A construction method of pre-mixed fluidized solidified soil pre-hole filling pile under low temperature and water environment

Abstract

The application discloses a construction method of pre-mixed fluidized solidified soil pre-hole filling pile under low-temperature water environment and relates to the field of pile foundation construction of geotechnical engineering, which comprises the following steps: pre-holing and measuring the volume of free water in the hole; preparing the first filling solidified soil, wherein the water amount for mixing is the product of the target water amount, the volume of free water in the hole and a water deduction coefficient; preparing the main filling solidified soil mixed with anti-dispersion components and heat storage components; and sequentially filling the first filling special solidified soil and the main filling solidified soil through a pipe, wherein the lower end of the pipe is kept 2-4 m below the surface of the filled solidified soil; according to the construction method, the water is accurately deducted for the first filling section, the anti-dispersion bottom is dug for the main section and the low-temperature heat loss is compensated by three-stage gradient heat storage, so that the dilution and segregation of the water in the hole are reduced, and the integrity and strength of the pile body are improved.

Description

Technical Field

[0001] This invention relates to geotechnical engineering pile foundation construction technology, specifically to a construction method for pre-drilled cast-in-place piles in premixed fluidized solidified soil under low-temperature and water-containing environments. Background Technology

[0002] Premixed fluidized bed soil is a fluid mixture formed by mixing excavated soil, solidifying agent, water, and admixtures in a certain proportion. It can be used for backfilling and pile construction of pre-drilled cast-in-place piles. During construction in low-temperature seasons and strata with high groundwater levels, a certain thickness of water often remains inside the borehole after drilling. The sources of this water mainly include groundwater infiltration, residual mud from the drilling process, and inflow from rainfall or surface water. Due to the considerable depth of the pre-drilled holes, it is difficult to completely pump out the water at the bottom, especially in highly permeable strata such as silt and sand. After pumping, groundwater often replenishes the water within a short period.

[0003] In existing technologies, the typical construction process for pre-mixed fluidized solidified soil pre-drilled piles is as follows: after pre-drilling, submersible pumps or air-lift reverse circulation are used to remove as much water as possible from the hole. Then, fluidized solidified soil mixed according to the design mix ratio is continuously poured into the hole through a tremie pipe until the design elevation is reached. To cope with low-temperature environments, measures such as hot water mixing, adding early-strength agents or antifreeze agents, and covering the hole opening for insulation are usually used.

[0004] The existing construction methods described above have the following problems in low-temperature, water-containing environments:

[0005] Water accumulation within the borehole is difficult to completely remove, and excessive pumping may cause borehole wall instability. In silty soil and sand layers with high groundwater levels, groundwater will replenish the borehole shortly after cleaning, leaving a certain thickness of water at the bottom. When uniformly proportioned fluidized solidified soil is injected into the borehole through a tremie pipe, the solidified soil comes into contact with and mixes with the water. The water is relatively concentrated at the bottom of the borehole, and the local water-to-solid ratio is significantly higher than the design value after the solidified soil mixes with the water. The cementitious material is diluted, the concentration of hydration products decreases, and it is difficult to form a continuous hydration product network, resulting in segregation and bleeding of the solidified soil. At the same time, the low temperature environment reduces the cement hydration rate and slows early strength development. The diluted area remains in a low-strength state for a long time, which easily leads to the formation of weak interlayers at the pile bottom. During the grouting process, if water in the borehole seeps down along the borehole wall and mixes with the rising solidified soil, it may also cause local mud inclusions and segregation. The above problems ultimately manifest as poor pile integrity, large strength dispersion, and decreased pile end resistance.

[0006] Hot water mixing can only raise the initial temperature of the mixture. After the solidified soil is inserted into the hole, the heat is rapidly lost to the soil around the hole wall and the water inside the hole, resulting in a limited effective temperature rise. Early-strength agents and antifreeze agents can improve low-temperature hydration to some extent, but they cannot eliminate the dilution and segregation problems caused by water entering the hole. Hole-mouth insulation can only reduce heat loss at the hole opening and cannot create a continuous and effective heating environment inside the pile. Summary of the Invention

[0007] The purpose of this invention is to provide a construction method for pre-drilled cast-in-place piles of premixed fluidized solidified soil in a low-temperature, water-containing environment, in order to solve the problems in the prior art where water accumulation in the hole leads to dilution and segregation of the solidified soil, low temperature inhibits hydration, and results in poor pile integrity and low strength.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing pre-drilled cast-in-place piles in premixed fluidized solidified soil under low-temperature and water-containing conditions, comprising the following steps:

[0009] S1. Pre-drill holes and measure the volume of free water accumulation inside the holes;

[0010] S2. Prepare the first-injection solidified soil according to the volume of the first injection section corresponding to the initial burial depth of the guide pipe. The mixing water volume is the target water volume corresponding to the final design water-solid ratio minus the water volume of the free water accumulation in the hole.

[0011] S3. Prepare the main grouting solidified soil according to the designed water-solid ratio;

[0012] S4. Inject the first-stage solidified soil into the bottom of the hole through the guide pipe. After the first-stage solidified soil is completed, continuously inject the main solidified soil. The lower end of the guide pipe should always be buried 2-4m below the surface of the solidified soil until the design elevation is reached.

[0013] The first-fill solidified soil and the main-fill solidified soil also include anti-dispersion components and heat storage components; the anti-dispersion components include 0.1% to 0.3% anionic polyacrylamide and 5% to 8% silica fume based on the total mass of cementitious materials; the heat storage components include 3% to 5% high-alumina cement, 10% to 15% rapid-hardening sulfoaluminate cement and 5% to 8% lightly calcined active MgO based on the total mass of cementitious materials.

[0014] Furthermore, the proportion of the free water accumulation volume within the hole is set as follows:

[0015]

[0016] in, Let be the free water volume inside the hole, and k be the water deduction coefficient, where 0 ≤ k ≤ 0.8.

[0017] Furthermore, in step S1, before measuring the volume of free water accumulation in the borehole, the wall-protecting and solidifying soil is injected from the bottom of the borehole through the grouting pipe, while liquid is pumped out from the borehole opening and the liquid level in the borehole is kept constant to form a wall-protecting layer with a thickness of 8 to 12 cm. After standing for 1.5 to 2 hours, the volume of free water accumulation in the borehole is measured.

[0018] Furthermore, the wall-protecting and solidifying soil comprises, by weight parts: 70-80 parts of engineering waste soil, 10-15 parts of fly ash, 8-10 parts of composite curing agent, 3-4 parts of composite antifreeze and rust inhibitor, 2-4 parts of modified sodium bentonite, 0.2-0.5 parts of calcium lignosulfonate retarder, and 12-15 parts of mixing water; the mass ratio of ordinary silicate cement to rapid-hardening sulfoaluminate cement in the composite curing agent is 2:1; the mass ratio of calcium nitrite to calcium nitrate in the composite antifreeze and rust inhibitor is 1:1; and the fluidity of the wall-protecting and solidifying soil is 220-240 mm.

[0019] Furthermore, the method also includes real-time monitoring of the pile body temperature; when the core temperature of the pile body is lower than 5°C within 48 hours after grouting, lime slurry is injected through the grouting pipe reserved at the orifice to compensate for the local temperature rise.

[0020] Furthermore, in step S4, before injecting the initial grouting and solidification soil, 0.1–0.2 m of grout is first injected into the bottom of the hole through a guide pipe. 3 The quick-hardening and water-reducing slurry is left to stand for 5-10 minutes. The quick-hardening and water-reducing slurry is composed of 60-70 parts by weight of quick-hardening sulfoaluminate cement, 30-40 parts by weight of lightly calcined active MgO, and water, with a water-to-solid ratio of 0.6.

[0021] Furthermore, in step S2, the first-fill solidified soil is also mixed with 3% to 5% barite powder or iron ore powder based on the total mass of the cementitious materials.

[0022] Furthermore, in step S3, the activity value of the lightly calcined active MgO is 60-80s, the peak value of hydration expansion is 3-7 days after hydration, and the free expansion rate is 0.02%-0.04%.

[0023] Furthermore, after step S4 is completed, cover the borehole opening with a double layer of thermal insulation cotton quilt and foam board, and attach thermal insulation extruded polystyrene board to the borehole wall within a 3m range above the pile body, and then allow it to cure naturally until the designed age.

[0024] Furthermore, in step S3, the main grouting solidified soil is also mixed with 10% to 15% fly ash or slag powder based on the total mass of the cementitious materials.

[0025] Compared with existing technologies, the present invention provides a construction method for pre-mixed fluidized solidified soil pre-drilled piles in a low-temperature, water-rich environment. By dividing the solidified soil grouting section into an initial grouting section and a main section, the initial grouting section is designed with water deduction to ensure that the water-to-solid ratio of the initial grout mixed with the water at the bottom of the hole is close to the design value, thereby reducing dilution and segregation at the source. The main section is prepared according to the design water-to-solid ratio and incorporates anti-dispersion components to ensure uniform underwater grouting. A three-stage gradient heat storage component releases hydration heat at different time periods to compensate for low-temperature heat loss, maintain the temperature required for pile hydration, and improve the integrity and strength of the pile in a low-temperature, water-rich environment.

[0026] In addition, the water-reducing slurry first consumes some of the water accumulated at the bottom of the hole and binds the sediment, reducing the amount of free water in contact with the initial grout; the water depletion in the initial grouting section further ensures that the water-to-solid ratio of the initial grout mixed with the remaining accumulated water is close to the design value. The wall protection layer and the hole opening insulation measures supplement the internal heat storage in a low-temperature environment: the modified sodium-based bentonite in the wall protection layer reduces the rate of external cold and groundwater transfer to the pile body, and the hole opening insulation reduces heat loss to the outside of the hole, so that more of the heat released by the three-level gradient heat storage components can be used to maintain the hydration temperature of the pile body. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0028] Figure 1 A flowchart illustrating the method steps provided in an embodiment of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] In the following examples, the excavated soil is cohesive soil or silty clay with a moisture content not exceeding 5%; the ordinary silicate cement is P·O 42.5 grade; the rapid-hardening sulfoaluminate cement is R·SAC 42.5 grade; the high-alumina cement is CA50 grade; the lightly calcined active MgO is industrial grade with an activity value of 60-80s from the citric acid method; the fly ash is grade II; the silica fume is semi-dense silica fume; the anionic polyacrylamide has a molecular weight of 12 million; and the polycarboxylate superplasticizer is water-retaining with a water reduction rate of 20%-30%. All of the above materials are commercially available industrial products.

[0031] The volume of free water in the borehole, V_w, was determined using a dual-measurement method combining the depth of the measuring rope and the detection of the sediment interface, distinguishing between free water and sediment pore water, and calculated based on the effective free water volume. The underwater grouting process using the tremie pipe method was performed in accordance with the current industry standard "Technical Specification for Building Pile Foundations" JGJ 94. Underwater anti-dispersion performance was tested according to "Test Procedure for Underwater Non-Dispersion Concrete" DL / T 5117.

[0032] In the three-stage gradient heat storage components, high-alumina cement hydrates rapidly, releasing heat within 1–6 hours after grouting, enabling the solidified soil to achieve early temperature rise during the plastic stage; rapid-hardening sulfoaluminate cement hydrates and releases heat within 12–24 hours, providing the main heat source and promoting early strength development; lightly calcined active MgO continuously hydrates and releases heat within 24–72 hours, while simultaneously generating magnesium hydroxide, which produces micro-expansion to compensate for low-temperature shrinkage and fill interfacial micro-cracks. The peak heat release times of the three components are sequentially linked, covering the critical stages of solidified soil from plastic setting to hardening and warming under low-temperature conditions.

[0033] The basic components of the initial and main grouting solidified soil are: engineering waste soil, cementing materials (including at least ordinary silicate cement), water, and optional mineral admixtures such as fly ash or slag powder.

[0034] As attached Figure 1 As shown:

[0035] Example 1:

[0036] This invention provides a method for constructing pre-drilled cast-in-place piles using premixed fluidized solidified soil in a low-temperature, water-rich environment.

[0037] This embodiment corresponds to a mild working condition: ambient temperature 3℃, water accumulation thickness in the borehole is 1 / 6 of the pile length, groundwater recharge rate is about 3mm / h, borehole wall is stable, and no wall protection construction is carried out.

[0038] The pile diameter is 800mm and the pile length is 12m. The volume of free water accumulation in the hole was measured after the hole was pre-drilled. It is 0.48m 3 The target water-to-solid ratio for the solidified soil is 0.55, the total amount of cementitious material is 3.0t, and the target total water consumption is 1.65m³. 3 The initial irrigation section volume is calculated based on an initial burial depth of 2m for the conduit, and is approximately 1.0m. 3 .

[0039] S1. After pre-drilling the holes, the free water volume is measured using a dual-measurement method. =0.48m 3 .

[0040] S2. Preparation of the initial solidified soil: Take 600 kg of excavated soil, 250 kg of ordinary Portland cement, 150 kg of fly ash, 15 kg of high-alumina cement, 30 kg of rapid-hardening sulfoaluminate cement, 15 kg of lightly calcined active MgO, 24 kg of silica fume, 0.3 kg of anionic polyacrylamide, 6 kg of water-retaining polycarboxylate superplasticizer, and 15 kg of barite powder. The amount of mixing water is the target water consumption minus... ×0.8=0.384m 3 The actual amount of mixing water added was 0.616m. 3 The initial slump of the poured material was 150mm, and the density was approximately 1.82g / cm³. 3 .

[0041] S3. Preparation of the main grouting solidified soil: The mix proportions are the same as the initial grouting material, except that barite powder is not added and the mixing water is not reduced. The slump of the main material exiting the machine is 190mm, and the density is approximately 1.72g / cm³. 3 .

[0042] S4. Underwater grouting: Inject approximately 1.0m of initial grouting and solidification soil into the bottom of the borehole through a guide pipe. 3 Then, the main grouting for soil stabilization is continuously poured in. The lower end of the duct is always kept 2-4m below the surface of the stabilized soil, and the grouting is continued until it reaches 0.8m above the design elevation. The orifice is covered with double-layered insulation cotton blankets and foam boards.

[0043] In this embodiment, the water-to-solid ratio of the initial grout mixed with the water at the bottom of the hole was close to 0.55, with no significant dilution or segregation. The pre-embedded temperature sensor showed that the peak core temperature of the pile was 8℃ 12 hours after grouting, and remained at 5.5℃ after 48 hours. Core sampling after 28 days yielded an average compressive strength of 7.0 MPa for the pile; the core samples were intact, with no broken piles or weak interlayers.

[0044] Example 2:

[0045] This embodiment is basically the same as the previous embodiment, except that: this embodiment corresponds to a moderate working condition: ambient temperature -4℃, water thickness in the hole is 1 / 5 of the pile length, groundwater recharge rate is about 6mm / h, and there are slight signs of collapse on the hole wall.

[0046] The pile diameter is 800mm and the pile length is 12m. After pre-drilling the hole, the retaining wall construction is carried out first: The retaining wall solidification soil is prepared by taking the following proportions by weight: 75 parts of excavated soil, 12 parts of fly ash, 6 parts of ordinary Portland cement, 3 parts of rapid-hardening sulfoaluminate cement, 1.75 parts of calcium nitrite, 1.75 parts of calcium nitrate, 3 parts of modified sodium bentonite, 0.3 parts of calcium lignosulfonate, and 13 parts of mixing water. The retaining wall solidification soil is injected from the bottom of the hole through a grouting pipe with side holes, while simultaneously pumping out liquid from the hole opening and maintaining a constant liquid level inside the hole, forming a retaining wall layer with a thickness of approximately 10cm. This layer is then left to stand for 1.5 hours. The volume of free water accumulation inside the hole is measured again. It is 0.42m 3 .

[0047] S1. Measurement of free water volume after retaining wall construction. =0.42m 3 .

[0048] S2. Preparation of the initial solidified soil: Take 600 kg of excavated soil, 250 kg of ordinary Portland cement, 150 kg of fly ash, 25 kg of high-alumina cement, 50 kg of rapid-hardening sulfoaluminate cement, 25 kg of lightly calcined active MgO, 30 kg of silica fume, 0.5 kg of anionic polyacrylamide, 7 kg of water-retaining polycarboxylate superplasticizer, and 20 kg of barite powder. The amount of mixing water is the target water consumption minus... ×0.6=0.252m 3 The actual amount of mixing water added was 1.398m. 3 The initial slump of the poured material was 150mm, and the density was approximately 1.85g / cm³. 3 .

[0049] S3. Preparation of main grouting solidified soil: The mix proportions are the same as the initial grouting material, except that the heavy crystal powder is not added and the mixing water is not reduced. The slump of the main material exiting the machine is 190mm.

[0050] Before injecting the initial fill material, first inject 0.15m of fill material into the bottom of the hole through a guide pipe. 3 The quick-setting, water-reducing primer is composed of 65 parts by weight of quick-setting sulfoaluminate cement, 35 parts by weight of lightly calcined active MgO, and water, with a water-to-solid ratio of 0.6. Let it stand for 8 minutes.

[0051] S4. Underwater grouting: First, inject approximately 1.0m of initial grout to solidify the soil. 3 Subsequently, the main grouting was continuously poured to solidify the soil. The tremie pipe was buried at a depth of 2-4m, and the grouting was carried out to 1.0m above the design elevation. Extruded polystyrene insulation boards were pasted on the borehole wall within the upper 3m of the pile body, and the borehole opening was covered with double-layer insulation cotton blankets and foam boards.

[0052] In this embodiment, the retaining layer stabilizes the borehole wall and reduces external water supply, while the bottom slurry consumes the water accumulated at the bottom of the borehole and binds the sediment. After the initial grout mixes with the remaining accumulated water, the water-to-solid ratio is close to the design value. Pre-embedded temperature sensors show that the peak core temperature of the pile body is 10℃ 12 hours after grouting, and remains at 6℃ after 48 hours. The average compressive strength of the core samples taken after 28 days is 7.5 MPa, and the core samples are intact. The pile periphery and retaining layer are tightly bonded, and the side friction resistance is increased by approximately 16% compared to the mud slurry retaining layer process.

[0053] Example 3:

[0054] This embodiment is basically the same as the previous embodiment, except that: this embodiment corresponds to heavy working conditions: ambient temperature -8℃, water accumulation thickness in the hole is greater than 1 / 4 of the pile length, groundwater recharge rate is about 8mm / h, the hole wall is stable but external water recharge is relatively fast.

[0055] The pile diameter is 800mm and the pile length is 12m. The volume of free water accumulation within the hole was measured after pre-drilling. It is 0.78m 3 Since the water accumulation exceeds 1 / 4 of the pile length, the water deduction coefficient k=0 according to the rules, meaning that no water is deducted for the first pour.

[0056] S1. Measure the free water accumulation volume after pre-drilling the hole. =0.78m 3 .

[0057] S2. Preparation of the first-fill solidified soil: The mix proportion is the same as the first-fill material in Example 2, but the mixing water is not deducted; that is, water is added normally according to the designed water-solid ratio. The slump of the first-fill material at the discharge point is 150mm.

[0058] S3. Preparation of main grouting solidified soil: The mix proportions are the same as those in Example 2. The slump of the main material exiting the machine is 190mm.

[0059] Before injecting the initial fill material, first inject 0.2m of fill material into the bottom of the hole through a guide pipe. 3 The quick-hardening and water-reducing base slurry is prepared with the same proportions as in Example 2 and left to stand for 10 minutes.

[0060] S4. Underwater grouting: First, inject approximately 1.0m of initial grout to solidify the soil. 3 Subsequently, the main grouting was continuously poured to solidify the soil. The tremie pipe was buried at a depth of 2-4m, and the grouting was carried out to 1.0m above the design elevation. The borehole opening was covered with double-layer insulation cotton quilts and foam boards, and extruded polystyrene insulation boards were pasted on the borehole wall within 3m of the top of the pile.

[0061] In this embodiment, the water-blocking design is eliminated, and quality is ensured by relying on anti-dispersion components and water-reducing grout. Pre-embedded temperature sensors show that the peak core temperature of the pile body was 9℃ 12 hours after grouting, and remained at 5℃ after 48 hours. Core samples taken after 28 days showed an average compressive strength of 6.8 MPa, with intact core samples and no obvious weak interlayers at the pile bottom.

[0062] Comparative Example 1

[0063] The same pile diameter, pile length, water volume in the hole and mix ratio as in Example 1 are used. The difference is that the mixing water is not deducted for the first pour of special solidified soil. That is, the first pour of material is filled with water normally according to the design water-solid ratio. The rest of the steps are the same as in Example 1.

[0064] The results showed that segregation and weak interlayers appeared in the core samples at the pile bottom. The compressive strength of the core samples at the pile bottom after 28 days was 3.2 MPa, which was lower than the average compressive strength of 7.0 MPa of the pile body in Example 1.

[0065] Comparative Example 2

[0066] The same pile diameter, pile length, water accumulation volume in the hole, and initial water-cutting method as in Example 1 were used. The difference was that the three-level gradient heat storage components were not added to the main grouting and solidification soil, that is, high alumina cement, rapid hardening sulfoaluminate cement and lightly calcined active MgO were not added, and ordinary silicate cement was used instead. The remaining steps were the same as in Example 1.

[0067] The results showed that the pre-embedded temperature sensor indicated that the core temperature of the pile body dropped to 2℃ after 48 hours of grouting, which was lower than 5℃; the average compressive strength of the core sample after 28 days was 4.1MPa, which was lower than 7.0MPa in Example 1.

[0068] Comparative Example 3

[0069] The same pile diameter, pile length, water accumulation volume in the hole, and initial water injection method as in Example 1 were used. The difference was that anionic polyacrylamide and silica fume were not added to the main grouting and solidification soil. The remaining steps were the same as in Example 1.

[0070] The results showed that the solidified soil underwent segregation and bleeding underwater during the grouting process. Honeycomb-like segregation was visible in the 28-day core sample, and the average compressive strength was 3.8 MPa, which was lower than 7.0 MPa in Example 1.

[0071] It should be noted that the specific material ratios and parameters in the above embodiments can be adjusted within the scope defined by the claims according to actual engineering conditions.

[0072] All materials used in the method of this invention are commercially available industrial products and require no special preparation. The construction equipment is compatible with conventional pre-drilled bored pile equipment, requiring only a change in mix ratio at the mixing plant and the addition of a bottom grout injection step, making on-site operation simple.

[0073] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for constructing pre-drilled cast-in-place piles using premixed fluidized solidified soil in a low-temperature, water-rich environment, characterized in that... Includes the following steps: S1. Pre-drill holes and measure the volume of free water accumulation inside the holes; S2. Prepare the first-injection solidified soil according to the volume of the first injection section corresponding to the initial burial depth of the guide pipe. The mixing water volume is the target water volume corresponding to the final design water-solid ratio minus the water volume of the free water accumulation in the hole. S3. Mainly grout and solidify the soil according to the designed water-solid ratio; S4. Inject the first-stage solidified soil into the bottom of the hole through the guide pipe. After the first-stage solidified soil is completed, continuously inject the main solidified soil. The lower end of the guide pipe should always be buried 2-4m below the surface of the solidified soil until the design elevation is reached. The first-fill solidified soil and the main-fill solidified soil also include anti-dispersion components and heat storage components; the anti-dispersion components include 0.1% to 0.3% anionic polyacrylamide and 5% to 8% silica fume based on the total mass of cementitious materials; the heat storage components include 3% to 5% high-alumina cement, 10% to 15% rapid-hardening sulfoaluminate cement and 5% to 8% lightly calcined active MgO based on the total mass of cementitious materials.

2. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 1, characterized in that, The proportion of the free water volume inside the hole is set as follows: in, Let be the free water volume inside the hole, and k be the water deduction coefficient, where 0 ≤ k ≤ 0.

8.

3. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 1, characterized in that, In step S1, before measuring the volume of free water accumulation in the borehole, the wall-protecting and solidifying soil is injected from the bottom of the borehole through the grouting pipe, while liquid is pumped out from the borehole opening and the liquid level in the borehole is kept constant to form a wall-protecting layer with a thickness of 8 to 12 cm. After standing for 1.5 to 2 hours, the volume of free water accumulation in the borehole is measured.

4. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 3, characterized in that, The wall-protecting and solidifying soil comprises, by weight, 70-80 parts of excavated soil, 10-15 parts of fly ash, 8-10 parts of composite curing agent, 3-4 parts of composite antifreeze and rust inhibitor, 2-4 parts of modified sodium bentonite, 0.2-0.5 parts of calcium lignosulfonate retarder, and 12-15 parts of mixing water; the mass ratio of ordinary silicate cement to rapid-hardening sulfoaluminate cement in the composite curing agent is 2:1; the mass ratio of calcium nitrite to calcium nitrate in the composite antifreeze and rust inhibitor is 1:1; and the fluidity of the wall-protecting and solidifying soil is 220-240 mm.

5. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 1, characterized in that, The method also includes real-time monitoring of pile body temperature; when the core temperature of the pile body is lower than 5°C within 48 hours after grouting, lime slurry is injected through the grouting pipe reserved at the orifice to compensate for local temperature rise.

6. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 1, characterized in that, In step S4, before injecting the initial grouting and solidification soil, 0.1–0.2 m of the grout is first injected into the bottom of the hole through a guide pipe. 3 The quick-hardening and water-reducing slurry is left to stand for 5-10 minutes. The quick-hardening and water-reducing slurry is composed of 60-70 parts by weight of quick-hardening sulfoaluminate cement, 30-40 parts by weight of lightly calcined active MgO, and water, with a water-to-solid ratio of 0.

6.

7. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 1, characterized in that, In step S2, the first-fill solidified soil is also mixed with 3% to 5% barite powder or iron ore powder based on the total mass of cementitious materials.

8. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 1, characterized in that, In step S3, the activity value of the lightly calcined active MgO is 60-80s, the peak value of hydration expansion is 3-7 days after hydration, and the free expansion rate is 0.02%-0.04%.

9. The construction method for pre-drilled cast-in-place piles of premixed fluidized solidified soil in a low-temperature, water-rich environment according to claim 1, characterized in that, After step S4 is completed, cover the borehole opening with a double layer of thermal insulation cotton quilt and foam board, and attach thermal insulation extruded polystyrene board to the borehole wall within a 3m range above the pile body, and then allow it to cure naturally until the designed age.

10. The construction method for pre-mixed fluidized solidified soil pre-drilled cast-in-place piles in a low-temperature, water-rich environment according to claim 1, characterized in that, In step S3, the main grouting solidified soil is also mixed with 10% to 15% fly ash or slag powder based on the total mass of cementitious materials.

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