coefficient α i Both are taken as 0.50. After calculation, the ultimate bearing capacity P f =3422.3kN, while the ultimate bearing capacity of a conventional unexpanded reinforced core composite pile under the same conditions is about 2236.8kN. Therefore, compared with conventional reinforced core composite piles, the bearing capacity of the double-layer rotary jet reinforced core composite pile expanded by bag extrusion of the present invention can be increased by 53.0%.

[0080] Example 3

[0081] A construction method for a double-layer rotary jet reinforced core composite pile with bag extrusion and expansion, such as Figure 11 , the steps are as follows:

[0082] S1. Construction preparation: Survey the soil density γ, moisture content w, cohesion c, and internal friction angle of each soil layer at the construction site Physical and mechanical parameters such as elastic modulus E and Poisson's ratio μ, as well as groundwater level, site leveling, measurement and layout, and marking of foundation pile locations.

[0083] In this embodiment, ① plain fill, γ1=17.5kN / m 3 , moisture content w1 = 30.2%, cohesion c1 = 30kPa, internal friction angle

[0084] E1 = 50 MPa, Poisson's ratio μ1 = 0.30; ② Muddy clay, γ2 = 17.8 kN / m 3 , moisture content w2 = 50.8%, cohesion c2 = 20kPa, internal friction angle E2 = 30 MPa, Poisson's ratio μ2 = 0.30; ③ Fine sand, γ3 = 18.2 kN / m 3 , moisture content w3 = 50.8%, cohesion c3 = 20kPa, internal friction angle E3 = 100 MPa, Poisson's ratio μ3 = 0.30. The groundwater level is 5.0 m below the surface.

[0085] S2. Positioning of construction machinery and tools and pre-mixing and sinking: Use a tower crane or hoist to align the construction machinery and tools with the foundation pile point, and let the pile pipe 1 sink vertically by static pressure or free fall. At the same time, use a motor to drive the pile pipe 1 to rotate, thereby causing the side mixing blades 2 and bottom mixing blades 3 to mix the soil.

[0086] S3. Construction of the First Mixing Body: Calculate the required thickness h1 of the first mixing body 14. In this embodiment, h1 = 1.0 m. When the pile pipe 1 is lowered to the required depth of 0.5 m, the first grouting member 6 injects the prepared first cementitious material into the stratum through the first grouting pipe 6f and the spraying port 1a at a grouting pressure p1. In this embodiment, the first cementitious material is a mineral powder-based polymer. The pile pipe 1 is repeatedly lowered and raised, and the first cementitious material is then uniformly mixed with the soil using the side mixing blades 2 and bottom mixing blades 3.

[0087] S4. Construction of the Second Mixing Body: After the first mixing body 14 is constructed to the designed thickness h1, the second grouting member 7 is used to inject the prepared second cementitious material into the stratum through the second grouting pipe 7f and the spraying port 1a at a grouting pressure p2. In this embodiment, the second cementitious material is slow-setting cement. The pile pipe 1 is repeatedly lowered and raised, and the second cementitious material is then uniformly mixed with the soil using the side mixing blades 2 and bottom mixing blades 3.

[0088] S5. Bag squeezing and expanding: After the construction of the second mixing body 15 is completed, the pile pipe 1, the first grouting piece 6, the second grouting piece 7, the end sleeve 8 and the top sleeve 9 are taken out by a crane or a tower crane, and the drainage board 11, the pore water pressure sensor 17 and the air bag 12 are left in the first mixing body 14 and the second mixing body 15 to drain the water in the soil and eliminate the excess pore water pressure. Figure 7 The hardened first stirring body 14 plays a blocking role to ensure that the slurry of the second stirring body 15 does not leak to the surface when it is squeezed and expanded. Before the air bag 12 is pressurized, the second stirring body 15 has not yet reached the initial setting state, while the first stirring body 14 hardens to the compressive strength f cu,1 Reaching 450kPa, meeting the requirements.

[0089] S6. Drainage and pore water pressure monitoring: Use the drainage board 11 in conjunction with the water pump to pump water, while monitoring the pore water pressure of the second mixing body 15 and the surrounding soil through the pore water pressure sensor 17. To ensure that the excess pore water pressure is fully dissipated, before releasing the air pressure recovery airbag 12, the pore water pressure monitored by the pore water pressure sensor 17 must meet the following conditions:

[0090]

[0091] Where: u wThe pore water pressure is monitored by the pore water pressure sensor 17; h w is the water head height between the pore water pressure sensor 17 and the groundwater level; γ w The weight of water.

[0092] In this embodiment, the water head height between the pore water pressure sensor 17 and the groundwater level is 5.0 m. After 24 hours of drainage, the pore water pressure u monitored by the pore water pressure sensor 17 is w =80kPa, Meet the requirements.

[0093] S7, bag pressure relief, recovery, and concrete pouring: After the second mixing body 15 reaches the initial setting state and the pore water pressure is released to meet the requirements, the air pressure in the air bag 12 is released so that the second mixing body 15 can maintain its shape. The air bag 12 and the pore water pressure sensor 17 are recovered, and a hole is left in the second mixing body 15. The mixed concrete is poured into the hole and hardened to form a strong core 16. The concrete volume Q required for the pouring construction of the strong core (16) can be estimated by the following formula:

[0094]

[0095] Where n is the number of soil layers that the second mixing body (15) passes through; h 1-i is the thickness of the i-th soil layer.

[0096] In this embodiment, the concrete pouring volume Q = 0.875m 3 .

Claims

1. A double-layer rotary jet reinforced core composite pile construction device with bag extrusion and expansion, characterized in that: The invention comprises a pile pipe (1), wherein a plurality of grouting ports (1a) and lateral stirring blades (2) are arranged at the lower part of the pile pipe (1); a plurality of flap pile tips (4) are hingedly connected to the bottom of the pile pipe (1); the flap pile tips (4) are arranged along the circumference of the pile pipe (1); a plurality of bottom stirring blades (3) are arranged on the outer periphery of the flap pile tips (4); a sleeve is arranged on the inner side of the pile pipe (1); a first grouting member (6) and a second grouting member (7) are installed between the pile pipe (1) and the sleeve; the first grouting member (6) and the second grouting member (7) are communicated with the grouting port (1a); the first grouting member (6) and the second grouting member (7) are fixedly connected to the pile pipe (1) and are connected to the pile pipe (1). The casing is rotatably connected; a drainage plate (11) is installed in the casing along the circumferential direction, an air bag (12) is installed inside the drainage plate (11), and a pore water pressure sensor (17) is provided at the bottom of the air bag (12); a plurality of first grouting bins (6g) are sequentially connected in series from top to bottom to form a first grouting piece (6), and a plurality of second grouting bins (7g) are sequentially connected in series from top to bottom to form a second grouting piece (7); the first grouting piece (6) and the second grouting piece (7) are spaced apart from each other along the circumferential direction of the pile pipe (1); wherein the first grouting bins (6g) in the same layer are connected to each other through the first connecting pipe (6e), and the second grouting bins (7g) in the same layer are connected to each other through the first connecting pipe (6e). The two grouting bins (7g) are interconnected via a second connecting pipe (7e); the first grouting member (6) comprises a first grouting bin (6g) in the middle, a first grouting channel (6c) formed at the bottom of the first grouting bin (6g), and a first interface (6d) matched with the first grouting channel (6c) formed at the top; the first grouting bin (6g) is open on the side opposite to the grouting port (1a), and a first sealing gasket (6a) is fixed on the outer periphery of the opening; a first steel ball (6b) is installed on the side opposite to the sleeve of the first grouting bin (6g); the second grouting member (7) has the same structure as the first grouting member (6); the sleeve comprises An end sleeve (8) is provided, wherein the top of the end sleeve (8) is threadedly connected to the top sleeve (9), a pressure plate (8a) is provided at the bottom of the end sleeve (8), a first supporting plate (1b) is formed at the bottom of the pile pipe (1), the first supporting plate (1b) is located below the pressure plate (8a), and a plurality of groups of steel balls (5) are installed between the pressure plate (8a) and the first supporting plate (1b); a guide plate for separating the first grouting piece (6) and the second grouting piece (7) is provided on the side wall of the end sleeve (8), a guide groove (8b) is formed between adjacent guide plates, and the first grouting piece (6) and the second grouting piece (7) are located in the guide groove (8b).

2. The double-layer rotary jet reinforced core composite pile construction device with bag extrusion and expansion as claimed in claim 1 is characterized in that: A second supporting plate (9a) is provided on the upper portion of the top sleeve (9), a limiting plate is fixed to the second supporting plate (9a), limiting grooves (9b) are formed between adjacent limiting plates, a centering device (10) located in the limiting grooves (9b) is arranged on the top surface of the second supporting plate (9a), and a third steel ball (10a) is installed at the outer end of the centering device (10).

3. A construction method for double-layer rotary jet reinforced core composite piles with bag extrusion and expansion, characterized in that: The construction is carried out using the double-layer rotary jet reinforced core composite pile construction device with bag extrusion and expansion according to claim 1 or 2, which specifically includes the following steps: Step 1. Construction preparation: Survey the physical and mechanical parameters of each soil layer and the groundwater level at the construction site, level the site, measure and stake out, and mark the foundation pile points; the physical and mechanical parameters include gravity γ, moisture content w, cohesion c, internal friction angle Elastic modulus E and Poisson's ratio μ; Step 2: Mixing and grouting: the pile pipe (1) is aligned with the foundation pile point and vertically sunk downwards to stir the soil. After reaching a preset depth, the first cementitious material is injected and the first cementitious material and the soil are uniformly mixed. After the pile pipe (1) continues to sink to reach a preset depth, the second cementitious material is injected and the soil is uniformly mixed. The first cementitious material sets faster than the second cementitious material and the first cementitious material is located above the second cementitious material. Step 3: Bag extrusion and expansion: before the first cementitious material is initially solidified, the pile pipe (1), the first grouting piece (6), the second grouting piece (7) and the casing are taken out; after the first cementitious material is initially solidified, a first stirring body (14) is formed, and the thickness h1 of the first stirring body (14) is such that when the air bag (12) exerts a designed air pressure p0 on the second cementitious material, the second cementitious material will not leak to the surface; when the first stirring body (14) hardens to a compressive strength f cu,1 When the second gelling material is not fractured by the second gelling material and the second gelling material is not solidified, a designed air pressure p0 is applied in the air bag (12) to squeeze and expand the second gelling material outward; Step 4: Drainage and pore water pressure monitoring: using the drainage board (11) in conjunction with the water pump to pump water, while monitoring the pore water pressure of the second cementitious material and the surrounding soil; Step 5, bag pressure relief, recovery and pouring of concrete: After the second cementitious material reaches the initial setting state to form a second mixing body (15), and the pore water pressure is released to meet the requirements, the air pressure in the air bag (12) is released, the air bag (12) and the pore water pressure sensor (17) are recovered, and a hole is left in the second mixing body (15). The mixed concrete is poured in the hole and hardened to form a strong core (16).

4. The construction method of double-layer rotary jet reinforced core composite pile with bag extrusion and expansion as claimed in claim 3 is characterized in that: In the step 3, the thickness h1 of the first stirring body (14) satisfies the following conditions: The first stirring body (14) needs to be hardened to a compressive strength f cu,1 The following conditions must be met: Wherein, D1 is the diameter of the airbag (12) before expansion; D2 is the diameter of the second stirring body (15) before expansion; f1 is the interfacial friction between the first stirring body (14) and the surrounding soil; and p0 is the air pressure applied to the airbag (12).

5. The construction method of double-layer rotary jet reinforced core composite pile with bag extrusion and expansion as claimed in claim 4 is characterized in that: The ultimate bearing capacity of the double-layer jet-jet reinforced core composite pile is P f for: Where h 2-i is the thickness of the i-th soil layer in the layered foundation; f 2-i is the interfacial friction between the second stirring body (15) and the i-th soil layer, c i and are the interfacial bonding force and interfacial friction angle between the second stirring body (15) and the i-th layer of soil respectively; α i is the interface normal stress loss coefficient; D ′ 2-i is the diameter of the second stirring body (15) in the i-th layer of soil after the air bag (12) is pressurized and expanded, and D2 is the diameter of the second stirring body (15) before expansion; so that the ultimate bearing capacity of the double-layer jet-jet reinforced core composite pile is P f Not less than the required ultimate bearing capacity.

6. The construction method of double-layer rotary jet reinforced core composite pile with bag extrusion and expansion as claimed in claim 5, characterized in that: D ′ 2-i The method for determining is as follows: Where, μ i is the Poisson's ratio of the i-th layer of soil in the layered foundation; E i is the elastic modulus of the i-th soil layer.

7. The construction method of double-layer rotary jet reinforced core composite pile with bag extrusion and expansion as described in any one of claims 3 to 6, characterized in that: In step 5, before releasing the air pressure recovery airbag (12), the pore water pressure monitored by the pore water pressure sensor (17) must meet the following conditions: Where: u w The pore water pressure is monitored by the pore water pressure sensor (17); h w is the water head height between the pore water pressure sensor (17) and the groundwater level; γ w is the weight of water; p0 is the air pressure applied to the air bag (12); The concrete volume Q required for the pouring of the core (16) is estimated by the following formula: Where n is the number of soil layers that the second mixing body (15) passes through; h 1-i is the thickness of the i-th soil layer; D ′ 1-i is the diameter of the stiffener (16) in the i-th layer of soil after expansion,

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