A method for constructing a micro precast pile

Abstract

The present application belongs to the field of electric power construction, and particularly relates to a micro precast pile construction method, characterized by comprising the following steps: leveling the land, then pile position lofting and determining the pile position; hole forming; pile sinking; preparing cement slurry and grouting; and terminating the grouting; in the present application, compared with the traditional hole digging foundation, the micro pile foundation has the advantages of: 1. saving the amount of concrete, steel and other materials, energy saving and emission reduction; 2. improving the construction quality of the foundation engineering by factory precasting the foundation components; 3. improving the mechanization degree of the power transmission line foundation construction, greatly shortening the foundation construction and maintenance period; 4. small earthwork excavation, no need of on-site concrete pouring, greatly reducing the compensation cost of green seedlings, and outstanding environmental protection effect; relatively low cost, high economic benefit.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electric power construction, and particularly relates to a micro precast pile construction method. BACKGROUND

[0002] The bearing platform is a reinforced concrete platform connecting the tops of piles, which is arranged on the top of the pile to bear and distribute the load transmitted by the pier body, bears the load of the upper power tower and transmits it to the foundation pile, and distributes the load to the foundation pile. When there are multiple pile foundations under the bearing platform, the bearing platform can evenly distribute the load to each pile body, so that the pile force is balanced.

[0003] The traditional pile and bearing platform connection adopts the form of welding steel bars and sealing concrete. This method increases the workload of construction, requires more steel bars and cement, is not conducive to cost saving, and is extremely inconvenient for welding construction and a small amount of concrete pouring in mountainous areas, thereby increasing the construction period. SUMMARY

[0004] To solve the above problems, the purpose of the present application is to disclose a micro precast pile construction method, which is realized by the following technical scheme.

[0005] A micro precast pile construction method, characterized by comprising the following steps:

[0006] Step 10: leveling the land, and then laying out the pile position to determine the pile position.

[0007] Step 20: hole forming, a plurality of drill holes are formed on the ground at the pile position in step 10 by using a vertical rotary drilling machine.

[0008] Step 30: pile sinking, first, the bearing platform is hoisted into position to ensure that the bearing platform reserved hole is aligned with the drill hole; then, the connecting seat and the pipe pile are pre-connected, the pile head is connected by hoisting bolts, and is hoisted and vertically sunk into the drill hole until the pipe pile is sunk to the design elevation.

[0009] Step 40: preparing cement slurry and grouting, a specially prepared cement slurry is prepared in a mixer, an external grouting pipe is connected to the top end of the pipe pile, the external grouting pipe is communicated with the grouting pipe, the specially prepared cement slurry is pressed into the grouting pipe cavity through the external grouting pipe from the grouting pipe, and then enters the gap between the drill hole and the pipe pile through the grouting hole on the side of the lower part of the pipe pile, and then the cement slurry is cooled.

[0010] Step 50: terminate grouting, when the ground returns slurry during the grouting process, and the color of the returned slurry is consistent with the color of the poured cement slurry, the grouting is terminated.

[0011] The above-described method for constructing micro precast piles is characterized by a further step 21 between steps 20 and 30: hole fixing, in which a hole fixing ring is fitted onto the formed borehole opening. The hole fixing ring is composed of a hole fixing ring body, with a through hole formed inside the hole fixing ring body. A horizontal ring edge is fixed at the upper end of the hole fixing ring body. The wall thickness of the hole fixing ring body is in the range of [0.1mm~0.2mm]. The diameter of the horizontal ring edge is greater than or equal to 10 times the borehole diameter. The length of the hole fixing ring body is greater than or equal to 0.5m. The outer wall of the hole fixing ring body is in contact with the inner wall of the borehole.

[0012] The above-described method for constructing micro precast piles is characterized in that, in step 20, when local collapse of the borehole wall or shrinkage of the borehole occurs, a rotary drilling rig is required to clean the borehole.

[0013] The above-described method for constructing micro precast piles is characterized in that the hole-forming method in step 20 is either mud slurry wall protection or dry drilling.

[0014] The above-described method for constructing micro precast piles is characterized in that the cement slurry mix ratio in step 40 is as follows: the water content is 0.55% of the cement mass with an error of 5%; the expansion agent content is 12% of the cement mass with an error of 5%; and the water-reducing agent content is 1% of the cement mass with an error of 5%.

[0015] The above-described method for constructing micro precast piles is characterized in that the mixer in step 40 is a conventional mixer or a high-speed mixer, wherein the rotational speed range of the conventional mixer is less than or equal to 100 r / min, and the rotational speed range of the high-speed mixer is greater than or equal to 1000 r / min; the mixing time of the cement slurry should be no less than 3 minutes when using a conventional mixer and no less than 30 seconds when using a high-speed mixer.

[0016] The above-described method for constructing micro precast piles is characterized in that, in step 40, when the air temperature is below 0°C and the slurry temperature is not less than 5°C, heat protection and sun protection measures should be taken when the air temperature is above 35°C and the slurry temperature should not exceed 40°C; the maximum retention time of the cement slurry from mixing to use should not exceed 2 hours.

[0017] The above-described method for constructing micro precast piles is characterized in that, in step 40, the grout outlet 9 is located on the lower end sidewall of the pipe pile.

[0018] The above-described method for constructing micro precast piles is characterized in that step 40 employs a double-cylinder, double-liquid grouting machine.

[0019] The above-described method for constructing micro precast piles is characterized in that a check valve is provided on the grout outlet hole 9 in step 40; during grouting, the check valve opens under the pressure of the grout, and the grout flows out along the grout outlet hole; when grouting stops or during the grouting interval, the check valve closes to prevent grout backflow.

[0020] The above-described method for constructing micro precast piles is characterized in that when mud slurry is used for hole forming in step 20, the initial grouting pressure range is 4.0±0.5 MPa, and the grouting pressure range after stabilization is: 0.5~1.0 MPa for general gravel foundation soil; 0.5~1.0 MPa for cohesive soil and other foundation soils.

[0021] Compared with traditional bored foundations, micropile foundations in this invention: 1. save on materials such as concrete and steel, resulting in energy conservation and emission reduction; 2. prefabricate foundation components in the factory, improving the construction quality of foundation engineering; 3. increase the mechanization of power transmission line foundation construction, significantly shortening the foundation construction and maintenance period; 4. require less earthwork excavation, eliminate the need for on-site concrete pouring, significantly reduce crop damage compensation costs, and have outstanding environmental benefits; and have relatively lower costs and higher economic benefits.

[0022] Therefore, the present invention has the advantages of high construction efficiency, short construction period, material saving, good environmental benefits and low cost. Attached Figure Description

[0023] Figure 1 This is a construction flowchart of Embodiment 1 of the present invention.

[0024] Figure 2 This is a structural diagram of Embodiment 1 of the present invention after construction is completed.

[0025] Figure 3 This is a cross-sectional view of the pipe pile in Embodiment 1 of the present invention.

[0026] Figure 4 This is a construction flowchart for Embodiment 2 of the present invention.

[0027] Figure 5 This is a schematic diagram of the three-dimensional structure of the solid hole ring in Embodiment 2 of the present invention.

[0028] In the figure: 1. Foundation, 2. Ground, 3. Pile hole, 4. Pipe pile, 5. Connecting seat, 6. Grouting pipe, 7. Grouting pipe cavity, 8. Grouting cavity, 9. Grout outlet hole, 10. Hole fixing ring, 101. Horizontal ring edge, 102. Through hole, 103. Hole fixing ring body. Detailed Implementation

[0029] Example 1

[0030] Please see Figures 1 to 3 A method for constructing micro precast piles, characterized by comprising the following steps:

[0031] Step 10: Level the land, then mark out the pile positions to determine the pile locations.

[0032] Step 20: Hole Formation. Multiple holes are formed in the ground at the pile location from Step 10 using a vertical rotary drilling rig.

[0033] Step 30: Pile driving. First, hoist the pile cap 1 into place, ensuring that the reserved hole of the pile cap 1 is aligned with the borehole. Then, connect the connecting seat 5 to the pipe pile 4, connect the pile head with the hoisting bolts, lift it, and sink it vertically into the borehole until the pipe pile 4 is driven to the design elevation.

[0034] Step 40: Prepare cement grout and pressurize it. Prepare special cement grout in a mixer. Connect the external grouting pipe to the top of the pipe pile 4 so that the external grouting pipe is connected to the grouting pipe 6. Press the special cement grout into the grouting cavity 7 from the grouting pipe 6 through the external grouting pipe. Then, it enters the gap between the borehole and the pipe pile 4 through the grout outlet hole 9 on the lower side of the pipe pile 4. Wait for the cement grout to cool.

[0035] Step 50: Terminate grouting. When grout returns to the ground during the grouting process, and the color of the returned grout is consistent with the color of the injected cement grout, terminate the grouting process.

[0036] Example 2

[0037] Please see Figure 4 , Figure 5 and refer to Figure 2 and Figure 3 A method for constructing micro precast piles, characterized by comprising the following steps:

[0038] Step 10: Level the land, then mark out the pile positions to determine the pile locations.

[0039] Step 20: Hole Formation. Multiple holes are formed in the ground at the pile location from Step 10 using a vertical rotary drilling rig.

[0040] Step 21: Hole fixing. A hole fixing ring 10 is fitted onto the formed drill hole. The hole fixing ring 10 is composed of a hole fixing ring body 103. A through hole 102 is formed inside the hole fixing ring body 103. A horizontal ring edge 101 is fixed at the upper end of the hole fixing ring body 103. The wall thickness of the hole fixing ring body 103 is in the range of [0.1mm~0.2mm]. The diameter of the horizontal ring edge 101 is greater than or equal to 10 times the diameter of the drill hole. The length of the hole fixing ring body 103 is greater than or equal to 0.5m. The outer wall of the hole fixing ring body 103 is in contact with the inner wall of the drill hole.

[0041] Step 30: Pile driving. First, hoist the pile cap 1 into place, ensuring that the reserved hole of the pile cap 1 is aligned with the borehole. Then, connect the connecting seat 5 to the pipe pile 4, connect the pile head with the hoisting bolts, lift it, and sink it vertically into the borehole until the pipe pile 4 is driven to the design elevation.

[0042] Step 40: Prepare cement grout and pressurize it. Prepare special cement grout in a mixer. Connect the external grouting pipe to the top of the pipe pile 4 so that the external grouting pipe is connected to the grouting pipe 6. Press the special cement grout into the grouting cavity 7 from the grouting pipe 6 through the external grouting pipe. Then, it enters the gap between the borehole and the pipe pile 4 through the grout outlet hole 9 on the lower side of the pipe pile 4. Wait for the cement grout to cool.

[0043] Step 50: Terminate grouting. When grout returns to the ground during the grouting process, and the color of the returned grout is consistent with the color of the injected cement grout, terminate the grouting process.

[0044] The method for constructing micro precast piles according to any of the above embodiments is characterized in that, in step 20, when local collapse of the hole wall or shrinkage of the hole occurs, a rotary drilling rig is required to clean the hole.

[0045] The method for constructing a micro precast pile according to any of the above embodiments is characterized in that the hole forming method in step 20 is mud wall protection hole forming or dry drilling hole forming.

[0046] The method for constructing a micro precast pile according to any of the above embodiments is characterized in that the cement slurry in step 40 has the following proportions: water content is 0.55% of cement mass with an error of 5%; expansion agent content is 12% of cement mass with an error of 5%; and water-reducing agent content is 1% of cement mass with an error of 5%.

[0047] The method for constructing micro precast piles according to any of the above embodiments is characterized in that the mixer in step 40 is a conventional mixer or a high-speed mixer, wherein the rotation speed range of the conventional mixer is less than or equal to 100 r / min, and the rotation speed range of the high-speed mixer is greater than or equal to 1000 r / min; the mixing time of the cement slurry should be no less than 3 minutes when using a conventional mixer and no less than 30 seconds when using a high-speed mixer.

[0048] The method for constructing micro precast piles according to any of the above embodiments is characterized in that, in step 40, when preparing the slurry in cold seasons, the temperature of the cement slurry should not be less than 5°C, and when preparing the slurry in hot seasons, heat protection and sun protection measures should be taken, and the temperature of the slurry should not exceed 40°C; the maximum retention time of the cement slurry from mixing to use should not exceed 2 hours.

[0049] The construction method of a micro precast pile described in any of the above embodiments is characterized in that the grout outlet 9 in step 40 is provided on the lower end side wall of the pipe pile.

[0050] The micro precast pile construction method described in any of the above embodiments is characterized in that step 40 uses a double-cylinder double-liquid grouting machine.

[0051] The method for constructing a micro precast pile according to any of the above embodiments is characterized in that a check valve is provided on the grout outlet hole 9 in step 40; during grouting, the check valve opens under the action of grout pressure, and the grout flows out along the grout outlet hole; when grouting stops or during the grouting interval, the check valve closes to prevent grout backflow.

[0052] In any of the above embodiments of the micro precast pile construction method, grouting should be continuous and completed in one go, without interruption. Approximately 6 hours after grouting, the grout exceeding the top surface of the borehole should be removed, if necessary.

[0053] The method for constructing a micro precast pile according to any of the above embodiments is characterized in that when mud slurry is used for hole forming in step 20, the initial grouting pressure range is 4.0±0.5 MPa, and the grouting pressure is maintained at 1.0±0.5 MPa after stabilization.

[0054] The grouting pressure after stabilization in any of the above embodiments of the micro precast pile construction method can be calculated using the following empirical formula:

[0055] Grouting pressure in gravelly foundation soil: [P] c ]= ,

[0056] In the formula, [P c To allow for grouting pressure after stabilization;

[0057] β is a coefficient between 1 and 3;

[0058] γ is the unit weight (kN / m³) of the soil layer below ground level and above the grouting section. 3 );

[0059] T is the thickness of the foundation overburden layer;

[0060] K is a coefficient related to the grouting method, with K=0.6 from bottom to top and K=0.8 from top to bottom;

[0061] λ is 0.5 for loosely structured and highly permeable strata, and 1.0 for tightly structured and poorly permeable strata.

[0062] h is the depth (m) from the ground to the grouting section.

[0063] Grouting pressure for cohesive soils and others: [P] c ]= σ t

[0064] In the formula, [P cTo allow for grouting pressure after stabilization;

[0065] h is the height of the soil column above the grouting point (m);

[0066] γ is the natural unit weight of the grouting foundation soil (kN / m³). 3 );

[0067] σ t This represents the tensile strength of the soil (kPa).

[0068] Based on the above empirical formula, when the depth is within 15 meters, the grouting pressure for general gravel foundation soil can be taken as 0.5 to 1.0 MPa; for cohesive soil and other foundations, the grouting pressure can be taken as 1.5 to 2.0 MPa.

[0069] The applicant conducted three pilot projects: the Suizhou 220kV project (single circuit), the Huangshi 110kV project (double circuit), and the Huanggang 110kV project (single circuit), and analyzed the construction period, environmental benefits, safety benefits, and costs of the three pilot projects.

[0070] Construction period: The construction time of the pile foundation using this invention is shortened by 3 days, 1.2 days, and 1.3 days respectively compared with the traditional bored foundation, reducing the construction period by more than 80%. Furthermore, the tower can be erected in just 2 days, while traditional bored foundations require 7 days of curing before tower erection. The following is a comparison table of construction periods:

[0071] Pilot project Drilling time Precast component installation Grouting time Total time Excavation foundation duration Proportion Suzhou project 120 minutes 60 minutes 60 minutes 0.5 days 3.5 days 14.3% Huangshi project 60 minutes 45 minutes 45 minutes 0.313 days 1.5 days 20.8% Huanggang project 30 minutes 30 minutes 30 minutes 0.188 days 1.5 days 12.5%

[0072] Environmental benefits: The micropile foundation components of this invention are manufactured in a factory and constructed on-site using micro-drilling machinery. The process is simple and efficient, fully utilizing the high bearing capacity and low deformation of the original soil foundation. On-site construction involves minimal excavation, little excess soil, and eliminates the need for on-site concrete pouring, using precast pile caps for connection. The steel and concrete consumption (per leg) of the precast micropile foundations in the three pilot projects is compared with that of traditional bored foundations in the following table:

[0073]

[0074] 1. The foundation construction involves a small amount of excavation and minimal excess soil. Conventional foundation construction requires excavation of a foundation pit and the arrival of concrete trucks. The construction work area is approximately 900 square meters. 2 The construction work area is relatively large, while the micropile foundation construction work area is 540m. 2 Compared with conventional foundations, it reduces the construction work area by 40% and reduces damage to the vegetation around the foundation.

[0075] 2. Concrete usage is reduced by more than 70%. Precast micropile foundations utilize the mechanical properties of the original soil. By grouting the precast pipe piles with the soil, they achieve resistance to compression, displacement, and horizontal displacement. They do not use concrete for pouring, thus avoiding the use of materials such as sand and gravel, reducing transportation volume, and are not affected by concrete production stoppages caused by environmental protection, which has a positive effect on reducing environmental pollution.

[0076] 3. Basic curing only takes 2 days. The micropile foundation, including the pile body and pile cap, is made entirely of precast components. After construction, it can be assembled after only 2 days of curing, which greatly shortens the construction cycle, reduces the time spent on the work surface, and helps to reduce vegetation damage and promote rapid vegetation recovery.

[0077] Safety benefits: The entire process of micropile foundation construction is carried out using mechanized construction, which results in fast construction progress, less manpower required, and no on-site work such as drilling, rebar tying, or pouring. This completely avoids the safety risks of collapse, confined space work, and falls caused by deep foundation pit excavation, and the inherent risk level of construction is low.

[0078] Cost analysis:

[0079]

[0080] As can be seen from the table above, the cost of precast micropile foundations is about 17%-67% higher than that of traditional bored pile foundations. However, due to the use of mechanical drilling and grouting technology, and the fact that they are prefabricated components in factories, the quality is easy to guarantee, the construction speed is fast, the amount of concrete used is reduced by more than 70%, and the amount of steel used is reduced by more than 30%. The construction work area is reduced by 30% per month compared to other types of foundations, and the land occupation time is reduced by nearly 20 days. This can reduce the difficulty of civil coordination and the costs of compensation for land occupation and temporary land occupation, resulting in significant benefits.

[0081] Based on the above analysis, compared with traditional bored foundations, micropile foundations: 1. save on materials such as concrete and steel, resulting in energy conservation and emission reduction; 2. prefabricate foundation components in the factory, improving the construction quality of foundation engineering; 3. increase the mechanization of power transmission line foundation construction, significantly shortening the foundation construction and maintenance period; 4. require less earthwork excavation, eliminate the need for on-site concrete pouring, significantly reduce crop damage compensation costs, and have outstanding environmental benefits; and have relatively lower costs and higher economic benefits.

[0082] The basic principles, main features, and advantages of this invention have been described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for constructing a micro-precast pile, characterized in that Comprising the following steps: Step 10: Level the ground, then stake out the pile position, determine the pile position; Step 20: Form a hole, form a plurality of drill holes on the ground at the pile position in step 10 by using a vertical rotary drill; Step 30: Sink the pile, first hoist the pile cap (1) into position, ensure that the pile cap (1) is aligned with the drill hole; Then connect the seat (5) and the pipe pile (4) pre-connect, hoist the pile head by connecting the bolt, and sink vertically into the drill hole until the pipe pile (4) is sunk to the design elevation; Step 40: Prepare the cement slurry and grouting, prepare the special cement slurry in the mixer, connect the external grouting pipe with the top end of the pipe pile (4), make the external grouting pipe communicate with the grouting pipe (6), and press the special cement slurry from the grouting pipe (6) into the grouting pipe cavity (7) through the external grouting pipe, then into the gap between the drill hole and the pipe pile (4) through the slurry outlet hole (9) on the lower side of the pipe pile (4), and wait for the cement slurry to cool; The stable grouting pressure is calculated by the following empirical formula: Gravel ground soil grouting pressure: [Pc]= , wherein [Pc] is the allowable stable grouting pressure; β is a coefficient between 1 and 3; γ is the unit weight of the soil layer below the ground and above the grouting section (kN / m 3 ); T is the thickness of the ground cover layer; K is a coefficient related to the grouting mode, K=0.6 from bottom to top and K=0.8 from top to bottom; λ is 0.5 for a structure with loose structure and strong permeability, and 1.0 for a structure with tight structure and weak permeability; and h is the depth from the ground to the grouting section (m). Soil and other grouting pressure: [Pc]= , wherein [Pc] is the allowable stable grouting pressure; h is the height of the soil column above the grouting (m); γ is the natural density of the soil of the grouting foundation (kN / m 3 ); and σt is the tensile strength of the soil (kPa). According to the above empirical formula, the grouting pressure of general sandy gravel foundation soil is 0.5-1.0 MPa when the depth is within 15 meters; The grouting pressure of clay and other foundations is 1.5-2.0 MPa; Step 50: Terminate the grouting process when ground backflow occurs during the grouting process, and the backflow color is consistent with the color of the grouting cement.

2. The method for constructing a micro-precast pile according to claim 1, characterized in that There is also a step 21 between steps 20 and 30: hole fixing, a hole fixing ring (10) is sleeved on the drill hole after forming, the hole fixing ring (10) is composed of a hole fixing ring body (103), a through hole (102) is formed in the hole fixing ring body (103), a horizontal ring edge (101) is fixedly arranged on the upper end of the hole fixing ring body (103), the wall thickness of the hole fixing ring body (103) is [0.1mm-0.2mm], the diameter of the horizontal ring edge (101) is greater than or equal to (10) times the diameter of the drill hole, and the length of the hole fixing ring body (103) is greater than or equal to 0.5m, and the outer wall of the hole fixing ring body (103) is in close contact with the inner wall of the drill hole.

3. A method of constructing a micropile according to claim 1 or claim 2, wherein The hole forming of step 20 is mud wall protection hole forming or dry drilling hole forming.

4. The method according to claim 3, wherein The cement slurry in step 40 is mixed in a ratio of 0.55% water, 5% error, 12% expansion agent, and 1% water reducing agent, with an error of 5%.

5. The method according to claim 4, wherein The mixer in step 40 is a general mixer or a high-speed mixer, the rotating speed of the general mixer is less than or equal to 100 r / min, and the rotating speed of the high-speed mixer is greater than or equal to 1000 r / min; The stirring time of the cement slurry is not less than 3 minutes when using the general mixer, and not less than 30 seconds when using the high-speed mixer.

6. The method according to claim 5, wherein When the temperature is lower than 0℃ in step 40, the temperature of the cement slurry should be not less than 5℃, and when the temperature is higher than 35℃, heat and sun protection measures should be taken, and the temperature of the slurry should be not more than 40℃; The longest retention time of the cement slurry from mixing to use is not more than 2 hours.

7. The method according to claim 6, wherein The slurry outlet hole in step 40 is arranged on the lower end of the side wall of the pipe pile.

8. The method according to claim 7, wherein The slurry outlet hole in step 40 is provided with a check valve.

9. The method according to claim 8, wherein The step 40 adopts a double-cylinder double-liquid grouting machine.

10. The method according to claim 9, wherein When the step 20 adopts the slurry wall protection hole forming, the initial grouting pressure range is 4.0±0.5Mpa, and the stable grouting pressure range is: 0.5-1.0MPa for general sandy gravel foundation soil; 0.5-1.0MPa for clay and other foundations.

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