Construction method of large-diameter spiral blade spiral pile foundation in permafrost

Abstract

The application discloses a construction method of a large-diameter spiral blade spiral pile foundation in permafrost, and belongs to the technical field of engineering foundation construction. The method comprises the following steps: surveying a permafrost stratum, and determining a pile position; drilling a plurality of holes around the pile position, and requiring that an area surrounded by the holes is greater than a diameter range of the spiral blade, and the hole depth is greater than the pile depth; placing electrodes into the holes, injecting a conductive medium into the holes, and then electrifying and heating to thaw the permafrost between the electrodes to a degree that the spiral pile can be rotated into construction, and then pulling out the electrodes; then rotating the large-diameter spiral blade spiral pile into construction to a design depth by using a machine according to a conventional method; installing a circulating refrigeration system, and circulating low-temperature brine refrigeration in the spiral pile hole; after the thawed soil body around the spiral pile is refrozen, the brine in the spiral pile hole is pumped out and removed, and a foam expanding agent is used for hole sealing. The method can solve the problem that the large-diameter spiral blade spiral pile is difficult to construct in permafrost.

Description

Technical Field

[0001] This invention belongs to the field of engineering foundation construction technology, specifically relating to a construction method for a large-diameter spiral blade helical pile foundation in permafrost. Background Technology

[0002] Foundation construction is a crucial step in the development of power transmission towers. However, the Qinghai-Tibet Plateau region is characterized by a fragile ecosystem and widespread permafrost. Traditional cast-in-place pile foundation construction methods are prone to environmental damage due to excavation, require lengthy pile curing times, and pose a risk of thawing permafrost due to hydration heat. These methods fail to meet the stringent mechanical, environmental, and quality requirements for foundation construction in the permafrost region of the Qinghai-Tibet Plateau. Large-diameter helical blade pile foundations offer advantages such as rapid construction, high mechanization, and minimal environmental impact, making them an ideal type of foundation for power transmission towers in the Qinghai-Tibet Plateau. However, the extreme hardness of permafrost prevents the direct insertion of helical piles into the permafrost layer using traditional methods, thus limiting the potential application of helical piles in related engineering projects in the Qinghai-Tibet Plateau region. Summary of the Invention

[0003] To address the technical problem that existing helical piles are difficult to drive into the ground in permafrost regions, thus limiting their application in engineering projects in permafrost areas such as the Qinghai-Tibet Plateau, this invention provides a construction method for large-diameter helical blade helical pile foundations in permafrost. This method not only enables efficient and rapid construction of helical piles in permafrost regions but also restores the original state of the permafrost after construction, preventing damage to the permafrost.

[0004] To achieve the above objectives, the present invention employs the following technical means:

[0005] A construction method for large-diameter helical blade pile foundations in permafrost is disclosed, applicable to the construction of large-diameter helical pile foundations in permafrost regions. The steps are as follows:

[0006] S1: Accurately locate the pile hole position, conduct a detailed survey of the frozen soil foundation within the pile foundation area, measure the soil layer distribution, electrical conductivity, resistivity, thermal conductivity, and heat absorption coefficient of the frozen soil foundation, level the site, and determine the entire construction plan.

[0007] S2: Prepare construction equipment, including drilling rig, electrodes, power supply, large-diameter spiral blade helical piles, cooling device and brine;

[0008] S3: At each pile hole position precisely located in S1, drill 4 to 6 holes around the pile hole position, put the electrode into the hole, and fill all the holes with conductive medium (the purpose is to achieve electric heating thawing).

[0009] S4: connecting the electrode wires in S3, checking the electrode wires connection, turning on the power switch, heating and melting the frozen soil in the pile diameter range;

[0010] S5: after the frozen soil in the pile diameter range is melted and softened by the electric heating, the power is turned off to stop heating, the electrode is pulled out, and the large-diameter spiral blade spiral pile is rotated into the designed depth of the soil body;

[0011] S6: install the refrigeration cycle system, connect the spiral piles with water pipes and double-hole sealing pistons, the cooling device outlet pipe passes through the double-hole sealing piston into the bottom of the first spiral pile, one end of the other water pipe is connected to the sealing piston port, and the other end passes through the double-hole sealing piston of the adjacent spiral pile into the bottom of the adjacent spiral pile. After connecting the entire cooling pipeline system, start the cooling device, make the normal temperature salt water enter the cooling device, and the low temperature salt water after flowing out of the cooling device outlet flows into the bottom of the first spiral pile through the water inlet pipe. After filling the first spiral pile, it flows out from the outlet pipe and flows into the bottom of the next spiral pile, and the cycle refrigeration is carried out in turn to cool the previously heated and melted frozen soil until it is frozen again;

[0012] S7: use the water pump to pump out the residual salt water in the spiral pile hole, then use the foam expanding agent to seal the spiral pile top hole, and then carry out the construction of the upper structure.

[0013] Preferably, in step S1, the frozen soil area is distributed as seasonal active layer and frozen soil layer, and the thickness of the seasonal active layer and the frozen soil layer is measured.

[0014] Preferably, in step S2, the electrode is φ16-φ25 steel bar with a sharp lower end, the length of the electrode is 10-15 cm above the ground after being put into the hole; the spiral pile meets the specification requirements in pile diameter, wall thickness, pile length and spiral blade thickness, and can normally bear in low temperature environment in frozen soil area; the cooling device can cool the salt water to minus ten degrees Celsius to realize the refreezing of the thawed soil layer.

[0015] Preferably, in step S3, the determination of the pile hole position is strictly according to the design, the electrodes in all the holes put into each pile hole position can melt the frozen soil range slightly larger than the pile body diameter of the spiral pile after being heated, and the depth is consistent with the pile length of the spiral pile; the injected conductive medium has good conductivity.

[0016] The electric wire in step S4 is preferably an insulated sheath aluminum wire, and the load of the connecting electrode wire is large enough, and the size is determined according to the load of each line, and the temporary line for electric heating must be laid on the electric pole, and the distance from the ground is not less than 2.5 m, and the electricity can be connected after the connection is determined to be correct, and the current of each branch line is measured at intervals, and once the abnormal condition is found, it needs to be treated in time, and the construction personnel must wear insulating gloves and shoes during the construction process.

[0017] The electric heating time in step S5 is preferably determined according to the on-site experiment, so as to ensure that the frozen soil between the electrodes is thawed and softened, so as to prevent the frozen soil from being difficult to be screwed into the spiral pile when the spiral pile is drilled.

[0018] The diameter of the water pipe used in step S6 is preferably slightly smaller than half of the diameter of the reserved hole of the spiral pile; the double-hole sealing piston can seal the spiral pile hole, so that the low-temperature brine entering the hole can only flow out through the other side of the sealing piston, and reach the bottom of the next reserved hole through the water pipe, so as to ensure that the thawed soil layer is completely refrozen.

[0019] In step S7, after the brine in the reserved hole of the spiral pile is pumped out, the dry agent is put into the hole to absorb the small amount of brine remaining in the hole, and then the foam expander is used to seal the top of the pile.

[0020] The beneficial effects of the present application are that:

[0021] The present application can solve the problem that the large-diameter spiral blade spiral pile is difficult to construct in permafrost, so that the construction of the spiral pile in the permafrost area can be efficiently and quickly carried out, and the permafrost is restored to the original state after the construction is completed, and the permafrost is not damaged. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a flow chart of the construction method of the present application;

[0023] Figure 2 It is a pile hole position and electrode position layout diagram;

[0024] Figure 3 It is an electrode plane layout and electric wire connection schematic diagram;

[0025] Figure 4 It is a schematic diagram of electrode heating and melting frozen soil between electrodes;

[0026] Figure 5 It is a schematic diagram of the spiral pile being screwed into the thawed frozen soil;

[0027] Figure 6 It is a schematic diagram of the refrigeration cycle system refreezing the soil layer;

[0028] Figure 7 It is a schematic diagram of the double-hole sealing piston structure;

[0029] Figure 8 Schematic diagram for re-freezing soil layer for refrigeration system;

[0030] Figure 9 Schematic diagram for installing upper structure after spiral pile installation is completed;

[0031] In the above figure, 1, seasonal active layer; 2, permafrost layer; 3, electrode; 4, spiral pile; 4-1, pile hole; 5, frozen soil between electrodes; 6, frozen soil after re-freezing; 7, thawed frozen soil; 8, reserved hole; 9, conductive medium; 10, brine; 11, insulated aluminum wire; 12, power supply; 13, water pipe; 14, upper structure; 15, cooling device; 15-1, brine inlet; 15-2, low-temperature brine outlet; 16, double-hole sealing piston. DETAILED DESCRIPTION

[0032] The technical scheme of the present application will be described below in detail Figures 1 to 9 with reference to the following embodiments, which are only used to more clearly illustrate the technical scheme of the present application, and therefore cannot be used to limit the protection scope of the present application.

[0033] As Figure 1 shown, the present application provides a construction method of large-diameter spiral blade spiral pile foundation in permafrost, which comprises the following steps:

[0034] S1, detailed survey is performed on the permafrost area required for construction, the position of the pile hole (such as the pile hole 4-1 in the above figure) is accurately positioned, the soil layer distribution, electrical conductivity, resistivity, thermal conductivity and heat absorption coefficient of the permafrost foundation are measured, the site is leveled, and the entire construction scheme is determined; Figure 2

[0035] S2, the necessary construction instruments such as a drilling machine, an electrode 3, a power supply 12, a spiral pile 4, a cooling device 15 and brine 10 are prepared, the electrode 3 is a steel bar with a sharp lower end with a diameter of φ16~φ25, the length of the electrode 3 satisfies that the top thereof is exposed from the ground by 10~15 cm after being placed into the drilling hole, the spiral pile 4 has a hole 8 left in the middle thereof, and the parameters such as the pile diameter, wall thickness, pile length and spiral blade thickness of the spiral pile 4 all meet the specification requirements and can normally bear in the low-temperature environment of the permafrost area;

[0036] S3, as Figure 2 shown, a plurality of drilling holes with a designed depth are drilled around each drilling hole position at each pile hole position (such as the pile hole 4-1) determined according to the design, it is required that the area surrounded by the drilling holes is greater than the diameter range of the spiral blade, the hole depth is greater than the pile depth, the electrode 3 is placed into the drilling hole, and the drilling holes are filled with a brine mixture as a conductive medium 9;

[0037] S4, as Figure 3 shown, the spiral pile 4 is placed into the pile hole 4-1, the electrode 3 is connected to the power supply 12, the water pipe 13 is connected to the cooling device 15, the brine inlet 15-1 of the cooling device 15 is connected to the water pipe 13, and the low-temperature brine outlet 15-2 of the cooling device 15 is connected to the water pipe 13.As shown, all the electrodes 3 that have been drilled to the designed depth are connected with insulated aluminum wires 11, and after checking the connection of each electrode wire, the power supply 12 switch is turned on to heat and melt the frozen soil 5 between the electrodes;

[0038] S5, as shown in Figure 4 , Figure 5 As shown, after the frozen soil 5 between the electrodes is melted and softened after a period of heating, the heating time is determined according to the actual geological conditions on site, voltage, freezing depth, and field experiments, etc. to ensure that after heating is completed, the frozen soil area passed through when the screw pile 4 is rotated into the soil is thawed and softened into melted frozen soil 7. The power supply is turned off to stop heating, the electrode 3 is pulled out, and the screw pile 4 is rotated into the melted frozen soil 7 inside the designed depth using the drilling machine;

[0039] S6, as shown in Figure 6 , Figure 7 , Figure 8 As shown, a refrigeration cycle system is installed, and the water pipes 13 are connected together to the reserved holes 8 of the screw piles 4, wherein the water pipe at one end of the screw pile reserved hole passes through the double-hole sealing piston 16 into the bottom, the water pipe is connected to the other outlet of the sealing piston, and then the cooling device 15 is started. The normal temperature salt water 10 is placed in the container, enters the cooling device 15 through the salt water inlet 15-1, and is cooled. The low-temperature salt water after flowing out of the low-temperature salt water outlet 15-2 of the cooling device 15 reaches each screw pile 4 through the water pipe 13, and finally flows back to the container to form a circulating cooling. The diameter of the water pipe 13 used is slightly smaller than half the diameter of the screw pile reserved hole 8; the sealing piston 16 can seal the screw pile hole 8, so that the low-temperature salt water 10 entering the hole can only flow out through the other side of the sealing piston, and reach the bottom of the next reserved hole through the water pipe, so as to reciprocatingly cool; the cooling time needs to be determined according to the actual situation and experiments on site to ensure that the melted frozen soil 7 is completely changed into frozen soil again;

[0040] S7, as shown in Figure 9 The residual salt water 10 in the screw pile hole 8 is pumped out using a water pump, and a certain amount of drying agent is put into the hole to absorb the small amount of remaining salt water. Then, a foam expanding agent is used to seal the top hole of the screw pile, and the upper structure 14 of the screw pile 4 is constructed.

Claims

1. A construction method for large-diameter helical blade piles in permafrost, characterized in that, The construction method described herein is applicable to the construction of large-diameter helical blade piles in permafrost strata, and includes the following steps: S1: Accurately locate the pile hole position, conduct a detailed survey of the frozen soil foundation within the pile foundation area, measure the soil layer distribution, electrical conductivity, resistivity, thermal conductivity, and heat absorption coefficient of the frozen soil foundation, level the site, and determine the entire construction plan; S2: Prepare construction equipment, including drilling rig, electrodes, power supply, large-diameter spiral blade helical piles, cooling device and brine; S3: At each pile hole position precisely located in S1, drill several holes of the designed depth, place the electrode into the hole, and fill all the holes with conductive medium. S4: Connect the electrodes in S3 to the wires. After checking that all the electrode wires are connected correctly, turn on the power switch and heat to melt the frozen soil between the electrodes. S5: After the electric heating melts and softens the frozen soil between the electrodes, turn off the power to stop heating, pull out the electrodes, and screw the large-diameter spiral blade helical pile into the soil to the designed depth. S6: Install a refrigeration circulation system. Connect the spiral piles using water pipes and double-hole sealing pistons. The cooling device outlet pipe passes through the double-hole sealing piston and enters the bottom of the first spiral pile. One end of the other water pipe is connected to the sealing piston port, and the other end passes through the double-hole sealing piston of the adjacent spiral pile and enters the bottom of the adjacent spiral pile. Continue in this manner. After connecting the entire cooling pipe system, start the cooling device to allow room temperature brine to enter and cool. The low temperature brine flowing out of the cooling device outlet passes through the cooling device outlet pipe through the double-hole sealing piston to the bottom of the first spiral pile. After filling the first spiral pile, it flows out from the other water pipe connected to the double-hole sealing piston and flows into the bottom of the next spiral pile. This cycle of refrigeration cools the previously heated and melted frozen soil until it freezes again. S7: Use a pump to drain the residual salt water in the helical pile hole, then use a foam expansion agent to seal the top hole of the helical pile, and carry out the construction of the superstructure on the helical pile.

2. The construction method according to claim 1, characterized in that, In step S2, the electrode is made of φ16~φ25 steel bar with pointed bottom, and the length of the electrode is such that its top protrudes 10~15cm above the ground after being inserted into the borehole; the spiral pile has a pre-reserved hole in the middle, and its pile diameter, wall thickness, pile length and spiral blade thickness all meet the specifications and can bear the load normally in the low temperature environment of frozen soil areas; the cooling device can cool the brine to minus ten degrees Celsius, so as to refreeze the thawed soil layer.

3. The construction method according to claim 1, characterized in that, In step S3, the distance and depth between the boreholes are designed according to the size of the helical pile and the actual engineering conditions. The transverse range of frozen soil that can be melted by the electrodes in all the boreholes placed in each pile hole after being heated by electricity is greater than the diameter of the helical pile, and the longitudinal depth is consistent with the length of the helical pile.

4. The construction method according to claim 1, characterized in that, In step S3, the conductive medium is a salt water mixture.

5. The construction method according to claim 1, characterized in that, In step S4, the wire is an insulated aluminum wire, the size of which is determined according to the load of each line. The line is laid on the utility pole, at least 2.5m above the ground. Power can only be supplied after the wiring is confirmed to be correct. The current of each branch line is measured at regular intervals. Any abnormalities must be dealt with in time. During the construction process, the construction personnel must wear insulated shoes.

6. The construction method according to claim 1, characterized in that, In step S5, the heating time is determined based on the actual geological conditions, voltage level, freezing depth, and field experiments, so that the frozen soil area passed through when the helical pile is driven in will thaw and soften after heating.

7. The construction method according to claim 1, characterized in that, In step S6, room temperature brine is placed in a container, and low temperature brine, cooled by a cooling device, flows through water pipes to each spiral pile and finally flows back into the container, forming a circulating cooling system. The diameter of the water pipes used must match the orifice diameter of the double-hole sealing piston of the sealing spiral pile to ensure that no leakage occurs during the circulating cooling process. The low temperature brine flows into the bottom of the spiral pile from the water pipe passing through the sealing piston hole, flows out from the water pipe passing through another sealing piston hole, and flows into the bottom of the next spiral pile, and so on, to ensure that all the thawed soil layer refreezes.

8. The construction method according to claim 1, characterized in that, In step S7, after the brine in the pre-reserved hole of the helical pile is drained, a desiccant is placed in the hole to absorb the remaining brine, and then a foam expansion agent is used to seal the top of the pile.

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